Microarray-based analysis of the Staphylococcus aureus σB regulon

Microarray-based analysis of the transcriptional profiles of the genetically distinct Staphylococcus aureus strains COL, GP268, and Newman indicate that a total of 251 open reading frames (ORFs) are influenced by sigma(B) activity. While sigma(B) was found to positively control 198 genes by a factor of greater than or equal to 2 in at least two of the three genetic lineages analyzed, 53 ORFs were repressed in the presence of sigma(B). Gene products that were found to be influenced by sigma(B) are putatively involved in all manner of cellular processes, including cell envelope biosynthesis and turnover, intermediary metabolism, and signaling pathways. Most of the genes and/or operons identified as upregulated by sigma(B) were preceded by a nucleotide sequence that resembled the sigma(B) consensus promoter sequence of Bacillus subtilis. A conspicuous number of virulence-associated genes were identified as regulated by sigma(B) activity, with many adhesins upregulated and prominently represented in this group, while transcription of various exoproteins and toxins were repressed. The data presented here suggest that the sigma(B) of S. aureus controls a large regulon and is an important modulator of virulence gene expression that is likely to act conversely to RNAIII, the effector molecule of the agr locus. We propose that this alternative transcription factor may be of importance for the invading pathogen to fine-tune its virulence factor production in response to changing host environments.