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Widespread association of a Rickettsiales-like bacterium with reef-building corals

Authors

  • Veronica Casas,

    1. San Diego State University, Department of Biology, LS301, 5500 Campanile Drive, San Diego, CA 92182–4614, USA.
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  • David I. Kline,

    1. San Diego State University, Department of Biology, LS301, 5500 Campanile Drive, San Diego, CA 92182–4614, USA.
    2. University of California, San Diego, Scripps Institution of Oceanography, La Jolla, CA 92093–0202, USA.
    3. Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panama.
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  • Linda Wegley,

    1. San Diego State University, Department of Biology, LS301, 5500 Campanile Drive, San Diego, CA 92182–4614, USA.
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  • Yanan Yu,

    1. San Diego State University, Department of Biology, LS301, 5500 Campanile Drive, San Diego, CA 92182–4614, USA.
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  • Mya Breitbart,

    1. San Diego State University, Department of Biology, LS301, 5500 Campanile Drive, San Diego, CA 92182–4614, USA.
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  • Forest Rohwer

    Corresponding author
    1. San Diego State University, Department of Biology, LS301, 5500 Campanile Drive, San Diego, CA 92182–4614, USA.
    2. Center for Microbial Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182–4614, USA.
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*E-mail forest@sunstroke.sdsu.edu; Tel. (+1) 619 594 1336; Fax (+1) 619 594 5676.

Summary

White band disease type I (WBD I) has been a major cause of the dramatic decline of Acroporid coral populations throughout the Caribbean during the last two decades, yet the aetiological agent of this disease is unknown. In this study, the bacterial communities associated with both healthy and diseased Acropora species were compared by 16S rDNA analyses. The bacterial communities of both healthy and diseased Acropora spp. were dominated by a single ribotype with 90% identity to a bacterium in the order Rickettsiales. Screening by nested PCR specific to the coral-associated Rickettsiales 1 (CAR1) bacterium showed that this microbe was widespread in both healthy and diseased A. cervicornis and A. palmata corals from ‘healthy’ (i.e. low WBD I incidence) and ‘stressed’ reefs (i.e. high WBD I incidence). These results indicate that there were no dramatic changes in the composition of the microbial community associated with WBD I. CAR1 was also associated with non-Acroporid corals of the Caribbean, as well as with two Acroporid corals native to the Pacific. CAR1 was not present in the water column. This bacterium was also absent from preserved Caribbean Acroporid samples collected between 1937 and 1980 before the outbreak of WBD I. These results suggest CAR1 is a relatively new bacterial associate of Acroporids and that a non-bacterial pathogen might be the cause of WBD I.

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