Influence of a Functional sigB Operon on the Global Regulators sar and agr in Staphylococcus aureus

Abstract

The growth phase-dependent activity profile of the alternate transcription factor ς B and its effects on the expression of sar and agr were examined in three different Staphylococcus aureus strains by Northern blot analyses and by the use of reporter gene fusion experiments. Significant ς B activity was detectable only in the clinical isolates MSSA1112 and Newman, carrying the wild-type rsbU allele, but not in the NCTC8325 derivative BB255, which is defective in rsbU . ς B activity peaked in the late exponential phase and diminished towards the stationary phase when bacteria were grown in Luria-Bertani medium. Transcriptional analysis and a sarP1-sarP2-sarP3 ( sarP1-P2-P3 )-driven firefly luciferase ( luc +) reporter gene fusion demonstrated a strong ς B activity- and growth phase-dependent increase in sar expression that was totally absent in either rsbU or Δ rsbUVWsigB mutants. In contrast, expression of the agr locus, as measured by RNAIII levels and by an hldp :: luc + fusion, was found to be higher in the absence of ς B activity, such as in rsbU or Δ rsbUVWsigB mutants, than in wild-type strains. Overexpression of ς B in BB255 derivatives resulted in a clear increase in sarP1-P2-P3 :: luc + expression as well as a strong decrease in hldp :: luc + expression. The data presented here suggest that ς B increases sar expression while simultaneously reducing the RNAIII level in a growth phase-dependent manner.