Isolation and Identification of Priestia  megaterium  and Its Growth Promoting Effect on Tomato

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In this study, nine strains were isolated from robustly growing tomato roots and inter-root soil, and one strain was isolated from purchased bacterial fertiliser. They were identified as Priestia megaterium . The growth promoting ability was identified by applying P. megaterium to tomato. In addition, the phosphorus solubilising ability of the strains was measured, and the resistance-related enzyme activities and genes were measured on tomato leaves after the application of the strains, in order to preliminarily investigate the growth promotion and resistance mechanism of P. megaterium . The results showed that P. megaterium could promote the growth of tomato, increase the chlorophyll content of leaves, increase the PPO and POD activities, and promote the expression of LOX-D , ERF2 and PR-1a in tomato leaves. Priestia megaterium growth promotion antagonistic capacity plant growth-promoting rhizobacteria Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction Plant growth-promoting rhizobacteria ( PGPR ) are a kind of active microorganisms that live in the rhizosphere of plants and can colonize plant roots, promote plant growth, control plant diseases, and increase crop yield and quality (Bashan et al. 1993 ; Pieterse et al. 2002 ; Chakraborty et al. 2006 ). PGPR colonizes in plant roots or rhizosphere soil, and has the ability to dissolve phosphorus, fix nitrogen, dissolve potassium and secrete plant hormones, which can significantly promote plant growth (Li et al. 2020 ). Interplant root-promoting bacteria promote plant growth through a variety of mechanisms, including: (1) nitrogen fixation, which converts atmospheric nitrogen into plant-available nitrogen; (2) dissolution of insoluble phosphate in the soil to increase the effectiveness of phosphorus (Jia et al., 2023) ;(3) secretion of growth hormones, cytokinins and gibberellins, etc. to regulate plant growth; and (4) production of iron carriers to help plants absorb iron and alleviate iron deficiency symptoms. In addition, it can also induce plants to produce systemic resistance, reduce the adverse effects of pathogens and degradation of pollutants on plants (Zhou et al. 2023 ). The main PGPR species screened to date are Paenibacillus , Achromobacter , Klebsiella , Arthrobacter , Pseudomonas , Azospirillum , Enterobacter , Bacillus , Burkholderia , Herbaspirillum , Chryseobacterium , Citrobacter , Pantoea and Rhizobium (Burdman et al. 1999 )). In 2020, Gupta et al. reclassified Bacillus megaterium as Priestia megaterium through systematic and comparative genomic analyses(Gupta et al. 2020 ). P. megaterium is a kind of microorganism with the functions of solubilizing phosphorus and promoting potassium. Some strains can also secrete metabolites such as indole acetic acid and various organic acids to promote plant growth (Chandra et al. 2021 ; Guzmán-Moreno et al. 2022 ). The application of P. megaterium can change the soil microbial flora, reduce the abundance of harmful flora, and optimize the soil microbial community structure (Ma et al. 2019 ; Zhao et al. 2021 ). The application of P. megaterium can also repair cadmium-contaminated soil (Li et al. 2024 ). Previously, tomatoes grown in the greenhouse of the Horticultural Experiment Station of Northeast Agricultural University were affected by the disease, and only three disease-resistant plants survived. In this study, we extracted the inter-root-promoting bacteria from the roots of these disease-resistant plants and from the root soil to investigate their promoting and disease-resisting effects and their mechanisms. Materials and methods Isolation and screening of strains Selected vigorously growing tomato roots, rinsed them in water, dried them and cut them into small pieces. In an ultra-clean bench, the roots were soaked in 70% alcohol for 30 seconds and then rinsed with sterile water three times for 1 minute each time. The roots were crushed in a mortar filled with sterile water and dipped in sterile water to line on the LB medium. The medium were placed in a constant temperature incubator at 28 ℃ for 1-2 d. The single strain was obtained after isolated and purified several times. Inter-root soil of actively growing tomato plants was selected, weighed 5 g of soil after passing through a 2 mm sieve and placed in a triangular vial containing 50 ml of sterile water and shaken to make the soil fully suspended. Suspension diluted 10 2 , 10 3 and 10 4 -fold with sterile water, 100 µL was then spread onto the LB plate and incubated in the incubator at 28 °C for 1-2 d. The single strains were obtained after isolated and purified several times.The isolated strains were subjected to Gram staining and flagellar staining. Molecular identification of bacteria The obtained strains were identified by PCR sequencing using 16S rDNA primers, reaC gene specific primers and phaC gene specific primers, the primer sequences are shown in Table 1.The PCR amplification procedure was as follows: pre-denaturation: 95 ℃, 3 min; cycling reaction: 95 ℃ 1 5 s, 55 ℃ 15 s, 72 ℃ 30 s, the number of cycles was 35 times; final extension: 72 ℃, 5 min.The sequencing results were subjected to NCBI-BLAST comparison (NCBI: https: //www.ncbi.nlm.nih.gov/), and a phylogenetic tree was constructed using MEGA 7.0 software. The isolated strains were subjected to Gram staining and flagellar staining. Table 1. Primer sequences required for strain identification Gene Primer name Primer sequence 16s rDNA 27F 5’-AGAGTTTGATCCTGGCTCAG-3’ 1492R 5'-ACGGCTACCTTGTTACGACTT-3' recA recA-F 5’-CAACAGCAGGGCGGACAGGC-3' recA-R 5’-TGTTCACGCACTTGTCCCGCA-3’ phaC phaC-F 5’-TGACAACAGAAGCGGAAC-3’ PhaC-R 5’-CACGAATCCACTGACGATA-3’ Determination of antagonistic capacity of strains against pathogenic bacteria Simultaneously inoculate the test strains and Phytophthora nicothianae and Phytophthora capsici on the PDA plate, and place them in a constant temperature incubator at 28 ℃ for cultivation. Observe the growth of pathogenic bacteria and determine whether the experimental strains have antagonistic effect on pathogenic bacteria. Determination of the growth-promoting ability of strains The same variety of tomato sown at the same time and with the same growth condition were used as test materials, inoculated with the test strains in groups, and a blank control was set. Each group was replicated three times. Stem thickness, plant height, above ground fresh weight, above ground dry weight, below ground dry weight of tomato and chlorophyll contentwere determined at the seedling stage. Chlorophyll content was determined by 95% ethanol extraction (Liu et al. 2022), and chlorophyll a, chlorophyll b and carotenoids were measured in the experimental and control groups. Phosphate-solubilizing ability test of strai n Inoculate 1% bacterial suspension in inorganic phosphorus liquid medium, incubate at 28 ℃ with 150 rmp shaking for 48 h, inoculate sterile water as control. After transferring to a centrifuge tube, the cells were broken by ultrasonic waves and centrifuged at 4000 r/min for 20 min. The standard curve of phosphorus was plotted with reference to the method of Ding (Ding et al. 2024), and 200 μl of the supernatant was taken to determine the effective phosphorus content in the supernatant using the molybdenum antimony antimony colourimetric method (Smith and Goodman 1999). Effect of application of 9 strains on inter-root soil microbial community Select tomato plants exhibiting identical growth patterns during the same period as experimental samples. Administer inoculation treatment to the soil surrounding each plant, establishing a blank control. Ensure identical inoculation quantities across all treatments.Soil samples were collected at 45 days after treatment, and three replicates were set up each group of treatments, with three plant root system soil mixes sampled in each replicate. The number of bacteria, fungi and actinomycetes in the soil was determined by dilution plate method to determine the changes in the soil microflora after the application of the test strains. Bacteria were cultured using LB culture, fungi were cultured using PDA medium and actinomycetes were cultured using Gauze’s Medium No.1. Effect of application of 9 strains on defence genes in tomato Nine strains were used to treat tomatoes with the same growth at the same period, and a blank control was set. Tomato leaf tissues were collected at 24 h, 48 h and 96 h after treatment and RNA was extracted and reverse transcribed. LOX-D gene-specific primer sequences were designed with reference to Abdallah et al.(Rania et al. 2017), ERF2 gene-specific primers were designed with reference to Wang et al. (Wang 2010), PR-1a gene-specific primers were designed with reference to Wang et al (Wang et al. 2017), Actin gene-specific primers were designed with reference to Babu et al(Narendra Babu et al. 2015). The primer sequences required for qPCR are shown in Table2. The qPCR amplification procedure was as follows: pre-denaturation: 95 ℃, 2 min; cycling reaction: 95 ℃ 1 5 s, 57 ℃ 15 s, 72 ℃ 30 s, the number of cycles was 40 times. Table2. Primer sequences required for qPCR Gene Primer name Primer sequence LOX-D LOX-D-F 5’-CCTGAAATCTATGGCCCTCA-3’ LOX-D -R 5'-ATGGGCTTAAGTGTGCCAAC-3' ERF2 ERF2-F 5’-GGCTGCTGAAATTCGTGACC-3' recA-R 5’-GGGGCTCTGGATGACTGTAG-3’ PR-1a PR-1a-F 5’-GCTGTGAAGATGTGGGACGA-3’ PR-1a-R 5’-ACCGACTTACGCCATACCAC-3’ Actin Actin-F 5’-GTGCGAGTGTCCTGTCTGTT-3’ Actin-R 5’-TACCGTGCATTCATAGCCCC-3’ Effect of application 9 strains on the growth of tomatoes at low temperatures Tomato seedlings that were sown at the same time and had uniform growth conditions were selected and placed in a low-temperature environment. The temperature was set to 10 °C during the day and 4 °C at night, with a light duration of 12 hours. On the first day of exposure to the low-temperature environment, the inoculation treatment was carried out and two control groups were set up: a low-temperature control group (CK1) and a normal-temperature control group (CK2). The temperature was restored to normal (28°C during the day and 18°C at night) after 14 days of growth. On the 14th day of temperature recovery, the height, stem thickness, fresh weight and dry weight of the tomato were measured. Effect of Mixed Inoculation of Strains on Tomato Growth Based on preliminary experimental results, four dominant bacterial strains were selected and inoculated onto tomato plants sown simultaneously and exhibiting consistent growth conditions. Concurrently, a single-strain inoculation experimental group and a blank control group were established. Each treatment involved inoculating ten tomato plants, with three replicates established. Fourteen days post-inoculation, the experimental tomato plants were measured for plant height, stem diameter, fresh weight, and dry weight. Data statistics and analysis The statistical analysis of the data in this study was done using SPSS 25.0.The significance of the difference between the treatments was tested using analysis of variance (ANOVA) and when P<0.05, it was considered to be significantly different. Results Morphological identification of strains A total of 9 strains were isolated from tomato roots and inter-root soil. The strains were numbered B1-B9. It was observed that the colonies of the above 9 strains were round and yellowish (Fig. 1a). The edges were smooth at the early stage of culture, and the surface was slightly wrinkled with the growth of time. All 9 strains were rod-shaped, Gram-positive (Fig. 1b) bacteria with flagella(Fig. 1c). Molecular identification of strains The isolated strains were amplified by PCR using bacterial 16S rDNA universal primers 1492R and 27F, and the resulting sequences were compared by BLAST on NCBI, which showed that the sequence matches of the 9 strains with Bacillus spp. were up to 100%, and it was known that the strains were Bacillus spp. In adddition, specific primers were designed for phaC and r ecA of Bacillus , and the sequences obtained after PCR amplification of the strains were compared on NCBI. It was found that the phaC -specific fragment could match up to 99.11%~100% with the sequence of P. megaterium , and the recA -specific fragment could match up to 99.27%~100% with the sequence of P. megaterium . A three-gene tandem evolutionary tree based on 16S r DNA, phaC and recA showed the closest affinity to P. megaterium (Fig. 1d) . Combining the above comparison results, it was determined that all test strains were P. megaterium . Antagonistic ability of 9 strains against pathogenic bacteria Nine strains were assayed for their antagonistic ability against Phytophthora nicothianae and Phytophthora capsici . It was found that the test strains had no antagonistic effect on these two pathogens (Fig. 2a,b). Effect of 9 strains on the growth of tomato After inoculation with strains 15 days, various indicators of tomato were measured. It was found that the strains promoted the growth of tomato, but the growth-promoting effect varied among different strains (Fig. 3). The results showed that B1, B2, B3, B4, B7 strains had better growth promotion effect on tomato plant height (Fig. 3a), above ground fresh weight and dry weight, underground fresh weight and dry weight compared with other strains (Fig. 3c-f). B1 strains had better growth promotion effect on tomato stem thickness (Fig. 3b). The chlorophyll a, chlorophyll b and carotenoid contents of tomato leaves were determined after inoculation with the strains 14 days , and it was found that the strains promoted the chlorophyll contents of tomato leaves (Fig. 4). The more effective chlorophyll promoters of tomato were the B6 and B7 strains (Fig. 4a-c). The growth rates of chlorophyll a, chlorophyll b and carotenoids were 32.52%, 36.51% and 20.51%, in the B6 strain group compared to the control group. The growth rates of chlorophyll a, chlorophyll b and carotenoids were 31.31%, 36.51% and 17.95%, in the B7 strain group compared with the control group. The above results indicate that P. megaterium was able to increase the chlorophyll content and improve the photosynthetic rate of tomato leaves, and promote the growth and development of plants. Phosphorus solubilising capacity of 9 strains Through the qualitative determination of the phosphorus solubilising ability of 9 strains, it was found that all 9 strains could form a phosphorus solubilising circle, which indicated that all 9 strains had a certain phosphorus solubilising ability. Through quantitative determination of phosphorus solubilising capacity, it was found that the phosphorus solubilising capacity of strains B1, B2, B3 and B4 was relatively better, and the phosphorus content in the solution was 16.8 mg/L, 17.7 mg/L, 21.4 mg/L and 16.4 mg/L ,respectively, when cultured for 48h(Fig. 5a). Effect of applied 9 strains on soil inter-root microorganisms The treatment with the strains had a certain effect on the number of bacteria, fungi and actinomycetes in the inter-root soil after 45 days of treatment. The number of bacteria and actinomycetes increased after treatment with the experimental strains (Fig. 5b,d). B6 strain showed the greatest increase in inter-root bacterial counts and the bacterial content of the soil could reach 14.67×10 5 CFU/g, and there was also a significant increase in the number of bacteria after treatment of other strains as compared to the control (Fig. 5b) The actinomycetes’ number of the soil increased in the treatment with the strains B1, B2, B3, B4 and B7 and differed significantly from that of the control group. Among them, B7 strain showed the greatest increase in the number of inter-root soil actinomycetes after treatment (Fig. 5d). After using the 9 strains to treat the inter-root of tomato, the number of soil fungi in the inter-root of tomato did not show any significant change except for B8 and B9 which showed a significant increase in the number of fungi in the inter-root soil of tomato (Fig. 5c). After 45 days of treatment using the 9 strains, the bacterial/fungal ratios were 180.6, 181.2, 238.8, 250, 320.4, 423.1, 234.2, 176.5, 149.1, and 399.6, which were higher than that of the control group at 94.8 (Table 3). The above results indicated that the application of the above experimental strains were able to change the inter-root soil microbial environment. Table 3. Bacteria:Fungi ratio in soil after 45 days of treatment with 9 strains of P. megaterium Strains B1 B2 B3 B4 B5 B6 B7 B8 B9 CK bacterial:fungal ratio 180.6 181.2 238.8 250 320.4 423.1 234.2 176.5 149.1 94.8 Effect of the application of 9 strains on the activity of defence enzymes in tomato leaves Effect of 9 strains on PPO activity of tomato leaves Polyphenol oxidase (PPO) is a widespread enzyme found in plants, animals and fungus. PPO enhances disease resistance and adaptability to adversity in plants and plays an important role in plant resistance mechanisms. After inoculation with 9 strains, the PPO activity of tomato leaves showed a tendency of increasing and then decreasing (Fig. 6a). Compared with the control group, at 24 h of inoculation, all treatment groups except B6 and B8 significantly increased the PPO activity of tomato leaves. PPO activity was up to 198.85 U·min -1 -g -1 FW. At 96 h, the PPO activity of the B5, B7, B8 and B9 treatment groups was higher than that of the control group with significant differences, and it was up to 98.2 U·min -1 -g -1 FW. There was no significant change in PPO activity in the control group during the assay time range. The above results indicate that P. megaterium enhanced PPO activity to a certain extent and helped to improve tomato plant resistance. Effect of 9 strains on POD activity of tomato leaves Peroxidase (POD) is a class of chemical reaction enzymes that catalyses catalase and other peroxides, which catalyzes a redox reaction using H 2 O 2 as an oxidant and reduces H 2 O 2 to H 2 O to protect the plant. The POD activities of tomato leaves in the experimental group were all significantly increased compared to the control group (Fig. 6b). At 24 h after treatment, the highest POD enzyme activities were observed in the B1, B4 and B7 treatment groups, which could reach 223.31 U·min -1 -g -1 FW, 217.43 U·min -1 -g -1 FW, 219.05 U·min -1 -g -1 FW, and 151.45%~158.25% higher compared with the control group. At 48 h of treatment, the highest POD enzyme activity of B9 strain treatment group could reach 295.71 U·min -1 -g -1 FW, which increased by 215.49% compared with the control group. At 96 h of treatment, the highest POD enzyme activity was found in the treatment groups of B3 and B7 strains, which could reach 255.77 U·min -1 -g -1 FW and 242.74 U·min -1 -g -1 FW, which increased by 178.98% to 164.77% compared with the control group. The results showed that P. megaterium could enhance POD activity to a certain extent, resulting in increased resistance of the plant to environmental adaptation. Effect of 9 strains on SOD activity of tomato leaves Superoxide Dismutase (SOD) is also an important antioxidant enzyme that can reduce oxidative stress by scavenging superoxide anion and protect cells from oxygen radical damage. The results show that only strain B7 showed a significant increase in SOD enzyme activity after 96 h of treatment with activity up to 247.58 U·min -1 -g -1 FW, which was 36.45% higher compared to the control (Fig. 6c).The other strains showed no significant changes compared to the controls. Effect of applied strains on the relative expression of defence genes in tomato leaves Effect of 9 strains on the relative expression of LOX-D in tomato LOX-D (lipoxygenase D) is an important member of the plant lipoxygenase gene family, which plays a key role in the jasmonic acid (JA) synthesis pathway, and is widely involved in stress response processes such as insect, disease, and drought resistance in plants.The results show that the application of 9 strains had an effect on LOX-D expression, and there was a significant difference in LOX-D expression among each treatment group and at different times (Fig. 6d). After treatment with B3, B4, and B5 strains, the relative expression of LOX-D showed an upward trend, which showed a decreasing and then increasing trend compared with CK group. It reached the highest at the 96 h, which was 1.5~3.8 times of the CK group. After treatment with B1, B2, B6, B7, B8, B9 strains, the relative expression of LOX-D showed a tendency of decreasing, then increasing and then decreasing. It reached the highest at 48h, which was 1.3~3.3 times of the CK group. The results suggest that P. megaterium may be involved in the JA signalling pathway to stimulate plant tomato resistance. Effect of 9 strains on the relative expression of ERF 2 in tomato ERF2 (Ethylene Response Factor 2) is a core member of the AP2/ERF transcription factor family. It integrates ethylene signalling with downstream physiological processes by recognising ethylene (ET)) response elements (e.g. GCC-box, ERELEE4) in the promoters of target genes, coordinating plant development, stress response and quality formation.The results show that the application of the test strains had a significant effect on ERF2 expression, and there was a significant difference in ERF2 expression among the treatment groups (Fig. 6e). Except for the B6 treatment group, the rest of the treatment groups compared with the control group showed a trend of decreasing, then increasing and then decreasing, and reached the maximum at 48 h, which was 1.89~4.39 times of the CK group. Compared with the CK group the B6 treatment group showed a tendency of decreasing and then increasing, reaching a maximum at 96 h, which was 1.19 times that of the CK group. The results suggest that P. megaterium may be involved in the ethylene pathway to stimulate plant tomato resistance. Effect of 9 strains on the relative expression of PR-1a in tomato PR-1a acts as a salicylic acid (SA) pathway hub to activate systemic resistance.The results show that the application of the test strains had a significant effect on the relative expression of PR-1a , and there was a significant difference in the expression of PR-1a among each treatment group (Fig. 6f). Except for the B4 treatment group, PR-1a showed a trend of decreasing then increasing and then decreasing in the rest of the treatment groups. The expression reached the highest at 48 h, which was 1.11~8.64 times of that of the CK group. The relative expression of PR-1a in B4 treatment group showed a decreasing and then increasing trend compared with that of CK group.The relative expression of PR-1a in B4 group reached the highest at 96 h, which was 2.43 times higher than that of CK group. The results indicated that P. megaterium might be involved in the SA signalling pathway to stimulate tomato resistance. Effect of 9 strains on soluble sugar content and fruits weight of tomato fruits The soluble sugar content of ripe tomato was tested in different treatment groups and the results are shown in figure 8a. It can be seen that there was a significant enhancement in the soluble sugar content of ripe tomato fruits after treatment with B3 and B7 strains. The B3 and B7 treated groups were enhanced by 32.27%, 32.38%, 44.66% , respectively, compared to the control group (Fig. 7a). From the figure 8b, it can be seen that the application of 9 strains can have an effect on tomato fruit weight. After treatment with B2, B3, B5 and B6 strains, tomato fruit weight was significantly increased compared with the control group. Among them, B3 treatment groups showed the most significant increase in tomato fruit weight, which increased by 60.99% and 52.86% compared with CK group (Fig. 7b). Effects of 9 strains on tomato growth under low temperature conditions The results showed that the application of the test strains had a certain effect on the growth of tomato under low temperature conditions. Compared with CK1, the plant height of tomato treated with B9 strain was significantly increased (Fig. 8.a), and the plant stem thickness, fresh weight and dry weight did not change significantly (Fig. 7b-d). There was no significant difference in the data of other treatment groups compared with CK1(Fig. 8a-d). The experimental results show that the B9 strain may have higher activity at low temperature than other strains, and can improve the cold resistance of tomato. The Effect of Mixed Planting on Tomato Growth Conditions Measurements of plant height, stem diameter, fresh weight, and dry weight were taken for tomatoes inoculated with mixed strains, single strains, and the control group(Fig. 9). Compared to the control group, both mixed-strain inoculation and single-strain inoculation increased plant height, fresh weight, and dry weight(Fig. 9a,c-e),with no significant change in stem diameter(Fig. 9b). Furthermore, the growth-promoting effect of mixed-strain inoculation on tomatoes was more pronounced than that of single-strain inoculation. Discussion The traditional large-scale use of plant-promoting products are chemicals, while the long-term use of chemicals can increase the harmful substances in the soil, causing an imbalance in the ecology of the rhizosphere soil, which in turn, nutritive plant growth (Yu et al. 2009 ). Whereas, the use of bacterial manure can effectively enhance soil fertility and promote plant growth (Khan et al. 2007 ; Glick 2012 ; Bhattacharyya and Jha 2012 ). The main functions of the growth-promoting bacteria are to significantly increase plant growth vigour and inhibit the growth of pathogenic bacteria. Bacillus is proven to be an inter-root growth promoting bacterium. In this paper, it was found that the P. megaterium used in the experiment had no antagonistic effect on the common solanaceous crop pathogens P.nicothianae and P.capsici , but had a certain growth-promoting effect on the plants. The results of this study indicate that the favourable effects of P. megaterium on plants were mainly growth-promoting rather than pathogen-inhibiting. The growth-promoting effect of P. megaterium application may vary slightly in different crop species. It has been reported that the prophylactic effect of PGPR is related to their phosphorus solubilising function ((Akgul and Mirik 2008 ; Zhu et al. 2023 ).Through this study, it was found that the B1, B2 and B3 strains have more obvious phosphorus solubilising effect, also have better growth promotion effect on tomato. However, only the B9 strain had a significant effect on tomato plant height under low temperature conditions. Changes in defence enzyme activities are also important factors affecting plant growth (Latha et al. 2009 ). It has been found that a variety of defence enzymes can promote plant growth and increase plant resistance. A number of studies have been conducted to show that Bacillus can enhance defence enzyme activities in plants. Zheng et al. found that Bacillus amyloliquefaciens enhanced PPO activity in tomato leaves (Zheng et al. 2018 ); Sun et al. found that treatment of banana with Bacillus subtilis increased the PPO and POD activities (Sun et al. 2010 ). In this study, we found that the application of the experimental strains were able to enhance the PPO and POD activities of tomato leaves, but the effect on SOD activity was not significant. This suggests that P. megaterium may enhance plant resistance and promote plant growth by enhancing PPO and POD activities. Chlorophyll is a very important pigment in plants, which is mainly involved in photosynthesis, energy conversion, and production of nutrients needed for plant growth, which in turn affects plant growth (Yan et al. 2021 ). In this study, the application of P. megaterium showed a significant increase in the chlorophyll content of tomato leaves compared with the control group, indicating that P. megaterium was able to effectively increase the chlorophyll content of the plants. Soluble sugars are sugars that can melt in water, including monosaccharides and oligosaccharides. Soluble sugar is an important source of energy in plants, which operates in various parts of plants and affects fruit quality. The results of this study showed that P. megaterium could increase the soluble sugar content of tomato fruits and improve fruit quality. The explanation is that, P. megaterium enhances the quality of tomatoes by increasing the chlorophyll content, thereby promoting photosynthesis and carbohydrate synthesis. Resistance mechanisms in plants are associated with a variety of hormonal signalling pathways such as salicylic acid, jasmonic acid and ethylene pathways. They can make plants resistant to pathogens through mutual antagonism (Kunkel and Brooks 2002 ), and can also cause various physiological and biochemical changes in the plant body, thus resisting the infection of various pathogens (Li et al. 2013 ). In this paper, the results showed that the application of the 9 strains of P. megaterium able to increase the relative expression of LOX-D , ERF2 and PR-1a in tomato, suggesting that P. megaterium may be involved in the JA signalling pathway, the ethylene signalling pathway and the SA signalling pathway to increase plant systemic resistance. The effect of the experimental strain on the PR-1a was more pronounced, which may indicate that P. megaterium used in the experiment is more involved in the SA signalling pathway. However, the effects on the three genes were slightly different among different strains, which may be related to the differences in the strains' own genes. The specific genes controlled by what need to be further studied. Soil microorganisms are an important part of the soil, decomposing organic matter for plant uptake, participating in soil nutrient cycling and influencing plant growth (Clark and Paul 1970 ). It has been found that a high soil bacterial:fungal ratio favours plant growth (Frey et al. 1999 ; Yao and Wu 2010 ). In this study, it was found that the bacterial counts were all increased after treatment with 9 strains and the bacterial:fungal ratio was increased compared to the control group. It suggests that P. megaterium may be influencing the soil microflora species, resulting in an increase in beneficial bacteria, which promotes plant growth. Actinomycetes are an important group of soil microorganisms that decompose organic matter, produce antibiotics and promote plant growth. In this study, it was found that all the strains except B6, B8 and B9 strains increased the number of actinomycetes in the soil. This suggests that P. megaterium may increase the number of actinomycetes in the soil thereby increasing the nutrients in the soil and promoting plant growth. Conclusion In this paper, 9 strains were isolated from robustly growing tomato roots and root soil, identified as P. megaterium , Gram-positive, with flagella. It was found that the P. megaterium could promote the growth of tomato, increase the chlorophyll content, and have some phosphorus solubilising effect. Treatment of tomato with P. megaterium also increased leaf PPO and POD enzyme activities, increased LOX-D , ERF2 and PR-1a expression, and increased the number of bacteria and actinomycetes in the soil. Only the B9 strain was able to improve the cold-resistant characteristics of the plants and promote tomato growth and development at low temperatures. Compared to single strains, mixed strains exhibit a more pronounced growth-promoting effect on tomatoes. Declarations Author Contribution Yaowei Zhang, Ran Gu and Yan Liu conceived the project, Yulu Tang and Yang yang collected the experimental data, Wei Luan analyzed the experimental data and wrote the manuscript. Funding This work was supported by the National Natural Science Foundation of China (32202510) and the Key Research and Development Program of Heilongjiang Province of China (SC2022ZX02C0202). Data availability All the necessary data is available in the manuscript. The authors declare no conflict of interest exits. References Akgul DS, Mirik M (2008) Biocontrol of Phytophthora capsici on pepper plants by Bacillus megaterium strains. J PLANT Pathol 90:29–34 Bashan Y, Holguin G, Lifshitz R (1993) Isolation and Characterization of Plant Growth-Promoting Rhizobacteria Bhattacharyya PN, Jha DK (2012) Plant growth-promoting rhizobacteria (PGPR): emergence in agriculture. 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Plant Prot 50:24-31+60. https://doi.org/10.16688/j.zwbh.2023424 Frey SD, Elliott ET, Paustian K (1999) Bacterial and fungal abundance and biomass in conventional and no-tillage agroecosystems along two climatic gradients. Soil Biol Biochem 31:573–585. https://doi.org/10.1016/S0038-0717(98)00161-8 Glick BR (2012) Plant Growth-Promoting Bacteria: Mechanisms and Applications. Scientifica 2012:1–15. https://doi.org/10.6064/2012/963401 Gupta RS, Patel S, Saini N, Chen S (2020) Robust demarcation of 17 distinct Bacillus species clades, proposed as novel Bacillaceae genera, by phylogenomics and comparative genomic analyses: description of Robertmurraya kyonggiensis sp. nov. and proposal for an emended genus Bacillus limiting it only to the members of the Subtilis and Cereus clades of species. Int J Syst Evol Microbiol 70:5753–5798. https://doi.org/10.1099/ijsem.0.004475 Guzmán-Moreno J, García-Ortega LF, Torres-Saucedo L, et al (2022) Bacillus megaterium HgT21: a Promising Metal Multiresistant Plant Growth-Promoting Bacteria for Soil Biorestoration. Microbiol Spectr 10:e00656-22. https://doi.org/10.1128/spectrum.00656-22 Khan MS, Zaidi A, Wani PA (2007) Role of phosphate-solubilizing microorganisms in sustainable agriculture — A review. Agron Sustain Dev 27:29–43. https://doi.org/10.1051/agro:2006011 Kunkel BN, Brooks DM (2002) Cross talk between signaling pathways in pathogen defense. Curr Opin Plant Biol 5:325–331. https://doi.org/10.1016/S1369-5266(02)00275-3 Latha P, Anand T, Ragupathi N, et al (2009) Antimicrobial activity of plant extracts and induction of systemic resistance in tomato plants by mixtures of PGPR strains and Zimmu leaf extract against Alternaria solani . Biol Control 50:85–93. https://doi.org/10.1016/j.biocontrol.2009.03.002 Li B, Wang J, Sun S (2013) Research progress on mechanism of plant induced disease resistance. China Plant Prot Li HY, Qiu YZ, Yao T, et al (2020) Effects of PGPR microbial inoculants on the growth and soil properties of Avena sativa, Medicago sativa, and Cucumis sativus seedlings. Soil Tillage Res 199:104577. https://doi.org/10.1016/j.still.2020.104577 Li JP, Yang XQ, Zhang XX, Zhang L (2024) Effects and mechanisms of microbial ecology and diversity on phytoremediation of cadmium-contaminated soil under the influence of biodegradable organic acids. Int J Phytoremediation 1–12. https://doi.org/10.1080/15226514.2024.2391025 Liu P, Bi JT, Luo CK, et al (2022) Effects of salt-tolerant bacteria on rice seed germination and seedling growth under salt stress. J Agro-Environ Sci Ma HY, Huang YY, Liu SR, et al (2019) Effects of microbial agents on nutrient and bacterial community diversity in rhizosphere soil of eggplant cultivated in facilities. Microbiol China 47:140–150. https://doi.org/10.13344/j.microbiol.china.190275 Narendra Babu A, Jogaiah S, Ito S, et al (2015) Improvement of growth, fruit weight and early blight disease protection of tomato plants by rhizosphere bacteria is correlated with their beneficial traits and induced biosynthesis of antioxidant peroxidase and polyphenol oxidase. Plant Sci 231:62–73. https://doi.org/10.1016/j.plantsci.2014.11.006 Pieterse CMJ, Van Wees SCM, Ton J, et al (2002) Signalling in Rhizobacteria‐Induced Systemic Resistance in Arabidopsis thaliana . Plant Biol 4:535–544. https://doi.org/10.1055/s-2002-35441 Rania ABA, Stedel C, Garagounis C, et al (2017) Involvement of lipopeptide antibiotics and chitinase genes and induction of host defense in suppression of Fusarium wilt by endophytic Bacillus spp. in tomato. Crop Prot 99:45–58. https://doi.org/10.1016/j.cropro.2017.05.008 Smith KP, Goodman RM (1999) Host variation for interactions with beneficial piant-associated microbes. Annu Rev Phytopathol 37:473–491. https://doi.org/10.1146/annurev.phyto.37.1.473 Sun JB, Wang YG, Zhao PJ, Sun HY (2010) Colonization of Biocontrol Strain XB16 against Fusarium Wilt Pathogen of Banana and Its Effect on Defense-related enzymes. Chin J Trop Crops 31:212–216. https://doi.org/10.1080/00949651003724790 Wang AY (2010) Study on the disease resistance of tomato induced by Pythium oligandrum RCU1 strain and oligandrin. Ph.D Dissertation, Zhejiang University Wang LY, Jiang PP, Gan Y, et al (2017) Increase of Defense Enzyme Activity and Up-expression of Defense Gene in Tomato Induced by Bacillus amyloliquefaciens B1619. Chin J Biol Control 33:234. https://doi.org/10.16409/j.cnki.2095-039x.2017.02.014 Yan YY, Hou P, Duan FY, et al (2021) Improving photosynthesis to increase grain yield potential: an analysis of maize hybrids released in different years in China. Photosynth Res 150:295–311. https://doi.org/10.1007/s11120-021-00847-x Yao HY, Wu FZ (2010) Soil microbial community structure in cucumber rhizosphere of different resistance cultivars to fusarium wilt: Soil microbial community structure in cucumber rhizosphere. FEMS Microbiol Ecol 72:456–463. https://doi.org/10.1111/j.1574-6941.2010.00859.x Yu YL, Chu XQ, Pang GH, et al (2009) Effects of repeated applications of fungicide carbendazim on its persistence and microbial community in soil. J Environ Sci 21:179–185. https://doi.org/10.1016/S1001-0742(08)62248-2 Zhao Y, Mao XX, Zhang MS, et al (2021) The application of Bacillus Megaterium alters soil microbial community composition, bioavailability of soil phosphorus and potassium, and cucumber growth in the plastic shed system of North China. Agric Ecosyst Environ 307:107236. https://doi.org/10.1016/j.agee.2020.107236 Zheng YY, Wang XD, Liu SY, et al (2018) The Endochitinase of Clonostachysrosea Expression in Bacillus amyloliquefaciens Enhances the Botrytis cinerea Resistance of Tomato. Int J Mol Sci 19:2221. https://doi.org/10.3390/ijms19082221 Zhou YF, Bai YS, Yue T, et al (2023) Research progress on the growth-promoting characteristics of plant growth-promoting rhizobacteria. Microbiol China 50:644–666. https://doi.org/10.13344/j.microbiol.china.220446 Zhu Q l, Zhou J cao, Sun M, et al (2023) A newly isolated Bacillus megaterium OQ560352 promotes maize growth in saline soils by altering rhizosphere microbial communities and organic phosphorus utilization. Rhizosphere 27:100746. https://doi.org/10.1016/j.rhisph.2023.100746 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 02 Feb, 2026 Reviewers invited by journal 02 Feb, 2026 Editor assigned by journal 19 Dec, 2025 First submitted to journal 16 Dec, 2025 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. 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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-8383217","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":584343094,"identity":"63b7aa2a-47ec-4af5-be60-02111f04bccd","order_by":0,"name":"Wei Luan","email":"","orcid":"","institution":"Northeast Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Luan","suffix":""},{"id":584343095,"identity":"52c95c4e-ae54-463c-8a47-c0ef1f95c55a","order_by":1,"name":"Yulu Tang","email":"","orcid":"","institution":"Northeast Agricultural 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08:18:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8383217/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8383217/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101881832,"identity":"7534ad69-ebe2-4713-b454-fb4d09eedf17","added_by":"auto","created_at":"2026-02-04 15:16:57","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":266385,"visible":true,"origin":"","legend":"\u003cp\u003eMorphological identification of \u003cem\u003eP. megaterium\u003c/em\u003e strains (a), colony morphology, (b), Gram stain, positive, (c), flagellar staining, periplasmic flagellum, (d), three-gene tandem evolutionary tree.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/77c78dfff3cb3072b9d26011.png"},{"id":101881869,"identity":"a619607d-3e60-4299-823d-4d4d7177dcef","added_by":"auto","created_at":"2026-02-04 15:17:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":182069,"visible":true,"origin":"","legend":"\u003cp\u003eAntagonistic ability of 9 species of bacteria (a),antagonistic effect on \u003cem\u003ePhytophthora nicothianae\u003c/em\u003e, (b), antagonistic effect on \u003cem\u003ePhytophthora capsici\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/e6bbcaff5c51b9ad79540a07.png"},{"id":101881728,"identity":"1b25dccc-8ea9-4503-8d6d-899af849fa6f","added_by":"auto","created_at":"2026-02-04 15:15:32","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":300508,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of 9 strains on the growth of tomato (a), effect on plant height of tomato , (b), effect on thickness tomato stem, (c), effect on fresh weight of above-ground parts of tomato, (d), effect on dry weight of above-ground parts of tomato, (e), effect on the fresh weight of underground parts of tomato, (f), effect on the dry weight of underground parts of tomato\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/828dc2453d8872ae42cbeafc.png"},{"id":101852474,"identity":"406f7922-2b72-4488-9dec-1ef621749caa","added_by":"auto","created_at":"2026-02-04 10:16:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":55089,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of 9 strains on chorophyll content (a), effects on tomato chlorophyll a, (b), effects on tomato chlorophyll b, (c), effects on tomato\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/1d99c94ddea4ee8365fbfcae.png"},{"id":101881783,"identity":"24c8bd1e-a4e0-42d9-81e0-f9c12f22f006","added_by":"auto","created_at":"2026-02-04 15:16:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":57258,"visible":true,"origin":"","legend":"\u003cp\u003ePhosphorus solubilising capacity and effects on soil microorganisms of 9 species of bacteria (a), effect on phosphorus content of bacterial liquid (b), effect on bacterial count, (c), effect on fungal count, (d), effect on actionomycetes count.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/b483122c94a6231ea6582e74.png"},{"id":101881438,"identity":"09e6e186-5d3b-496f-89e2-f6cfa2504aff","added_by":"auto","created_at":"2026-02-04 15:12:09","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":110983,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of applied strains on defence enzymes and defence genes in tomato leaves(a), effect on PPO activity ,(b), effect on POD activity, (c), effect on SOD activity, (d), effect on relative expression of \u003cem\u003eLOX-D\u003c/em\u003e, (e), effect on relative expression of \u003cem\u003eERF2\u003c/em\u003e,(f), effect on relative expression of \u003cem\u003ePR-1a\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/83546c3196cfcda7ae9f6e48.png"},{"id":101852483,"identity":"5874f70b-c818-404b-8963-65c0ba6374e6","added_by":"auto","created_at":"2026-02-04 10:16:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":69561,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of applied strains on tomato soluble sugar content and tomato fruit weight(a), effect on tomato soluble sugar content,(b), effect on tomato fruit weight.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/b857140bd800a13a6934f7d6.png"},{"id":101881431,"identity":"670e36b3-03b0-422d-98d8-1011cec37554","added_by":"auto","created_at":"2026-02-04 15:12:07","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":317538,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of strain application on tomato growth under low temperature conditions(a), effect on tomato plant height,(b), effect on tomato stem thickness,(c),effect on tomato fresh weight,(d),effect on tomato dry weight.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/a1cff8fe152412dc630f1197.png"},{"id":101881283,"identity":"9e3afa90-453e-4be6-8f62-78c71934936f","added_by":"auto","created_at":"2026-02-04 15:11:22","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":317588,"visible":true,"origin":"","legend":"\u003cp\u003eFigure legend not provided with this version\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/e96f55e99a9aa17063468842.png"},{"id":102397725,"identity":"99916486-795a-4d00-8b52-0513c9111380","added_by":"auto","created_at":"2026-02-11 10:19:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2736588,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8383217/v1/5ae191bb-2fe3-44bb-adb4-d94823df4265.pdf"}],"financialInterests":"","formattedTitle":"Isolation and Identification of Priestia megaterium and Its Growth Promoting Effect on Tomato","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePlant growth-promoting rhizobacteria ( PGPR ) are a kind of active microorganisms that live in the rhizosphere of plants and can colonize plant roots, promote plant growth, control plant diseases, and increase crop yield and quality (Bashan et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Pieterse et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Chakraborty et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). PGPR colonizes in plant roots or rhizosphere soil, and has the ability to dissolve phosphorus, fix nitrogen, dissolve potassium and secrete plant hormones, which can significantly promote plant growth (Li et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Interplant root-promoting bacteria promote plant growth through a variety of mechanisms, including: (1) nitrogen fixation, which converts atmospheric nitrogen into plant-available nitrogen; (2) dissolution of insoluble phosphate in the soil to increase the effectiveness of phosphorus (Jia et al., 2023) ;(3) secretion of growth hormones, cytokinins and gibberellins, etc. to regulate plant growth; and (4) production of iron carriers to help plants absorb iron and alleviate iron deficiency symptoms. In addition, it can also induce plants to produce systemic resistance, reduce the adverse effects of pathogens and degradation of pollutants on plants (Zhou et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The main PGPR species screened to date are \u003cem\u003ePaenibacillus\u003c/em\u003e, \u003cem\u003eAchromobacter\u003c/em\u003e, \u003cem\u003eKlebsiella\u003c/em\u003e, \u003cem\u003eArthrobacter\u003c/em\u003e, \u003cem\u003ePseudomonas\u003c/em\u003e, \u003cem\u003eAzospirillum\u003c/em\u003e, \u003cem\u003eEnterobacter\u003c/em\u003e, \u003cem\u003eBacillus\u003c/em\u003e, \u003cem\u003eBurkholderia\u003c/em\u003e, \u003cem\u003eHerbaspirillum\u003c/em\u003e, \u003cem\u003eChryseobacterium\u003c/em\u003e, \u003cem\u003eCitrobacter\u003c/em\u003e, \u003cem\u003ePantoea\u003c/em\u003e and \u003cem\u003eRhizobium\u003c/em\u003e (Burdman et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1999\u003c/span\u003e)).\u003c/p\u003e \u003cp\u003eIn 2020, Gupta et al. reclassified \u003cem\u003eBacillus megaterium\u003c/em\u003e as \u003cem\u003ePriestia megaterium\u003c/em\u003e through systematic and comparative genomic analyses(Gupta et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003cem\u003eP. megaterium\u003c/em\u003e is a kind of microorganism with the functions of solubilizing phosphorus and promoting potassium. Some strains can also secrete metabolites such as indole acetic acid and various organic acids to promote plant growth (Chandra et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Guzm\u0026aacute;n-Moreno et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The application of \u003cem\u003eP. megaterium\u003c/em\u003e can change the soil microbial flora, reduce the abundance of harmful flora, and optimize the soil microbial community structure (Ma et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Zhao et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The application of \u003cem\u003eP. megaterium\u003c/em\u003e can also repair cadmium-contaminated soil (Li et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePreviously, tomatoes grown in the greenhouse of the Horticultural Experiment Station of Northeast Agricultural University were affected by the disease, and only three disease-resistant plants survived. In this study, we extracted the inter-root-promoting bacteria from the roots of these disease-resistant plants and from the root soil to investigate their promoting and disease-resisting effects and their mechanisms.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e\u003cstrong\u003eIsolation and screening of strains\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Selected vigorously growing tomato roots, rinsed them in water, dried them and cut them into small pieces. In an ultra-clean bench, the roots were soaked in 70% alcohol for 30 seconds and then rinsed with sterile water three times for 1 minute each time. The roots were crushed in a mortar filled with sterile water and dipped in sterile water to line on the LB medium. The medium were placed in a constant temperature incubator at 28 ℃ for 1-2 d. The single strain was obtained after isolated and purified several times.\u003c/p\u003e\n\u003cp\u003eInter-root soil of actively growing tomato plants was selected, weighed 5 g of soil after passing through a 2 mm sieve and placed in a triangular vial containing 50 ml of sterile water and shaken to make the soil fully suspended. Suspension diluted 10\u003csup\u003e2\u003c/sup\u003e, 10\u003csup\u003e3\u003c/sup\u003e and 10\u003csup\u003e4\u003c/sup\u003e-fold with sterile water, 100 \u0026micro;L was then spread onto the LB plate and incubated in the incubator at 28 \u0026deg;C for 1-2 d. The single strains were obtained after isolated and purified several times.The isolated strains were subjected to Gram staining and flagellar staining.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMolecular identification of bacteria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe obtained strains were identified by PCR sequencing using 16S rDNA primers,\u003cem\u003e\u0026nbsp;reaC\u003c/em\u003e gene specific primers and \u003cem\u003ephaC\u003c/em\u003e gene specific primers, the primer sequences are shown in Table 1.The PCR amplification procedure was as follows: pre-denaturation: 95 ℃, 3 min; cycling reaction: 95 ℃ 1 5 s, 55 ℃ 15 s, 72 ℃ 30 s, the number of cycles was 35 times; final extension: 72 ℃, 5 min.The sequencing results were subjected to NCBI-BLAST comparison (NCBI: https: //www.ncbi.nlm.nih.gov/), and a phylogenetic tree was constructed using MEGA 7.0 software. The isolated strains were subjected to Gram staining and flagellar staining.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Primer sequences required for strain identification\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"659\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eGene\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 134px;\"\u003e\n \u003cp\u003ePrimer name\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 402px;\"\u003e\n \u003cp\u003ePrimer sequence\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 123px;\"\u003e\n \u003cp\u003e16s rDNA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 134px;\"\u003e\n \u003cp\u003e27F\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 402px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-AGAGTTTGATCCTGGCTCAG-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 134px;\"\u003e\n \u003cp\u003e1492R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 402px;\"\u003e\n \u003cp\u003e5\u0026apos;-ACGGCTACCTTGTTACGACTT-3\u0026apos;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cem\u003erecA\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 134px;\"\u003e\n \u003cp\u003erecA-F\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 402px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-CAACAGCAGGGCGGACAGGC-3\u0026apos;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 134px;\"\u003e\n \u003cp\u003erecA-R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 402px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-TGTTCACGCACTTGTCCCGCA-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cem\u003ephaC\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 134px;\"\u003e\n \u003cp\u003ephaC-F\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 402px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-TGACAACAGAAGCGGAAC-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 134px;\"\u003e\n \u003cp\u003ePhaC-R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 402px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-CACGAATCCACTGACGATA-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eDetermination of antagonistic capacity of strains against pathogenic bacteria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSimultaneously inoculate the test strains and \u003cem\u003ePhytophthora nicothianae\u003c/em\u003e and \u003cem\u003ePhytophthora capsici\u003c/em\u003e on the PDA plate, and place them in a constant temperature incubator at 28 ℃ for cultivation. Observe the growth of pathogenic bacteria and determine whether the experimental strains have antagonistic effect on pathogenic bacteria.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDetermination of the growth-promoting ability of strains\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe same variety of tomato sown at the same time and with the same growth condition were used as test materials, inoculated with the test strains in groups, and a blank control was set. Each group was replicated three times. Stem thickness, plant height, above ground fresh weight, above ground dry weight, below ground dry weight of tomato and chlorophyll contentwere determined at the seedling stage. Chlorophyll content was determined by 95% ethanol extraction (Liu et al. 2022), and chlorophyll a, chlorophyll b and carotenoids were measured in the experimental and control groups.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhosphate-solubilizing ability test of strai\u003c/strong\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInoculate 1% bacterial suspension in inorganic phosphorus liquid medium, incubate at 28 ℃ with 150 rmp shaking for 48 h, inoculate sterile water as control. After transferring to a centrifuge tube, the cells were broken by ultrasonic waves and centrifuged at 4000 r/min for 20 min. The standard curve of phosphorus was plotted with reference to the method of Ding (Ding et al. 2024), and 200 \u0026mu;l of the supernatant was taken to determine the effective phosphorus content in the supernatant using the molybdenum antimony antimony colourimetric method (Smith and Goodman 1999).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of application of 9 strains on inter-root soil microbial community\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSelect tomato plants exhibiting identical growth patterns during the same period as experimental samples. Administer inoculation treatment to the soil surrounding each plant, establishing a blank control. Ensure identical inoculation quantities across all treatments.Soil samples were collected at 45 days after treatment, and three replicates were set up each group of treatments, with three plant root system soil mixes sampled in each replicate. The number of bacteria, fungi and actinomycetes in the soil was determined by dilution plate method to determine the changes in the soil microflora after the application of the test strains. Bacteria were cultured using LB culture, fungi were cultured using PDA medium and actinomycetes were cultured using Gauze\u0026rsquo;s Medium No.1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of application of 9 strains on defence genes in tomato\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNine strains were used to treat tomatoes with the same growth at the same period, and a blank control was set. Tomato leaf tissues were collected at 24 h, 48 h and 96 h after treatment and RNA was extracted and reverse transcribed. \u003cem\u003eLOX-D\u003c/em\u003e gene-specific primer sequences were designed with reference to Abdallah et al.(Rania et al. 2017), \u003cem\u003eERF2\u003c/em\u003e gene-specific primers were designed with reference to Wang et al. (Wang 2010), \u003cem\u003ePR-1a\u003c/em\u003e gene-specific primers were designed with reference to Wang et al (Wang et al. 2017), \u003cem\u003eActin\u003c/em\u003e gene-specific primers were designed with reference to Babu et al(Narendra Babu et al. 2015). The primer sequences required for qPCR are shown in Table2. The qPCR amplification procedure was as follows: pre-denaturation: 95 ℃, 2 min; cycling reaction: 95 ℃ 1 5 s, 57 ℃ 15 s, 72 ℃ 30 s, the number of cycles was 40 times.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable2.\u003c/strong\u003e Primer sequences required for qPCR\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003eGene\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003ePrimer name\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 424px;\"\u003e\n \u003cp\u003ePrimer sequence\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cem\u003eLOX-D\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003eLOX-D-F\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-CCTGAAATCTATGGCCCTCA-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003eLOX-D\u003cem\u003e-R\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026apos;-ATGGGCTTAAGTGTGCCAAC-3\u0026apos;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cem\u003eERF2\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003eERF2-F\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-GGCTGCTGAAATTCGTGACC-3\u0026apos;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003erecA-R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-GGGGCTCTGGATGACTGTAG-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cem\u003ePR-1a\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003ePR-1a-F\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-GCTGTGAAGATGTGGGACGA-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003ePR-1a-R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-ACCGACTTACGCCATACCAC-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cem\u003eActin\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003eActin-F\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-GTGCGAGTGTCCTGTCTGTT-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 135px;\"\u003e\n \u003cp\u003eActin-R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 424px;\"\u003e\n \u003cp\u003e5\u0026rsquo;-TACCGTGCATTCATAGCCCC-3\u0026rsquo;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eapplication\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;9 strains on the growth of tomatoes at low temperatures\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTomato seedlings that were sown at the same time and had uniform growth conditions were selected and placed in a low-temperature environment. The temperature was set to 10 \u0026deg;C during the day and 4 \u0026deg;C at night, with a light duration of 12 hours. On the first day of exposure to the low-temperature environment, the inoculation treatment was carried out and two control groups were set up: a low-temperature control group (CK1) and a \u0026nbsp;normal-temperature control group (CK2). The temperature was restored to normal (28\u0026deg;C during the day and 18\u0026deg;C at night) after 14 days of growth. On the 14th day of temperature recovery, the height, stem thickness, fresh weight and dry weight of the tomato were measured.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of Mixed Inoculation of Strains on Tomato Growth\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBased on preliminary experimental results, four dominant bacterial strains were selected and inoculated onto tomato plants sown simultaneously and exhibiting consistent growth conditions. Concurrently, a single-strain inoculation experimental group and a blank control group were established. Each treatment involved inoculating ten tomato plants, with three replicates established. Fourteen days post-inoculation, the experimental tomato plants were measured for plant height, stem diameter, fresh weight, and dry weight.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData statistics and analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe statistical analysis of the data in this study was done using SPSS 25.0.The significance of the difference between the treatments was tested using analysis of variance (ANOVA) and when P\u0026lt;0.05, it was considered to be significantly different.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eMorphological identification of strains\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA total of 9 strains were isolated from tomato roots and inter-root soil. The strains were numbered B1-B9. It was observed that the colonies of the above 9 strains were round and yellowish (Fig. 1a). The edges were smooth at the early stage of culture, and the surface was slightly wrinkled with the growth of time. All 9 strains were rod-shaped, Gram-positive (Fig. 1b) bacteria with flagella(Fig. 1c).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMolecular identification of strains\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe isolated strains were amplified by PCR using bacterial 16S rDNA universal primers 1492R and 27F, \u0026nbsp;and the resulting sequences were compared by BLAST on NCBI, which showed that the sequence matches of the 9 strains with \u003cem\u003eBacillus\u003c/em\u003e spp. were up to 100%, and it was known that the strains were \u003cem\u003eBacillus\u003c/em\u003e spp. In adddition, specific primers were designed for \u003cem\u003ephaC\u003c/em\u003e and r\u003cem\u003eecA\u003c/em\u003e of \u003cem\u003eBacillus\u003c/em\u003e, and the sequences obtained after PCR amplification of the strains were compared on NCBI. It was found that the \u003cem\u003ephaC\u003c/em\u003e-specific fragment could match up to 99.11%~100% with the sequence of \u003cem\u003eP. megaterium\u003c/em\u003e, and the \u003cem\u003erecA\u003c/em\u003e-specific fragment could match up to 99.27%~100% with the sequence of\u003cem\u003e\u0026nbsp;P. megaterium\u003c/em\u003e. A three-gene tandem evolutionary tree based on 16S r DNA, \u003cem\u003ephaC\u003c/em\u003e and \u003cem\u003erecA\u003c/em\u003e showed the closest affinity to \u003cem\u003eP. megaterium\u0026nbsp;\u003c/em\u003e(Fig. 1d)\u003cem\u003e.\u0026nbsp;\u003c/em\u003eCombining the above comparison results, it was determined that all test strains were\u003cem\u003e\u0026nbsp;P. megaterium\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAntagonistic ability of 9 strains against pathogenic bacteria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNine strains were assayed for their antagonistic ability against \u003cem\u003ePhytophthora nicothianae\u003c/em\u003e and \u003cem\u003ePhytophthora capsici\u003c/em\u003e. It was found that the test strains had no antagonistic effect on these two pathogens (Fig. 2a,b).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on the growth of tomato\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter inoculation with strains 15 days, various indicators of tomato were measured. It was found that the strains promoted the growth of tomato, but the growth-promoting effect varied among different strains (Fig. 3). The results showed that B1, B2, B3, B4, B7 strains had better growth promotion effect on tomato plant height (Fig. 3a), above ground fresh weight and dry weight, underground fresh weight and dry weight compared with other strains (Fig. 3c-f). B1 strains had better growth promotion effect on tomato stem thickness (Fig. 3b).\u003c/p\u003e\n\u003cp\u003eThe chlorophyll a, chlorophyll b and carotenoid contents of tomato leaves were determined after inoculation with the strains 14 days , and it was found that the strains promoted the chlorophyll contents of tomato leaves (Fig. 4). The more effective chlorophyll promoters of tomato were the B6 and B7 strains (Fig. 4a-c). The growth rates of chlorophyll a, chlorophyll b and carotenoids were 32.52%, 36.51% and 20.51%, in the B6 strain group compared to the control group. The growth rates of chlorophyll a, chlorophyll b and carotenoids were 31.31%, 36.51% and 17.95%, in the B7 strain group compared with the control group. The above results indicate that \u003cem\u003eP. megaterium\u003c/em\u003e was able to increase the chlorophyll content and improve the photosynthetic rate of tomato leaves, and promote the growth and development of plants.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhosphorus solubilising capacity of 9 strains\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThrough the qualitative determination of the phosphorus solubilising ability of 9 strains, it was found that all 9 strains could form a phosphorus solubilising circle, which indicated that all 9 strains had a certain phosphorus solubilising ability. Through quantitative determination of phosphorus solubilising capacity, it was found that the phosphorus solubilising capacity of strains B1, B2, B3 and B4 was relatively better, and the phosphorus content in the solution was 16.8 mg/L, 17.7 mg/L, 21.4 mg/L and 16.4 mg/L ,respectively, when cultured for 48h(Fig. 5a).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of applied 9 strains on soil inter-root microorganisms\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe treatment with the strains had a certain effect on the number of bacteria, fungi and actinomycetes in the inter-root soil after 45 days of treatment. The number of bacteria and actinomycetes increased after treatment with the experimental strains (Fig. 5b,d). B6 strain showed the greatest increase in inter-root bacterial counts and the bacterial content of the soil could reach 14.67\u0026times;10\u003csup\u003e5\u003c/sup\u003eCFU/g, and there was also a significant increase in the number of bacteria after treatment of other strains as compared to the control (Fig. 5b) The actinomycetes\u0026rsquo; number of the soil increased in the treatment with the strains B1, B2, B3, B4 and B7 and differed significantly from that of the control group. Among them, B7 strain showed the greatest increase in the number of inter-root soil actinomycetes after treatment (Fig. 5d). After using the 9 strains to treat the inter-root of tomato, the number of soil fungi in the inter-root of tomato did not show any significant change except for B8 and B9 which showed a significant increase in the number of fungi in the inter-root soil of tomato (Fig. 5c). After 45 days of treatment using the 9 strains, the bacterial/fungal ratios were 180.6, 181.2, 238.8, 250, 320.4, 423.1, 234.2, 176.5, 149.1, and 399.6, which were higher than that of the control group at 94.8 (Table 3). The above results indicated that the application of the above experimental strains were able to change the inter-root soil microbial environment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3.\u003c/strong\u003e Bacteria:Fungi ratio in soil after 45 days of treatment with 9 strains of \u003cem\u003eP. megaterium\u003c/em\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStrains\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 58px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 44px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 48px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCK\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003ebacterial:fungal ratio\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 58px;\"\u003e\n \u003cp\u003e180.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003e181.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e238.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 44px;\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e320.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003e423.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003e234.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003e176.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e149.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e94.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of the application of 9 strains on the activity of defence enzymes in tomato leaves\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on PPO activity of tomato leaves\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePolyphenol oxidase (PPO) is a widespread enzyme found in plants, animals and\u0026nbsp;fungus. PPO enhances disease resistance and adaptability to adversity in plants and plays an important role in plant resistance mechanisms. After inoculation with 9 strains, the PPO activity of tomato leaves showed a tendency of increasing and then decreasing (Fig. 6a). Compared with the control group, at 24 h of inoculation, all treatment groups except B6 and B8 significantly increased the PPO activity of tomato leaves. PPO activity was up to 198.85 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW. At 96 h, the PPO activity of the B5, B7, B8 and B9 treatment groups was higher than that of the control group with significant differences, and it was up to 98.2 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW. There was no significant change in PPO activity in the control group during the assay time range. The above results indicate that \u003cem\u003eP. megaterium\u003c/em\u003e enhanced PPO activity to a certain extent and helped to improve tomato plant resistance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on POD activity of tomato leaves\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePeroxidase (POD) is a class of chemical reaction enzymes that catalyses catalase and other peroxides, which catalyzes a redox reaction using H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e as an oxidant and reduces H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to H\u003csub\u003e2\u003c/sub\u003eO to protect the plant. The POD activities of tomato leaves in the experimental group were all significantly increased compared to the control group (Fig. 6b). At 24 h after treatment, the highest POD enzyme activities were observed in the B1, B4 and B7 treatment groups, which could reach 223.31 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW, 217.43 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW, 219.05 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW, and 151.45%~158.25% higher compared with the control group. At 48 h of treatment, the highest POD enzyme activity of B9 strain treatment group could reach 295.71 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW, which increased by 215.49% compared with the control group. At 96 h of treatment, the highest POD enzyme activity was found in the treatment groups of B3 and B7 strains, which could reach 255.77 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW and 242.74 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW, which increased by 178.98% to 164.77% compared with the control group. The results showed that \u003cem\u003eP. megaterium\u003c/em\u003e could enhance POD activity to a certain extent, resulting in increased resistance of the plant to environmental adaptation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on SOD activity of tomato leaves\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSuperoxide Dismutase (SOD) is also an important antioxidant enzyme that can reduce oxidative stress by scavenging superoxide anion and protect cells from oxygen radical damage. The results show that only strain B7 showed a significant increase in SOD enzyme activity after 96 h of treatment with activity up to 247.58 U\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e-g\u003csup\u003e-1\u003c/sup\u003eFW, which was 36.45% higher compared to the control (Fig. 6c).The other strains showed no significant changes compared to the controls.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of applied strains on the relative expression of defence genes in tomato leaves\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on the relative expression of \u003cem\u003eLOX-D\u003c/em\u003e in tomato\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eLOX-D\u003c/em\u003e (lipoxygenase D) is an important member of the plant lipoxygenase gene family, which plays a key role in the jasmonic acid (JA) synthesis pathway, and is widely involved in stress response processes such as insect, disease, and drought resistance in plants.The results show that the application of 9 strains had an effect on \u003cem\u003eLOX-D\u003c/em\u003e expression, and there was a significant difference in \u003cem\u003eLOX-D\u003c/em\u003e expression among each treatment group and at different times (Fig. 6d). After treatment with B3, B4, and B5 strains, the relative expression of \u003cem\u003eLOX-D\u003c/em\u003e showed an upward trend, which showed a decreasing and then increasing trend compared with CK group. It reached the highest at the 96 h, which was 1.5~3.8 times of the CK group. After treatment with B1, B2, B6, B7, B8, B9 strains, the relative expression of \u003cem\u003eLOX-D\u003c/em\u003e showed a tendency of decreasing, then increasing and then decreasing. It reached the highest at 48h, which was 1.3~3.3 times of the CK group. The results suggest that \u003cem\u003eP. megaterium\u003c/em\u003e may be involved in the JA signalling pathway to stimulate plant tomato resistance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on the relative expression of \u003cem\u003eERF\u003c/em\u003e2 in tomato\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eERF2\u003c/em\u003e (Ethylene Response Factor 2) is a core member of the AP2/ERF transcription factor family. It integrates ethylene signalling with downstream physiological processes by recognising ethylene (ET)) response elements (e.g. GCC-box, ERELEE4) in the promoters of target genes, coordinating plant development, stress response and quality formation.The results show that the application of the test strains had a significant effect on \u003cem\u003eERF2\u003c/em\u003e expression, and there was a significant difference in \u003cem\u003eERF2\u003c/em\u003e expression among the treatment groups (Fig. 6e). Except for the B6 treatment group, the rest of the treatment groups compared with the control group showed a trend of decreasing, then increasing and then decreasing, and reached the maximum at 48 h, which was 1.89~4.39 times of the CK group. Compared with the CK group the B6 treatment group showed a tendency of decreasing and then increasing, reaching a maximum at 96 h, which was 1.19 times that of the CK group. The results suggest that \u003cem\u003eP. megaterium\u003c/em\u003e may be involved in the ethylene pathway to stimulate plant tomato resistance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on the relative expression of \u003cem\u003ePR-1a\u003c/em\u003e in tomato\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ePR-1a\u003c/em\u003e acts as a salicylic acid (SA) pathway hub to activate systemic resistance.The results show that the application of the test strains had a significant effect on the relative expression of \u003cem\u003ePR-1a\u003c/em\u003e, and there was a significant difference in the expression of \u003cem\u003ePR-1a\u003c/em\u003e among each treatment group (Fig. 6f). Except for the B4 treatment group, \u003cem\u003ePR-1a\u003c/em\u003e showed a trend of decreasing then increasing and then decreasing in the rest of the treatment groups. The expression reached the highest at 48 h, which was 1.11~8.64 times of that of the CK group. The relative expression of \u003cem\u003ePR-1a\u003c/em\u003e in B4 treatment group showed a decreasing and then increasing trend compared with that of CK group.The relative expression of \u003cem\u003ePR-1a\u0026nbsp;\u003c/em\u003ein B4 group reached the highest at 96 h, which was 2.43 times higher than that of CK group. The results indicated that \u003cem\u003eP. megaterium\u003c/em\u003e might be involved in the SA signalling pathway to stimulate tomato resistance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of 9 strains on soluble sugar content and fruits weight of tomato fruits\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe soluble sugar content of ripe tomato was tested in different treatment groups and the results are shown in figure 8a. It can be seen that there was a significant enhancement in the soluble sugar content of ripe tomato fruits after treatment with B3 and B7 strains. The B3 and B7 treated groups were enhanced by 32.27%, 32.38%, 44.66% , respectively, compared to the control group (Fig. 7a).\u003c/p\u003e\n\u003cp\u003eFrom the figure 8b, it can be seen that the application of 9 strains can have an effect on tomato fruit weight. After treatment with B2, B3, B5 and B6 strains, tomato fruit weight was significantly increased compared with the control group. Among them, B3 treatment groups showed the most significant increase in tomato fruit weight, which increased by 60.99% and 52.86% compared with CK group (Fig. 7b).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffects of 9 strains on tomato growth under low temperature conditions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe results showed that the application of the test strains had a certain effect on the growth of tomato under low temperature conditions. Compared with CK1, the plant height of tomato treated with B9 strain was significantly increased (Fig. 8.a), and the plant stem thickness, fresh weight and dry weight did not change significantly (Fig. 7b-d). There was no significant difference in the data of other treatment groups compared with CK1(Fig. 8a-d). The experimental results show that the B9 strain may have higher activity at low temperature than other strains, and can improve the cold resistance of tomato.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe Effect of Mixed Planting on Tomato Growth Conditions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMeasurements of plant height, stem diameter, fresh weight, and dry weight were taken for tomatoes inoculated with mixed strains, single strains, and the control group(Fig. 9). Compared to the control group, both mixed-strain inoculation and single-strain inoculation increased plant height, fresh weight, and dry weight(Fig. 9a,c-e),with no significant change in stem diameter(Fig. 9b). Furthermore, the growth-promoting effect of mixed-strain inoculation on tomatoes was more pronounced than that of single-strain inoculation.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe traditional large-scale use of plant-promoting products are chemicals, while the long-term use of chemicals can increase the harmful substances in the soil, causing an imbalance in the ecology of the rhizosphere soil, which in turn, nutritive plant growth (Yu et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Whereas, the use of bacterial manure can effectively enhance soil fertility and promote plant growth (Khan et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Glick \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Bhattacharyya and Jha \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The main functions of the growth-promoting bacteria are to significantly increase plant growth vigour and inhibit the growth of pathogenic bacteria. \u003cem\u003eBacillus\u003c/em\u003e is proven to be an inter-root growth promoting bacterium. In this paper, it was found that the \u003cem\u003eP. megaterium\u003c/em\u003e used in the experiment had no antagonistic effect on the common solanaceous crop pathogens \u003cem\u003eP.nicothianae\u003c/em\u003e and \u003cem\u003eP.capsici\u003c/em\u003e, but had a certain growth-promoting effect on the plants. The results of this study indicate that the favourable effects of \u003cem\u003eP. megaterium\u003c/em\u003e on plants were mainly growth-promoting rather than pathogen-inhibiting. The growth-promoting effect of \u003cem\u003eP. megaterium\u003c/em\u003e application may vary slightly in different crop species. It has been reported that the prophylactic effect of PGPR is related to their phosphorus solubilising function ((Akgul and Mirik \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Zhu et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).Through this study, it was found that the B1, B2 and B3 strains have more obvious phosphorus solubilising effect, also have better growth promotion effect on tomato. However, only the B9 strain had a significant effect on tomato plant height under low temperature conditions.\u003c/p\u003e \u003cp\u003eChanges in defence enzyme activities are also important factors affecting plant growth (Latha et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). It has been found that a variety of defence enzymes can promote plant growth and increase plant resistance. A number of studies have been conducted to show that \u003cem\u003eBacillus\u003c/em\u003e can enhance defence enzyme activities in plants. Zheng et al. found that \u003cem\u003eBacillus amyloliquefaciens\u003c/em\u003e enhanced PPO activity in tomato leaves (Zheng et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2018\u003c/span\u003e); Sun et al. found that treatment of banana with \u003cem\u003eBacillus subtilis\u003c/em\u003e increased the PPO and POD activities (Sun et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). In this study, we found that the application of the experimental strains were able to enhance the PPO and POD activities of tomato leaves, but the effect on SOD activity was not significant. This suggests that \u003cem\u003eP. megaterium\u003c/em\u003e may enhance plant resistance and promote plant growth by enhancing PPO and POD activities.\u003c/p\u003e \u003cp\u003eChlorophyll is a very important pigment in plants, which is mainly involved in photosynthesis, energy conversion, and production of nutrients needed for plant growth, which in turn affects plant growth (Yan et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In this study, the application of \u003cem\u003eP. megaterium\u003c/em\u003e showed a significant increase in the chlorophyll content of tomato leaves compared with the control group, indicating that \u003cem\u003eP. megaterium\u003c/em\u003e was able to effectively increase the chlorophyll content of the plants. Soluble sugars are sugars that can melt in water, including monosaccharides and oligosaccharides. Soluble sugar is an important source of energy in plants, which operates in various parts of plants and affects fruit quality. The results of this study showed that \u003cem\u003eP. megaterium\u003c/em\u003e could increase the soluble sugar content of tomato fruits and improve fruit quality. The explanation is that, \u003cem\u003eP. megaterium\u003c/em\u003e enhances the quality of tomatoes by increasing the chlorophyll content, thereby promoting photosynthesis and carbohydrate synthesis.\u003c/p\u003e \u003cp\u003eResistance mechanisms in plants are associated with a variety of hormonal signalling pathways such as salicylic acid, jasmonic acid and ethylene pathways. They can make plants resistant to pathogens through mutual antagonism (Kunkel and Brooks \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), and can also cause various physiological and biochemical changes in the plant body, thus resisting the infection of various pathogens (Li et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In this paper, the results showed that the application of the 9 strains of \u003cem\u003eP. megaterium\u003c/em\u003e able to increase the relative expression of \u003cem\u003eLOX-D\u003c/em\u003e, \u003cem\u003eERF2\u003c/em\u003e and \u003cem\u003ePR-1a\u003c/em\u003e in tomato, suggesting that \u003cem\u003eP. megaterium\u003c/em\u003e may be involved in the JA signalling pathway, the ethylene signalling pathway and the SA signalling pathway to increase plant systemic resistance. The effect of the experimental strain on the \u003cem\u003ePR-1a\u003c/em\u003e was more pronounced, which may indicate that \u003cem\u003eP. megaterium\u003c/em\u003e used in the experiment is more involved in the SA signalling pathway. However, the effects on the three genes were slightly different among different strains, which may be related to the differences in the strains' own genes. The specific genes controlled by what need to be further studied.\u003c/p\u003e \u003cp\u003eSoil microorganisms are an important part of the soil, decomposing organic matter for plant uptake, participating in soil nutrient cycling and influencing plant growth (Clark and Paul \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1970\u003c/span\u003e). It has been found that a high soil bacterial:fungal ratio favours plant growth (Frey et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Yao and Wu \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). In this study, it was found that the bacterial counts were all increased after treatment with 9 strains and the bacterial:fungal ratio was increased compared to the control group. It suggests that \u003cem\u003eP. megaterium\u003c/em\u003e may be influencing the soil microflora species, resulting in an increase in beneficial bacteria, which promotes plant growth. Actinomycetes are an important group of soil microorganisms that decompose organic matter, produce antibiotics and promote plant growth. In this study, it was found that all the strains except B6, B8 and B9 strains increased the number of actinomycetes in the soil. This suggests that \u003cem\u003eP. megaterium\u003c/em\u003e may increase the number of actinomycetes in the soil thereby increasing the nutrients in the soil and promoting plant growth.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this paper, 9 strains were isolated from robustly growing tomato roots and root soil, identified as \u003cem\u003eP. megaterium\u003c/em\u003e, Gram-positive, with flagella. It was found that the \u003cem\u003eP. megaterium\u003c/em\u003e could promote the growth of tomato, increase the chlorophyll content, and have some phosphorus solubilising effect. Treatment of tomato with \u003cem\u003eP. megaterium\u003c/em\u003e also increased leaf PPO and POD enzyme activities, increased \u003cem\u003eLOX-D\u003c/em\u003e, \u003cem\u003eERF2\u003c/em\u003e and \u003cem\u003ePR-1a\u003c/em\u003e expression, and increased the number of bacteria and actinomycetes in the soil. Only the B9 strain was able to improve the cold-resistant characteristics of the plants and promote tomato growth and development at low temperatures. Compared to single strains, mixed strains exhibit a more pronounced growth-promoting effect on tomatoes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eYaowei Zhang, Ran Gu and Yan Liu conceived the project, Yulu Tang and Yang yang collected the experimental data, Wei Luan analyzed the experimental data and wrote the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (32202510) and the Key Research and Development Program of Heilongjiang Province of China (SC2022ZX02C0202).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the necessary data is available in the manuscript.\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest exits.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAkgul DS, Mirik M (2008) Biocontrol of Phytophthora capsici on pepper plants by Bacillus megaterium strains. 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Rhizosphere 27:100746. https://doi.org/10.1016/j.rhisph.2023.100746\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"acta-physiologiae-plantarum","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acpp","sideBox":"Learn more about [Acta Physiologiae Plantarum](http://link.springer.com/journal/11738)","snPcode":"11738","submissionUrl":"https://www.editorialmanager.com/acpp/default2.aspx","title":"Acta Physiologiae Plantarum","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Priestia megaterium, growth promotion, antagonistic capacity, plant growth-promoting rhizobacteria","lastPublishedDoi":"10.21203/rs.3.rs-8383217/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8383217/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePlant growth-promoting rhizobacteria ( PGPR ) can promote plant growth and increase yield. In this study, nine strains were isolated from robustly growing tomato roots and inter-root soil, and one strain was isolated from purchased bacterial fertiliser. They were identified as \u003cem\u003ePriestia megaterium\u003c/em\u003e. The growth promoting ability was identified by applying \u003cem\u003eP. megaterium\u003c/em\u003e to tomato. In addition, the phosphorus solubilising ability of the strains was measured, and the resistance-related enzyme activities and genes were measured on tomato leaves after the application of the strains, in order to preliminarily investigate the growth promotion and resistance mechanism of \u003cem\u003eP. megaterium\u003c/em\u003e. The results showed that \u003cem\u003eP. megaterium\u003c/em\u003e could promote the growth of tomato, increase the chlorophyll content of leaves, increase the PPO and POD activities, and promote the expression of \u003cem\u003eLOX-D\u003c/em\u003e, \u003cem\u003eERF2\u003c/em\u003e and \u003cem\u003ePR-1a\u003c/em\u003e in tomato leaves.\u003c/p\u003e","manuscriptTitle":"Isolation and Identification of Priestia megaterium and Its Growth Promoting Effect on Tomato","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-04 10:16:16","doi":"10.21203/rs.3.rs-8383217/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-02-02T15:27:19+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-02T12:47:08+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-19T05:33:40+00:00","index":"","fulltext":""},{"type":"submitted","content":"Acta Physiologiae Plantarum","date":"2025-12-17T03:18:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"acta-physiologiae-plantarum","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acpp","sideBox":"Learn more about [Acta Physiologiae Plantarum](http://link.springer.com/journal/11738)","snPcode":"11738","submissionUrl":"https://www.editorialmanager.com/acpp/default2.aspx","title":"Acta Physiologiae Plantarum","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3a471306-0d2b-4070-a6fe-df932a8614e5","owner":[],"postedDate":"February 4th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-02-04T10:16:16+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-04 10:16:16","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8383217","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8383217","identity":"rs-8383217","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}