[Detection of cadmium by a double-promoters based Escherichia coli biosensor]

To detect cadmium ions, we constructed a specific microbial sensor and screened detecting cassettes and different fluorescence proteins. Blue fluorescence protein mTagBFP2 was selected as a reporter and a double-promoters model was used in the construction of the fusion reporter vector Pmer::merR-m-Pmer::mTagBFP2-pMD19-T. The reporter vector was then transformed into Escherichia coli MC4100 wild type strain. The medium, incubation time, initial density for induction, and the optimal detection range were determined. The specificity of the biosensor was also checked. The biosensor responded specifically to cadmium irons with low background, and the linear concentration range detection ranged from 0.1 to 75 μmol/L at the initial OD600 = 0.1 with 2 h incubation in IHMM medium. Thus we successfully constructed a specific biosensor to detect cadmium irons and provided useful strategies for development and optimization of microbial sensors to detect heavy metals.