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Phenotypic and genotypic characterization of multiple strains of the diazotrophic cyanobacterium, Crocosphaera watsonii, isolated from the open ocean

Authors

  • Eric A. Webb,

    Corresponding author
    1. Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
      *E-mail eawebb@usc.edu; Tel. (+1) 213 940 7954; Fax (+1) 213 740 2600.
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      Department of Biological Sciences, Marine Environmental Biology Section, University of Southern California, 3616 Trousdale Parkway, Los Angeles, CA 90089-0371, USA;
  • Ian M. Ehrenreich,

    1. Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
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      ‡Department of Biology and Center for Genomics and Systems Biology, New York University, New York, NY 10003, USA, and Department of Genetics, North Carolina State University, Raleigh, NC 27695, USA.
  • Susan L. Brown,

    1. Department of Oceanography, University of Hawaii at Manoa, Honolulu, HI 96822, USA.
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  • Frederica W. Valois,

    1. Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
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  • John B. Waterbury

    1. Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
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  • Present address: Department of Biological Sciences, Marine Environmental Biology Section, University of Southern California, 3616 Trousdale Parkway, Los Angeles, CA 90089-0371, USA; Department of Biology and Center for Genomics and Systems Biology, New York University, New York, NY 10003, USA, and Department of Genetics, North Carolina State University, Raleigh, NC 27695, USA.

*E-mail eawebb@usc.edu; Tel. (+1) 213 940 7954; Fax (+1) 213 740 2600.

Summary

Diazotrophic cyanobacteria have long been recognized as important sources of reduced nitrogen (N) and therefore are important ecosystem components. Until recently, species of the filamentous cyanobacterium Trichodesmium were thought to be the primary sources of fixed N to the open ocean euphotic zone. It is now recognized that unicellular cyanobacteria are also important contributors, with members of the oligotrophic genus Crocosphaera being the only cultured examples. Herein we genetically and phenotypically characterize 10 strains isolated from the tropical Atlantic and North Pacific Oceans, and show that although all of the strains are highly similar at the genetic level, with the internal transcribed sequence (ITS) region sequence varying by ∼2 bp on average, there are many unexpected phenotypic differences between the isolates (e.g. cell size, temperature optima and range, extracellular material excretion and variability in rates of nitrogen fixation). However based on the observed sequence similarity, we propose that all of these isolates are members of the genus Crocosphaera (type strain Crocosphaera watsonii WH8501), and that the phenotypic diversity we see may reflect ecologically important variation relevant for modelling N2 fixation in the oligotrophic ocean.

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