Extracellular proteins of Staphylococcus aureus and the role of SarA and sigma(B)

Staphlococcus aureus synthesizes a large number of extracellular proteins t hat have been postulated to play a role in bacterial virulence. The proteom ic approach was used to analyse the pattern of extracellular proteins of tw o different S. aureus strains, RN6390 and COL. Thirty-nine protein spots we re identified by N-terminal sequencing or MALDI-TOF-MS. the differences of the extracellular protein patterns between both strains are striking. Among the 18 proteins identified in S. aureus COL there are nine proteins not ye t discovered in S. aureus RN6390. These are enterotoxin B, leukotoxin D, en terotoxin, serin proteases (SpIA and SpIC), thermonuclease, an IgG binding protein and two so far unknown proteins in S. aureus with similarities to S ceD precursor in Staphylococcus carnosus and to synergohymenotropic toxin p recursor in Streptococcus intermedius. In contrast, lipase as well as staph ylokinase identified in S. aureus RN6390 were not detectable in S. aureus C OL under the same conditions. By using a regulatory mutant of sarA (ALC136) isogenic to strain RN6390 we identified five proteins positively regulated by SarA and 12 proteins negatively regulated by SarA. Besides V8 protease (StsP) and HIb already described to be regulated by the sar locus new putat ively sarA-dependent proteins were identified, e.g. glycerolester hydrolase and autolysin both down-regulated in the sarA mutant, and aureolysin, stap hylokinase, staphopain and format tetrahydrofolate lyase up-regulated in th e mutant. Moreover, the role of sigma (B) in expression of extracellular pr oteins was studied. Interestingly, we found 11 proteins at an enhanced leve l in a sigB mutant of S. aureus COL, among them enterotoxin B, alpha and be ta hemolysin, serine proteases SpIA and SpIB, leukotoxin D, and staphopain homologues. The sigma (B)-dependent repression of gene expression occurs at the transcriptional level. Only one protein, SceD, was identified whose sy nthesis was down-regulated in the mutant indicating that its gene belongs t o the sigma (B)-dependent general stress regulon.