Saccharides enhance iron bioavailability to southern ocean p

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TitleSaccharides enhance iron bioavailability to southern ocean phytoplanktonAbstractIron limits primary productivity in vast regions of the ocean. Given that marine phytoplankton contribute up to 40% of global biological carbon fixation, it is important to understand what parameters control the availability of iron (iron bioavailability) to these organisms. Most studies on iron bioavailability have focused on the role of siderophores; however, eukaryotic phytoplankton do not produce or release siderophores. Here, we report on the pivotal role of saccharides - which may act like an organic ligand - in enhancing iron bioavailability to a Southern Ocean cultured diatom, a prymnesiophyte, as well as to natural populations of eukaryotic phytoplankton. Addition of a monosaccharide (>2 nM of glucuronic acid, GLU) to natural planktonic assemblages from both the polar front and subantarctic zones resulted in an increase in iron bioavailability for eukaryotic phytoplankton, relative to bacterioplankton. The enhanced iron bioavailability observed for several groups of eukaryotic phytoplankton (i.e., cultured and natural populations) using three saccharides, suggests it is a common phenomenon. Increased iron bioavailability resulted from the combination of saccharides forming highly bioavailable organic associations with iron and increasing iron solubility, mainly as colloidal iron. As saccharides are ubiquitous, present at nanomolar to micromolar concentrations, and produced by biota in surface waters, they also satisfy the prerequisites to be important constituents of the poorly defined Äºigand soup, Ìknown to weakly bind iron. Our findings point to an additional type of organic ligand, controlling iron bioavailability to eukaryotic phytoplankton - a key unknown in iron biogeochemistry.AcknowledgementsThe authors tha,nk Brian Griffiths and Andrew Bowie for water sampling and the opportunity to join the SAZ-Sense oceano graphic campaign; the laboratory of Ken Bruland for SAFe reference seawater; Ros Watson and Jeanette O'Sullivan for ICP-MS analysis; Lesley Clementson and Corina Brussaard for HPLC pigments and flow cytometry analysis, respectively; and Tom Trull, Richard Matear, and Brian Griffiths for comments. The authors also thank the Australian Research Council for funding (DP 1092892), the Australian Antarctic Division (Australian Antarctic Science Project 2720), and the Antarctic Climate and Ecosystems Cooperative Research Center. CS.H. was funded by the Commonwealth Scientific and Industrial Research Organization (CSIRO) Office of the Chief Executive Post doctoral Fellowship and the University of Technology Sydney Chancellor Fellowship; CM.N. was supported by a Postdoctoral Fellowship. The Belgian Federal Science Policy Office (Contract SD/CA/03A), Belgian French Commu nity (Actions de Recherche Concertee Contract 2/07-287) and the Netherlands Organisation for Scientific Research (Netherlands Polar Project 851.20.046) provided financial support to V.S. The New Zealand Foundation for Research Science and Technology Coasts and Oceans Outcome Based Investment funded P.W.B. This study is also a contribution to the Surface Ocean-Lower Atmosphere Study international research initiative and the European Net work of Excellence EUR-OCEANS (Contract 511106-2).

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1st AuthorHassler, C.AuthorHassler, C.Schoemann, V.Nichols, C.Butler, E.Boyd, P.Year2011JournalProceedings of the National Academy of Sciences of the United States of AmericaVolume108Number3Pages1076-1081DOI10.1073/pnas.1010963108URLhttps://www.scopus.com/inward/recor.....b2a5b4e47a59318c9233ea647Keywordscarbohydrateglucuronic acidironmonosaccharidesurface water, articlebacterioplanktonbioavailabilitybiogeochemistrybiotaconcentration (parameters)diatomeukaryoteHaptophytanatural populationnonhumanphytoplanktonplanktonpriority journalseasolubility, Antarctic RegionsBiological AvailabilityDiatomsGlucuronic AcidIronLigandsMass SpectrometryModels, BiologicalMonosaccharidesOceans and SeasPhytoplankton, BacillariophytaEukaryotaHaptophyceae, rank1Author KeywordsCarbohydratesExopolymeric substancesOrganic matterPlanktonTrace metals

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TypeArticleCitationHassler, C., Schoemann, V., Nichols, C., Butler, E. and Boyd, P. (2011). Saccharides enhance iron bioavailability to southern ocean phytoplankton. Proceedings of the National Academy of Sciences of the United States of America, 108(3): 1076-1081 IdentifierHassler2011Relevancerank1