PandemicVibrio choleraeacquired competitive traits from an environmentalVibriospecies

Abstract

Vibrio choleraeis a human pathogen that thrives in estuarine environments. Within the environment and human host,V. choleraeuses the type VI secretion system (T6SS) to inject toxic effectors into neighboring microbes and to establish its replicative niche.V. choleraestrains encode a wide variety of horizontally shared effectors, but pandemic isolates encode an identical set of distinct effectors. Effector set retention in pandemic strains despite mobility between disparate strains suggests that horizontal acquisition of these effectors was crucial for evolving pandemicV. cholerae. We attempted to locate the donor of the pandemic effectors toV. cholerae. To this end, we identified potential gene transfer events of the pandemic-associated T6SS clusters between a fish pathogen,Vibrio anguillarum, andV. cholerae. We supported the likelihood of interaction between these species by demonstrating that homologous effector-immunity pairs fromV. choleraeandV. anguillarumcan cross-neutralize one another. Thus,V. anguillarumconstitutes an environmental reservoir of pandemic-associatedV. choleraeT6SS effectors that may have initially facilitated competition between pre-pandemicV. choleraeandV. anguillarumfor an environmental niche.