Modulation of CrbS-Dependent Activation of the Acetate Switch inVibrio cholerae
ABSTRACTVibrio choleraecontrols the pathogenicity of interactions with arthropod hosts via the activity of the CrbS/R two-component system. This signaling pathway regulates the consumption of acetate, which in turn alters the relative virulence of interactions with arthropods, includingDrosophila melanogaster. CrbS is a histidine kinase that links a transporter-like domain to its signaling apparatus via putative STAC and PAS domains. CrbS and its cognate response regulator are required for the expression of acetyl coenzyme A (acetyl-CoA) synthetase (product ofacs), which converts acetate to acetyl-CoA. We demonstrate that the STAC domain of CrbS is required for signaling in culture; without it,acstranscription is reduced in LB medium, andV. choleraecannot grow on acetate minimal media. However, the strain remains virulent towardDrosophilaand expressesacssimilarly to the wild type during infection. This suggests that there is a unique signal or environmental variable that modulates CrbS in the gastrointestinal tract ofDrosophila. Second, we present evidence in support of CrbR, the response regulator that interacts with CrbS, binding directly to theacspromoter, and we identify a region of the promoter that CrbR may target. We further demonstrate that nutrient signals, together with the cAMP receptor protein (CRP)-cAMP system, controlacstranscription, but regulation may occur indirectly, as CRP-cAMP activates the expression of thecrbSandcrbRgenes. Finally, we define the role of the Pta-AckA system inV. choleraeand identify redundancy built into acetate excretion pathways in this pathogen.IMPORTANCECrbS is a member of a unique family of sensor histidine kinases, as its structure suggests that it may link signaling to the transport of a molecule. However, mechanisms through which CrbS senses and communicates information about the outside world are unknown. In theVibrionaceae, orthologs of CrbS regulate acetate metabolism, which can, in turn, affect interactions with host organisms. Here, we situate CrbS within a larger regulatory framework, demonstrating thatcrbSis regulated by nutrient-sensing systems. Furthermore, CrbS domains may play various roles in signaling during infection and growth in culture, suggesting a unique mechanism of host recognition. Finally, we define the roles of additional pathways in acetate flux, as a foundation for further studies of this metabolic nexus point.