Role of SigB and Staphyloxanthin in Radiation Survival of Staphylococcus aureus

Staphylococcus aureus is a potent human pathogen. The virulence of this bacterium depends on a multitude of factors that it produces. One such virulence factor is the golden pigment, staphyloxanthin, which has been shown to protect the bacterium from oxidative stress. Expression of the staphyloxanthin biosynthetic pathway is dependent on SigB, a global stress response regulator in S. aureus. This study investigated the role of staphyloxanthin and SigB in protection of S. aureus from radiation damage. Using stationary-phase bacterial cells, it was determined that the staphyloxanthin-deficient (crt mutant) strain was significantly sensitive to UV radiation (~ threefold), but not sensitive to X-radiation. However, a SigB-deficient S. aureus that also lacks staphyloxanthin, was significantly sensitive to both UV- and X-radiation. To confirm that protection from X-radiation was due to hydroxyl radicals, effect of 3 M glycerol, a known hydroxyl scavenger, was also investigated. Glycerol increased the survival of the S. aureus sigB mutant to the wild-type level suggesting that the X-radiation sensitivity of these mutants was due to deficiency in scavenging hydroxyl radicals. In summary, SigB is critical for protection of S. aureus cells from radiation damage.