Role of sigmaB in regulating the compatible solute uptake systems of XXXX : osmotic induction of opuC is sigmaB dependent.

@entity5125 @entity526 @entity6211
The regulation of the compatible solute transport systems in @entity5125 by the stress-inducible sigma factor sigma(B) was investigated. Using wild-type strain 10403S and an otherwise isogenic strain carrying an in-frame deletion in sigB, we have examined the role of sigma(B) in regulating the ability of cells to utilize betaine and @entity6211 during growth under conditions of hyperosmotic stress. Cells lacking sigma(B) were defective for the utilization of @entity6211 but retained the ability to utilize betaine as an osmoprotectant. When compatible solute transport studies were performed, the initial rates of uptake of both betaine and @entity6211 were found to be reduced in the sigB mutant; @entity6211 transport was almost abolished, whereas betaine transport was reduced to approximately 50% of that of the parent strain. Analysis of the cytoplasmic pools of compatible solutes during balanced growth revealed that both @entity6211 and betaine steady-state pools were reduced in the sigB mutant. Transcriptional reporter fusions to the opuC (which encodes an ABC @entity6211 transporter) and betL (which encodes an a secondary betaine transporter) operons were generated by using a promoterless copy of the gus gene from @entity526 . Measurement of beta-glucuronidase activities directed by opuC-gus and betL-gus revealed that transcription of opuC is largely sigma(B) dependent, consistent with the existence of a potential sigma(B) consensus promoter motif upstream from opuCA. The transcription of betL was found to be sigB independent. Reverse transcriptase PCR experiments confirmed these data and indicated that the transcription of all three known compatible solute uptake systems (opuC, betL, and gbu), as well as a gene that is predicted to encode a compatible solute transporter subunit (lmo1421) is induced in response to elevated osmolarity. The osmotic induction of opuCA and lmo1421 was found to be strongly sigma(B) dependent. Together these observations suggest that sigma(B) plays a major role in the regulation of @entity6211 utilization by @entity5125 but is not essential for betaine utilization by this pathogen.
