Characterization of the ς(B) Regulon in Staphylococcus aureus

The ς(B)-dependent stress regulon in gram-positive bacteria might fulfill a physiological role in stress response and virulence similar to that of the ς(S) regulon in Escherichia coli and other gram-negative bacteria. In order to obtain evidence for the function of the ς(B) regulon of Staphylococcus aureus, especially in virulence control, ς(B)-dependent stress genes were identified. The two-dimensional protein pattern of wild-type cells of S. aureus COL was compared with that of an isogenic sigB mutant. By this approach, we found that the synthesis of about 27 cytoplasmic proteins seemed to be under the positive control of ς(B). N-terminal sequencing of 18 proteins allowed the identification of their genes on the almost finished genome sequence of S. aureus COL and the analysis of the promoter structure. Transcriptional analyses of 11 of these genes confirmed their ς(B) dependency, and moreover, about 7 additional ς(B)-dependent genes were found which are cotranscribed with the newly detected genes, forming operons. Altogether, we identified 23 ς(B)-dependent genes and their corresponding proteins. Among them are proteins probably involved in the generation of NADH or in membrane transport mechanisms. Furthermore, at least one clpC-homologous gene was localized on the S. aureus sequence solely transcribed by ς(B). In contrast, a second clpC-homologous gene in S. aureus forming an operon with ctsR, yacH, and yacI was ς(B) independently expressed.