Derivatives of the widely used laboratory strain Staphylococcus aureus NCTC
8325, which are natural rsbU mutants, were shown to be unable to produce Rs
bU, a positive regulator of the alternative sigma factor sigma (B). The lac
k of RsbU prevented the heat-dependent production of os-controlled transcri
pts and resulted in reduced H2O2 and UV tolerance, enhanced alpha-hemolysin
activity, and the inability to produce the alkaline shock protein Asp23, A
fter 48 h of growth, rsbU mutant strains failed to accumulate staphyloxanth
in, the major stationary-phase carotenoid, Transcription of Asp23 was found
to be exclusively controlled by sigma (B), making it an excellent target f
or the study of sigma (B) activity in S. aureus. Reporter gene experiments,
using the firefly luciferase gene (luc+) fused to the sigma (B)-dependent
promoter(s) of asp23, revealed that sigma (B) is almost inactive in 8325 de
rivatives, cis complementation of the 8325 derivative BB255 with the wild-t
ype rsbU gene from strain COL produced the rsbU(+) derivative GP268, a stra
in possessing a sigma (B) activity profile comparable to that of the rsbU() wild-type strain Newman. In GP268, the heat inducibility of sigma (B)-dep
endent genes, Asp23 production, alpha-hemolysin activity, pigmentation, and
susceptibility to H2O2 were restored to the levels observed in strain Newm
an, clearly demonstrating that RsbU is needed for activation of sigma (B) i
n S. aureus.