Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 23, Pages 8607-8612Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0600540103
Keywords
bacteria; cyanobacteria; genomics; lipids; marine phosphorus cycle
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There is growing evidence that dissolved phosphorus can regulate planktonic production in the oceans' subtropical gyres, yet there is little quantitative information about the biochemical fate of phosphorus in planktonic communities. We observed in the North Pacific Subtropical Gyre (NPSG) that the synthesis of membrane lipids accounted for 18-28% of the phosphate (pO(4)(3-)) taken up by 4 the total planktonic community. Paradoxically, Prochlorococcus, the cyanobacterium that dominates NPSG phytoplankton, primarily synthesizes sulfoquinovosylcliacylglycerol (SQDG), a lipid that contains sulfur and sugar instead of phosphate. In axenic cultures of Prochlorococcus, it was observed that < 1% of the total pO(4)(3-) uptake was incorporated into membrane lipids. Liquid chromatography/mass spectrometry of planktonic lipids in the NPSG confirmed that SQDG was the dominant membrane lipid. Furthermore, the analyses of SQDG synthesis genes from the Sargasso Sea environmental genome showed that the use of sulfolipids in subtropical gyres was confined primarily to picocyanobacteria; no sequences related to known heterotrophic bacterial SQDG lineages were found. This biochemical adaptation by Prochlorococcus must be a significant benefit to these organisms, which compete against phospholipid-rich heterotrophic bacteria for pO(4)(3-). Thus, evolution of this sulfur-for-phosphorus strategy set the stage for the success of picocyanobacteria in oligotrophic environments and may have been a major event in Earth's early history when the relative availability of sulfate and pO(4)(3-) were significantly different 4 from today's ocean.
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