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Bacteriophage VP1 is a typing phage used for the phage subtyping of Vibrio cholerae O1 biotype El Tor, but the molecular mechanisms of its receptor recognition and the resistance of its host to infection are mostly unknown. In this study, we aimed to identify the host receptor and its role in resistance in natural VP1-resistant strains. Generating spontaneous resistance mutations and genome sequencing mutant strains found the polyQ protein VcpQ, which carries 46 glutamine residues in its Q-rich region, to be responsible for infection by VP1. VcpQ is a membrane protein and possibly forms homotrimers. VP1 adsorbed to V. cholerae through VcpQ. Sequence comparisons showed that 72% of natural VP1-resistant strains have fewer glutamines in the VcpQ Q-rich stretch than VP1-sensitive strains. This difference did not affect the membrane location and oligomer of VcpQ but abrogated VP1 adsorption. These mutant VcpQs did not recover VP1 infection sensitivity in a V. cholerae strain with vcpQ deleted. Our study revealed that the polyQ protein VcpQ is responsible for the binding of VP1 during its infection of V. cholerae and that glutamine residue reduction in VcpQ affects VP1 adsorption to likely be the main cause of VP1 resistance in natural resistant strains. The physiological functions of this polyQ protein in bacteria need further clarification; however, mutations in the polyQ stretch may endow V. cholerae with phage resistance and enhance survival against VP1 or related phages. [ABSTRACT FROM AUTHOR]

The genus Shewanella comprises a group of marine-dwelling species with worldwide distribution. Several species are regarded as causative agents of food spoilage and opportunistic pathogens of human diseases. In this study, a standard multilocus sequence analysis (MLSA) based on six protein-coding genes (gyrA, gyrB, infB, recN, rpoA and topA) was established as a rapid and accurate identification tool in fifty-nine type Shewanella strains. This method yielded sufficient resolving power in regard to enough informative sites, adequate sequence divergences and distinct interspecies branches. The stability of phylogenetic topology was supported by high bootstrap values and concordance with different methods. The reliability of the MLSA scheme was further validated by identical phylogenies and high correlations of genomes. The MLSA approach provided a robust system to exhibit evolutionary relationships in the Shewanella genus. The split network tree proposed twelve distinct monophyletic clades with identical G+C contents and high genetic similarities. Eighty-six tested strains were investigated to explore the population biology of the Shewanella genus in China. The most prevalent Shewanella species were Shewanella algae, Shewanella xiamenensis, Shewanella chilikensis, Shewanella indica, Shewanella seohaensis and Shewanella carassii. The strains frequently isolated from clinical and food samples highlighted the importance of increasing the surveillance of Shewanella species. Combined with the genetic, genomic and phenotypic analyses, Shewanella upenei should be considered a synonym of S. algae, and Shewanella pacifica should be reclassified as a synonym of Shewanella japonica. IMPORTANCE The MLSA scheme based on six housekeeping genes (HKGs) (gyrA, gyrB, infB, recN, rpoA and topA) is well established as a reliable tool for taxonomic, evolutionary and population diversity analyses of the genus Shewanella in this study. The standard MLSA method allows researchers to make rapid, economical and precise identification of Shewanella strains. The robust phylogenetic network of MLSA provides profound insight into the evolutionary structure of the genus Shewanella. The population genetics of Shewanella species determined by the MLSA approach plays a pivotal role in clinical diagnosis and routine monitoring. Further studies on remaining species and genomic analysis will enhance a more comprehensive understanding of the microbial systematics, phylogenetic relationships and ecological status of the genus Shewanella. [ABSTRACT FROM AUTHOR]