Genetic analysis of the role of the conserved inner membrane protein CvpA in EHEC resistance to deoxycholate

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 ∆cvpA EHEC mutant to DOC. These screens demonstrated that mutations predicted to activate the σE-mediated extracytoplasmic stress response bypass the ∆cvpA mutant’s susceptibility to DOC. Consistent with this idea, we found that deletions in rseA and msbB and direct overexpression of rpoE restored DOC resistance to the ∆cvpA mutant. Analysis of the distribution of CvpA homologs revealed that this inner membrane protein is conserved across diverse bacterial phyla, in both enteric and non-enteric bacteria that are not exposed to bile. Together, our findings suggest that CvpA plays a role in cell envelope homeostasis in response to DOC and similar stress stimuli in diverse bacteria. We performed transposon-insertion sequencing (Tn-Seq) on transposon mutagenized libraries in wild-type (WT) enterohemorrhagic E. coli EDL933 and a strain in which cvpA gene is deleted (∆cvpA).