Modular small RNA drives the emergence of virulence traits and environmental trade-offs in Vibrio cholerae

To date, the specific molecular drivers and fitness trade-offs that enable some strains within a population to undergo this process remain enigmatic. Here, we describe a small RNA (sRNA) with a unique modular structure that shapes the evolution of toxigenic Vibrio cholerae, the agent of cholera.

The sRNA comprises of a highly variable 5’ module located within the ompU ORF and a conserved 3’ one downstream from the gene. The bimodular nature of the OmpU-encoded sRNA (OueS) generates allelic variants that differentially contribute to the emergence of virulence potential in some strains and associated fitness trade-offs between human infection and environmental survival. Unlike environmental counterparts, the OueS allele from toxigenic strains controls phenotypes essential during host colonization: a) stringently inhibits biofilm formation by suppressing the iron-responsive sRNA RyhB, and b) confers resistance against intestinal bacteriophages by activating the CBASS phage defense system.