Molecular Analysis and Organization of the sigma super(B) Operon in Staphylococcus aureus

• Published in: Journal of bacteriology Vol. 187; no. 23; pp. 8006 - 8019
• Main Authors: Senn, Maria Magdalena, Giachino, Philipp, Homerova, Dagmar, Steinhuber, Andrea, Strassner, Jochen, Kormanec, Jan, Flueckiger, Ursula, Berger-Baechi, Brigitte, Bischoff, Markus
• Format: Journal Article
• Language: English
• Published: 01.12.2005
• Subjects: Bacillus subtilis; Saccharomyces cerevisiae; Staphylococcus aureus
• ISSN: 0021-9193; 1098-5530

The alternative sigma factor sigma super(B) of Staphylococcus aureus controls the expression of a variety of genes, including virulence determinants and global regulators. Genetic manipulations and transcriptional start point (TSP) analyses showed that the sigB operon is transcribed from at least two differentially controlled promoters: a putative sigma super(A)-dependent promoter, termed sigB sub(p1), giving rise to a 3.6-kb transcript covering sa2059-sa2058-rsbU-rsbV-rsbW-sigB, and a sigma super(B)-dependent promoter, sigB sub(p3), initiating a 1.6-kb transcript covering rsbV-rsbW-sigB. TSP and promoter-reporter gene fusion experiments indicated that a third promoter, tentatively termed sigB sub(p2) and proposed to lead to a 2.5-kb transcript, including rsbU-rsbV-rsbW-sigB, might govern the expression of the sigB operon. Environmental stresses, such as heat shock and salt stress, induced a rapid response within minutes from promoters sigB sub(p1) and sigB sub(p3). In vitro, the sigB sub(p1) promoter was active in the early growth stages, while the sigB sub(p2) and sigB sub(p3) promoters produced transcripts throughout the growth cycle, with sigB sub(p3) peaking around the transition state between exponential growth and stationary phase. The amount of sigB transcripts, however, did not reflect the concentration of sigma super(B) measured in cell extracts, which remained constant over the entire growth cycle. In a guinea pig cage model of infection, sigB transcripts were as abundant 2 and 8 days postinoculation as values found in vitro, demonstrating that sigB is indeed transcribed during the course of infection. Physical interactions between staphylococcal RsbU-RsbV, RsbV-RsbW, and RsbW- sigma super(B) were inferred from a yeast (Saccharomyces cerevisiae) two-hybrid approach, indicating the presence of a partner-switching mechanism in the sigma super(B) activation cascade similar to that of Bacillus subtilis. The finding that overexpression of RsbU was sufficient to trigger an immediate and strong activation of sigma super(B), however, signals a relevant difference in the regulation of sigma super(B) activation between B. subtilis and S. aureus in the cascade upstream of RsbU.