A novel redox sensor in Geobactersulfurreducens? Potentially. Identifying new components for expression of genes at low redox potential
Geobacter sulfurreducens is a bacterium that respires many forms of manganese and iron. To maximize the energy produced by reduction of these environmental metals, G. sulfurreducens modulates its expression of respiratory genes such as cbcBA. CbcBA is a cytochrome essential for reduction of Fe(III) below -0.21V vs SHE. In low redox potential environments, cbcBA transcription is induced 3,000-fold by an uncharacterized pathway. This study sought to identify factors involved in induction of cbcBA expression. Here we used a luciferase reporter and gene knock-outs to show the role of bccS and bccR in inducing expression of the cbcBApromoter. Structural predictions indicate BccRfunctions as a σ54 dependent response regulator; BccS is predicted to have sensor-kinase activity with two heme binding motifs in the periplasm. These findings suggest that BccS may directly sense the redox potential of the environment to trigger the induction of cbcBA expression.