Taxonomic resolution, ecotypes and the biogeography of Prochlorococcus

Authors

  • Adam C. Martiny,

    Corresponding author
    1. Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
    2. Departments of Earth System Science and
    3. Ecology and Evolutionary Biology, University of California – Irvine, Irvine, CA 92697, USA.
      *E-mail amartiny@uci.edu; Tel. (+1) 9498249713; Fax (+1) 9498243874;
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  • Amos P. K. Tai,

    1. Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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    • Present address: Harvard Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.

  • Daniele Veneziano,

    1. Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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  • François Primeau,

    1. Departments of Earth System Science and
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  • Sallie W. Chisholm

    Corresponding author
    1. Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
      **E-mail chisholm@mit.edu; Tel. (+1) 6172531771; Fax (+1) 6173240336.
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*E-mail amartiny@uci.edu; Tel. (+1) 9498249713; Fax (+1) 9498243874;

**E-mail chisholm@mit.edu; Tel. (+1) 6172531771; Fax (+1) 6173240336.

Summary

In order to expand our understanding of the diversity and biogeography of Prochlorococcus ribotypes, we PCR-amplified, cloned and sequenced the 16S/23S rRNA ITS region from sites in the Atlantic and Pacific oceans. Ninety-three per cent of the ITS sequences could be assigned to existing Prochlorococcus clades, although many novel subclades were detected. We assigned the sequences to operational taxonomic units using a graduated scale of sequence identity from 80% to 99.5% and correlated Prochlorococcus diversity with respect to environmental variables and dispersal time between the sites. Dispersal time was estimated using a global ocean circulation model. The significance of specific environmental variables was dependent on the degree of sequence identity used to define a taxon: light correlates with broad-scale diversity (90% cut-off), temperature with intermediate scale (95%) whereas no correlation with phosphate was observed. Community structure was correlated with dispersal time between sample sites only when taxa were defined using the finest sequence similarity cut-off. Surprisingly, the concentration of nitrate, which cannot be used as N source by the Prochlorococcus strains in culture, explains some variation in community structure for some definitions of taxa. This study suggests that the spatial distribution of Prochlorococcus ecotypes is shaped by a hierarchy of environmental factors as well dispersal limitation.

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