Multilocus Sequence Analysis Reveals that <i>Vibrio harveyi</i> and <i>V. campbellii</i> Are Distinct Species

  • Fabiano L. Thompson
    Department of Genetics, Institute of Biology, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
  • Bruno Gomez-Gil
    CIAD Mazatlan Unit for Aquaculture, AP 711 Mazatlan, Sinaloa 82000, Mexico
  • Ana Teresa Ribeiro Vasconcelos
    Nacional Laboratory for Scientific Computing, Department of Applied and Computational Mathematics, Laboratory of Bioinformatics, Av. Getúlio Vargas 333, Quitandinha, 25651-070, Petropolis, RJ, Brazil
  • Tomoo Sawabe
    Laboratory of Microbiology, Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan

抄録

<jats:title>ABSTRACT</jats:title> <jats:p> Identification and classification of <jats:italic>Vibrio</jats:italic> species have relied upon band pattern methods (e.g., amplified fragment length polymorphism) and DNA-DNA hybridization. However, data generated by these methods cannot be used to build an online electronic taxonomy. In order to overcome these limitations, we developed the first standard multilocus sequence scheme focused on the ubiquitous and pathogenic <jats:italic>Vibrio harveyi</jats:italic> species group (i.e., <jats:italic>V. harveyi</jats:italic> , <jats:italic>V. campbellii</jats:italic> , <jats:italic>V. rotiferianus</jats:italic> , and a new as yet unnamed species). We examined a collection of 104 isolates from different geographical regions and hosts using segments of seven housekeeping genes. These two species formed separated clusters on the basis of <jats:italic>topA</jats:italic> , <jats:italic>pyrH</jats:italic> , <jats:italic>ftsZ</jats:italic> , and <jats:italic>mreB</jats:italic> gene sequences. The phylogenetic picture obtained by the other three loci, i.e., <jats:italic>gyrB</jats:italic> , <jats:italic>recA</jats:italic> , and <jats:italic>gapA</jats:italic> , was more complex though. <jats:italic>V. campbellii</jats:italic> appeared nested within <jats:italic>V. harveyi</jats:italic> in the <jats:italic>recA</jats:italic> trees, whereas <jats:italic>V. harveyi</jats:italic> formed a tight nested cluster within <jats:italic>V. campbellii</jats:italic> by <jats:italic>gapA</jats:italic> . The <jats:italic>gyrB</jats:italic> gene had no taxonomic resolution and grouped the two species together. The fuzziness observed in these three genes seems not be related to recombination but to low divergence due to the accumulation of only a few substitutions. In spite of this, the concatenated sequences provided evidence that the two species form two separated clusters. These clusters did not arise by recombination but by accumulation of point mutations. <jats:italic>V. harveyi</jats:italic> and <jats:italic>V. campbellii</jats:italic> isolates can be readily identified through the open database resource developed in this study ( <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="url" xlink:href="http://www.taxvibrio.lncc.br/">http://www.taxvibrio.lncc.br/</jats:ext-link> ). We argue that the species should be defined by evolutionary criteria. Strains of the same species will share at least 95% concatenated sequence similarity using the seven loci, and, most importantly, cospecific strains will form cohesive readily recognizable phylogenetic clades. </jats:p>

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