σE controlled regulation of porin OmpU in Vibrio cholerae

Bile resistance is essential for enteric pathogens, as exemplified by Vibrio cholerae, the causative agent of cholera. The outer membrane porin OmpU confers bacterial survival and colonization advantages in the presence of host-derived antimicrobial peptides as well as bile. Expression of ompU is controlled by the virulence regulator ToxR. rpoE knockouts are accompanied by suppressor mutations causing ompU downregulation. Therefore, OmpU constitutes an intersection of the ToxR regulon and the sigma(E)-pathway in V. cholerae. To understand the mechanism by which the sigma factor sigma(E) regulates OmpU synthesis, we performed transcription studies using ompU reporter fusions and immunoblot analysis. Our data revealed an increase in ompU promoter activity in Delta rpoE strains, as well as in a Delta ompU background, indicating a negative feedback regulation circuit of ompU expression. This regulation seems necessary, since elevated lethality rates of Delta rpoE strains occur upon ompU overexpression. Manipulation of OmpU's C-terminal portion revealed its relevance for protein stability and potency of sigma(E) release. Furthermore, Delta rpoE strains are still capable of elevating OmpU levels under membrane stress conditions triggered by the bile salt sodium deoxycholate. This study provides new details about the impact of sigma(E) on ompU regulation, which is critical to the pathogen's intestinal survival.

Automated summary

This study reveals the importance of OmpU in Vibrio cholerae and the mechanism by which sigma(E) regulates OmpU synthesis, demonstrating a negative feedback regulation circuit of OmpU expression.