σB-dependent yabJ-spoVG operon involved in regulation of extracellular nuclease, lipase and protease expression in Staphylococcus aureus

The alternative sigma factor σB of Staphylococcus aureus is involved in the coordination of the general stress response, expression of virulence determinants and modulation of antibiotic resistance levels. It controls a large regulon, either directly by recognizing conserved σB promoter sequences, or indirectly via σB-dependent elements. The σB-controlled yabJ-spoVG operon encodes two such putative downstream elements. We report here transcriptome analysis in S. aureus Newman showing that inactivation of the yabJ-spoVG operon had primarily a repressing effect on a small subregulon comprising mainly virulence factors, including a nuclease (nuc), a protease (splE) and a lipase (lip).. As a consequence extracellular nuclease, protease and lipase activities were reduced in a yabJspoVG mutant. Trans-complementation by SpoVG was sufficient to restore their reduced phenotypic expression and lowered transcription due to yabJ-spoVG deletion. It did not restore, however, the changes triggered by σB inactivation, indicating that both regulons do only partially overlap, despite the σB dependency of the yabJ-spoVG expression. Thus, σB is likely to control additional, SpoVG-independent factors affecting the expression of numerous hydrolytic enzymes. SpoVG, on the other hand, seems to fine-tune the σB-dependent regulation of a subset of virulence factors by antagonizing the σB effect.