The vprAB-ompV-virK operon of Vibrio cholerae senses antimicrobial peptides and activates the expression of multiple resistance systems
Antimicrobial peptides are small cationic molecules produced by eukaryotic cells to combat infection, as well as by bacteria for niche competition. Polymyxin B (PmB), a cationic cyclic antimicrobial peptide, is used prophylactically in livestock for infection prevention and as a last-resort treatment for multidrug-resistant bacterial infections in humans. In this study, a transcriptomic analysis in Vibrio cholerae showed that expression of the uncharacterized gene ompV is stimulated in response to PmB. We found that ompV is organized in a conserved four-gene operon with the two-component system vprAB (carRS) and virK in V. cholerae, and that these genes are also upregulated in response to PmB treatment. A virK deletion mutant was more sensitive to the human cathelicidin LL-37 than the wild-type strain, while an ompV mutant was more sensitive to PmB and LL-37, suggesting that both OmpV and VirK contribute to antimicrobial resistance in V. cholerae. This increased sensitivity to antimicrobial peptides was not due to membrane destabilization or reduced sequestration by membrane vesicles as a result of ompV deletion. Instead, our transcriptomic analysis showed that the efflux pump vexAB, a known effector of PmB resistance, was also upregulated in the presence of PmB in an ompV-dependent manner. Examination of the predicted structure of OmpV revealed a lateral opening in the {beta}-barrel wall with access to an electronegative pocket in the barrel lumen that can accommodate PmB. Such an interaction could facilitate intracellular signaling through a conformational change in OmpV. This is the first evidence of a specialized operon governing multiple systems for antimicrobial resistance in V. cholerae. Author SummaryIn this study, we identified the first specialized operon controlling multiple systems of antimicrobial resistance in V. cholerae. The operon encodes the two-component system vprAB, which activates the main mechanism of polymyxin B resistance in V. cholerae, and the uncharacterized genes ompV and virK. We provide evidence that OmpV and VirK are implicated in antimicrobial resistance and show that OmpV has a membrane-accessible lateral opening into a pocket that could accommodate the antimicrobial peptide polymyxin B. We propose that OmpV acts as an outer membrane sensor that signals the presence of antimicrobial peptides to activate the expression of the operon, leading to the activation of multiple mechanisms of resistance, including modifications of the outer membrane and the multi-drug efflux system vexAB.