Repression of Staphylococcus aureus SrrAB using inducible antisense srrA alters growth and virulence factor transcript levels

Our laboratory has previously identified the staphylococcal respiratory response (SrrAB), a Staphylococcus aureus two-component system that acts in the global regulation of virulence factors. In strain RN4220, SrrAB downregulated production of agr RNAIII, protein A, and TSST-1, particularly under low-oxygen conditions. Work by another group showed that SrrAB regulates energy metabolism genes and indicated that SrrAB may regulate energy transduction in response to changes in oxygen availability. In this study we investigate the role of SrrAB in regulating RNAIII, tst, spa, icaR, and icaA in a clinical isolate of S. aureus, MN8. We employ an inducible antisense vector, pYJY4, in order to repress transcription of srrAB. Transcript levels were assessed by reverse transcription followed by quantitative PCR. Repression of srrAB in rich media under aerobic growth conditions shows that SrrAB is required for expression of tst, spa, and icaR transcripts at wild-type levels. Comparisons made between rich media under aerobic conditions vs low-oxygen conditions show that srrAB transcript levels are not altered by oxygen alone. Previous studies performed on strain RN4220 under low-oxygen conditions indicate that SrrAB represses tst and spa transcript when the amount of oxygen is limited. We propose that, under aerobic conditions, SrrAB enhances the levels of tst, spa, and icaR, while under low-oxygen conditions, SrrAB decreases the levels of these three transcripts.