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Diversity of Fe acquisition mechanisms in marine phytoplankton |
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Over the last decade, it has become clear that Fe limits phytoplankton growth and C export to the deep sea in 30% of the world's ocean. To improve our Eventhough we have begun unraveling the mechanisms of Fe acquisition by marine diatoms, very little is known about other important phytoplankton taxa,including prymnesiophytes (Phaeocystis sp. and Emiliana huxleyi), We are presently investigating the cellular mechanisms of Fe uptake in a variety of ecologically significant marine phytoplankton, and the adaptations of these organisms to trace metal limitation. Besides laboratory experiments, this research is complemented by field expeditions to marine ecosystems encompassing a variety of environmental conditions and phytoplankton communities, including the Fe-limited regions of the Subarctic Pacific and the Southern Ocean. This work will provide fundamental insights as to how these organisms may subsist under conditions of extreme iron deficiency and how temporal changes in Fe availability over geological past may have influenced their relative abundances.
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last updated October 28, 2004
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understanding of the C cycle and its effect on climate, it is critical to investigate the metabolic pathways controlling Fe uptake and utilization by marine microorganisms. To date, very little is known about the availability of organic Fe complexes to marine primary producers. This issue is highly significant because organic complexes constitute more than 99% of the limiting dissolved Fe pool in oceanic waters. Thus far, detailed laboratory investigations provide strong evidence for a reductive mechanism at the cell surface of marine diatoms as the mean of accessing organic Fe. Field studies in the Atlantic, Pacific, and the Southern Ocean show that plankton can acquire Fe bound to strong organic ligands, and that a biological Fe(III) reductive mechanism operates at sea; however, the specific phytoplankton responsible for this activity are presently unknown. These results emphasize the biological importance of the organic Fe pool in seawater, and the need to understand better the mechanisms by which marine phytoplankton acquire scarce Fe in the sea. 
dinoflagellates and cyanobacteria. These organisms play important and distinct roles in ocean ecology and biogeochemistry, and it is essential that we understand how they satisfy their Fe requirements for growth. For example, Phaeocystis is an important contributor to ocean carbon and sulfur cycling. This organism is responsible for a large fraction of Southern Ocean carbon export, as well as a major producer of the precursor of dimethysulfide -a gas whose atmospheric oxidation yields cloud-inducing sulfur aerosols. Evidence from ancient sediments and polar ice cores suggests that the abundance of Phaeocystis may be tightly coupled to Fe supply over glacial-interglacial cycles. The physiological mechanism behind this link remains unknown.