ς B Activity in Staphylococcus aureus Is Controlled by RsbU and an Additional Factor(s) during Bacterial Growth

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Abstract
Two genes of the sigB operon, rsbU and rsbV , were deleted in an rsbU + strain (FDA486) to evaluate the contribution of these two genes to ς B activity in Staphylococcus aureus. The ς B protein level and the transcription of two ς B -dependent promoters ( sigB and sarA P3 transcripts) were analyzed in the constructed mutants. A deletion of the first gene ( rsbU ) within the sigB operon led only to a partial reduction in ς β activity. A deletion of the second gene ( rsbV ) resulted in a more dramatic reduction in the ς B protein level and its activity than did the deletion of rsbU , thus indicating that RsbV can be activated independent of RsbU. In the parental strain, the ς B -dependent transcript initiated upstream of rsbV was 28-fold higher than the ς A -dependent transcript originating from the rsbU promoter. The level of the ς B -dependent transcript decreased up to 50% in the rsbU mutant and up to 90% in the rsbV mutant compared with the transcript in the wild type. The yellow pigment of S . aureus colonies, a ς B -dependent phenotype, was partially reduced in the rsbU and rsbV mutants, whereas alpha-hemolysin was increased. Additionally, the sarA P3 promoter activity of the parental strain was induced to a higher level in response to pH 5.5 than was that of the rsbU or rsbV mutant, indicating that RsbU is the major activator of the ς B response to acid stress. Using a tetracycline-inducible system to modulate the expression of RsbW, we progressively repressed pigment production, presumably by reducing the free ς B level. Collectively, our data indicated that RsbU and RsbV in S . aureus contributed to different levels of ς B protein expression and varying ς B activities. Although RsbV can activate ς B independent of RsbU, RsbU remains the major activator of ς B during acid stress.