Whole-cell bacterial sensors for the monitoring of phosphate bioavailability.
A phosphate sensor plasmid was constructed, in which the inducible promoter of the alkaline phosphatase gene (phoA) from Escherichia coli is fused to the bioluminescence genes from Vibrio fischeri. The reporter construct was introduced into E. coli MG1655 and the rhizosphere coloniser Pseudomonas fluorescens DF57, which produced light in a dose-dependent manner when exogenous phosphate concentrations fell below 60 and 40 microM, respectively. These strains also responded to various organic and inorganic phosphorus compounds. Their ability to distinguish the bioavailable portion of phosphate in standard solution was demonstrated using different phosphate ligands. When applying the bioassay to wastewater samples, luminescence patterns correlated with phosphate concentrations determined by standard chemical procedure. These results indicated that phoA::lux-based bacterial sensors may serve as tools for the assessment of phosphate bioavailability.