The influence of SaeRS and σB on the expression of superantigens in different Staphylococcus aureus isolates

Abstract Staphylococcus aureus is a major human pathogen. Superantigens (SAg) are important virulence factors in S. aureus , but the regulation of SAg gene expression is largely unknown. Using 2 sequenced S. aureus strains (COL and Newman) and 4 clinical isolates, regulation of gene expression was investigated in more detail for 12 SAgs. The SAg-encoding genes were expressed in a growth phase-dependent manner: while the egc operon was mainly transcribed at low optical densities, the transcription of seb was induced at high optical densities. The transcript levels of sea , sek , seq , sep , and tst-1 did not change significantly during growth. The T cell-mitogenic activity of supernatants correlated with the transcription data. SaeRS and σ B strongly influenced SAg gene transcription. σ B activated transcription of seh , tst-1 , and of the egc operon. A possible σ B -dependent promoter was identified in front of the egc operon. In contrast, a loss of σ B enhanced the transcript level of seb , suggesting an indirect effect of the alternative sigma factor on the transcription of this gene. Transcriptional studies of an saeS mutant showed that the two-component system only activates transcription of seb . The influence of σ B and SaeRS on the expression of SAg genes was validated by T cell proliferation assays. For sigB mutants in different strains, different effects on the T cell-mitogenic potential were observed depending on the SAg gene repertoire of the isolates.