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Genomic signatures of obligate host dependence in the luminous bacterial symbiont of a vertebrate

Authors

  • Tory A. Hendry,

    Corresponding author
    1. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA
    Current affiliation:
    1. The School of Plant Sciences, University of Arizona, Tucson, AZ, USA
    • For correspondence. E-mail thendry@umich.edu; Tel. (+1) 518 744 2890; Fax (+1) 734 763 0544.

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  • Jeffrey R. de Wet,

    1. Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, MI, USA
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  • Paul V. Dunlap

    1. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA
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Summary

The majority of bacteria engaged in bioluminescent symbiosis are environmentally acquired and facultatively symbiotic. A few enigmatic bioluminescent symbionts have not been successfully cultured, which has led to speculation that they may be obligately dependent on their hosts. Here, we report the draft genome of the uncultured luminous symbiont of an anomalopid flashlight fish, ‘Candidatus Photodesmus katoptron’. The genome of the anomalopid symbiont is reduced by 80% compared with close relatives and lacks almost all genes necessary for amino acid synthesis and for metabolism of energy sources other than glucose, supporting obligate dependence on the host for growth. ‘Candidatus Photodesmus katoptron’ is the first described obligate mutualistic symbiont of a vertebrate. Unlike most other obligate mutualists, the anomalopid symbiont genome has retained complete pathways for chemotaxis and motility as well as most genes involved in cell wall production, consistent with the hypothesis that these bacteria may be transmitted environmentally during an extra-host phase.

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