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Infection and Immunity, December 2001, p. 7858-7865, Vol. 69, No. 12
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.12.7858-7865.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

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

Marco Palma1,2 and Ambrose L. Cheung1,*

Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 03755,1 and Department of Immunology, Microbiology, Pathology, and Infectious Diseases, Karolinska Institutet, Huddinge University Hospital, S-141 86 Huddinge, Sweden2

Received 12 July 2001/Returned for modification 13 August 2001/Accepted 5 September 2001

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 sigma B activity in Staphylococcus aureus. The sigma B protein level and the transcription of two sigma 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 sigma beta activity. A deletion of the second gene (rsbV) resulted in a more dramatic reduction in the sigma 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 sigma B-dependent transcript initiated upstream of rsbV was 28-fold higher than the sigma A-dependent transcript originating from the rsbU promoter. The level of the sigma 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 sigma 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 sigma 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 sigma B level. Collectively, our data indicated that RsbU and RsbV in S. aureus contributed to different levels of sigma B protein expression and varying sigma B activities. Although RsbV can activate sigma B independent of RsbU, RsbU remains the major activator of sigma B during acid stress.

* Corresponding author. Mailing address: Department of Microbiology, Dartmouth Medical School, Vail 206, Hanover, NH 03755. Phone: (603) 650-1310. Fax: (603) 650-1362. E-mail: Ambrose.Cheung{at}Dartmouth.EDU.

Infection and Immunity, December 2001, p. 7858-7865, Vol. 69, No. 12
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.12.7858-7865.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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