Synthetic Biology Approaches for Optimizing Bod Degradation in Hydroponic Systems for Future Food Production

Synthetic Biology Approaches for Optimizing Bod Degradation in Hydroponic Systems for Future Food Production | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF book-review Synthetic Biology Approaches for Optimizing Bod Degradation in Hydroponic Systems for Future Food Production Oluwasanmi Anuoluwapo ADEYEMI, Bukola Margaret Popoola, Oyindamola John Samson This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8879143/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The growing world-wide population and climate-induced agricultural setbacks demand innovative approaches to sustainable food production. Hydroponic systems offer promising solutions through resource-efficient, soilless cultivation methods suitable for urban and drought-prone regions. However, the build-up of organic matter in recirculating nutrient solutions elevates biochemical oxygen demand (BOD), leading to dissolved oxygen depletion, disrupted microbial balance, compromised plant health, and potential food safety risks through pathogen proliferation. This review examines synthetic biology as a strategy for optimising BOD degradation in hydroponic systems. We explore the application of genetically engineered microorganisms, including Bacillus subtilis , Pseudomonas putida , and Rhodococcus species, equipped with enhanced catabolic pathways for targeted organic matter degradation. Advanced genetic tools such as CRISPR-Cas9 gene editing, metabolic pathway engineering, and synthetic microbial consortia design are evaluated for their efficacy in maintaining water quality while supporting crop productivity. The integration of biosensor technologies, Internet of Things (IoT) platforms, and real-time monitoring systems allows for dynamic, feedback-responsive bioremediation strategies. Comparative assessments demonstrate synthetic biology's benefits over traditional BOD management methods in terms of specificity, energy efficiency, adaptability, and environmental sustainability. We address biosafety mechanisms (kill switches, auxotrophy), regulatory frameworks, ethical implications, and public acceptance challenges. This review highlights successful pilot implementations, discusses scalability for commercial operations, and identifies future research directions, emphasising interdisciplinary approaches, long-term ecological impact assessments, and cost-effective designs for small-scale farmers. Ultimately, synthetic biology-based BOD optimisation offers a strategic pathway toward resilient, sustainable, and safe hydroponic food production systems that contribute to global food security. Environmental Biotechnology Biochemical Oxygen Demand Genetically Modified Microorganisms Food Security Water Quality Management Sustainable Development Goals Figures Figure 1 Figure 2 1. INTRODUCTION In modern times, synthetic biology has rapidly emerged as a transformative discipline that combines biological research with engineering principles to enable the rational design and construction of biological systems (Shapira et al., 2017 ). This interdisciplinary field converges life sciences, engineering, information science, and even social sciences to pursue fundamental objectives of wiring biological circuits to achieve precise cellular control and elucidating the design principles governing complex biological networks. By leveraging synthetic biology, researchers can design and assemble novel biomolecular components, pathways, and regulatory networks, thereby reprogramming organisms into engineered cell factories (Lv et al., 2021 ), with applications spanning biotechnology, medicine, industrial bioproduction and food production. According to Long et al. ( 2015 ), the global population is expected to rise by nearly 2 billion by 2050, necessitating new and state-of-the-art solutions to improve agricultural yield and guarantee food security. Numerous factors, however, still pose as obstacles, including the loss of agricultural land due to increased urbanisation, erosion, and climate change (Grier, n.d.). Furthermore, shifts in living standards, particularly the rise in meat consumption, have created a growing demand for increased production of plant-based proteins for use in animal feed. Higher yields were achieved through the introduction and widespread use of synthetic and natural fertilisers, particularly nitrogen, phosphorus, and potassium, as well as the Green Revolution, which included breeding efforts to optimise plant design and light harvesting. This is currently insufficient, and to meet the food demands of the rising world population, agricultural production must double in the next 30 years, reflecting an annual yield increase of 2.2% (Roell and Zurbriggen, 2020 ). Hence, the rapid growth of the global population is driving an escalating demand for essential resources such as food, water, and arable land, posing significant challenges for future generations (Wilmoth et al., 2023 ). Concurrently, populations in arid and semi-arid regions are increasingly vulnerable to prolonged droughts, water scarcity, and the emergence of food deserts. These conditions severely constrain conventional agricultural practices, leading to a marked decline in food availability (Qtaishat et al., 2022 ). 1.1. The Role of Hydroponics in Future Food Security The Global Report on Food Crises (GRFC) 2025 highlights that strife, economic shocks, weather extremes, and unplanned displacement continue as the primary drivers of food insecurity and malnutrition worldwide, with devastating consequences for already fragile regions. In 2024, over 295 million people across 53 countries and territories experienced severe hunger, an increase of 13.7 million compared to 2023 (FSIN and GNAFC, 2025). In 2021, approximately 828 million people, nearly one in ten worldwide, experienced hunger, which is around 150 million more individuals than in 2019. Additionally, approximately 2.3 billion people faced moderate or severe food insecurity, 350 million more than before the pandemic (Sousa et al., 2024 ). The current unrest in Eastern Europe further threatens food security, as both nations involved are major exporters of grains, fertilisers, and energy. Supply disruptions have contributed to soaring food prices; in 2020, 47% of countries experienced rising food costs according to the United Nations Department of Economic and Social Affairs ( 2022 ), and by August 2025, the FAO Food Price Index reached a record 130.1 points, although 18.8 per cent below its peak reached in March 2022 (FAO, 2025). These rising input costs have exposed the structural vulnerability of global food systems, particularly their reliance on imported energy, fertilisers, and animal feed. This dependence amplifies production costs and erodes consumer purchasing power, making food less affordable for many populations (European Commission, 2022 ). In answer to these obstacles, hydroponics, a soilless cultivation technique utilising water-based nutrient solutions, has emerged as a promising agricultural innovation. It is a common method of growing plants without soil in a controlled condition by providing a nutrient solution (Sharma et al., 2018 ). A solid understanding of hydroponics is essential, in this soilless cultivation method, plants receive all their required nutrients directly through a water-based solution rather than from soil. Hydroponic systems can take many forms, such as nutrient film technique (NFT), deep water culture (DWC), and aeroponics. Regardless of the specific system, two key factors, water quality and dissolved oxygen availability, play a decisive role in determining plant health and growth outcomes. The integration of hydroponic production with wastewater treatment systems presents numerous benefits: it achieves higher yields compared to traditional farming with appropriate maintenance, eliminates the need for soil, promotes urban farming, mitigates soil-borne diseases (Aishwarya and Vidhya, 2023 ), serves as an alternative to freshwater in agriculture effectively removes microorganisms to acceptable levels, and demonstrates greater water use efficiency along with cost-effectiveness compared to conventional farming methods (Gumisiriza et al., 2022 ). The prospective challenge of freshwater demand and enhanced productivity can be addressed through the adoption of this technique in both urban and rural settings. The majority of wastewater contains nitrogen, phosphorus, potassium, and organic loads. Using this integrated system, the hydroponic system recovers nutrients from wastewater, leaving the outlet water within acceptable limits. Integrating hydroponic irrigation with wastewater treatment offers a nature-inspired solution for nutrient removal, using plants to absorb excess nitrogen and phosphorus directly from the effluent (Recsetar et al., 2021 ). This approach not only closes the nutrient loop but also allows the reuse of substrate media, reducing waste and resource demand (Aishwarya and Vidhya, 2023 ). Such systems hold great promise as a sustainable technology, simultaneously improving water quality and supporting safe food production. Moreover, by decoupling crop production from traditional soil and climate constraints, hydroponics offers significant potential to improve food security, particularly in drought-prone regions with limited arable land and freshwater resources (Pomoni et al., 2023 ). Moreover, this soilless cultivation technique offers several other advantages, including precise nutrient management, high-density planting, and significant reductions in both land and water requirements (Ekaputri et al., 2021 ). Owing to its robustness and capacity for high yields, hydroponics is particularly valuable in arid and drought-prone regions. The resilience of this system is largely attributed to its integration with controlled environment agriculture (CEA), wherein key parameters such as temperature, humidity, and light are carefully regulated. Beyond environmental control, CEA mitigates the effects of water scarcity and provides a sustainable, year-round solution to global food production challenges by optimising crop productivity (Al-Shrouf, 2017 ). In essence, hydroponic systems not only offer a resource-efficient approach to agriculture but also immensely contribute to global food security. These systems provide a viable alternative during periods when conventional farming is disrupted, such as during extreme weather events, including droughts and monsoons. Designed for year-round operation, hydroponic systems demonstrate resilience to diverse climatic conditions, making them a practical strategy for mitigating food shortages. Furthermore, the adoption of hydroponic farming enhances local food sovereignty, fosters the development of regional food markets, and contributes to lowering food prices. Collectively, these benefits improve community access to affordable and nutritious food (Zee et al., 2024 ). It is also worth noting that hydroponic farming demonstrates high efficiency in the utilisation of water and fertilisers while significantly reducing reliance on chemical pesticides and disease-control agents. Consequently, this method presents a viable alternative for addressing food shortages and promoting sustainable agricultural practices (Al Meselmani, 2024 ). 1.2. Challenges of High BOD in Hydroponics and Pathways to Solutions The increasing adoption of hydroponic systems represents a promising path toward addressing global food security, as these systems enable high-yield, resource-efficient crop production with minimal land use. Yet, one of the key challenges lies in the buildup of organic matter within recirculating nutrient solutions, which can significantly raise the BOD. High BOD in hydroponic systems poses significant challenges to maintaining water quality, plant health, and overall system performance. It poses a major challenge by depleting dissolved oxygen (DO) and disrupting the balance between plant needs (Roosta, 2024 ) and microbial activity, making oxygen management a critical challenge. This implies that heightened BOD indicates increased organic and microbial loads, which increase oxygen demand and decrease dissolved oxygen levels. Oxygen is not just a supplementary factor but a fundamental requirement for root health, water and nutrient uptake, and overall plant performance. Under optimal oxygen levels, roots respire efficiently, supporting vigorous growth and nutrient absorption. However, when BOD drives DO levels too low, the system can slip into anaerobic conditions, leading to root rot, accumulation of toxic metabolites, and reduced plant productivity. These effects not only compromise yield but can also create an environment conducive to pathogenic microorganisms, posing potential risks to food safety. It was observed that excessive BOD prevented hydroponic systems from achieving required phosphorus (P) and nitrogen (N) removal targets, as oxygen was preferentially consumed by heterotrophic microorganisms rather than nitrifying bacteria (Clyde-Smith and Campos, 2023 ). This oxygen competition hindered nitrification, which proceeded efficiently when BOD was kept below 45 mg/L (Clyde-Smith and Campos, 2023 ). Such oxygen limitations can compromise nutrient cycling, reduce plant growth, and increase the risk of pathogenic microbial survival, ultimately affecting food safety. Despite these risks, limited research has been conducted on how different hydroponic or aeroponic designs influence DO levels, rhizosphere oxygen availability, and microbial communities (Aishwarya and Vidhya, 2023 ). These challenges highlight a pressing need to rethink how we manage organic pollution in hydroponic systems. Finding innovative, science-driven strategies to optimise BOD degradation is crucial not just for system efficiency but also for safeguarding food safety and ensuring long-term sustainability. According to Cameron et al. ( 2014 ), synthetic biology is the application of engineering, science, and technology to modify the genetic material of living organisms, thereby enabling them to execute novel roles. Microorganisms have been produced with synthetic biology tools to detect, measure, and report specific environmental pollutants (Brutesco et al., 2017 ). Such interventions offer not only technical efficiency but also a pathway to more resilient and sustainable food production systems. Furthermore, the food industry is undergoing a significant transformation driven by advances in synthetic biology, where the integration of synthetic biology with food science provides powerful strategies to address persistent challenges in food safety, nutritional quality, and the sustainability issues inherent in conventional production systems (Roell and Zurbriggen, 2020 ). In this framework, synthetic biology enables the design and engineering of microorganisms with enhanced capabilities for breaking down organic matter. This can be achieved by manipulating metabolic pathways, gene circuits, and regulatory networks. It is possible to generate microbial strains that more effectively break down complex organic compounds, thereby lowering BOD levels in hydroponic solutions. These approaches not only improve system performance but also advance the development of closed-loop, environmentally sustainable agricultural practices. This review, therefore, explores synthetic biology-based strategies to optimise BOD degradation in hydroponic systems, aiming to advance the efficiency and sustainability of soilless crop production. 2. Biochemical Oxygen Demand (BOD) as a Critical Water Quality Parameter The success of hydroponic systems relies heavily on maintaining optimal water quality to ensure healthy plant growth and maximise productivity. Biochemical oxygen demand (BOD) is, however, a key indicator of water quality and a crucial metric for evaluating the extent of organic pollution. When BOD levels are high, it means there is an excess of organic matter, whether from plant residues, animal waste, or human activities, placing heavy pressure on oxygen resources in the water. This brings about a reduction in available oxygen for fish, plants, and other aquatic life, ultimately signalling poor water quality. Conversely, low BOD levels suggest cleaner water, where less oxygen is consumed in breaking down organic materials, leaving more available to sustain aquatic ecosystems. Managing and reducing BOD is essential for protecting not only aquatic environments but also human health. Elevated BOD often points to contamination, including possible faecal pollution or increased loads of dissolved and particulate organic carbon. Left unchecked, this can trigger oxygen depletion, fish kills, foul odours, and unsafe conditions for human use. BOD testing is widely applied in wastewater treatment to predict the short-term impact of effluents on receiving waters. Under natural conditions, the standard 5-day BOD of unpolluted rivers generally does not exceed 2 mg/L. In comparison, the maximum permissible BOD for water used in agricultural, industrial, and aquaculture applications is 5 mg/L, whereas drinking water should ideally have a BOD of less than 1 mg/L (Zhou et al., 2024 ). Elevated BOD levels in hydroponic systems can deplete dissolved oxygen, disrupt microbial balance, and compromise nutrient availability, ultimately reducing crop yield and system efficiency. In essence, BOD is an indispensable parameter as it provides a direct and quantifiable measure of the potential for oxygen depletion in aquatic systems caused by organic pollution. It serves as a vital early warning indicator of environmental degradation, supporting informed decision-making in wastewater treatment, pollution control, and the preservation of aquatic biodiversity. The absence of regular BOD monitoring would greatly hinder the ability to evaluate anthropogenic impacts on water quality and to formulate effective, evidence-based water resource management strategies. Because the BOD₅ test requires a five-day incubation duration, it is impractical for real-time monitoring or operational control of wastewater treatment systems. Consequently, the chemical oxygen demand (COD) test was developed to provide a faster and more immediate measure of organic load. Although with the limitation of having to measure all substances that can be chemically oxidised, instead of just biodegradable organic matter (Hlordzi et al., 2020 ). 2.1. Sources of organic load in hydroponic systems (plant exudates, microbial metabolites, nutrient residues) While hydroponics provides an efficient solution to various challenges, it also raises new concerns about water quality management, as previously stated. A central issue is the accumulation of organic loads, derived from plant root exudates, microbial metabolites, and residual nutrients, which directly contribute to elevated biochemical oxygen demand (BOD) in hydroponic systems. Elevated BOD signifies a higher concentration of organic matter in the solution, leading to potential depletion of dissolved oxygen, alterations in microbial community dynamics, and jeopardising both crop health and food safety (Zhou et al., 2024 ). Organic hydroponics, often referred to as bioponics , uses organic nutrient sources such as compost tea, fish emulsions, seaweed extracts, vinasses, and other natural by-products to sustain plant growth (Fang and Chung, 2018 ). Microorganisms are often deliberately introduced into these systems to decompose complex organic materials and liberate nutrients in forms accessible to plants, underscoring the strong connection between nutrient management and microbial activity. Aquaponics, where nutrients are derived from fish waste, is also considered a branch of bioponics (Fang and Chung, 2018 ). Regardless of the system, nutrient solutions must be carefully balanced within narrow pH ranges to ensure nutrient solubility and plant uptake. While conventional hydroponics relies heavily on synthetic inorganic fertilisers (Park and Williams, 2024 ), organic hydroponics seeks to avoid these inputs, instead leveraging organic waste streams, even municipal solid waste composts, as potential nutrient sources. One advantage of using organic nutrient inputs is their potential to reduce nitrate accumulation in leafy vegetables, which poses health risks when consumed in excess. Studies by Fang and Chung ( 2018 ) demonstrated that lettuce treated with organic fertiliser solutions showed nitrate concentrations ranging from 800 to 2000 ppm, compared to 5000 to 5500 ppm in conventionally fertilised crops. Growing consumer demand for organic products, the improved flavour profiles sometimes associated with organic inputs, and the perceived health benefits, including reduced nitrate accumulation, are boosting interest in organic hydroponics. Additionally, organic inputs can serve as biostimulants, enhancing plant resilience and growth. In urban settings, organic hydroponic systems provide a way to supply fresh, organic produce where traditional soil-based organic farming is not feasible. Crucially, this method also supports emerging strategies to close the loop between food, water, energy, and waste by reusing organic by-products as valuable nutrient sources (Park and Williams, 2024 ). 2.2. Impacts of high BOD on water quality, crop health, and productivity High BOD indicates excessive organic matter in water, resulting in rapid depletion of DO. This sharp reduction in oxygen availability places aquatic life under severe stress, often leading to suffocation and, in extreme cases, the death of fish and other organisms. Elevated BOD typically stems from inputs such as domestic sewage, industrial effluents, agricultural runoff, and animal waste. The consequences are much like those observed when DO is critically low: ecosystems become imbalanced, biodiversity declines, and natural food webs are disrupted. Beyond oxygen depletion, high BOD often fuels nutrient enrichment that accelerates eutrophication, further exhausting oxygen reserves and creating “dead zones” inhospitable to most aquatic life. Environmental stressors such as rising temperatures intensify this cycle, worsening oxygen loss and destabilising fragile ecosystems (Hu et al., 2024 ). For these reasons, BOD is more than a laboratory metric; it is a vital signal of water quality and ecological health. Elevated readings indicate pollution and environmental distress, while low BOD reflects balanced, oxygen-rich conditions where aquatic organisms can thrive. Sustaining low BOD is therefore essential not only for the survival of fish and other species but also for maintaining resilient, functioning ecosystems capable of supporting life into the future. BOD also has a serious impact on crop health and productivity. Soil health, defined by its biological, physical, and chemical properties, forms the basis of crop productivity, much like water quality does in hydroponic systems. Edaphic factors, including soil texture, pH, nutrient levels, and microbial diversity, directly determine crop growth, just as BOD reflects the availability of oxygen for sustaining microbial and plant health in water-based systems (Hu et al., 2024 ). When soils are degraded, for instance by poor water retention in sandy soils or acidity that restricts nutrient uptake (Naorem et al., 2023 ), crops suffer reduced vigour; similarly, high BOD in hydroponic water limits dissolved oxygen, creating conditions that stress plants and favour opportunistic pathogens. The interaction between crop roots and microbial communities in soils provides a natural buffer, enhancing nutrient cycling, disease resistance, and tolerance to stress (Wei et al., 2024 ). In hydroponics, however, excessive organic matter accumulation raises BOD, disrupting this balance by driving microbial overgrowth and oxygen depletion, an aquatic parallel to nutrient imbalances and microbial instability in soils. Just as planting methods, tillage, and crop rotations influence soil pH, organic matter, and microbial dynamics (Khmelevtsova et al., 2022 ), the management of nutrient solutions directly shapes microbial composition in hydroponic systems. Failure to regulate these inputs can destabilise the ecosystem, impair nutrient uptake, and reduce crop yield. Ultimately, the synergy between crops, soil, and microorganisms in terrestrial systems mirrors the delicate crop-water-microbe relationship in hydroponics. In both cases, disruptions, whether through soil compaction or elevated BOD, reduce ecosystem stability, hinder nutrient cycling, and compromise agricultural sustainability. A deeper understanding of these interactions is therefore essential, not only for optimising soil environments but also for safeguarding hydroponic water quality, ensuring crop health, and sustaining productivity under future food production systems. Food Safety Risks in Hydroponics: Pathogen Proliferation in High-BOD Water Hydroponic fruit and vegetable production is expanding rapidly, driven by consumer demand for fresh, locally sourced produce available year-round. In the United States alone, the sector is valued at approximately USD 961.8 million and is projected to grow at an annual rate of 10.7% (Ivey et al., 2025 ). Alongside this growth, however, concerns about food safety have intensified, particularly the risk of contamination with human pathogens. In recent years, several foodborne illness outbreaks and product recalls have been directly linked to hydroponic leafy greens. For example, a 2021 multistate outbreak of Salmonella associated with hydroponic leafy greens resulted in 31 confirmed cases, including four hospitalisations (FDA, 2021). Investigations identified the contamination as originating from water sources and lapses in food safety practices along the supply chain (McClure et al ., 2021). Since then, multiple recalls have been issued across the U.S. due to potential contamination of hydroponic produce with pathogens such as Salmonella spp. and Listeria monocytogenes (Ivey et al., 2025 ). Besides, hydroponic farming introduces distinctive food safety challenges Carstens et al ., 2017). In these systems, crops are in constant contact with the recirculating nutrient solution, which can serve as a direct pathway for pathogen transmission. Contaminants may enter the solution through multiple routes, including the substrate, source water (surface, groundwater, or municipal), workers, or contact surfaces, where they can spread rapidly and cross-contaminate the edible portions of crops (Ilic et al., 2017 ). Unlike in soil-based production, root exudates in hydroponics do not remain confined to the rhizosphere but leach into the shared nutrient solution. These organic compounds elevate the biochemical oxygen demand (BOD), creating a nutrient-rich environment that supports bacterial growth and promotes biofilm formation (Thomas et al., 2023 ). Moreover, the aeration of nutrient solutions, while necessary for plant health, produces oxygen-rich conditions that intensify microbial dynamics and can accelerate pathogen proliferation (Garay, 2024 ). With no clean breaks in continuous production cycles, biofilms readily establish on system surfaces, creating persistent reservoirs of contamination (Hamilton et al., 2023 ). Without effective intervention strategies, these high-BOD, microbially active environments pose significant risks to the food safety of hydroponically grown crops. 3. Synthetic Biology Tools for BOD Management 3.1 Model Microorganisms and Metabolic Pathways The strategic implementation of synthetic biology in hydroponic systems for biochemical oxygen demand (BOD) management hinges on selecting microbial chassis that exhibit robust growth, genetic tractability, and metabolic versatility. Ideal candidates must demonstrate non-pathogenic characteristics and maintain functional stability in nutrient-dense aqueous environments typical of controlled-environment agriculture. Among the most extensively characterised organisms are Escherichia coli , Bacillus subtilis , Pseudomonas putida , and members of the Rhodococcus genus—each distinguished by their capacity to metabolise diverse organic compounds (Geng et al., 2023 ; Sun et al., 2022 ). Bacillus subtilis , a Gram-positive bacterium renowned for its prolific secretion of hydrolytic enzymes, has undergone genetic engineering to express elevated levels of proteases, cellulases, and lipases. These enzymes facilitate the degradation of proteinaceous, cellulosic, and lipid-based waste materials commonly accumulated in hydroponic nutrient solutions (Li et al., 2021 ). Pseudomonas putida , recognised for its innate capacity to degrade aromatic hydrocarbons, has been further enhanced through the integration of expanded catabolic pathways using synthetic promoters and optimised ribosome binding sites, thereby amplifying the degradation of recalcitrant organic compounds that contribute to elevated BOD levels (Nikel and de Lorenzo, 2018 ). Additionally, Rhodococcus jostii has emerged as a particularly promising candidate owing to its metabolic flexibility and capacity to oxidise recalcitrant compounds under aerobic conditions (Patel et al., 2020 ). The metabolic pathways implicated in BOD reduction are equally diverse. The β-ketoadipate pathway, critical for aromatic compound degradation, has been extensively studied in Pseudomonas species and represents a central route for the catabolism of lignin-derived phenolic compounds (Martinez et al., 2025 ). Laccase-mediated oxidation offers an alternative enzymatic route for complex organic molecule breakdown, particularly effective against recalcitrant polymeric structures (Rodriguez et al., 2025 ). The strategic focus on microorganisms with established safety profiles remains paramount, given their deployment in food production systems where biosafety cannot be compromised (Smith et al., 2023 ). However, several considerations merit deeper examination. The adaptability of these model organisms to the distinctive physicochemical conditions of hydroponic systems—characterised by nutrient richness, fluctuating dissolved oxygen levels, and periodic pH variations—differs substantially from traditional wastewater treatment contexts (Wang et al., 2021 ). Furthermore, expanding the repertoire of candidate microorganisms to include extremophilic or facultatively anaerobic species may broaden the applicability of synthetic biology approaches across diverse hydroponic configurations (Rodriguez et al., 2025 ). Table 1 provides a comparative assessment of key model microorganisms and their performance metrics in BOD degradation applications. Table 1 Comparative performance of model microorganisms in BOD degradation within hydroponic systems. Organisms Target Substrate Degradation Efficiency Oxygen Requirement Reference Pseudomonas putida Phenolic compounds 85% in 48 hours Aerobic Gao et al., 2024 Bacillus subtilis Carbohydrates, proteins 70% in 72 hours Aerobic Martinez et al., 2025 Rhodococcus erythropolis Lignin derivatives 65% in 96 hours Aerobic Rodriguez et al., 2025 Rhodococcus jostii Recalcitrant compounds 68% in 84 hours Aerobic Patel et al., 2020 3.2 Synthetic Biology Techniques for Enhanced Bioremediation CRISPR-Cas9 Gene Editing technology has fundamentally transformed the landscape of microbial engineering, offering unprecedented precision in genome editing and enabling the targeted enhancement of metabolic pathways critical to BOD degradation. By facilitating the knockout of metabolic repressor genes or the chromosomal integration of catabolic gene cassettes, researchers can engineer strains with substantially elevated expression of key enzymes, including oxygenases, laccases, hydrolases, and dehydrogenases—all essential for the breakdown of BOD-inducing organic compounds (Liu et al., 2024 ; Wang et al., 2020 ). The principal advantages of CRISPR-based approaches include their precision, scalability, and rapidity compared to conventional mutagenesis or homologous recombination methods. For instance, engineered B. subtilis strains incorporating CRISPR-mediated overexpression of the aprE gene have demonstrated markedly improved protein degradation efficiency in recirculating hydroponic systems (Zhou et al., 2022 ). Similarly, the enhancement of Pseudomonas species for phenol degradation addresses a critical gap, as phenolic compounds are prevalent contaminants in hydroponic nutrient solutions derived from root exudates and organic substrate decomposition (Chen et al., 2025 ). Nevertheless, potential off-target effects in complex microbial genomes remain a concern, particularly regarding long-term genetic stability in field applications. Comprehensive whole-genome sequencing and phenotypic validation are therefore essential to ensure the reliability and biosafety of CRISPR-engineered strains destined for deployment in food production systems (Wright et al., 2022 ). Table 2 summarises recent advances in CRISPR-based metabolic engineering for BOD management. Table 2 Recent applications of CRISPR-Cas9 technology in engineering microorganisms for enhanced BOD degradation. Target Organism Gene Target Metabolic Enhancement Application Reference Bacillus subtilis aprE Enhanced protease secretion Protein degradation Zhou et al., 2022 Pseudomonas putida pheA, catA Improved phenol metabolism Aromatic compound removal Chen et al., 2025 Escherichia coli lacZ, cel5A Cellulase expression Cellulose degradation Li et al., 2021 Rhodococcus jostii ligD, dypB Lignin peroxidase activity Lignin breakdown Patel et al., 2020 Beyond individual gene editing, synthetic biology enables the modular reprogramming of entire metabolic networks to optimise substrate flux through degradation metabolic pathways. This holistic approach employs techniques including promoter engineering, dynamic gene regulation, and metabolic pathway balancing to achieve coordinated enzyme expression patterns (Yang et al., 2023 ). A particularly elegant strategy involves the incorporation of inducible promoters responsive to organic load thresholds, allowing coordinated enzyme expression that tracks BOD levels. This dynamic regulation minimises metabolic burden during low-pollutant phases while ensuring robust degradation capacity when organic loads increase. Research has demonstrated the successful integration of multi-gene pathway assemblies for lignin, cellulose, and protein hydrolysis into a single microbial chassis. These synthetic operons coordinate the sequential expression of enzymes required for complex substrate degradation, thereby enhancing overall efficiency while reducing lag times associated with oxygen consumption (Yang et al., 2023 ). The strategic use of synthetic biology circuits that link sensing, processing, and actuation functions represents a paradigm shift from static genetic modifications toward dynamic, responsive bioremediation systems. Biosafety Mechanisms: Kill Switches and Containment Strategies: The deployment of genetically engineered microorganisms (GEMs) in food production environments necessitates robust biosafety frameworks to mitigate risks associated with environmental persistence and horizontal gene transfer. Synthetic biology offers multiple safeguards through the implementation of genetic kill switches—engineered circuits that trigger programmed cell death in response to specific environmental cues, such as nutrient depletion, antibiotic absence, or temperature changes (Wright et al., 2022 ). Auxotrophic strains engineered to depend on synthetic amino acids unavailable in natural environments provide an additional containment layer. These organisms cannot survive outside controlled systems, thereby preventing ecological establishment (Lu et al., 2021 ). Furthermore, genetic firewall technologies, including gene guard systems that prevent horizontal gene transfer through the use of non-standard genetic codes or orthogonal replication systems, are under active investigation. These multilayered biosafety approaches are essential for gaining regulatory approval and public acceptance of synthetic biology in agriculture. 3.3 Hydroponic Systems as Testbeds for Synthetic Biology Applications Hydroponic cultivation systems offer uniquely advantageous platforms for synthetic biology research and development. Their closed-loop architecture, controlled environmental parameters, and ease of sampling enable rigorous evaluation of engineered microbial strains under reproducible conditions. Nutrient Film Technique (NFT) systems cultivating fast-growing crops such as lettuce ( Lactuca sativa ) are particularly well-suited as model systems for pilot-scale experiments targeting BOD control (Gruda, 2020 ). These systems provide reproducible conditions for evaluating engineered strain performance across varying organic loads, light intensities, temperature regimes, and nutrient flux patterns. The inherent scalability of hydroponic systems facilitates the transition from laboratory prototypes to commercial implementations in urban vertical farms and industrial greenhouses. Moreover, the integration of real-time monitoring technologies in hydroponics aligns seamlessly with the feedback-responsive capabilities of synthetic biology circuits, enabling adaptive bioremediation strategies (He et al., 2023 ). 3.4 BOD Measurement and Real-Time Monitoring Technologies The Standard five-day biochemical oxygen demand test (BOD₅) (APHA Method 5210 B) remains the gold standard for regulatory compliance and baseline assessment of organic pollution in aqueous systems. The method involves sample incubation in darkness at 20°C for five days, with dissolved oxygen depletion measured as a proxy for microbial respiration and organic matter oxidation (APHA, 2022). While providing reliable quantitative data, BOD₅ testing suffers from inherent limitations, including lengthy analysis time, labour intensity, and unsuitability for real-time management of dynamic hydroponic systems where rapid decision-making is critical. Technological advances have yielded real-time biosensor systems capable of providing continuous, in situ monitoring of organic pollution levels, thereby overcoming the temporal limitations of conventional BOD₅ testing. Microbial fuel cell (MFC)-based biosensors employ electroactive bacteria that generate measurable electrical currents proportional to organic substrate concentrations, enabling near-instantaneous BOD assessment (Wei et al., 2021 ). These systems can be directly integrated into hydroponic recirculation loops, providing continuous water quality surveillance. Optical and fluorescence-based biosensors incorporating engineered microbial reporters offer complementary detection capabilities. These systems can be engineered to respond specifically to target organic compounds or oxygen depletion events with high sensitivity and selectivity (Xu et al., 2023 ). When coupled with data acquisition systems and cloud-based analytics platforms, biosensors support feedback control loops for dynamic activation of microbial degradation pathways and provide early warning of contamination events. This integration of sensing and actuation represents a transformative shift toward intelligent, self-regulating hydroponic systems. 3.5 Designing Synthetic Microbial Consortia for Enhanced BOD Degradation While monocultures of engineered microorganisms offer precision and predictability, they often exhibit limitations in long-term stability, functional breadth, and resilience to environmental perturbations. In contrast, synthetic microbial consortia leverage functional specialisation, metabolic cooperation, and ecological complementarity to achieve enhanced performance characteristics (Zuniga et al., 2020 ). These engineered communities can integrate aerobic and facultatively anaerobic species that synergistically degrade a broader spectrum of organic pollutants while maintaining system oxygen homeostasis. Key design principles for synthetic consortia include the implementation of quorum-sensing control mechanisms for synchronised metabolic activity, spatial structuring through biofilm-forming capabilities, and deliberate division of labour among specialist strains. For example, B. subtilis engineered for proteolysis can be co-cultivated with P. putida specialised in hydrocarbon degradation, creating a metabolically balanced system for efficient BOD reduction (Schreiber et al., 2022 ). Computational tools such as OptCom and the COBRA toolbox facilitate the optimisation of metabolic flux distributions and interaction networks within consortia, enabling rational design rather than empirical trial-and-error approaches (Zuniga et al., 2020 ). 3.6 Data Analytics and Predictive Modelling for BOD Optimisation The convergence of synthetic biology with computational modelling and machine learning represents a frontier in BOD management. Data streams from biosensors, environmental monitors, and microbial gene expression assays can be processed using artificial intelligence algorithms to predict BOD trends, optimise microbe deployment schedules, and dynamically adjust nutrient inputs (Aghamohammadi et al., 2023 ). Digital twin technology—virtual simulations that mirror physical hydroponic systems in real-time—enables the modelling of complex interactions among engineered microbes, organic loads, and environmental variables, facilitating proactive rather than reactive management strategies. Machine learning models trained on historical BOD and microbial performance data can recommend optimal strain combinations, pathway enhancements, and operational parameters tailored to specific crop systems and environmental conditions. This data-driven approach accelerates the design–build–test–learn cycle fundamental to synthetic biology, reducing development timelines and improving translation from laboratory to field. The integration of artificial intelligence with engineered biological systems marks a transformative evolution toward truly autonomous, self-optimising agricultural production systems (He et al., 2023 ). 4. Comparative Assessment, Biosafety, and Regulatory Considerations 4.1 Efficacy Comparison: Synthetic Biology versus Traditional BOD Management Traditional methodologies for managing BOD in hydroponic systems—including mechanical aeration, periodic water replacement, and chemical oxidation using ozone or hydrogen peroxide—have been employed extensively due to their operational simplicity and immediate efficacy. However, these approaches are inherently reactive, energy-intensive, and often inefficient in addressing the persistent accumulation of complex organic waste (Chatterjee et al., 2023 ). Moreover, they lack substrate specificity and may disrupt beneficial microbial communities while potentially damaging plant root systems or destabilising nutrient balances. In contrast, synthetic biology offers targeted, adaptive strategies for BOD reduction. Engineered microbial systems can be designed to selectively degrade specific organic pollutant classes through customised catabolic pathways, enabling proactive removal of BOD-causing compounds at their source (Nikel and de Lorenzo, 2018 ). Genetically modified strains of B. subtilis and P. putida have demonstrated superior performance compared to conventional chemical treatments, accelerating degradation rates while maintaining overall system stability (Sun et al., 2022 ). Furthermore, synthetic biological systems can be engineered for inducible activation in response to BOD fluctuations, thereby conserving metabolic resources during low-load periods. When integrated with biosensor networks and feedback control loops, synthetic microbes respond dynamically to environmental changes—a capability unattainable with conventional physicochemical methods (Wright et al., 2022 ). The efficacy of synthetic biology lies fundamentally in its precision, sustainability, and adaptability, positioning it as a superior alternative for water quality management in controlled agriculture. Table 3 Comparative assessment of traditional and synthetic biology-based BOD management strategies in hydroponic systems. Criterion Traditional Methods Synthetic Biology Key Advantage Reference Specificity Non-selective, broad-spectrum Highly targeted, pathway-specific Synthetic biology Riglar and Silver ( 2018 ); Chen et al. ( 2020 ) Energy consumption High (continuous aeration/UV) Low (self-regulating) Synthetic biology McCarty et al. ( 2011 ); Guo et al. ( 2021 ) Adaptability Reactive, manual adjustment Dynamic, feedback-responsive Synthetic biology Huang et al. ( 2022 ); Bartley et al. ( 2021 ) Environmental impact Chemical discharge, disruption Minimal, controlled biodegradation Synthetic biology Khalid et al. ( 2021 ); Arora and Bae ( 2023 ) Implementation time Immediate Requires development phase Traditional methods Cheng and Lu ( 2020 ); Voyvodic et al. ( 2023 ) Long-term cost High operational expenses Lower after initial investment Synthetic biology Zhang et al. ( 2022 ); Carbonell et al. ( 2019 ) Regulatory clarity Well-established frameworks Evolving, region-dependent Traditional methods Aas et al. ( 2023 ); Kaebnick et al. ( 2024 ) 4.2 Implications for Food Safety: Mitigating Microbial Risks in Hydroponic Produce Microbial contamination of hydroponic produce represents a significant food safety concern, particularly for leafy greens consumed raw. Elevated BOD levels can create anaerobic microenvironments that favour the proliferation of pathogenic and opportunistic microorganisms, including Escherichia coli , Salmonella spp., and Listeria monocytogenes (Jaiswal et al., 2022 ). This challenge is particularly acute in recirculating systems where water is reused across multiple cultivation cycles, potentially amplifying pathogen populations. Synthetic biology provides innovative approaches to mitigate these risks. Engineered microorganisms can be designed to perform dual functions: degrading organic pollutants while simultaneously secreting antimicrobial peptides or producing competitive exclusion factors that inhibit pathogen colonisation (Cameron et al., 2021 ). Additionally, synthetic systems incorporating quorum-sensing inhibition (QSI) can disrupt cell-to-cell communication among pathogenic bacteria, thereby preventing biofilm formation and enhancing overall system hygiene (Schreiber et al., 2022 ). By maintaining consistently lower BOD levels and fostering beneficial microbial communities, synthetic biology approaches indirectly enhance the microbiological safety of hydroponic produce. These systems can be designed to align with international food safety standards, including Codex Alimentarius guidelines and the U.S. FDA Produce Safety Rule. However, achieving full regulatory acceptance requires demonstrating the absence of transgenic material persistence on harvested crops—a challenge being addressed through innovations in containment strategies and genetic clearance technologies (Wright et al., 2022 ). 4.3 Scalability for Urban and Commercial Hydroponic Operations Scalability represents a critical determinant of biotechnological adoption in agriculture. Conventional water treatment systems in hydroponics—such as ultraviolet sterilisation or periodic system flushing—scale linearly with system size but often become economically and logistically prohibitive in large-scale or urban farming environments (Al-Kodmany, 2018 ). Synthetic biology, conversely, offers scalability through modular microbial systems that can be expanded, regulated, and monitored with minimal infrastructural modifications. Bioreactors embedded within hydroponic recirculation loops can house synthetic consortia that automatically adapt to varying organic loads, making them particularly suitable for vertical farms and large greenhouse operations (Aghamohammadi et al., 2023 ). Integration with Internet-of-Things (IoT) technologies enables centralised monitoring coupled with decentralised microbial deployment, facilitating real-time control across dispersed farming units. This distributed intelligence architecture is particularly advantageous for urban agriculture networks comprising multiple small-to-medium production facilities (He et al., 2023 ). However, large-scale applications introduce complexities including interspecies competition, genetic drift, and susceptibility to environmental perturbations. Strategies such as microbial encapsulation, immobilised biofilms, and rationally designed consortia are being explored to enhance robustness and reproducibility across scales (Zuniga et al., 2020 ). The emerging application of digital twin technology to model and optimise microbial behaviour in commercial contexts before field deployment represents a significant advancement in de-risking scale-up processes. 4.4 Economic Feasibility: Cost-Benefit Analysis of Microbial Bioreactors Economic viability often determines the pace of technology adoption within the agri-food sector. While initial capital expenditure for designing and deploying engineered microbial systems may exceed that of traditional approaches, comprehensive life-cycle analyses reveal potential net savings through improved water reuse efficiency, reduced chemical inputs, minimised crop losses, and decreased downtime from contamination events (Raghav et al., 2021 ). Recent techno-economic assessments of microbial bioreactors suggest that systems incorporating low-maintenance biofilms or immobilised consortia can operate efficiently over extended periods with minimal intervention, achieving cost competitiveness with conventional methods within 2–3 operational years (Schreiber et al., 2022 ). Furthermore, the proliferation of open-source genetic toolkits and community biofoundries has significantly reduced strain development costs, lowering entry barriers for small-to-medium growers (Wurtzel et al., 2023 ). Investment from public-private partnerships and venture capital in agricultural biotechnology continues to accelerate, recognising that sustainable agriculture solutions must balance ecological and economic imperatives. Synthetic biology platforms offering plug-and-play compatibility with existing hydroponic infrastructure hold particular promise for widespread adoption, as they minimise retrofit costs and technical barriers (Brown et al., 2021 ). 4.5 Stakeholder Perspectives: Farmers, Industry, and Consumers Successful deployment of synthetic biology in hydroponics requires understanding and addressing the diverse perspectives of key stakeholders. Farmers prioritise ease of use, regulatory clarity, and return on investment. Synthetic biological solutions presented as user-friendly, low-maintenance systems supported by comprehensive technical documentation are more likely to gain adoption among grower communities (Brown et al., 2021 ). Training programs and accessible decision-support tools are essential for bridging the knowledge gap between biotechnology developers and end-users. Industry stakeholders—including agricultural technology firms, food distributors, and retailers- increasingly view synthetic biology as a driver of innovation and sustainability. However, concerns regarding public perception, particularly around genetically modified organisms (GMOs) in food production, remain constraining factors. Transparency, traceability, and independent third-party validation are critical elements influencing industry acceptance (Cressey, 2022 ). Consumer acceptance hinges on assurances of food safety, environmental sustainability, and ethical deployment. Recent surveys indicate growing openness to synthetic biology applications when communicated within frameworks of climate resilience and food security, particularly among younger demographics and environmentally conscious consumer segments (Wright et al., 2022 ). Continued public education, transparent communication, and meaningful regulatory engagement are essential for aligning societal values with technological progress. 4.6 Limitations and Challenges: Stability, Integration, and Regulatory Uncertainty Despite its transformative potential, synthetic biology for BOD management faces substantial challenges. Long-term microbial stability represents a primary concern, as engineered strains may lose functionality through mutational drift, horizontal gene transfer, or evolutionary pressures within complex microbial communities (Lu et al., 2021 ). Interactions between introduced microorganisms and native microbiota can yield unpredictable outcomes, necessitating sophisticated monitoring and modelling systems to ensure predictable performance. Integration challenges also merit consideration. Factors including fluid dynamics, nutrient concentrations, pH fluctuations, and dissolved oxygen levels can profoundly influence microbial viability and efficacy. Ensuring compatibility between engineered organisms and the physicochemical environments of diverse hydroponic configurations—including Nutrient Film Technique (NFT), Deep Water Culture (DWC), and aeroponic systems requires iterative optimisation and extensive real-world validation (Han et al., 2020 ). Regulatory uncertainty surrounding synthetic biology and genetically engineered microbes in food production remains a significant barrier in many jurisdictions. International regulatory frameworks vary substantially, creating challenges for global technology deployment. Harmonising biosafety standards and developing robust environmental risk assessment protocols are necessary prerequisites for unlocking the full potential of this transformative approach (Tessnow and De Lorenzo, 2023 ). Proactive engagement with regulatory agencies, transparent communication of risk assessment data, and demonstration of containment efficacy will be essential for advancing the field. 5. Practical Applications and Future Directions 5.1 Implementation in Urban Hydroponic Farms for Sustainable Food Production Urban agriculture has emerged as a transformative response to converging challenges of climate change, land scarcity, and population growth. Within this context, hydroponics, the soilless cultivation of crops using nutrient-enriched water, offers space-efficient, high-yield production methods for fresh food in metropolitan areas. However, hydroponic sustainability is frequently compromised by organic waste accumulation in recirculating water, which elevates BOD and threatens both plant health and food safety (Gruda, 2020 ). The integration of synthetic biology provides an elegant solution to this bottleneck. Engineered microorganisms with enhanced catabolic pathways can be deployed directly into urban hydroponic systems for in situ degradation of organic residues. This biotechnological intervention minimises water replacement frequency, reduces chemical usage, and improves water reuse rates, attributes ideally suited for resource-constrained urban environments (Cameron et al., 2021 ). Successful pilot implementations have been documented in Singapore and the Netherlands, where synthetic strains of B. subtilis and P. putida have demonstrated effective water quality management without compromising plant yields or safety parameters (Zhou et al., 2022 ). 5.2 Water Reuse Strategies: Closed-Loop Bioaugmentation Models Water efficiency lies at the heart of hydroponic agriculture's environmental value proposition. However, recirculating systems face the persistent challenge of organic waste accumulation, which elevates BOD and increases pathogen proliferation risks. Closed-loop bioaugmentation—the strategic introduction of engineered or enriched microbial consortia—is gaining traction as an ecologically sound approach to restore water quality and reduce treatment costs (Jaiswal et al., 2022 ). Synthetic biology enables the design of microbial strains or consortia specifically tailored to degrade distinct categories of organic matter—proteins, carbohydrates, lipids—thereby maintaining consistently low BOD levels throughout extended operational periods. These bioaugmented systems operate in self-regulating modes, with microbial activity responding dynamically to fluctuations in organic load (Zuniga et al., 2020 ). Empirical studies have demonstrated that modular microbial units can increase water reuse rates by up to 90%, extend nutrient solution operational lifespans, and substantially reduce dependence on synthetic disinfectants (Wang et al., 2021 ). 5.3 Integration with Internet of Things for Automated Water Quality Management The convergence of synthetic biology with Internet of Things (IoT) technologies represents a paradigm shift in precision agriculture. By embedding biosensors and microbial activity monitors within hydroponic systems, growers can achieve real-time surveillance of BOD levels, oxygen saturation, microbial viability, and nutrient dynamics (He et al., 2023 ). These sensor networks, typically linked to cloud-based analytics platforms, provide actionable intelligence that informs system adjustments—including nutrient dosing, aeration control, or timed release of engineered microbes. Advanced implementations include genetically encoded biosensors engineered to produce fluorescent or electrochemical signals in response to specific organic pollutants. These can be integrated with IoT dashboards to provide early warning of contamination events and facilitate automated control loops that dynamically activate or suppress microbial degradation pathways as needed (Xu et al., 2023 ). The result is a highly adaptive, labour-efficient intelligent environment that aligns with Industry 4.0 agricultural principles and urban smart farming objectives. 5.4 Case Studies: Real-World Implementations of Synthetic Biology in Hydroponics Several pioneering implementations illustrate the growing application of synthetic biology in commercial hydroponic operations. In Singapore, a collaborative initiative led by the Agency for Science, Technology and Research (A*STAR) developed a modular bioreactor system incorporating CRISPR-engineered B. subtilis for deployment in commercial lettuce cultivation. This system achieved a 75% reduction in BOD levels accompanied by measurable declines in pathogenic bacterial counts, demonstrating both efficacy and biosafety (Tan et al., 2022 ). In the Netherlands, researchers at Wageningen University partnered with an urban agriculture startup to deploy synthetic consortia comprising Pseudomonas, Comamonas , and Acinetobacter species for BOD control in commercial basil and kale production systems. This project demonstrated improved crop quality parameters and a 40% increase in water reuse efficiency (Schreiber et al., 2022 ). In North America, rooftop farms in New York and Toronto have tested IoT-integrated biosensor systems that trigger microbial capsule activation when BOD thresholds are exceeded. These installations have reportedly reduced operational costs by 20% compared to conventional chemical water treatment protocols while improving overall system stability (Brown et al., 2021 ). These case studies collectively demonstrate the technical feasibility and economic viability of synthetic biology approaches across diverse hydroponic contexts. 5.5 Capacity Building: Training and Knowledge Transfer for Farmers A critical barrier to synthetic biology adoption in hydroponics is the knowledge gap between technology developers and end-users. Many urban and peri-urban farmers possess limited familiarity with genetically engineered microbial technologies, biosensor interpretation, or digital feedback systems. Consequently, structured training programs and capacity-building initiatives are essential for successful technology implementation (Wurtzel et al., 2023 ). Effective training modalities include hands-on workshops, modular online courses, and cooperative extension programs covering topics such as safe handling of engineered microbes, biosensor signal interpretation, and appropriate responses to system alerts. Participatory design approaches, wherein farmers collaborate with synthetic biologists in system customisation, have proven particularly effective in increasing technology uptake, building trust, and accelerating innovation diffusion (Cressey, 2022 ). Government-supported programs, including the EU Horizon Europe framework and USAID's Feed the Future initiative, are increasingly incorporating synthetic biology components in their agricultural training curricula. 5.6 Contributions to Global Food Security and Sustainable Development Goals The broader significance of synthetic biology-based BOD management extends beyond technical performance metrics to encompass contributions toward global sustainability objectives. By enhancing the safety, efficiency, and resilience of hydroponic farming, these systems address multiple United Nations Sustainable Development Goals (SDGs): SDG 2 (Zero Hunger) : By enabling continuous, high-yield food production in urban and climate-stressed regions, synthetic biology tools support nutritional security and localised food access, particularly in resource-limited settings (FAO, 2021). SDG 6 (Clean Water and Sanitation) : Closed-loop microbial BOD management significantly reduces agricultural water consumption and wastewater discharge, promoting clean water systems and aquatic ecosystem protection (UN-Water, 2022 ). SDG 9 (Industry, Innovation, and Infrastructure) : The integration of biotechnology with IoT infrastructure exemplifies next-generation agricultural systems that are intelligent, efficient, and sustainable. SDG 13 (Climate Action) : Reducing the carbon footprint and water demands of agriculture through biological systems aligns with global efforts to mitigate climate change impacts. These multifaceted contributions position synthetic biology not merely as a technical innovation but as a strategic tool for addressing some of humanity's most pressing challenges in food security, environmental sustainability, and climate resilience. 6. Biosafety, Ethics, and Regulatory Frameworks 6.1 Containment Strategies for Engineered Microbes: Kill Switches, Auxotrophy, and Gene Guard Mechanisms Synthetic biology holds significant promise for optimising BOD degradation in hydroponic systems, yet its success depends on responsible stewardship. Containment strategies, ecological risk management, transparent regulations, and societal engagement must work in synergy. In hydroponic systems designed for future food production, engineered microbes offer the potential to accelerate biochemical oxygen demand (BOD) degradation, thereby improving water quality and crop yield (Mariam et al., 2025 ). However, their deployment must be accompanied by robust containment strategies to prevent uncontrolled proliferation. Kill switches—genetic circuits programmed to trigger cell death under specific conditions—are increasingly employed to ensure microbes cannot survive outside designated environments (Rottinghaus et al., 2022 ). Auxotrophy, where microbes are engineered to depend on a synthetic nutrient absent in natural ecosystems, further limits their environmental persistence. Gene guard mechanisms, such as toxin-antitoxin systems and CRISPR-based self-destruction codes, serve as an additional layer of biological security, ensuring engineered traits are not sustained if containment fails (Watters et al., 2021 ). 6.2 Horizontal Gene Transfer and Ecological Risk Assessment Horizontal gene transfer (HGT) poses a major ecological concern, as engineered genetic material could potentially move into native microbial communities. This could result in unforeseen metabolic activities or altered ecosystem dynamics, especially in aquaponic or hydroponic settings where water acts as a medium for microbial exchange (French et al., 2020 ). Risk assessments should include metagenomic surveillance to detect early signs of HGT, predictive ecological modelling to forecast potential impacts, and controlled microcosm experiments to evaluate survival, fitness, and adaptability of engineered strains (Emamalipour et al., 2020 ). The goal is to mitigate both immediate environmental hazards and long-term evolutionary consequences. A forward-looking regulatory framework should integrate biosafety, ethics, and socio-economic concerns. This could include mandatory ethical impact assessments alongside traditional environmental impact assessments, periodic public consultations, and adaptive governance that evolves with technological advances. Such integration ensures that regulatory decisions are not solely technical but also socially responsive (Lescrauwaet et al., 2022 ). 6.3 Regulatory Landscape: Global Biosafety Frameworks for Water and Food Biotech The governance of engineered microbes in water-based food production varies across regions. The Cartagena Protocol on Biosafety provides international guidance, focusing on the safe handling, transport, and use of genetically modified organisms (GMOs) (Pereira, 2022 ). In the European Union, EFSA (European Food Safety Authority) enforces stringent pre-market risk evaluations, while in the United States, the EPA, USDA, and FDA share oversight responsibilities depending on intended use. Countries like Japan and Australia adopt case-by-case assessments aligned with OECD principles (Samson et al., 2025 ). For hydroponic applications, the regulatory scope extends beyond agricultural safety to encompass water quality laws, making interdisciplinary compliance essential (Rajaseger et al., 2023 ). Beyond biosafety, ethical considerations influence the societal reception of engineered microbes. Public concerns often revolve around the “unnaturalness” of synthetic biology, potential impacts on biodiversity, and corporate monopolisation of biotechnologies. Ethical frameworks emphasise transparency in research objectives, open communication about risks and benefits, and inclusive decision-making processes involving farmers, consumers, regulators, and scientists. Upholding these principles can help bridge the trust gap between innovators and the general public (Dalziell and Rogers, 2023 ). Introducing engineered microbes into hydroponics could reduce operational costs, improve yield, and support urban food security. However, socio-economic disparities may arise if only large-scale commercial farms can afford the technology. Ethical adoption requires equitable access frameworks, possibly through open-source microbial strains or government-subsidised programs, ensuring that smallholder and resource-limited farmers also benefit from synthetic biology innovations (Chiaranunt and White, 2023 ). Effective communication strategies should balance technical accuracy with accessibility. Visual models showing how engineered microbes degrade BOD without harming crops, along with real-world pilot results, can counter misinformation (Table 4 ). Importantly, public engagement should occur early—during the research and development phase rather than post-commercialisation—to foster informed acceptance. This proactive approach shifts public perception from reactive resistance to collaborative evaluation. Table 4 Ethical Considerations and Public Acceptance of Engineered Microbes Ethical Concern Description Public Perception Challenge Mitigation Strategies References Environmental Safety Risk of engineered microbes escaping into natural ecosystems Fear of ecological imbalance Robust containment strategies, ecological monitoring Cummings et al. ( 2025 ) Food Safety Potential unintended effects on crops or consumers Distrust of GMOs in food Transparent safety testing, third-party certification Rajendran ( 2022 ) Biodiversity Impact Potential displacement of native microbial communities Concern over loss of natural diversity Use of targeted microbial strains with limited survival capacity Hardwick et al. ( 2024 ) Corporate Control Concentration of technology ownership Perceived monopolisation and farmer dependency Open-source licensing, public-private partnerships Kumar et al. ( 2018 ) Cultural Acceptance Ethical/religious objections to synthetic life Resistance from certain communities Inclusive dialogues, cultural sensitivity in outreach Samson et al. ( 2025 ) Data Transparency Limited access to research data Suspicion of hidden risks Open-access data sharing and public reporting Chiaranunt and White ( 2023 ) 7. Future Research Directions 7.1 Testing Across Diverse Hydroponic Crops and Systems Future research should emphasise evaluating engineered microbes for BOD degradation across a broad range of hydroponic crops and systems. While leafy greens are commonly studied due to their rapid growth cycles, fruiting plants such as tomatoes, cucumbers, and peppers may present different microbial interactions and nutrient dynamics (Cristofano et al., 2021 ). Similarly, research should extend beyond the nutrient-film technique (NFT) and deep-water culture (DWC) to include vertical farming and aquaponics. This will help determine the robustness, adaptability, and crop-specific optimisation of microbial consortia under diverse conditions (Gillani et al., 2023 ). For small-scale farmers, cost is a major barrier to adopting synthetic biology-based hydroponic enhancements. Traditional bioreactors are expensive, energy-intensive, and designed for industrial-scale production. Research should prioritise low-cost, modular bioreactors that use locally available materials, renewable energy sources (such as solar power), and simplified designs for easy operation and maintenance (Mihret et al., 2025 ). Innovations such as gravity-fed systems, biofilm-based reactors, and 3D-printed components could reduce costs significantly, making microbial cultivation and application feasible even in rural or low-income communities (Lazarus et al., 2024 ). 7.2 Long-Term Ecological Impacts of Engineered Microbes The long-term ecological stability of engineered microbes remains a critical knowledge gap. Hydroponic systems are semi-closed environments, yet microbial exchange with water sources, air, and human handlers is inevitable. Studies should investigate persistence, mutation rates, and interactions with non-target organisms over extended cultivation cycles (ElZein et al., 2024 ). Predictive ecological models and controlled multi-season trials are needed to assess cumulative risks and ensure that engineered microbes do not create unforeseen environmental burdens when integrated into food production systems (Taiwo et al., 2024 ). Bioreactor research should also address socio-economic contexts, ensuring designs are affordable, culturally acceptable, and adaptable to local farming practices. Participatory design, where farmers are directly involved in testing prototypes, can help align technological solutions with user needs (Palladino et al., 2024 ). Financial support mechanisms such as microloans, government subsidies, and cooperative ownership models could further ease adoption. The long-term vision should not only be technological feasibility but also economic sustainability and farmer empowerment (Jiang et al., 2024 ). 7.3 Interdisciplinary Approaches: Integrating Synthetic Biology with Other Technologies Optimising hydroponic performance requires synergy between synthetic biology and other technological domains. For example, coupling engineered microbes with IoT-based biosensors could enable real-time monitoring of microbial activity, nutrient levels, and BOD fluctuations (Arlyapov et al., 2022 ). Similarly, machine learning algorithms can process large datasets to predict microbial performance under different system conditions. Integrating nanotechnology, particularly nano-carriers for nutrient or microbial delivery, may further enhance efficiency. Such interdisciplinary approaches ensure that microbial innovations are not isolated but embedded into smarter, more adaptive hydroponic infrastructures (Alsulimani et al., 2024 ). Addressing global food security challenges requires cooperative frameworks that transcend national boundaries. Research consortia should promote open-source microbial strain libraries, accessible datasets, and shared pilot studies across regions. Collaboration between universities, government agencies, and private companies can reduce duplication of effort and accelerate innovation (Taiwo et al., 2024 ). Equally important is ensuring that knowledge transfer reaches small-scale farmers in resource-limited settings through training workshops, demonstration farms, and multilingual digital platforms. This global knowledge ecosystem will make advanced hydroponic solutions more inclusive and scalable (Mgendi et al., 2021 ). The integration of engineered microbes into hydroponics represents a transformative step for sustainable food production. However, achieving global impact requires a focus on adaptability, safety, affordability, and inclusivity. By testing across diverse systems, evaluating long-term impacts, embracing interdisciplinary tools, and fostering global collaboration, synthetic biology can be harnessed responsibly (Sousa et al., 2024 ). Cost-effective bioreactor designs, tailored to the needs of small-scale farmers, will be central to democratising these innovations and ensuring that future food systems are equitable, resilient, and environmentally sustainable (Table 5 ). Table 5 Development of Cost-Effective Bioreactor Designs for Small-Scale Farmers Design Principle Description Benefits for Small-Scale Farmers References Modular Construction Bioreactors built from interchangeable, scalable parts Easy to expand or reduce size based on farm needs Palladino et al. ( 2024 ) Locally Available Materials Use of affordable plastics, recycled containers, or clay-based vessels Reduces cost and dependency on imported equipment da Silva et al. ( 2021 ) Renewable Energy Integration Solar-powered pumps and aeration systems Lowers operational costs and supports off-grid use De et al. ( 2024 ) Gravity-Fed Flow Systems Simplified circulation without complex pumps Minimises energy consumption and maintenance Yu et al . (2024) Biofilm-Based Reactors Surfaces designed to enhance microbial adhesion Higher microbial efficiency with reduced input costs Gomes and Mergulhão ( 2021 ) 3D-Printed Components Low-cost, customizable parts produced locally Encourages innovation and community-based solutions Ajao et al. ( 2022 ) User-Friendly Interfaces Simple monitoring with colour indicators or mobile apps Makes technology accessible to non-experts Kim et al. ( 2023 ) 8. CONCLUSION This review demonstrates that synthetic biology offers a powerful solution to biochemical oxygen demand (BOD) management in hydroponic systems—a persistent challenge that limits efficiency, safety, and scalability of soilless agriculture. As global population growth and climate change intensify pressure on conventional farming, hydroponics optimised through engineered microorganisms provides a viable pathway to sustainable food production. Genetically modified organisms such as Bacillus subtilis , Pseudomonas putida , and Rhodococcus species, enhanced through CRISPR-Cas9 and metabolic engineering, offer targeted organic matter degradation superior to traditional methods (aeration, chemical treatment). When integrated with real-time biosensors, IoT platforms, and machine learning, these systems enable dynamic, self-regulating water quality management. Synthetic biology approaches excel in specificity, energy efficiency, and environmental sustainability, though traditional methods retain advantages in immediate implementation and regulatory clarity. Food safety improvements are significant, as engineered microbes reduce pathogenic proliferation by maintaining low BOD levels while producing antimicrobial compounds. However, successful deployment requires robust biosafety mechanisms (kill switches, auxotrophy), harmonised international regulations, transparent public communication, and equitable access frameworks to benefit both commercial operations and smallholder farmers. Real-world pilots in Singapore, the Netherlands, and North America validate technical feasibility, while future research must address long-term ecological impacts, cost-effective designs for small-scale farmers, and interdisciplinary integration with emerging technologies. By contributing to multiple UN Sustainable Development Goals—particularly food security, water management, and climate action—synthetic biology-based BOD optimisation represents not just a technical advancement but a strategic necessity for building resilient, sustainable food systems capable of meeting future global needs. 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Biosensors and Bioelectronics, 182, 113200. https://doi.org/10.1016/j.bios.2021.113200 Wei, X., Xie, B., Wan, C., Song, R., Zhong, W., Xin, S., and Song, K. (2024). Enhancing soil health and plant growth through microbial fertilisers: Mechanisms, benefits, and sustainable agricultural practices. Agronomy , 14 (3), 609. https://doi.org/10.3390/agronomy14030609 Wilmoth, J., Menozzi, C., Bassarsky , L., and Gu, D. (2023). As the World’s Population Surpasses 8 Billion, What Are the Implications for Planetary Health and Sustainability? United Nations.https://www.un.org/en/un-chronicle/world population-surpasses-8-billion-what-are-implications planetary-health-and sustainability. Wright, O., Stan, G. B., and Ellis, T. (2022). Building-in biosafety for synthetic biology. Microbiology, 168(2), 001141. https://doi.org/10.1099/mic.0.001141 Wurtzel, E. T., Kutchan, T. M., and Dixon, R. A. (2023). Open-source synthetic biology and democratized bioengineering for agriculture. 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Providing Food Security through Hydroponic Systems, Science-Policy Brief for the Multistakeholder Forum on Science, Technology and Innovation for the SDGs, https://sdgs.un.org/sites/default/files/2024-05/. Zhang, X., Chang, X., Zhang, Y., and Li, C. (2022). Cost-benefit analysis of synthetic biology applications in environmental remediation. Environmental Science and Pollution Research , 29 (43), 64651-64664. https://doi.org/10.1007/s11356-022-21582-6 Zhou, Y., Ma, J., and Feng, C. (2022). CRISPR-mediated enhancement of extracellular protease activity in Bacillus subtilis for water remediation. Biotechnology Letters, 44(9), 1173–1181. https://doi.org/10.1007/s10529-022-03289-4 Zhou, Y., Zheng, S. and Wei Qin, W. (2024). Electrochemical biochemical oxygen demand biosensors and their applications in aquatic environmental monitoring. Sensing and Bio-Sensing Research, 44, 100642, ISSN 2214-1804, https://doi.org/10.1016/j.sbsr.2024.100642. Zuniga, C., Zaramela, L., and Zengler, K. (2020). Elucidation of complexity and prediction of interactions in microbial communities. Microbial Biotechnology, 13(2), 383–394. https://doi.org/10.1111/1751-7915.13855 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8879143","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"book-review","associatedPublications":[],"authors":[{"id":595218167,"identity":"6b9d3dbf-f211-46b9-b7c0-2570094c37df","order_by":0,"name":"Oluwasanmi Anuoluwapo ADEYEMI","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8ElEQVRIiWNgGAWjYLACHhDBzHwAwjtAvBa2BFK1MPAYEKeFn/0A44c3FYfldNt5Pn742cYgx3cjge3hFzxaJHsSmCXnnDlsbHaYd7NkbxuDseSNBHZjGTxaDA4kMEjzth1O3HaYd4M0YxtD4gagLdIS+LScf8D8m/ff4fpth3ke/wZqqSesBaSAt+FwgtlhHjaQLQkgEckP+Pwy42Gb5Zxj6YbbDrOZWfackzCceeZhmzQeHQz8/MmHb7ypsZY3O3/48Y0fZTbyfMeTj0n+wKeHgbEBSDTDeBJgEWYevFrAoA7NGPy2jIJRMApGwQgDAIb4TYUoXXE2AAAAAElFTkSuQmCC","orcid":"","institution":"Ajayi Crowther University","correspondingAuthor":true,"prefix":"","firstName":"Oluwasanmi","middleName":"Anuoluwapo","lastName":"ADEYEMI","suffix":""},{"id":595218168,"identity":"280496c8-d350-41f4-bed1-185f1391a18d","order_by":1,"name":"Bukola Margaret Popoola","email":"","orcid":"","institution":"Ajayi Crowther University","correspondingAuthor":false,"prefix":"","firstName":"Bukola","middleName":"Margaret","lastName":"Popoola","suffix":""},{"id":595218169,"identity":"42fefa09-30de-4564-b85e-36761b4e9573","order_by":2,"name":"Oyindamola John Samson","email":"","orcid":"","institution":"Olabisi Onabanjo University","correspondingAuthor":false,"prefix":"","firstName":"Oyindamola","middleName":"John","lastName":"Samson","suffix":""}],"badges":[],"createdAt":"2026-02-14 10:23:39","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8879143/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8879143/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103220962,"identity":"682ffaab-427b-465a-b05a-fafc5fb1283e","added_by":"auto","created_at":"2026-02-23 10:20:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":445471,"visible":true,"origin":"","legend":"\u003cp\u003ePrimary Sources of Organic Load Contributing to BOD in Hydroponic Systems\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8879143/v1/d7ba82ba62374cccf7fcfce1.png"},{"id":103505416,"identity":"513607c7-4119-4846-ae50-2ad0ca4a9ff6","added_by":"auto","created_at":"2026-02-26 13:30:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":144716,"visible":true,"origin":"","legend":"\u003cp\u003eImpacts of High BOD on Water Quality, Crop Health, and Productivity\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8879143/v1/9b6387c2f57ad4d5a3a36295.png"},{"id":104782351,"identity":"336726a9-a1d3-4b5c-959a-a93fec3b094d","added_by":"auto","created_at":"2026-03-17 07:57:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2550002,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8879143/v1/600cc0ff-2a71-463e-ac3c-923ca1b2dbce.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eSynthetic Biology Approaches for Optimizing Bod Degradation in Hydroponic Systems for Future Food Production\u003c/p\u003e","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eIn modern times, synthetic biology has rapidly emerged as a transformative discipline that combines biological research with engineering principles to enable the rational design and construction of biological systems (Shapira et al., \u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This interdisciplinary field converges life sciences, engineering, information science, and even social sciences to pursue fundamental objectives of wiring biological circuits to achieve precise cellular control and elucidating the design principles governing complex biological networks. By leveraging synthetic biology, researchers can design and assemble novel biomolecular components, pathways, and regulatory networks, thereby reprogramming organisms into engineered cell factories (Lv et al., \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), with applications spanning biotechnology, medicine, industrial bioproduction and food production. According to Long et al. (\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), the global population is expected to rise by nearly 2\u0026nbsp;billion by 2050, necessitating new and state-of-the-art solutions to improve agricultural yield and guarantee food security. Numerous factors, however, still pose as obstacles, including the loss of agricultural land due to increased urbanisation, erosion, and climate change (Grier, n.d.).\u003c/p\u003e \u003cp\u003eFurthermore, shifts in living standards, particularly the rise in meat consumption, have created a growing demand for increased production of plant-based proteins for use in animal feed. Higher yields were achieved through the introduction and widespread use of synthetic and natural fertilisers, particularly nitrogen, phosphorus, and potassium, as well as the Green Revolution, which included breeding efforts to optimise plant design and light harvesting. This is currently insufficient, and to meet the food demands of the rising world population, agricultural production must double in the next 30 years, reflecting an annual yield increase of 2.2% (Roell and Zurbriggen, \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Hence, the rapid growth of the global population is driving an escalating demand for essential resources such as food, water, and arable land, posing significant challenges for future generations (Wilmoth et al., \u003cspan citationid=\"CR118\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Concurrently, populations in arid and semi-arid regions are increasingly vulnerable to prolonged droughts, water scarcity, and the emergence of food deserts. These conditions severely constrain conventional agricultural practices, leading to a marked decline in food availability (Qtaishat et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e1.1. The Role of Hydroponics in Future Food Security\u003c/h2\u003e \u003cp\u003eThe Global Report on Food Crises (GRFC) 2025 highlights that strife, economic shocks, weather extremes, and unplanned displacement continue as the primary drivers of food insecurity and malnutrition worldwide, with devastating consequences for already fragile regions. In 2024, over 295\u0026nbsp;million people across 53 countries and territories experienced severe hunger, an increase of 13.7\u0026nbsp;million compared to 2023 (FSIN and GNAFC, 2025). In 2021, approximately 828\u0026nbsp;million people, nearly one in ten worldwide, experienced hunger, which is around 150\u0026nbsp;million more individuals than in 2019. Additionally, approximately 2.3\u0026nbsp;billion people faced moderate or severe food insecurity, 350\u0026nbsp;million more than before the pandemic (Sousa et al., \u003cspan citationid=\"CR103\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The current unrest in Eastern Europe further threatens food security, as both nations involved are major exporters of grains, fertilisers, and energy. Supply disruptions have contributed to soaring food prices; in 2020, 47% of countries experienced rising food costs according to the United Nations Department of Economic and Social Affairs (\u003cspan citationid=\"CR110\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and by August 2025, the FAO Food Price Index reached a record 130.1 points, although 18.8 per cent below its peak reached in March 2022 (FAO, 2025). These rising input costs have exposed the structural vulnerability of global food systems, particularly their reliance on imported energy, fertilisers, and animal feed. This dependence amplifies production costs and erodes consumer purchasing power, making food less affordable for many populations (European Commission, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn answer to these obstacles, hydroponics, a soilless cultivation technique utilising water-based nutrient solutions, has emerged as a promising agricultural innovation. It is a common method of growing plants without soil in a controlled condition by providing a nutrient solution (Sharma et al., \u003cspan citationid=\"CR101\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). A solid understanding of hydroponics is essential, in this soilless cultivation method, plants receive all their required nutrients directly through a water-based solution rather than from soil. Hydroponic systems can take many forms, such as nutrient film technique (NFT), deep water culture (DWC), and aeroponics. Regardless of the specific system, two key factors, water quality and dissolved oxygen availability, play a decisive role in determining plant health and growth outcomes. The integration of hydroponic production with wastewater treatment systems presents numerous benefits: it achieves higher yields compared to traditional farming with appropriate maintenance, eliminates the need for soil, promotes urban farming, mitigates soil-borne diseases (Aishwarya and Vidhya, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), serves as an alternative to freshwater in agriculture effectively removes microorganisms to acceptable levels, and demonstrates greater water use efficiency along with cost-effectiveness compared to conventional farming methods (Gumisiriza et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The prospective challenge of freshwater demand and enhanced productivity can be addressed through the adoption of this technique in both urban and rural settings. The majority of wastewater contains nitrogen, phosphorus, potassium, and organic loads. Using this integrated system, the hydroponic system recovers nutrients from wastewater, leaving the outlet water within acceptable limits. Integrating hydroponic irrigation with wastewater treatment offers a nature-inspired solution for nutrient removal, using plants to absorb excess nitrogen and phosphorus directly from the effluent (Recsetar et al., \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This approach not only closes the nutrient loop but also allows the reuse of substrate media, reducing waste and resource demand (Aishwarya and Vidhya, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Such systems hold great promise as a sustainable technology, simultaneously improving water quality and supporting safe food production. Moreover, by decoupling crop production from traditional soil and climate constraints, hydroponics offers significant potential to improve food security, particularly in drought-prone regions with limited arable land and freshwater resources (Pomoni et al., \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMoreover, this soilless cultivation technique offers several other advantages, including precise nutrient management, high-density planting, and significant reductions in both land and water requirements (Ekaputri et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Owing to its robustness and capacity for high yields, hydroponics is particularly valuable in arid and drought-prone regions. The resilience of this system is largely attributed to its integration with controlled environment agriculture (CEA), wherein key parameters such as temperature, humidity, and light are carefully regulated. Beyond environmental control, CEA mitigates the effects of water scarcity and provides a sustainable, year-round solution to global food production challenges by optimising crop productivity (Al-Shrouf, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In essence, hydroponic systems not only offer a resource-efficient approach to agriculture but also immensely contribute to global food security. These systems provide a viable alternative during periods when conventional farming is disrupted, such as during extreme weather events, including droughts and monsoons. Designed for year-round operation, hydroponic systems demonstrate resilience to diverse climatic conditions, making them a practical strategy for mitigating food shortages. Furthermore, the adoption of hydroponic farming enhances local food sovereignty, fosters the development of regional food markets, and contributes to lowering food prices. Collectively, these benefits improve community access to affordable and nutritious food (Zee et al., \u003cspan citationid=\"CR124\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). It is also worth noting that hydroponic farming demonstrates high efficiency in the utilisation of water and fertilisers while significantly reducing reliance on chemical pesticides and disease-control agents. Consequently, this method presents a viable alternative for addressing food shortages and promoting sustainable agricultural practices (Al Meselmani, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.2. Challenges of High BOD in Hydroponics and Pathways to Solutions\u003c/h2\u003e \u003cp\u003eThe increasing adoption of hydroponic systems represents a promising path toward addressing global food security, as these systems enable high-yield, resource-efficient crop production with minimal land use. Yet, one of the key challenges lies in the buildup of organic matter within recirculating nutrient solutions, which can significantly raise the BOD. High BOD in hydroponic systems poses significant challenges to maintaining water quality, plant health, and overall system performance. It poses a major challenge by depleting dissolved oxygen (DO) and disrupting the balance between plant needs (Roosta, \u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) and microbial activity, making oxygen management a critical challenge. This implies that heightened BOD indicates increased organic and microbial loads, which increase oxygen demand and decrease dissolved oxygen levels. Oxygen is not just a supplementary factor but a fundamental requirement for root health, water and nutrient uptake, and overall plant performance. Under optimal oxygen levels, roots respire efficiently, supporting vigorous growth and nutrient absorption. However, when BOD drives DO levels too low, the system can slip into anaerobic conditions, leading to root rot, accumulation of toxic metabolites, and reduced plant productivity. These effects not only compromise yield but can also create an environment conducive to pathogenic microorganisms, posing potential risks to food safety. It was observed that excessive BOD prevented hydroponic systems from achieving required phosphorus (P) and nitrogen (N) removal targets, as oxygen was preferentially consumed by heterotrophic microorganisms rather than nitrifying bacteria (Clyde-Smith and Campos, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This oxygen competition hindered nitrification, which proceeded efficiently when BOD was kept below 45 mg/L (Clyde-Smith and Campos, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Such oxygen limitations can compromise nutrient cycling, reduce plant growth, and increase the risk of pathogenic microbial survival, ultimately affecting food safety. Despite these risks, limited research has been conducted on how different hydroponic or aeroponic designs influence DO levels, rhizosphere oxygen availability, and microbial communities (Aishwarya and Vidhya, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThese challenges highlight a pressing need to rethink how we manage organic pollution in hydroponic systems. Finding innovative, science-driven strategies to optimise BOD degradation is crucial not just for system efficiency but also for safeguarding food safety and ensuring long-term sustainability. According to Cameron et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), synthetic biology is the application of engineering, science, and technology to modify the genetic material of living organisms, thereby enabling them to execute novel roles. Microorganisms have been produced with synthetic biology tools to detect, measure, and report specific environmental pollutants (Brutesco et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Such interventions offer not only technical efficiency but also a pathway to more resilient and sustainable food production systems. Furthermore, the food industry is undergoing a significant transformation driven by advances in synthetic biology, where the integration of synthetic biology with food science provides powerful strategies to address persistent challenges in food safety, nutritional quality, and the sustainability issues inherent in conventional production systems (Roell and Zurbriggen, \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In this framework, synthetic biology enables the design and engineering of microorganisms with enhanced capabilities for breaking down organic matter. This can be achieved by manipulating metabolic pathways, gene circuits, and regulatory networks. It is possible to generate microbial strains that more effectively break down complex organic compounds, thereby lowering BOD levels in hydroponic solutions. These approaches not only improve system performance but also advance the development of closed-loop, environmentally sustainable agricultural practices. This review, therefore, explores synthetic biology-based strategies to optimise BOD degradation in hydroponic systems, aiming to advance the efficiency and sustainability of soilless crop production.\u003c/p\u003e \u003c/div\u003e"},{"header":"2. Biochemical Oxygen Demand (BOD) as a Critical Water Quality Parameter","content":"\u003cp\u003eThe success of hydroponic systems relies heavily on maintaining optimal water quality to ensure healthy plant growth and maximise productivity. Biochemical oxygen demand (BOD) is, however, a key indicator of water quality and a crucial metric for evaluating the extent of organic pollution. When BOD levels are high, it means there is an excess of organic matter, whether from plant residues, animal waste, or human activities, placing heavy pressure on oxygen resources in the water. This brings about a reduction in available oxygen for fish, plants, and other aquatic life, ultimately signalling poor water quality. Conversely, low BOD levels suggest cleaner water, where less oxygen is consumed in breaking down organic materials, leaving more available to sustain aquatic ecosystems. Managing and reducing BOD is essential for protecting not only aquatic environments but also human health. Elevated BOD often points to contamination, including possible faecal pollution or increased loads of dissolved and particulate organic carbon. Left unchecked, this can trigger oxygen depletion, fish kills, foul odours, and unsafe conditions for human use. BOD testing is widely applied in wastewater treatment to predict the short-term impact of effluents on receiving waters.\u003c/p\u003e \u003cp\u003eUnder natural conditions, the standard 5-day BOD of unpolluted rivers generally does not exceed 2 mg/L. In comparison, the maximum permissible BOD for water used in agricultural, industrial, and aquaculture applications is 5 mg/L, whereas drinking water should ideally have a BOD of less than 1 mg/L (Zhou et al., \u003cspan citationid=\"CR127\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Elevated BOD levels in hydroponic systems can deplete dissolved oxygen, disrupt microbial balance, and compromise nutrient availability, ultimately reducing crop yield and system efficiency. In essence, BOD is an indispensable parameter as it provides a direct and quantifiable measure of the potential for oxygen depletion in aquatic systems caused by organic pollution. It serves as a vital early warning indicator of environmental degradation, supporting informed decision-making in wastewater treatment, pollution control, and the preservation of aquatic biodiversity. The absence of regular BOD monitoring would greatly hinder the ability to evaluate anthropogenic impacts on water quality and to formulate effective, evidence-based water resource management strategies. Because the BOD₅ test requires a five-day incubation duration, it is impractical for real-time monitoring or operational control of wastewater treatment systems. Consequently, the chemical oxygen demand (COD) test was developed to provide a faster and more immediate measure of organic load. Although with the limitation of having to measure all substances that can be chemically oxidised, instead of just biodegradable organic matter (Hlordzi et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Sources of organic load in hydroponic systems (plant exudates, microbial metabolites, nutrient residues)\u003c/h2\u003e \u003cp\u003eWhile hydroponics provides an efficient solution to various challenges, it also raises new concerns about water quality management, as previously stated. A central issue is the accumulation of organic loads, derived from plant root exudates, microbial metabolites, and residual nutrients, which directly contribute to elevated biochemical oxygen demand (BOD) in hydroponic systems. Elevated BOD signifies a higher concentration of organic matter in the solution, leading to potential depletion of dissolved oxygen, alterations in microbial community dynamics, and jeopardising both crop health and food safety (Zhou et al., \u003cspan citationid=\"CR127\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOrganic hydroponics, often referred to as \u003cem\u003ebioponics\u003c/em\u003e, uses organic nutrient sources such as compost tea, fish emulsions, seaweed extracts, vinasses, and other natural by-products to sustain plant growth (Fang and Chung, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Microorganisms are often deliberately introduced into these systems to decompose complex organic materials and liberate nutrients in forms accessible to plants, underscoring the strong connection between nutrient management and microbial activity. Aquaponics, where nutrients are derived from fish waste, is also considered a branch of bioponics (Fang and Chung, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Regardless of the system, nutrient solutions must be carefully balanced within narrow pH ranges to ensure nutrient solubility and plant uptake. While conventional hydroponics relies heavily on synthetic inorganic fertilisers (Park and Williams, \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), organic hydroponics seeks to avoid these inputs, instead leveraging organic waste streams, even municipal solid waste composts, as potential nutrient sources.\u003c/p\u003e \u003cp\u003eOne advantage of using organic nutrient inputs is their potential to reduce nitrate accumulation in leafy vegetables, which poses health risks when consumed in excess. Studies by Fang and Chung (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) demonstrated that lettuce treated with organic fertiliser solutions showed nitrate concentrations ranging from 800 to 2000 ppm, compared to 5000 to 5500 ppm in conventionally fertilised crops. Growing consumer demand for organic products, the improved flavour profiles sometimes associated with organic inputs, and the perceived health benefits, including reduced nitrate accumulation, are boosting interest in organic hydroponics. Additionally, organic inputs can serve as biostimulants, enhancing plant resilience and growth. In urban settings, organic hydroponic systems provide a way to supply fresh, organic produce where traditional soil-based organic farming is not feasible. Crucially, this method also supports emerging strategies to close the loop between food, water, energy, and waste by reusing organic by-products as valuable nutrient sources (Park and Williams, \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Impacts of high BOD on water quality, crop health, and productivity\u003c/h2\u003e \u003cp\u003eHigh BOD indicates excessive organic matter in water, resulting in rapid depletion of DO. This sharp reduction in oxygen availability places aquatic life under severe stress, often leading to suffocation and, in extreme cases, the death of fish and other organisms. Elevated BOD typically stems from inputs such as domestic sewage, industrial effluents, agricultural runoff, and animal waste. The consequences are much like those observed when DO is critically low: ecosystems become imbalanced, biodiversity declines, and natural food webs are disrupted. Beyond oxygen depletion, high BOD often fuels nutrient enrichment that accelerates eutrophication, further exhausting oxygen reserves and creating \u0026ldquo;dead zones\u0026rdquo; inhospitable to most aquatic life. Environmental stressors such as rising temperatures intensify this cycle, worsening oxygen loss and destabilising fragile ecosystems (Hu et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). For these reasons, BOD is more than a laboratory metric; it is a vital signal of water quality and ecological health. Elevated readings indicate pollution and environmental distress, while low BOD reflects balanced, oxygen-rich conditions where aquatic organisms can thrive. Sustaining low BOD is therefore essential not only for the survival of fish and other species but also for maintaining resilient, functioning ecosystems capable of supporting life into the future.\u003c/p\u003e \u003cp\u003eBOD also has a serious impact on crop health and productivity. Soil health, defined by its biological, physical, and chemical properties, forms the basis of crop productivity, much like water quality does in hydroponic systems. Edaphic factors, including soil texture, pH, nutrient levels, and microbial diversity, directly determine crop growth, just as BOD reflects the availability of oxygen for sustaining microbial and plant health in water-based systems (Hu et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). When soils are degraded, for instance by poor water retention in sandy soils or acidity that restricts nutrient uptake (Naorem et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), crops suffer reduced vigour; similarly, high BOD in hydroponic water limits dissolved oxygen, creating conditions that stress plants and favour opportunistic pathogens. The interaction between crop roots and microbial communities in soils provides a natural buffer, enhancing nutrient cycling, disease resistance, and tolerance to stress (Wei et al., \u003cspan citationid=\"CR117\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In hydroponics, however, excessive organic matter accumulation raises BOD, disrupting this balance by driving microbial overgrowth and oxygen depletion, an aquatic parallel to nutrient imbalances and microbial instability in soils. Just as planting methods, tillage, and crop rotations influence soil pH, organic matter, and microbial dynamics (Khmelevtsova et al., \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), the management of nutrient solutions directly shapes microbial composition in hydroponic systems. Failure to regulate these inputs can destabilise the ecosystem, impair nutrient uptake, and reduce crop yield. Ultimately, the synergy between crops, soil, and microorganisms in terrestrial systems mirrors the delicate crop-water-microbe relationship in hydroponics. In both cases, disruptions, whether through soil compaction or elevated BOD, reduce ecosystem stability, hinder nutrient cycling, and compromise agricultural sustainability. A deeper understanding of these interactions is therefore essential, not only for optimising soil environments but also for safeguarding hydroponic water quality, ensuring crop health, and sustaining productivity under future food production systems.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eFood Safety Risks in Hydroponics: Pathogen Proliferation in High-BOD Water\u003c/b\u003e \u003c/p\u003e \u003cp\u003eHydroponic fruit and vegetable production is expanding rapidly, driven by consumer demand for fresh, locally sourced produce available year-round. In the United States alone, the sector is valued at approximately USD 961.8\u0026nbsp;million and is projected to grow at an annual rate of 10.7% (Ivey et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Alongside this growth, however, concerns about food safety have intensified, particularly the risk of contamination with human pathogens. In recent years, several foodborne illness outbreaks and product recalls have been directly linked to hydroponic leafy greens. For example, a 2021 multistate outbreak of \u003cem\u003eSalmonella\u003c/em\u003e associated with hydroponic leafy greens resulted in 31 confirmed cases, including four hospitalisations (FDA, 2021). Investigations identified the contamination as originating from water sources and lapses in food safety practices along the supply chain (McClure \u003cem\u003eet al\u003c/em\u003e., 2021). Since then, multiple recalls have been issued across the U.S. due to potential contamination of hydroponic produce with pathogens such as \u003cem\u003eSalmonella spp.\u003c/em\u003e and \u003cem\u003eListeria monocytogenes\u003c/em\u003e (Ivey et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBesides, hydroponic farming introduces distinctive food safety challenges Carstens \u003cem\u003eet al\u003c/em\u003e., 2017). In these systems, crops are in constant contact with the recirculating nutrient solution, which can serve as a direct pathway for pathogen transmission. Contaminants may enter the solution through multiple routes, including the substrate, source water (surface, groundwater, or municipal), workers, or contact surfaces, where they can spread rapidly and cross-contaminate the edible portions of crops (Ilic et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Unlike in soil-based production, root exudates in hydroponics do not remain confined to the rhizosphere but leach into the shared nutrient solution. These organic compounds elevate the biochemical oxygen demand (BOD), creating a nutrient-rich environment that supports bacterial growth and promotes biofilm formation (Thomas et al., \u003cspan citationid=\"CR109\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Moreover, the aeration of nutrient solutions, while necessary for plant health, produces oxygen-rich conditions that intensify microbial dynamics and can accelerate pathogen proliferation (Garay, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). With no clean breaks in continuous production cycles, biofilms readily establish on system surfaces, creating persistent reservoirs of contamination (Hamilton et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Without effective intervention strategies, these high-BOD, microbially active environments pose significant risks to the food safety of hydroponically grown crops.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Synthetic Biology Tools for BOD Management","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Model Microorganisms and Metabolic Pathways\u003c/h2\u003e \u003cp\u003eThe strategic implementation of synthetic biology in hydroponic systems for biochemical oxygen demand (BOD) management hinges on selecting microbial chassis that exhibit robust growth, genetic tractability, and metabolic versatility. Ideal candidates must demonstrate non-pathogenic characteristics and maintain functional stability in nutrient-dense aqueous environments typical of controlled-environment agriculture. Among the most extensively characterised organisms are \u003cem\u003eEscherichia coli\u003c/em\u003e, \u003cem\u003eBacillus subtilis\u003c/em\u003e, \u003cem\u003ePseudomonas putida\u003c/em\u003e, and members of the \u003cem\u003eRhodococcus\u003c/em\u003e genus\u0026mdash;each distinguished by their capacity to metabolise diverse organic compounds (Geng et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Sun et al., \u003cspan citationid=\"CR105\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cem\u003eBacillus subtilis\u003c/em\u003e, a Gram-positive bacterium renowned for its prolific secretion of hydrolytic enzymes, has undergone genetic engineering to express elevated levels of proteases, cellulases, and lipases. These enzymes facilitate the degradation of proteinaceous, cellulosic, and lipid-based waste materials commonly accumulated in hydroponic nutrient solutions (Li et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). \u003cem\u003ePseudomonas putida\u003c/em\u003e, recognised for its innate capacity to degrade aromatic hydrocarbons, has been further enhanced through the integration of expanded catabolic pathways using synthetic promoters and optimised ribosome binding sites, thereby amplifying the degradation of recalcitrant organic compounds that contribute to elevated BOD levels (Nikel and de Lorenzo, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Additionally, \u003cem\u003eRhodococcus jostii\u003c/em\u003e has emerged as a particularly promising candidate owing to its metabolic flexibility and capacity to oxidise recalcitrant compounds under aerobic conditions (Patel et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe metabolic pathways implicated in BOD reduction are equally diverse. The β-ketoadipate pathway, critical for aromatic compound degradation, has been extensively studied in \u003cem\u003ePseudomonas\u003c/em\u003e species and represents a central route for the catabolism of lignin-derived phenolic compounds (Martinez et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Laccase-mediated oxidation offers an alternative enzymatic route for complex organic molecule breakdown, particularly effective against recalcitrant polymeric structures (Rodriguez et al., \u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The strategic focus on microorganisms with established safety profiles remains paramount, given their deployment in food production systems where biosafety cannot be compromised (Smith et al., \u003cspan citationid=\"CR102\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHowever, several considerations merit deeper examination. The adaptability of these model organisms to the distinctive physicochemical conditions of hydroponic systems\u0026mdash;characterised by nutrient richness, fluctuating dissolved oxygen levels, and periodic pH variations\u0026mdash;differs substantially from traditional wastewater treatment contexts (Wang et al., \u003cspan citationid=\"CR113\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Furthermore, expanding the repertoire of candidate microorganisms to include extremophilic or facultatively anaerobic species may broaden the applicability of synthetic biology approaches across diverse hydroponic configurations (Rodriguez et al., \u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e provides a comparative assessment of key model microorganisms and their performance metrics in BOD degradation applications.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparative performance of model microorganisms in BOD degradation within hydroponic systems.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOrganisms\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTarget Substrate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDegradation Efficiency\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOxygen Requirement\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003ePseudomonas putida\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePhenolic compounds\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e85% in 48 hours\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAerobic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGao et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2024\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eBacillus subtilis\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCarbohydrates, proteins\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70% in 72 hours\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAerobic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMartinez et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2025\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eRhodococcus erythropolis\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLignin derivatives\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65% in 96 hours\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAerobic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRodriguez et al., \u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e2025\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eRhodococcus jostii\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRecalcitrant compounds\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e68% in 84 hours\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAerobic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePatel et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Synthetic Biology Techniques for Enhanced Bioremediation\u003c/h2\u003e \u003cp\u003eCRISPR-Cas9 Gene Editing technology has fundamentally transformed the landscape of microbial engineering, offering unprecedented precision in genome editing and enabling the targeted enhancement of metabolic pathways critical to BOD degradation. By facilitating the knockout of metabolic repressor genes or the chromosomal integration of catabolic gene cassettes, researchers can engineer strains with substantially elevated expression of key enzymes, including oxygenases, laccases, hydrolases, and dehydrogenases\u0026mdash;all essential for the breakdown of BOD-inducing organic compounds (Liu et al., \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR114\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe principal advantages of CRISPR-based approaches include their precision, scalability, and rapidity compared to conventional mutagenesis or homologous recombination methods. For instance, engineered \u003cem\u003eB. subtilis\u003c/em\u003e strains incorporating CRISPR-mediated overexpression of the \u003cem\u003eaprE\u003c/em\u003e gene have demonstrated markedly improved protein degradation efficiency in recirculating hydroponic systems (Zhou et al., \u003cspan citationid=\"CR126\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Similarly, the enhancement of \u003cem\u003ePseudomonas\u003c/em\u003e species for phenol degradation addresses a critical gap, as phenolic compounds are prevalent contaminants in hydroponic nutrient solutions derived from root exudates and organic substrate decomposition (Chen et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Nevertheless, potential off-target effects in complex microbial genomes remain a concern, particularly regarding long-term genetic stability in field applications. Comprehensive whole-genome sequencing and phenotypic validation are therefore essential to ensure the reliability and biosafety of CRISPR-engineered strains destined for deployment in food production systems (Wright et al., \u003cspan citationid=\"CR119\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarises recent advances in CRISPR-based metabolic engineering for BOD management.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRecent applications of CRISPR-Cas9 technology in engineering microorganisms for enhanced BOD degradation.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTarget Organism\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGene Target\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMetabolic Enhancement\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eApplication\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eBacillus subtilis\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eaprE\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEnhanced protease secretion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eProtein degradation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZhou et al., \u003cspan citationid=\"CR126\" class=\"CitationRef\"\u003e2022\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003ePseudomonas putida\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003epheA, catA\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eImproved phenol metabolism\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAromatic compound removal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChen et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2025\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eEscherichia coli\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003elacZ, cel5A\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCellulase expression\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCellulose degradation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLi et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eRhodococcus jostii\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eligD, dypB\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLignin peroxidase activity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLignin breakdown\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePatel et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eBeyond individual gene editing, synthetic biology enables the modular reprogramming of entire metabolic networks to optimise substrate flux through degradation metabolic pathways. This holistic approach employs techniques including promoter engineering, dynamic gene regulation, and metabolic pathway balancing to achieve coordinated enzyme expression patterns (Yang et al., \u003cspan citationid=\"CR122\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). A particularly elegant strategy involves the incorporation of inducible promoters responsive to organic load thresholds, allowing coordinated enzyme expression that tracks BOD levels. This dynamic regulation minimises metabolic burden during low-pollutant phases while ensuring robust degradation capacity when organic loads increase.\u003c/p\u003e \u003cp\u003eResearch has demonstrated the successful integration of multi-gene pathway assemblies for lignin, cellulose, and protein hydrolysis into a single microbial chassis. These synthetic operons coordinate the sequential expression of enzymes required for complex substrate degradation, thereby enhancing overall efficiency while reducing lag times associated with oxygen consumption (Yang et al., \u003cspan citationid=\"CR122\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The strategic use of synthetic biology circuits that link sensing, processing, and actuation functions represents a paradigm shift from static genetic modifications toward dynamic, responsive bioremediation systems.\u003c/p\u003e \u003cp\u003eBiosafety Mechanisms: Kill Switches and Containment Strategies: The deployment of genetically engineered microorganisms (GEMs) in food production environments necessitates robust biosafety frameworks to mitigate risks associated with environmental persistence and horizontal gene transfer. Synthetic biology offers multiple safeguards through the implementation of genetic kill switches\u0026mdash;engineered circuits that trigger programmed cell death in response to specific environmental cues, such as nutrient depletion, antibiotic absence, or temperature changes (Wright et al., \u003cspan citationid=\"CR119\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAuxotrophic strains engineered to depend on synthetic amino acids unavailable in natural environments provide an additional containment layer. These organisms cannot survive outside controlled systems, thereby preventing ecological establishment (Lu et al., \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Furthermore, genetic firewall technologies, including gene guard systems that prevent horizontal gene transfer through the use of non-standard genetic codes or orthogonal replication systems, are under active investigation. These multilayered biosafety approaches are essential for gaining regulatory approval and public acceptance of synthetic biology in agriculture.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Hydroponic Systems as Testbeds for Synthetic Biology Applications\u003c/h2\u003e \u003cp\u003eHydroponic cultivation systems offer uniquely advantageous platforms for synthetic biology research and development. Their closed-loop architecture, controlled environmental parameters, and ease of sampling enable rigorous evaluation of engineered microbial strains under reproducible conditions. Nutrient Film Technique (NFT) systems cultivating fast-growing crops such as lettuce (\u003cem\u003eLactuca sativa\u003c/em\u003e) are particularly well-suited as model systems for pilot-scale experiments targeting BOD control (Gruda, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These systems provide reproducible conditions for evaluating engineered strain performance across varying organic loads, light intensities, temperature regimes, and nutrient flux patterns. The inherent scalability of hydroponic systems facilitates the transition from laboratory prototypes to commercial implementations in urban vertical farms and industrial greenhouses. Moreover, the integration of real-time monitoring technologies in hydroponics aligns seamlessly with the feedback-responsive capabilities of synthetic biology circuits, enabling adaptive bioremediation strategies (He et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4 BOD Measurement and Real-Time Monitoring Technologies\u003c/h2\u003e \u003cp\u003eThe Standard five-day biochemical oxygen demand test (BOD₅) (APHA Method 5210 B) remains the gold standard for regulatory compliance and baseline assessment of organic pollution in aqueous systems. The method involves sample incubation in darkness at 20\u0026deg;C for five days, with dissolved oxygen depletion measured as a proxy for microbial respiration and organic matter oxidation (APHA, 2022). While providing reliable quantitative data, BOD₅ testing suffers from inherent limitations, including lengthy analysis time, labour intensity, and unsuitability for real-time management of dynamic hydroponic systems where rapid decision-making is critical.\u003c/p\u003e \u003cp\u003eTechnological advances have yielded real-time biosensor systems capable of providing continuous, \u003cem\u003ein situ\u003c/em\u003e monitoring of organic pollution levels, thereby overcoming the temporal limitations of conventional BOD₅ testing. Microbial fuel cell (MFC)-based biosensors employ electroactive bacteria that generate measurable electrical currents proportional to organic substrate concentrations, enabling near-instantaneous BOD assessment (Wei et al., \u003cspan citationid=\"CR116\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These systems can be directly integrated into hydroponic recirculation loops, providing continuous water quality surveillance. Optical and fluorescence-based biosensors incorporating engineered microbial reporters offer complementary detection capabilities. These systems can be engineered to respond specifically to target organic compounds or oxygen depletion events with high sensitivity and selectivity (Xu et al., \u003cspan citationid=\"CR121\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). When coupled with data acquisition systems and cloud-based analytics platforms, biosensors support feedback control loops for dynamic activation of microbial degradation pathways and provide early warning of contamination events. This integration of sensing and actuation represents a transformative shift toward intelligent, self-regulating hydroponic systems.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Designing Synthetic Microbial Consortia for Enhanced BOD Degradation\u003c/h2\u003e \u003cp\u003eWhile monocultures of engineered microorganisms offer precision and predictability, they often exhibit limitations in long-term stability, functional breadth, and resilience to environmental perturbations. In contrast, synthetic microbial consortia leverage functional specialisation, metabolic cooperation, and ecological complementarity to achieve enhanced performance characteristics (Zuniga et al., \u003cspan citationid=\"CR128\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These engineered communities can integrate aerobic and facultatively anaerobic species that synergistically degrade a broader spectrum of organic pollutants while maintaining system oxygen homeostasis. Key design principles for synthetic consortia include the implementation of quorum-sensing control mechanisms for synchronised metabolic activity, spatial structuring through biofilm-forming capabilities, and deliberate division of labour among specialist strains. For example, \u003cem\u003eB. subtilis\u003c/em\u003e engineered for proteolysis can be co-cultivated with \u003cem\u003eP. putida\u003c/em\u003e specialised in hydrocarbon degradation, creating a metabolically balanced system for efficient BOD reduction (Schreiber et al., \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Computational tools such as OptCom and the COBRA toolbox facilitate the optimisation of metabolic flux distributions and interaction networks within consortia, enabling rational design rather than empirical trial-and-error approaches (Zuniga et al., \u003cspan citationid=\"CR128\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Data Analytics and Predictive Modelling for BOD Optimisation\u003c/h2\u003e \u003cp\u003eThe convergence of synthetic biology with computational modelling and machine learning represents a frontier in BOD management. Data streams from biosensors, environmental monitors, and microbial gene expression assays can be processed using artificial intelligence algorithms to predict BOD trends, optimise microbe deployment schedules, and dynamically adjust nutrient inputs (Aghamohammadi et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Digital twin technology\u0026mdash;virtual simulations that mirror physical hydroponic systems in real-time\u0026mdash;enables the modelling of complex interactions among engineered microbes, organic loads, and environmental variables, facilitating proactive rather than reactive management strategies. Machine learning models trained on historical BOD and microbial performance data can recommend optimal strain combinations, pathway enhancements, and operational parameters tailored to specific crop systems and environmental conditions. This data-driven approach accelerates the design\u0026ndash;build\u0026ndash;test\u0026ndash;learn cycle fundamental to synthetic biology, reducing development timelines and improving translation from laboratory to field. The integration of artificial intelligence with engineered biological systems marks a transformative evolution toward truly autonomous, self-optimising agricultural production systems (He et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Comparative Assessment, Biosafety, and Regulatory Considerations","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Efficacy Comparison: Synthetic Biology versus Traditional BOD Management\u003c/h2\u003e \u003cp\u003eTraditional methodologies for managing BOD in hydroponic systems\u0026mdash;including mechanical aeration, periodic water replacement, and chemical oxidation using ozone or hydrogen peroxide\u0026mdash;have been employed extensively due to their operational simplicity and immediate efficacy. However, these approaches are inherently reactive, energy-intensive, and often inefficient in addressing the persistent accumulation of complex organic waste (Chatterjee et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Moreover, they lack substrate specificity and may disrupt beneficial microbial communities while potentially damaging plant root systems or destabilising nutrient balances.\u003c/p\u003e \u003cp\u003eIn contrast, synthetic biology offers targeted, adaptive strategies for BOD reduction. Engineered microbial systems can be designed to selectively degrade specific organic pollutant classes through customised catabolic pathways, enabling proactive removal of BOD-causing compounds at their source (Nikel and de Lorenzo, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Genetically modified strains of \u003cem\u003eB. subtilis\u003c/em\u003e and \u003cem\u003eP. putida\u003c/em\u003e have demonstrated superior performance compared to conventional chemical treatments, accelerating degradation rates while maintaining overall system stability (Sun et al., \u003cspan citationid=\"CR105\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Furthermore, synthetic biological systems can be engineered for inducible activation in response to BOD fluctuations, thereby conserving metabolic resources during low-load periods. When integrated with biosensor networks and feedback control loops, synthetic microbes respond dynamically to environmental changes\u0026mdash;a capability unattainable with conventional physicochemical methods (Wright et al., \u003cspan citationid=\"CR119\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The efficacy of synthetic biology lies fundamentally in its precision, sustainability, and adaptability, positioning it as a superior alternative for water quality management in controlled agriculture.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparative assessment of traditional and synthetic biology-based BOD management strategies in hydroponic systems.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCriterion\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTraditional Methods\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSynthetic Biology\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eKey Advantage\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecificity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNon-selective, broad-spectrum\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHighly targeted, pathway-specific\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSynthetic biology\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRiglar and Silver (\u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e2018\u003c/span\u003e); Chen et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnergy consumption\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigh (continuous aeration/UV)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLow (self-regulating)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSynthetic biology\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMcCarty et al. (\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e2011\u003c/span\u003e); Guo et al. (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAdaptability\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReactive, manual adjustment\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDynamic, feedback-responsive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSynthetic biology\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHuang et al. (\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2022\u003c/span\u003e); Bartley et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnvironmental impact\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChemical discharge, disruption\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMinimal, controlled biodegradation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSynthetic biology\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eKhalid et al. (\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2021\u003c/span\u003e); Arora and Bae (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eImplementation time\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eImmediate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRequires development phase\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTraditional methods\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCheng and Lu (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); Voyvodic et al. (\u003cspan citationid=\"CR112\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLong-term cost\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigh operational expenses\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLower after initial investment\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSynthetic biology\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZhang et al. (\u003cspan citationid=\"CR125\" class=\"CitationRef\"\u003e2022\u003c/span\u003e); Carbonell et al. (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRegulatory clarity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWell-established frameworks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEvolving, region-dependent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTraditional methods\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAas et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e); Kaebnick et al. (\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Implications for Food Safety: Mitigating Microbial Risks in Hydroponic Produce\u003c/h2\u003e \u003cp\u003eMicrobial contamination of hydroponic produce represents a significant food safety concern, particularly for leafy greens consumed raw. Elevated BOD levels can create anaerobic microenvironments that favour the proliferation of pathogenic and opportunistic microorganisms, including \u003cem\u003eEscherichia coli\u003c/em\u003e, \u003cem\u003eSalmonella\u003c/em\u003e spp., and \u003cem\u003eListeria monocytogenes\u003c/em\u003e (Jaiswal et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This challenge is particularly acute in recirculating systems where water is reused across multiple cultivation cycles, potentially amplifying pathogen populations. Synthetic biology provides innovative approaches to mitigate these risks. Engineered microorganisms can be designed to perform dual functions: degrading organic pollutants while simultaneously secreting antimicrobial peptides or producing competitive exclusion factors that inhibit pathogen colonisation (Cameron et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, synthetic systems incorporating quorum-sensing inhibition (QSI) can disrupt cell-to-cell communication among pathogenic bacteria, thereby preventing biofilm formation and enhancing overall system hygiene (Schreiber et al., \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBy maintaining consistently lower BOD levels and fostering beneficial microbial communities, synthetic biology approaches indirectly enhance the microbiological safety of hydroponic produce. These systems can be designed to align with international food safety standards, including Codex Alimentarius guidelines and the U.S. FDA Produce Safety Rule. However, achieving full regulatory acceptance requires demonstrating the absence of transgenic material persistence on harvested crops\u0026mdash;a challenge being addressed through innovations in containment strategies and genetic clearance technologies (Wright et al., \u003cspan citationid=\"CR119\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Scalability for Urban and Commercial Hydroponic Operations\u003c/h2\u003e \u003cp\u003eScalability represents a critical determinant of biotechnological adoption in agriculture. Conventional water treatment systems in hydroponics\u0026mdash;such as ultraviolet sterilisation or periodic system flushing\u0026mdash;scale linearly with system size but often become economically and logistically prohibitive in large-scale or urban farming environments (Al-Kodmany, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Synthetic biology, conversely, offers scalability through modular microbial systems that can be expanded, regulated, and monitored with minimal infrastructural modifications.\u003c/p\u003e \u003cp\u003eBioreactors embedded within hydroponic recirculation loops can house synthetic consortia that automatically adapt to varying organic loads, making them particularly suitable for vertical farms and large greenhouse operations (Aghamohammadi et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Integration with Internet-of-Things (IoT) technologies enables centralised monitoring coupled with decentralised microbial deployment, facilitating real-time control across dispersed farming units. This distributed intelligence architecture is particularly advantageous for urban agriculture networks comprising multiple small-to-medium production facilities (He et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). However, large-scale applications introduce complexities including interspecies competition, genetic drift, and susceptibility to environmental perturbations. Strategies such as microbial encapsulation, immobilised biofilms, and rationally designed consortia are being explored to enhance robustness and reproducibility across scales (Zuniga et al., \u003cspan citationid=\"CR128\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The emerging application of digital twin technology to model and optimise microbial behaviour in commercial contexts before field deployment represents a significant advancement in de-risking scale-up processes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Economic Feasibility: Cost-Benefit Analysis of Microbial Bioreactors\u003c/h2\u003e \u003cp\u003eEconomic viability often determines the pace of technology adoption within the agri-food sector. While initial capital expenditure for designing and deploying engineered microbial systems may exceed that of traditional approaches, comprehensive life-cycle analyses reveal potential net savings through improved water reuse efficiency, reduced chemical inputs, minimised crop losses, and decreased downtime from contamination events (Raghav et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Recent techno-economic assessments of microbial bioreactors suggest that systems incorporating low-maintenance biofilms or immobilised consortia can operate efficiently over extended periods with minimal intervention, achieving cost competitiveness with conventional methods within 2\u0026ndash;3 operational years (Schreiber et al., \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Furthermore, the proliferation of open-source genetic toolkits and community biofoundries has significantly reduced strain development costs, lowering entry barriers for small-to-medium growers (Wurtzel et al., \u003cspan citationid=\"CR120\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eInvestment from public-private partnerships and venture capital in agricultural biotechnology continues to accelerate, recognising that sustainable agriculture solutions must balance ecological and economic imperatives. Synthetic biology platforms offering plug-and-play compatibility with existing hydroponic infrastructure hold particular promise for widespread adoption, as they minimise retrofit costs and technical barriers (Brown et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.5 Stakeholder Perspectives: Farmers, Industry, and Consumers\u003c/h2\u003e \u003cp\u003eSuccessful deployment of synthetic biology in hydroponics requires understanding and addressing the diverse perspectives of key stakeholders. Farmers prioritise ease of use, regulatory clarity, and return on investment. Synthetic biological solutions presented as user-friendly, low-maintenance systems supported by comprehensive technical documentation are more likely to gain adoption among grower communities (Brown et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Training programs and accessible decision-support tools are essential for bridging the knowledge gap between biotechnology developers and end-users.\u003c/p\u003e \u003cp\u003eIndustry stakeholders\u0026mdash;including agricultural technology firms, food distributors, and retailers- increasingly view synthetic biology as a driver of innovation and sustainability. However, concerns regarding public perception, particularly around genetically modified organisms (GMOs) in food production, remain constraining factors. Transparency, traceability, and independent third-party validation are critical elements influencing industry acceptance (Cressey, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eConsumer acceptance hinges on assurances of food safety, environmental sustainability, and ethical deployment. Recent surveys indicate growing openness to synthetic biology applications when communicated within frameworks of climate resilience and food security, particularly among younger demographics and environmentally conscious consumer segments (Wright et al., \u003cspan citationid=\"CR119\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Continued public education, transparent communication, and meaningful regulatory engagement are essential for aligning societal values with technological progress.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.6 Limitations and Challenges: Stability, Integration, and Regulatory Uncertainty\u003c/h2\u003e \u003cp\u003eDespite its transformative potential, synthetic biology for BOD management faces substantial challenges. Long-term microbial stability represents a primary concern, as engineered strains may lose functionality through mutational drift, horizontal gene transfer, or evolutionary pressures within complex microbial communities (Lu et al., \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Interactions between introduced microorganisms and native microbiota can yield unpredictable outcomes, necessitating sophisticated monitoring and modelling systems to ensure predictable performance.\u003c/p\u003e \u003cp\u003eIntegration challenges also merit consideration. Factors including fluid dynamics, nutrient concentrations, pH fluctuations, and dissolved oxygen levels can profoundly influence microbial viability and efficacy. Ensuring compatibility between engineered organisms and the physicochemical environments of diverse hydroponic configurations\u0026mdash;including Nutrient Film Technique (NFT), Deep Water Culture (DWC), and aeroponic systems requires iterative optimisation and extensive real-world validation (Han et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRegulatory uncertainty surrounding synthetic biology and genetically engineered microbes in food production remains a significant barrier in many jurisdictions. International regulatory frameworks vary substantially, creating challenges for global technology deployment. Harmonising biosafety standards and developing robust environmental risk assessment protocols are necessary prerequisites for unlocking the full potential of this transformative approach (Tessnow and De Lorenzo, \u003cspan citationid=\"CR108\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Proactive engagement with regulatory agencies, transparent communication of risk assessment data, and demonstration of containment efficacy will be essential for advancing the field.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Practical Applications and Future Directions","content":"\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Implementation in Urban Hydroponic Farms for Sustainable Food Production\u003c/h2\u003e \u003cp\u003eUrban agriculture has emerged as a transformative response to converging challenges of climate change, land scarcity, and population growth. Within this context, hydroponics, the soilless cultivation of crops using nutrient-enriched water, offers space-efficient, high-yield production methods for fresh food in metropolitan areas. However, hydroponic sustainability is frequently compromised by organic waste accumulation in recirculating water, which elevates BOD and threatens both plant health and food safety (Gruda, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe integration of synthetic biology provides an elegant solution to this bottleneck. Engineered microorganisms with enhanced catabolic pathways can be deployed directly into urban hydroponic systems for \u003cem\u003ein situ\u003c/em\u003e degradation of organic residues. This biotechnological intervention minimises water replacement frequency, reduces chemical usage, and improves water reuse rates, attributes ideally suited for resource-constrained urban environments (Cameron et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Successful pilot implementations have been documented in Singapore and the Netherlands, where synthetic strains of \u003cem\u003eB. subtilis\u003c/em\u003e and \u003cem\u003eP. putida\u003c/em\u003e have demonstrated effective water quality management without compromising plant yields or safety parameters (Zhou et al., \u003cspan citationid=\"CR126\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Water Reuse Strategies: Closed-Loop Bioaugmentation Models\u003c/h2\u003e \u003cp\u003eWater efficiency lies at the heart of hydroponic agriculture's environmental value proposition. However, recirculating systems face the persistent challenge of organic waste accumulation, which elevates BOD and increases pathogen proliferation risks. Closed-loop bioaugmentation\u0026mdash;the strategic introduction of engineered or enriched microbial consortia\u0026mdash;is gaining traction as an ecologically sound approach to restore water quality and reduce treatment costs (Jaiswal et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSynthetic biology enables the design of microbial strains or consortia specifically tailored to degrade distinct categories of organic matter\u0026mdash;proteins, carbohydrates, lipids\u0026mdash;thereby maintaining consistently low BOD levels throughout extended operational periods. These bioaugmented systems operate in self-regulating modes, with microbial activity responding dynamically to fluctuations in organic load (Zuniga et al., \u003cspan citationid=\"CR128\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Empirical studies have demonstrated that modular microbial units can increase water reuse rates by up to 90%, extend nutrient solution operational lifespans, and substantially reduce dependence on synthetic disinfectants (Wang et al., \u003cspan citationid=\"CR113\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Integration with Internet of Things for Automated Water Quality Management\u003c/h2\u003e \u003cp\u003eThe convergence of synthetic biology with Internet of Things (IoT) technologies represents a paradigm shift in precision agriculture. By embedding biosensors and microbial activity monitors within hydroponic systems, growers can achieve real-time surveillance of BOD levels, oxygen saturation, microbial viability, and nutrient dynamics (He et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). These sensor networks, typically linked to cloud-based analytics platforms, provide actionable intelligence that informs system adjustments\u0026mdash;including nutrient dosing, aeration control, or timed release of engineered microbes.\u003c/p\u003e \u003cp\u003eAdvanced implementations include genetically encoded biosensors engineered to produce fluorescent or electrochemical signals in response to specific organic pollutants. These can be integrated with IoT dashboards to provide early warning of contamination events and facilitate automated control loops that dynamically activate or suppress microbial degradation pathways as needed (Xu et al., \u003cspan citationid=\"CR121\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The result is a highly adaptive, labour-efficient intelligent environment that aligns with Industry 4.0 agricultural principles and urban smart farming objectives.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e5.4 Case Studies: Real-World Implementations of Synthetic Biology in Hydroponics\u003c/h2\u003e \u003cp\u003eSeveral pioneering implementations illustrate the growing application of synthetic biology in commercial hydroponic operations. In Singapore, a collaborative initiative led by the Agency for Science, Technology and Research (A*STAR) developed a modular bioreactor system incorporating CRISPR-engineered \u003cem\u003eB. subtilis\u003c/em\u003e for deployment in commercial lettuce cultivation. This system achieved a 75% reduction in BOD levels accompanied by measurable declines in pathogenic bacterial counts, demonstrating both efficacy and biosafety (Tan et al., \u003cspan citationid=\"CR107\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the Netherlands, researchers at Wageningen University partnered with an urban agriculture startup to deploy synthetic consortia comprising \u003cem\u003ePseudomonas, Comamonas\u003c/em\u003e, and \u003cem\u003eAcinetobacter\u003c/em\u003e species for BOD control in commercial basil and kale production systems. This project demonstrated improved crop quality parameters and a 40% increase in water reuse efficiency (Schreiber et al., \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In North America, rooftop farms in New York and Toronto have tested IoT-integrated biosensor systems that trigger microbial capsule activation when BOD thresholds are exceeded. These installations have reportedly reduced operational costs by 20% compared to conventional chemical water treatment protocols while improving overall system stability (Brown et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These case studies collectively demonstrate the technical feasibility and economic viability of synthetic biology approaches across diverse hydroponic contexts.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section2\"\u003e \u003ch2\u003e5.5 Capacity Building: Training and Knowledge Transfer for Farmers\u003c/h2\u003e \u003cp\u003eA critical barrier to synthetic biology adoption in hydroponics is the knowledge gap between technology developers and end-users. Many urban and peri-urban farmers possess limited familiarity with genetically engineered microbial technologies, biosensor interpretation, or digital feedback systems. Consequently, structured training programs and capacity-building initiatives are essential for successful technology implementation (Wurtzel et al., \u003cspan citationid=\"CR120\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEffective training modalities include hands-on workshops, modular online courses, and cooperative extension programs covering topics such as safe handling of engineered microbes, biosensor signal interpretation, and appropriate responses to system alerts. Participatory design approaches, wherein farmers collaborate with synthetic biologists in system customisation, have proven particularly effective in increasing technology uptake, building trust, and accelerating innovation diffusion (Cressey, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Government-supported programs, including the EU Horizon Europe framework and USAID's Feed the Future initiative, are increasingly incorporating synthetic biology components in their agricultural training curricula.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section2\"\u003e \u003ch2\u003e5.6 Contributions to Global Food Security and Sustainable Development Goals\u003c/h2\u003e \u003cp\u003eThe broader significance of synthetic biology-based BOD management extends beyond technical performance metrics to encompass contributions toward global sustainability objectives. By enhancing the safety, efficiency, and resilience of hydroponic farming, these systems address multiple United Nations Sustainable Development Goals (SDGs):\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSDG 2 (Zero Hunger)\u003c/b\u003e: By enabling continuous, high-yield food production in urban and climate-stressed regions, synthetic biology tools support nutritional security and localised food access, particularly in resource-limited settings (FAO, 2021).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSDG 6 (Clean Water and Sanitation)\u003c/b\u003e: Closed-loop microbial BOD management significantly reduces agricultural water consumption and wastewater discharge, promoting clean water systems and aquatic ecosystem protection (UN-Water, \u003cspan citationid=\"CR111\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSDG 9 (Industry, Innovation, and Infrastructure)\u003c/b\u003e: The integration of biotechnology with IoT infrastructure exemplifies next-generation agricultural systems that are intelligent, efficient, and sustainable.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSDG 13 (Climate Action)\u003c/b\u003e: Reducing the carbon footprint and water demands of agriculture through biological systems aligns with global efforts to mitigate climate change impacts.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThese multifaceted contributions position synthetic biology not merely as a technical innovation but as a strategic tool for addressing some of humanity's most pressing challenges in food security, environmental sustainability, and climate resilience.\u003c/p\u003e \u003c/div\u003e"},{"header":"6. Biosafety, Ethics, and Regulatory Frameworks","content":"\u003cdiv id=\"Sec29\" class=\"Section2\"\u003e \u003ch2\u003e6.1 Containment Strategies for Engineered Microbes: Kill Switches, Auxotrophy, and Gene Guard Mechanisms\u003c/h2\u003e \u003cp\u003eSynthetic biology holds significant promise for optimising BOD degradation in hydroponic systems, yet its success depends on responsible stewardship. Containment strategies, ecological risk management, transparent regulations, and societal engagement must work in synergy. In hydroponic systems designed for future food production, engineered microbes offer the potential to accelerate biochemical oxygen demand (BOD) degradation, thereby improving water quality and crop yield (Mariam et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHowever, their deployment must be accompanied by robust containment strategies to prevent uncontrolled proliferation. Kill switches\u0026mdash;genetic circuits programmed to trigger cell death under specific conditions\u0026mdash;are increasingly employed to ensure microbes cannot survive outside designated environments (Rottinghaus et al., \u003cspan citationid=\"CR97\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Auxotrophy, where microbes are engineered to depend on a synthetic nutrient absent in natural ecosystems, further limits their environmental persistence. Gene guard mechanisms, such as toxin-antitoxin systems and CRISPR-based self-destruction codes, serve as an additional layer of biological security, ensuring engineered traits are not sustained if containment fails (Watters et al., \u003cspan citationid=\"CR115\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec30\" class=\"Section2\"\u003e \u003ch2\u003e6.2 Horizontal Gene Transfer and Ecological Risk Assessment\u003c/h2\u003e \u003cp\u003eHorizontal gene transfer (HGT) poses a major ecological concern, as engineered genetic material could potentially move into native microbial communities. This could result in unforeseen metabolic activities or altered ecosystem dynamics, especially in aquaponic or hydroponic settings where water acts as a medium for microbial exchange (French et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Risk assessments should include metagenomic surveillance to detect early signs of HGT, predictive ecological modelling to forecast potential impacts, and controlled microcosm experiments to evaluate survival, fitness, and adaptability of engineered strains (Emamalipour et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The goal is to mitigate both immediate environmental hazards and long-term evolutionary consequences.\u003c/p\u003e \u003cp\u003eA forward-looking regulatory framework should integrate biosafety, ethics, and socio-economic concerns. This could include mandatory ethical impact assessments alongside traditional environmental impact assessments, periodic public consultations, and adaptive governance that evolves with technological advances. Such integration ensures that regulatory decisions are not solely technical but also socially responsive (Lescrauwaet et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec31\" class=\"Section2\"\u003e \u003ch2\u003e6.3 Regulatory Landscape: Global Biosafety Frameworks for Water and Food Biotech\u003c/h2\u003e \u003cp\u003eThe governance of engineered microbes in water-based food production varies across regions. The Cartagena Protocol on Biosafety provides international guidance, focusing on the safe handling, transport, and use of genetically modified organisms (GMOs) (Pereira, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In the European Union, EFSA (European Food Safety Authority) enforces stringent pre-market risk evaluations, while in the United States, the EPA, USDA, and FDA share oversight responsibilities depending on intended use. Countries like Japan and Australia adopt case-by-case assessments aligned with OECD principles (Samson et al., \u003cspan citationid=\"CR98\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). For hydroponic applications, the regulatory scope extends beyond agricultural safety to encompass water quality laws, making interdisciplinary compliance essential (Rajaseger et al., \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBeyond biosafety, ethical considerations influence the societal reception of engineered microbes. Public concerns often revolve around the \u0026ldquo;unnaturalness\u0026rdquo; of synthetic biology, potential impacts on biodiversity, and corporate monopolisation of biotechnologies. Ethical frameworks emphasise transparency in research objectives, open communication about risks and benefits, and inclusive decision-making processes involving farmers, consumers, regulators, and scientists. Upholding these principles can help bridge the trust gap between innovators and the general public (Dalziell and Rogers, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIntroducing engineered microbes into hydroponics could reduce operational costs, improve yield, and support urban food security. However, socio-economic disparities may arise if only large-scale commercial farms can afford the technology. Ethical adoption requires equitable access frameworks, possibly through open-source microbial strains or government-subsidised programs, ensuring that smallholder and resource-limited farmers also benefit from synthetic biology innovations (Chiaranunt and White, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEffective communication strategies should balance technical accuracy with accessibility. Visual models showing how engineered microbes degrade BOD without harming crops, along with real-world pilot results, can counter misinformation (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Importantly, public engagement should occur early\u0026mdash;during the research and development phase rather than post-commercialisation\u0026mdash;to foster informed acceptance. This proactive approach shifts public perception from reactive resistance to collaborative evaluation.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEthical Considerations and Public Acceptance of Engineered Microbes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEthical Concern\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePublic Perception Challenge\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMitigation Strategies\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnvironmental Safety\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRisk of engineered microbes escaping into natural ecosystems\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFear of ecological imbalance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRobust containment strategies, ecological monitoring\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCummings et al. (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2025\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFood Safety\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePotential unintended effects on crops or consumers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDistrust of GMOs in food\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTransparent safety testing, third-party certification\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRajendran (\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiodiversity Impact\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePotential displacement of native microbial communities\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eConcern over loss of natural diversity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUse of targeted microbial strains with limited survival capacity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHardwick et al. (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCorporate Control\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConcentration of technology ownership\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePerceived monopolisation and farmer dependency\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOpen-source licensing, public-private partnerships\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eKumar et al. (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCultural Acceptance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEthical/religious objections to synthetic life\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eResistance from certain communities\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eInclusive dialogues, cultural sensitivity in outreach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSamson et al. (\u003cspan citationid=\"CR98\" class=\"CitationRef\"\u003e2025\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eData Transparency\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLimited access to research data\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSuspicion of hidden risks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOpen-access data sharing and public reporting\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChiaranunt and White (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"7. Future Research Directions","content":"\u003cdiv id=\"Sec33\" class=\"Section2\"\u003e \u003ch2\u003e7.1 Testing Across Diverse Hydroponic Crops and Systems\u003c/h2\u003e \u003cp\u003eFuture research should emphasise evaluating engineered microbes for BOD degradation across a broad range of hydroponic crops and systems. While leafy greens are commonly studied due to their rapid growth cycles, fruiting plants such as tomatoes, cucumbers, and peppers may present different microbial interactions and nutrient dynamics (Cristofano et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Similarly, research should extend beyond the nutrient-film technique (NFT) and deep-water culture (DWC) to include vertical farming and aquaponics. This will help determine the robustness, adaptability, and crop-specific optimisation of microbial consortia under diverse conditions (Gillani et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor small-scale farmers, cost is a major barrier to adopting synthetic biology-based hydroponic enhancements. Traditional bioreactors are expensive, energy-intensive, and designed for industrial-scale production. Research should prioritise \u003cb\u003elow-cost, modular bioreactors\u003c/b\u003e that use locally available materials, renewable energy sources (such as solar power), and simplified designs for easy operation and maintenance (Mihret et al., \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Innovations such as gravity-fed systems, biofilm-based reactors, and 3D-printed components could reduce costs significantly, making microbial cultivation and application feasible even in rural or low-income communities (Lazarus et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec34\" class=\"Section2\"\u003e \u003ch2\u003e7.2 Long-Term Ecological Impacts of Engineered Microbes\u003c/h2\u003e \u003cp\u003eThe long-term ecological stability of engineered microbes remains a critical knowledge gap. Hydroponic systems are semi-closed environments, yet microbial exchange with water sources, air, and human handlers is inevitable. Studies should investigate persistence, mutation rates, and interactions with non-target organisms over extended cultivation cycles (ElZein et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Predictive ecological models and controlled multi-season trials are needed to assess cumulative risks and ensure that engineered microbes do not create unforeseen environmental burdens when integrated into food production systems (Taiwo et al., \u003cspan citationid=\"CR106\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBioreactor research should also address socio-economic contexts, ensuring designs are affordable, culturally acceptable, and adaptable to local farming practices. Participatory design, where farmers are directly involved in testing prototypes, can help align technological solutions with user needs (Palladino et al., \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Financial support mechanisms such as microloans, government subsidies, and cooperative ownership models could further ease adoption. The long-term vision should not only be technological feasibility but also economic sustainability and farmer empowerment (Jiang et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec35\" class=\"Section2\"\u003e \u003ch2\u003e7.3 Interdisciplinary Approaches: Integrating Synthetic Biology with Other Technologies\u003c/h2\u003e \u003cp\u003eOptimising hydroponic performance requires synergy between synthetic biology and other technological domains. For example, coupling engineered microbes with IoT-based biosensors could enable real-time monitoring of microbial activity, nutrient levels, and BOD fluctuations (Arlyapov et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Similarly, machine learning algorithms can process large datasets to predict microbial performance under different system conditions. Integrating nanotechnology, particularly nano-carriers for nutrient or microbial delivery, may further enhance efficiency. Such interdisciplinary approaches ensure that microbial innovations are not isolated but embedded into smarter, more adaptive hydroponic infrastructures (Alsulimani et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAddressing global food security challenges requires cooperative frameworks that transcend national boundaries. Research consortia should promote open-source microbial strain libraries, accessible datasets, and shared pilot studies across regions. Collaboration between universities, government agencies, and private companies can reduce duplication of effort and accelerate innovation (Taiwo et al., \u003cspan citationid=\"CR106\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Equally important is ensuring that knowledge transfer reaches small-scale farmers in resource-limited settings through training workshops, demonstration farms, and multilingual digital platforms. This global knowledge ecosystem will make advanced hydroponic solutions more inclusive and scalable (Mgendi et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe integration of engineered microbes into hydroponics represents a transformative step for sustainable food production. However, achieving global impact requires a focus on adaptability, safety, affordability, and inclusivity. By testing across diverse systems, evaluating long-term impacts, embracing interdisciplinary tools, and fostering global collaboration, synthetic biology can be harnessed responsibly (Sousa et al., \u003cspan citationid=\"CR103\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Cost-effective bioreactor designs, tailored to the needs of small-scale farmers, will be central to democratising these innovations and ensuring that future food systems are equitable, resilient, and environmentally sustainable (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDevelopment of Cost-Effective Bioreactor Designs for Small-Scale Farmers\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDesign Principle\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBenefits for Small-Scale Farmers\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModular Construction\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBioreactors built from interchangeable, scalable parts\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEasy to expand or reduce size based on farm needs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePalladino et al. (\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLocally Available Materials\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUse of affordable plastics, recycled containers, or clay-based vessels\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReduces cost and dependency on imported equipment\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eda Silva et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRenewable Energy Integration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolar-powered pumps and aeration systems\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLowers operational costs and supports off-grid use\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDe et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGravity-Fed Flow Systems\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSimplified circulation without complex pumps\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMinimises energy consumption and maintenance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYu \u003cem\u003eet al\u003c/em\u003e. (2024)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiofilm-Based Reactors\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSurfaces designed to enhance microbial adhesion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHigher microbial efficiency with reduced input costs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGomes and Mergulh\u0026atilde;o (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3D-Printed Components\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLow-cost, customizable parts produced locally\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEncourages innovation and community-based solutions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAjao et al. (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUser-Friendly Interfaces\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSimple monitoring with colour indicators or mobile apps\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMakes technology accessible to non-experts\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eKim et al. (\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"8. CONCLUSION","content":"\u003cp\u003eThis review demonstrates that synthetic biology offers a powerful solution to biochemical oxygen demand (BOD) management in hydroponic systems\u0026mdash;a persistent challenge that limits efficiency, safety, and scalability of soilless agriculture. As global population growth and climate change intensify pressure on conventional farming, hydroponics optimised through engineered microorganisms provides a viable pathway to sustainable food production.\u003c/p\u003e \u003cp\u003eGenetically modified organisms such as \u003cem\u003eBacillus subtilis\u003c/em\u003e, \u003cem\u003ePseudomonas putida\u003c/em\u003e, and \u003cem\u003eRhodococcus\u003c/em\u003e species, enhanced through CRISPR-Cas9 and metabolic engineering, offer targeted organic matter degradation superior to traditional methods (aeration, chemical treatment). When integrated with real-time biosensors, IoT platforms, and machine learning, these systems enable dynamic, self-regulating water quality management. Synthetic biology approaches excel in specificity, energy efficiency, and environmental sustainability, though traditional methods retain advantages in immediate implementation and regulatory clarity.\u003c/p\u003e \u003cp\u003eFood safety improvements are significant, as engineered microbes reduce pathogenic proliferation by maintaining low BOD levels while producing antimicrobial compounds. However, successful deployment requires robust biosafety mechanisms (kill switches, auxotrophy), harmonised international regulations, transparent public communication, and equitable access frameworks to benefit both commercial operations and smallholder farmers.\u003c/p\u003e \u003cp\u003eReal-world pilots in Singapore, the Netherlands, and North America validate technical feasibility, while future research must address long-term ecological impacts, cost-effective designs for small-scale farmers, and interdisciplinary integration with emerging technologies. By contributing to multiple UN Sustainable Development Goals\u0026mdash;particularly food security, water management, and climate action\u0026mdash;synthetic biology-based BOD optimisation represents not just a technical advancement but a strategic necessity for building resilient, sustainable food systems capable of meeting future global needs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eO.A.A., B.M.P. and O.J.S. made substantial contributions to the conception or design of the work;O.A.A., B.M.P. and O.J.S. drafted the work or revised it critically for important intellectual content;O.A.A., B.M.P. and O.J.S. approved the version to be published; and O.A.A., B.M.P. and O.J.S. agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAas, C. 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Elucidation of complexity and prediction of interactions in microbial communities. Microbial Biotechnology, 13(2), 383\u0026ndash;394. https://doi.org/10.1111/1751-7915.13855\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Environmental Biotechnology, Biochemical Oxygen Demand, Genetically Modified Microorganisms, Food Security, Water Quality Management, Sustainable Development Goals","lastPublishedDoi":"10.21203/rs.3.rs-8879143/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8879143/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe growing world-wide population and climate-induced agricultural setbacks demand innovative approaches to sustainable food production. Hydroponic systems offer promising solutions through resource-efficient, soilless cultivation methods suitable for urban and drought-prone regions. However, the build-up of organic matter in recirculating nutrient solutions elevates biochemical oxygen demand (BOD), leading to dissolved oxygen depletion, disrupted microbial balance, compromised plant health, and potential food safety risks through pathogen proliferation. This review examines synthetic biology as a strategy for optimising BOD degradation in hydroponic systems. We explore the application of genetically engineered microorganisms, including \u003cem\u003eBacillus subtilis\u003c/em\u003e, \u003cem\u003ePseudomonas putida\u003c/em\u003e, and \u003cem\u003eRhodococcus\u003c/em\u003e species, equipped with enhanced catabolic pathways for targeted organic matter degradation. Advanced genetic tools such as CRISPR-Cas9 gene editing, metabolic pathway engineering, and synthetic microbial consortia design are evaluated for their efficacy in maintaining water quality while supporting crop productivity. The integration of biosensor technologies, Internet of Things (IoT) platforms, and real-time monitoring systems allows for dynamic, feedback-responsive bioremediation strategies. Comparative assessments demonstrate synthetic biology's benefits over traditional BOD management methods in terms of specificity, energy efficiency, adaptability, and environmental sustainability. We address biosafety mechanisms (kill switches, auxotrophy), regulatory frameworks, ethical implications, and public acceptance challenges. This review highlights successful pilot implementations, discusses scalability for commercial operations, and identifies future research directions, emphasising interdisciplinary approaches, long-term ecological impact assessments, and cost-effective designs for small-scale farmers. Ultimately, synthetic biology-based BOD optimisation offers a strategic pathway toward resilient, sustainable, and safe hydroponic food production systems that contribute to global food security.\u003c/p\u003e","manuscriptTitle":"Synthetic Biology Approaches for Optimizing Bod Degradation in Hydroponic Systems for Future Food Production","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-23 10:20:12","doi":"10.21203/rs.3.rs-8879143/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b392170d-2193-48a3-ac85-4e44abf60f04","owner":[],"postedDate":"February 23rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-15T17:09:40+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-23 10:20:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8879143","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8879143","identity":"rs-8879143","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}