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

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Natural diversification of CTXФ and ctxAB 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 of V. cholerae . This report, showing the occurrence of CTX ET comprising a novel variant of ctxAB in V. mimicus , points out a previously unnoticed evolutionary event that is independent of the evolutionary event associated with the El Tor strains of V. cholerae . Identification and cluster analysis of the newly discovered alleles of tcpA and toxT suggest their horizontal transfer from an uncommon clone of V. cholerae . The genomic contents of ToxT regulon and of tandemly arranged multiple pre-CTXФ Env and of a CTXФ ET in V. mimicus probably act as salient raw materials that induce natural recombination among the hallmark virulence genes of hybrid V. cholerae strains. This report provides valuable information to enrich our knowledge on the evolution of new variant CT and ToxT regulons.