Aerotolerance and peroxide resistance in peroxidase and PerR mutants of Streptococcus pyogenes

Survival in aerobic conditions is critical to the pathogenicity of many bac teria. To investigate the means of aerotolerance and resistance to oxidativ e stress in the catalase-negative organism Streptococcus pyogenes, we used a genomics-based approach to identify and inactivate homologues of two pero xidase genes, encoding alkyl hydraperoxidase (ahpC) and glutathione peroxid ase (gpoA). Single and double mutants survived as well as the wild type und er aerobic conditions. However, they were more susceptible than the wild ty pe to growth suppression by paraquat and cumene hydroperoxide. In addition, we show that S. pyogenes demonstrates an inducible peroxide resistance res ponse when treated with sublethal doses of peroxide. This resistance respon se was intact in ahpC and gpoA mutants but not in mutants lacking PerR, a r epressor of several genes including ahpC and catalase (katA) in Bacillus su btilis. Because our data indicate that these peroxidase genes are not essen tial for aerotolerance or induced resistance to peroxide stress in S. pyoge nes, genes for a novel mechanism of managing peroxide stress may be regulat ed by PerR in streptococci.