Genome Sequencing Reveals Unique Mutations in Characteristic Metabolic Pathways and the Transfer of Virulence Genes between V. mimicus and V. cholerae

Abstract

Vibrio mimicus, the species most similar to V. cholerae, is a microbe present in the natural environmental and sometimes causes diarrhea and internal infections in humans. It shows similar phenotypes to V. cholerae but differs in some biochemical characteristics. The molecular mechanisms underlying the differences in biochemical metabolism between V. mimicus and V. cholerae are currently unclear. Several V. mimicus isolates have been found that carry cholera toxin genes (ctxAB) and cause cholera-like diarrhea in humans. Here, the genome of the V. mimicus isolate SX-4, which carries an intact CTX element, was sequenced and annotated. Analysis of its genome, together with those of other Vibrio species, revealed extensive differences within the Vibrionaceae. Common mutations in gene clusters involved in three biochemical metabolism pathways that are used for discrimination between V. mimicus and V. cholerae were found in V. mimicus strains. We also constructed detailed genomic structures and evolution maps for the general types of genomic drift associated with pathogenic characters in polysaccharides, CTX elements and toxin co-regulated pilus (TCP) gene clusters. Overall, the whole-genome sequencing of the V. mimicus strain carrying the cholera toxin gene provides detailed information for understanding genomic differences among Vibrio spp. V. mimicus has a large number of diverse gene and nucleotide differences from its nearest neighbor, V. cholerae. The observed mutations in the characteristic metabolism pathways may indicate different adaptations to different niches for these species and may be caused by ancient events in evolution before the divergence of V. cholerae and V. mimicus. Horizontal transfers of virulence-related genes from an uncommon clone of V. cholerae, rather than the seventh pandemic strains, have generated the pathogenic V. mimicus strain carrying cholera toxin genes.

Population Structure and Evolution of Non-O1/Non-O139 Vibrio cholerae by Multilocus Sequence Typing

“…Five strains M1568, M1569, M1566, M1115 and M1567 were grouped together with our known V. mimicus strain M547 and five genome sequenced V. mimicus strains (VM603, VM573, VM223 MB451 and SX-4) [55], [66]–[68] (Figure 1), showing that these five “ V. cholerae ” strains were in fact V. mimicus that were initially misidentified. Maximum and average pairwise differences amongst the 11 isolates were 3.42% and 1.94%, respectively, while the maximum and average pairwise differences between V. cholerae and V. mimicus were 11.49% and 8.21%.…”

Genetic Relationships of Vibrio parahaemolyticus Isolates from Clinical, Human Carrier, and Environmental Sources in Thailand, Determined by Multilocus Sequence Analysis

“…It was proposed that such pathogeninduced blooms drive conjugative horizontal gene transfer between different Enterobacteriaceae and are responsible for the evolution of both pathogens and commensals. Thus, the human intestinal tract may represent an ecological niche that stimulates the occurrence of horizontal gene transfer both among different strains of V. parahaemolyticus and between V. parahaemolyticus and other commensal species (65)(66)(67)(68). What remains unknown is the frequency of such evolutionary events, although it is likely to be relatively low.…”

Rapid and Sensitive Quantification of Vibrio cholerae and Vibrio mimicus Cells in Water Samples by Use of Catalyzed Reporter Deposition Fluorescence In Situ Hybridization Combined with Solid-Phase Cytometry

“…Only recently, their classification as two different species has been confirmed (35). V. cholerae comprises more than 200 serotypes, but only serotypes O1 and O139 cause the severe diarrheal disease cholera (9,32).…”

“…Interestingly, several V. mimicus isolates carrying cholera toxin genes (ctxAB) have also been identified. It was suggested that horizontal transfers of virulence-related genes from an uncommon clone of V. cholerae have generated pathogenic V. mimicus strains carrying cholera toxin genes (35). All other V. cholerae serotypes, summarized as non-O1/non-O139, and V. mimicus strains are usually associated with less-severe gastrointestinal infections as well as blood, wound, and ear infections (7,16,28,35).…”

“…It was suggested that horizontal transfers of virulence-related genes from an uncommon clone of V. cholerae have generated pathogenic V. mimicus strains carrying cholera toxin genes (35). All other V. cholerae serotypes, summarized as non-O1/non-O139, and V. mimicus strains are usually associated with less-severe gastrointestinal infections as well as blood, wound, and ear infections (7,16,28,35). Besides their role as important human pathogens, both organisms are found worldwide in brackish water, coastal areas, and estuarine environments (8,35) and are therefore considered to be natural components of the bacterial community in aquatic ecosystems.…”