Development of a Simple, Low-Cost, Highly Specific Colorimetry-Based Whole-Cell Bacterial Biosensor for Cadmium Detection in the Environment

Abstract The urgent requirement for cost-effective technology to detect heavy metals in the environment is undeniable. This study introduces a novel approach: a low-cost colorimetry-based optical whole-cell bacterial biosensor utilizing a newly identified reporter gene, agarase (dagA), for the specific detection of cadmium (Cd). Through the incorporation of a Cd-sensing promoter (PcadR) upstream of agarase in Pseudomonas aeruginosa, a highly specific Cd biosensor was engineered. Initially developed in E. coli and subsequently in P. aeruginosa, these agarase (dagA) based optical whole-cell bacterial biosensors exhibited promising capabilities. Specifically, P. aeruginosa carrying the vector PcadR-dagA demonstrated a strong linear range detection for cadmium chloride concentrations ranging from 10 ppb to 500 ppm (R2 = 0.9851), with a correlation of 0.96 (Bland-Altman) to the standard inductively coupled plasma mass spectroscopy method. Furthermore, morphological alterations were observed through scanning electron microscopy. Notably, this colorimetry-based optical whole-cell bacterial biosensor presents itself as a straightforward, resilient, portable, and cost-effective solution, eliminating the need for complex sample preparation. Consequently, the biosensor platform proposed in this study stands as a viable, low-cost alternative for monitoring low levels of Cd in the environment.