σ B Activity in a Staphylococcus aureus hemB Mutant

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Abstract
Inactivation of hemB in Staphylococcus aureus strain Newman resulted in a small-colony phenotype and was accompanied by an altered expression pattern of global regulators and control of virulence factor production. Transcription profiles followed over 15 h by Northern blot analyses revealed that transcripts of the global regulators arl, rot, sae, sarR, sarS, srr, svrA, and sigB disappeared after the exponential phase and that both agr transcripts were completely absent in the hemB mutant. Apart from a general concentration of transcriptional activity to the exponential phase, premature gene expression was observed for rot, hla, and spa. Nevertheless, reported σB-dependent transcripts, such as sarC and clfA, were produced throughout the 15-h growth period monitored. The absence of these transcripts in a hemB sigB double mutant demonstrated their dependence on σB and indicated an unexpected, permanent σB activity in the hemB mutant. Variations in the extents of the directly σB-controlled asp23, rsbVW-sigB, and sarC transcripts argue for additional factors modulating σB activity. This study provides the first extended synopsis of the transcriptional patterns of different regulators over the entire growth cycle in the widely used Newman strain.