| Summary: | Cell-based biosensors harness a cell’s ability to respond to the environment by repurposing its sensing mechanisms. MerR family proteins are activator/repressor switches that regulate the expression of bacterial metal resistance genes and have been used in metal biosensors. Upon metal binding, a conformational change switches gene expression from off to on. The genomes of the multimetal resistant bacterial strains, <i>Stenotrophomonas maltophilia</i> Oak Ridge strain 02 (<i>S. maltophilia</i> 02) and <i>Enterobacter</i> sp. YSU, were recently sequenced. Sequence analysis and gene cloning identified three mercury resistance operons and three MerR switches in these strains. Transposon mutagenesis and sequence analysis identified <i>Enterobacter</i> sp. YSU zinc and copper resistance operons, which appear to be regulated by the protein switches, ZntR and CueR, respectively. Sequence analysis and reverse transcriptase polymerase chain reaction (RT-PCR) showed that a CueR switch appears to activate a <i>S. maltophilia</i> 02 copper transport gene in the presence of CuSO<sub>4</sub> and HAuCl<sub>4</sub>·3H<sub>2</sub>O. In previous studies, genetic engineering replaced metal resistance genes with the reporter genes for β-galactosidase, luciferase or the green fluorescence protein (GFP). These produce a color change of a reagent, produce light, or fluoresce in the presence of ultraviolet (UV) light, respectively. Coupling these discovered operons with reporter genes has the potential to create whole-cell biosensors for HgCl<sub>2</sub>, ZnCl<sub>2</sub>, CuSO<sub>4</sub> and HAuCl<sub>4</sub>·3H<sub>2</sub>O.
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