Cloning, characterization and expression of an Enterococcus faecalis gene responsive to heavy metals

Gene encoding stress response proteins are induced by a variety of environmental stimuli including the presence of heavy metals. To address the utility of this response for pollutant detection, one cadmium-induced gene in Enterococcus faecalis was isolated, sequenced and studied at the transcriptional level. csrA contains an open reading frame encoding a protein of 168 amino acids with homology to the enzyme peptide methionine sulfoxide reductase. The csrA mRNA was barely present in unstressed E. faecalis cells grown in M17-glucose medium, but accumulated at higher levels in cadmium-treated cells. Mercury also had an effect on csrA expression, whereas lead, copper and manganese induced csrA expression only at the highest doses tested. Our results suggest that biosensors based on E. faecalis may have potential applications for environmental monitoring and should be constructed.