Abstract
Vibrio cholerae inhabits aquatic environments worldwide and has over 200 recognized serogroups classified by O-polysaccharide specificity. Here, we report that V. cholerae selects either of two genetic traits during their evolution. Sequencing of the specific gene locus MS6_A0927 revealed that 339 of 341 strains of V. cholerae and closely related Vibrio species originating from 34 countries over a century carried either metY (M) (~1,269 bp) or luxR-hchA (LH) (~1,600 bp) genes, and consequently those vibrios were separated into two clusters, M (45.4%) and LH (54.6%). Only two strains contained both M and LH in the same locus. Moreover, extensive polymorphisms in those genes were detected in M and LH with 79 and 46 sequence variations, respectively. V. cholerae O1 strains isolated from cholera outbreaks worldwide, and some non-O1 strains evolving from O1 via exchange of genes encoding cell surface polysaccharides possessed LH alleles. Analysis of polymorphisms in the gene locus implicated a high degree of genetic diversity and identical subpopulations among the V. cholerae species.
Highlights
Vibrio cholerae is a gram-negative bacterial pathogen responsible for cholera, and several million cholera cases including 21,000–143,000 deaths occur worldwide each year[1]
We found that V. cholerae O1 genomes possess either metY or hchA/luxR on the specific gene locus MS6_ A0927 on a conserved syntenic region of the chromosome II26
BLAST searches were performed using M (1,269 bp) from V. cholerae strain MS6 and LH from V. cholerae strain O395 (1,600 bp) as query sequences against 186 genomes including 178 V. cholerae, 6 V. mimicus, 1 V. metecus, and 1 V. parilis obtained from the NCBI database
Summary
V. cholerae separates into two clusters based on the locus MS6_A0927. We investigated the distribution of the metY (M) gene and luxR-hchA (LH) genes among vibrios. We designed a multiplex PCR system for detection of M, LH, toxR, VC2346, tcpA, and ctxAB, and determined the sequences of M and LH in the locus MS6_A0927 of 153 strains of non-O1 V. cholerae and 2 strains of V. mimicus (Table 1). The DNA sequence of LH was clearly different from those in V. cholerae, except for the four strains N56, N79, N80, and N83 of subclade LH4 Based on these observations, V. cholerae commonly carried a single copy of the M and/or LH genes in the specific locus. Most of the non-toxigenic V. cholerae of O1 serogroup, such as strains 12129(1) and TM11079-80, belonged to different subclades, and phylogenetic lineages from the toxigenic O1 strains and their O1 antigen phenotype probably arose from horizontal gene exchange in the evolution of V. cholerae[13]. Our targeted gene sequencing of MS6_A0927 revealed divergent genetic traits among V. cholerae species
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