Regulation of Superoxide Dismutase (sod) Genes by SarA in Staphylococcus aureus

The scavenging of reactive oxygen species (ROS) within cells is regulated by several interacting factors, including transcriptional regulators. Involvement of sarA family genes in the regulation of proteins involved in the scavenging of ROS is largely unknown. In this report, we show that under aerobic conditions, the levels of sodM and sodA transcription, in particular the sodM transcript, are markedly enhanced in the sarA mutant among the tested sarA family mutants. Increased levels of sod expression returned to near the parental level in a single-copy sarA complemented strain. Under microaerophilc conditions, transcription of both sodM and sodA was considerably enhanced in the sarA mutant compared to the wild-type strain. Various genotypic, phenotypic, and DNA binding studies confirmed the involvement of SarA in the regulation of sod transcripts in different strains of Staphylococcus aureus. The sodA mutant was sensitive to an oxidative stress-inducing agent, methyl viologen, but the sarA sodA double mutant was more resistant to the same stressor than the single sodA mutant. These results suggest that overexpression of SodM, which occurs in the sarA background, can rescue the methyl viologen-sensitive phenotype observed in the absence of the sodA gene. Analysis with various oxidative stress-inducing agents indicates that SarA may play a greater role in modulating oxidative stress resistance in S. aureus. This is the first report that demonstrates the direct involvement of a regulatory protein (SarA) in control of sod expression in S. aureus.