Novel Cholera Toxin Variant and ToxT Regulon in Environmental Vibrio mimicus Isolates: Potential Resources for the Evolution of Vibrio cholerae Hybrid Strains

Natural diversification of CTXФ andctxAB genes certainly influences disease severity and shifting patterns in major etiological agents of cholera, e.g., the overwhelming emergence of hybrid El Tor variants, replacing the prototype El Tor strains ofV. cholerae . This report, showing the occurrence of CTXET comprising a novel variant ofctxAB inV. mimicus , points out a previously unnoticed evolutionary event that is independent of the evolutionary event associated with the El Tor strains ofV. cholerae . Identification and cluster analysis of the newly discovered alleles oftcpA andtoxT suggest their horizontal transfer from an uncommon clone ofV. cholerae . The genomic contents of ToxT regulon and of tandemly arranged multiple pre-CTXФEnv and of a CTXФET inV. mimicus probably act as salient raw materials that induce natural recombination among the hallmark virulence genes of hybridV. cholerae strains. This report provides valuable information to enrich our knowledge on the evolution of new variant CT and ToxT regulons.