The <i>Staphylococcus aureus</i> Alternative Sigma Factor ς ^B Controls the Environmental Stress Response but Not Starvation Survival or Pathogenicity in a Mouse Abscess Model

The role of sigmaB, an alternative sigma factor of Staphylococcus aureus, has been characterized in response to environmental stress, starvation-survival and recovery, and pathogenicity. sigmaB was mainly expressed during the stationary phase of growth and was repressed by 1 M sodium chloride. A sigB insertionally inactivated mutant was created. In stress resistance studies, sigmaB was shown to be involved in recovery from heat shock at 54 degreesC and in acid and hydrogen peroxide resistance but not in resistance to ethanol or osmotic shock. Interestingly, S. aureus acquired increased acid resistance when preincubated at a sublethal pH 4 prior to exposure to a lethal pH 2. This acid-adaptive response resulting in tolerance was mediated via sigB. However, sigmaB was not vital for the starvation-survival or recovery mechanisms. sigmaB does not have a major role in the expression of the global regulator of virulence determinant biosynthesis, staphylococcal accessory regulator (sarA), the production of a number of representative virulence factors, and pathogenicity in a mouse subcutaneous abscess model. However, SarA upregulates sigB expression in a growth-phase-dependent manner. Thus, sigmaB expression is linked to the processes controlling virulence determinant production. The role of sigmaB as a major regulator of the stress response, but not of starvation-survival, is discussed.