PerR vs OhrR: selective peroxide sensing in Bacillus subtilis.

Bacteria adapt to elevated levels of reactive oxygen species (ROS) by increasing the expression of detoxification enzymes and repair proteins. These defences are regulated by transcription factors that activate specific genes in response to ROS. In Bacillus subtilis, the adaptive response to peroxide stress is mainly under control of three proteins: sigma(B), PerR and OhrR. sigma(B) is a general stress response transcription factor. PerR is a dimeric zinc protein with a regulatory site that coordinates either a Fe(2+) or a Mn(2+) metal ion. In the presence of iron, PerR mediates strong induction of the perR regulon in response to hydrogen peroxide (H(2)O(2)). In contrast to PerR, the OhrR protein is weakly activated by H(2)O(2) but it shows a much higher reactivity for organic hydroperoxides. OhrR controls the expression of a thiol-dependent peroxidase that reduces organic hydroperoxides into their corresponding alcohols. In this review we emphasis peroxide sensing mechanisms for both proteins, focusing on recent biochemical and structural data.