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Phylogeny of the coral pathogen Vibrio coralliilyticus

Authors

  • F. Joseph Pollock,

    1. Australian Institute of Marine Science, PMB 3, Townsville 4810, Australia.
    2. College of Charleston, Charleston, SC 29412, USA.
    3. Hollings Marine Laboratory, Charleston, SC 29412, USA.
    4. ARC Centre of Excellence for Coral Reef Studies, School of Marine and Tropical Biology, James Cook University, Townsville 4811, Australia.
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  • Bryan Wilson,

    1. Australian Institute of Marine Science, PMB 3, Townsville 4810, Australia.
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  • Wesley R. Johnson,

    1. College of Charleston, Charleston, SC 29412, USA.
    2. Hollings Marine Laboratory, Charleston, SC 29412, USA.
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  • Pamela J. Morris,

    1. College of Charleston, Charleston, SC 29412, USA.
    2. Hollings Marine Laboratory, Charleston, SC 29412, USA.
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  • Bette L. Willis,

    1. ARC Centre of Excellence for Coral Reef Studies, School of Marine and Tropical Biology, James Cook University, Townsville 4811, Australia.
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  • David G. Bourne

    Corresponding author
    1. Australian Institute of Marine Science, PMB 3, Townsville 4810, Australia.
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E-mail d.bourne@aims.gov.au; Tel. (+61) 747534139; Fax (+61) 747725852.

Summary

A phenotypic and phylogenetic comparison of geographically disparate isolates of the coral pathogen Vibrio coralliilyticus was conducted to determine whether the bacterium exists as a single cosmopolitan clonal population, which might indicate rapid spread of a pandemic strain, or is grouped into endemic and genotypically distinct strains. All strains included in this study displayed similar phenotypic characteristics to those of the typed V. coralliilyticus strain LMG 20984T. Five phylogenetic marker genes (16S, rpoA, recA, pyrH and dnaJ) frequently used for discriminating closely related Vibrio species and a zinc-metalloprotease gene (vcpA) linked to pathogenicity were sequenced in 13 V. coralliilyticus isolates collected from corals, bivalves, and their surrounding seawater in the Red and Caribbean Seas, and Indian, Pacific and Atlantic Oceans. A high level of genetic polymorphism was observed with all isolates possessing unique genotypes at all six genetic loci examined. No consistent lineage structure was observed within the marker genes and homologous recombination was detected in the 16S and vcpA genes, suggesting that V. coralliilyticus does not possess a highly clonal population structure. Interestingly, two geographically distinct (Caribbean/south-Atlantic and Indo-Pacific/north-Atlantic) and highly divergent clades were detected within the zinc-metalloprotease gene, but it is not known if these clades correspond to phenotypic differences in virulence. These findings stress the need for a multi-locus approach for inferring V. coralliilyticus phylogeny and indicate that populations of this bacterium are likely an endemic component of coral reef ecosystems globally.

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