Collection and detection of natural iron-binding ligands from seawater |
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| Institution: | 1. FI-TRACE, Departamento de Química, Universidad de las Islas Baleares, Palma, Balearic Islands 07122, Spain;2. Laboratori Interdisciplinar sobre Canvi Climátic. Universidad de las Islas Baleares, Palma, Balearic Islands 07122, Spain;3. Department of Ecology and Coastal Management, Andalusian Institute for Marine Science, ICMAN (CSIC), Campus Universitario Río San Pedro, Puerto Real, Cádiz, Spain;4. National Institute of Oceanography, Dona Paula, Goa, India;5. Alfred-Wegener-Institut Helmholtz Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany;1. University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, P.O. Box 38, Solomons, MD 20688, USA;2. National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA;1. University of Geneva, Faculty of Science, Earth and Environmental Sciences, Institute F.-A. Forel, Marine and Lake Biogeochemistry, 10 rte de Suisse, 1290 Versoix, Switzerland;2. University of Technology Sydney, Plant Functional Biology and Climate Change Cluster, PO Box 123, Broadway 2007, NSW, Australia;3. CSIRO Materials Science and Engineering, c/o CSIRO Marine and Atmospheric Research, PO Box 1538, Hobart 7001, TAS, Australia;4. CSIRO Ocean and Atmosphere, PO Box 1538, Hobart 7001, TAS, Australia;5. Laboratory of Glaciology, Université Libre de Bruxelles, CP 160/03 Avenue F.D. Roosevelt, 50, B-1050 Bruxelles, Belgium;1. Department of Biochemistry and Microbiology, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada;2. School of Earth and Ocean Sciences, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada;3. Institute of Ocean Sciences, Department of Fisheries and Oceans, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada |
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| Abstract: | Iron (Fe) is an essential element for the biochemical and physiological functioning of terrestrial and oceanic organisms, including phytoplankton, which are responsible for the primary productivity in the world's oceans. However, due to the low solubility of Fe in seawater, phytoplankton are often limited by their inability to incorporate enough Fe to allow for optimal growth rates in regions with dissolved Fe concentrations below 1 nM. It has been postulated that certain phytoplankton may produce compounds to facilitate the uptake of Fe from seawater to overcome this limitation. Dissolved Fe in the oceans is overwhelmingly complexed (>99%) by strong organic ligands that may control the uptake of Fe by microbiota; however, the identity, origin, and chemical characteristics of these organic chelates are largely unknown. Although it has been implied that some components of natural Fe-binding ligands are siderophores, no direct analyses of such compounds from natural seawater have been conducted. Here, we present a simple solid-phase extraction technique employing Biobeads SM-2 and Amberlite XAD-16 resins for concentrating naturally occurring dissolved iron-binding compounds from large volumes (>200 l) of seawater. Additionally, we report on the first successful determination of molecular weight size classes and preliminary iron-binding functional group characterization within those size classes for isolates collected from the surface and below the photic zone (150 m) in the central California coastal upwelling system. Electrochemical analyses using competitive ligand equilibration/adsorptive cathodic stripping voltammetry (CLE-ACSV) showed that isolated compounds had conditional Fe-binding affinities (with respect to inorganic iron—Fe′) of KFeL,Fe′cond=1011.5–1011.9 M?1, similar to purified marine siderophores produced in laboratory cultures and to the ambient Fe-binding ligands observed in seawater. In addition, 63% of the extracted compounds from surface-collected samples fall within the defined size range of siderophores (300–1000 Da). Hydroxamate or catecholate Fe-binding functional groups were present in each compound for which Fe binding was detected. These results illustrate that the functional groups previously shown to be present in marine and terrestrial siderophores extracted and purified from laboratory cultures are also present in the natural marine environment. These data provide evidence that a significant fraction of the organic Fe-binding compounds we collected contain Fe-binding functional groups consistent with biologically produced siderophores. These results provide further insight into characteristics of the Fe-binding ligands that are thought to be important in controlling the biological availability of Fe in the oceans. |
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