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https://doi.org/10.5194/bg-2018-143
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Research article 11 Apr 2018

Research article | 11 Apr 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

Trichodesmium physiological ecology and phosphate reduction in the western Tropical South Pacific

Kyle R. Frischkorn1,2, Andreas Krupke3,a, Mónica Rouco2,b, Andrés E. Salazar Estrada1,2, Benjamin A. S. Van Mooy3, and Sonya T. Dyhrman1,2 Kyle R. Frischkorn et al.
  • 1Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA
  • 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA
  • 3Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
  • apresent address: Thermo Fisher Scientific, Life Science Solutions, 180 Oyster Point Blvd., South San Francisco, CA, USA
  • bpresent address: : K=1 Project, Center for Nuclear Studies, Columbia University, New York, NY, USA

Abstract. N2 fixation by the genus Trichodesmium is predicted to support a large proportion of the primary productivity across the oligotrophic oceans, regions that are considered among the largest biomes on Earth. Many of these environments remain poorly sampled, limiting our understanding of Trichodesmium physiological ecology in these critical oligotrophic regions. Trichodesmium colonies, communities that consisted of the Trichodesmium host and their associated microbiome, were collected across the oligotrophic western tropical South Pacific (WTSP). These samples were used to assess host clade distribution, host and microbiome (holobiont) metabolic potential, and functional gene expression, with a focus on identifying Trichodesmium physiological ecology in this region. Expression dynamics across the WTSP transect indicated potential co-limitation of Trichodesmium for phosphorus and iron. A gene cassette for phosphonate biosynthesis was detected in Trichodesmium, the expression of which co-varied with the abundance of Trichodesmium Clade III, which was unusually abundant relative to Clade I in this environment. Coincident with the expression of the gene cassette, phosphate reduction to phosphite and low molecular weight phosphonate compounds was measured in Trichodesmium colonies as well as genes that enable use of this reduced phosphorus in both Trichodesmium and the microbiome. Overall, these results highlight physiological strategies for survival by the Trichodesmium holobiont in the oligotrophic ocean, revealing mechanisms with the potential to influence the cycling of resources like nitrogen and phosphorus.

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Trichodesmium is a keystone genus of marine cyanobacteria that is estimated to supply nearly half of the ocean’s fixed nitrogen, fueling primary productivity and the cycling of carbon and nitrogen in the ocean. In our study we characterize Trichodesmium ecology across the western tropical South Pacific using gene and genome sequencing and geochemistry. We detected genes for phosphorus reduction, providing a mechanism for the noted importance of this organism in the ocean's phosphorus cycle.
Trichodesmium is a keystone genus of marine cyanobacteria that is estimated to supply nearly...
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