sigma(B) and the sigma(B)-dependent arlRS and yabJ-spoVG loci affect capsule formation in Staphylococcus aureus

The alternative transcription factor sigma(B) of Staphylococcus aureus affects the transcription of the cap gene cluster, required for the synthesis of capsular polysaccharide (CP), although this operon is lacking an apparent Cr B -dependent promoter. Regulation of cap expression and CP production in S. aureus strain Newman was shown here to be influenced by sigma(B), the two-component signal transduction regulatory system AARS, and the yabj-spoVG locus to different extents. Inactivation of ar1R or deletion of the sigB operon strongly suppressed capA (CP synthesis enzyme A) transcription. Deletion of spoVG had a polar effect on yabj-spoVG transcription and resulted in a two- to threefold decrease in capA transcription. Interestingly, immunofluorescence showed that CP production was strongly impaired in all three mutants, signaling that the yab,[-spoVG inactivation, despite its only partial effect on capA transcription, abolished capsule formation. trans-Complementation of the Delta spoVG mutant with yabJ-spoVG under the control of its native promoter restored CP-5 production and capA expression to levels seen in the wild type. Northern analyses revealed a strong impact of cro' on arIRS and yabJ-spoVG transcription. We hypothesize that ArIR and products of the yabj-spoVG locus may serve as effectors that modulate sigma(B) control over sigma(B) -dependent genes lacking an apparent UB promoter.