Genetic analyses link the conserved inner membrane protein CvpA to the σ^Eextracytoplasmic stress response

Abstract

The function of cvpA, a bacterial gene predicted to encode an inner membrane protein, is largely unknown. Early studies in E. coli linked cvpA to Colicin V secretion and recent work revealed that it is required for robust intestinal colonization by diverse enteric pathogens. In enterohemorrhagic E. coli (EHEC), cvpA is required for resistance to the bile salt deoxycholate (DOC). Here, we carried out genome-scale transposon-insertion mutagenesis and spontaneous suppressor analysis to uncover cvpA’s genetic interactions and identify common pathways that rescue the sensitivity of a ΔcvpA EHEC mutant to DOC. Collectively, these screens led to the hypothesis that the ΔcvpA mutant is impaired in its capacity to activate the σE-mediated stress response. This idea was supported by showing that mutations that activate σE, either indirectly or through its direct overexpression, can restore the ΔcvpA mutant’s resistance to DOC. Analysis of the distribution of CvpA homologs revealed that this inner membrane protein is conserved across bacterial phyla, in both enteric and non-enteric bacteria that are not exposed to bile. Together, our findings suggest that CvpA may function in triggering activation of the σE stress response pathway in response to DOC as well as additional stimuli.ImportanceSeveral enteric pathogens, including Enterohemorrhagic E. coli (EHEC), require cvpA to robustly colonize the intestine. This inner membrane is also important for secretion of a colicin and EHEC resistance to the bile salt deoxycholate, but its function is unknown. Genetic analyses carried out here suggest that cvpA is required to trigger the σE stress response pathway in response to deoxycholate. Since CvpA is conserved across diverse bacterial phyla, we propose that this inner membrane protein is important for activation of this stress response pathway in response to diverse perturbations of the cell envelope.