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      The Organic Complexation of Iron in the Marine Environment: A Review

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          Abstract

          Iron (Fe) is an essential micronutrient for marine organisms, and it is now well established that low Fe availability controls phytoplankton productivity, community structure, and ecosystem functioning in vast regions of the global ocean. The biogeochemical cycle of Fe involves complex interactions between lithogenic inputs (atmospheric, continental, or hydrothermal), dissolution, precipitation, scavenging, biological uptake, remineralization, and sedimentation processes. Each of these aspects of Fe biogeochemical cycling is likely influenced by organic Fe-binding ligands, which complex more than 99% of dissolved Fe. In this review we consider recent advances in our knowledge of Fe complexation in the marine environment and their implications for the biogeochemistry of Fe in the ocean. We also highlight the importance of constraining the dissolved Fe concentration value used in interpreting voltammetric titration data for the determination of Fe speciation. Within the published Fe speciation data, there appear to be important temporal and spatial variations in Fe-binding ligand concentrations and their conditional stability constants in the marine environment. Excess ligand concentrations, particularly in the truly soluble size fraction, seem to be consistently higher in the upper water column, and especially in Fe-limited, but productive, waters. Evidence is accumulating for an association of Fe with both small, well-defined ligands, such as siderophores, as well as with larger, macromolecular complexes like humic substances, exopolymeric substances, and transparent exopolymers. The diverse size spectrum and chemical nature of Fe ligand complexes corresponds to a change in kinetic inertness which will have a consequent impact on biological availability. However, much work is still to be done in coupling voltammetry, mass spectrometry techniques, and process studies to better characterize the nature and cycling of Fe-binding ligands in the marine environment.

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          Chemistry and biology of siderophores.

          Siderophores are compounds produced by bacteria, fungi and graminaceous plants for scavenging iron from the environment. They are low-molecular-weight compounds (500-1500 daltons) possessing a high affinity for iron(III) (Kf > 1030), the biosynthesis of which is regulated by iron levels and the function of which is to supply iron to the cell. This article briefly describes the classification and chemical properties of siderophores, before outlining research on siderophore biosynthesis and transport. Clinically important siderophores and the therapeutic potential of siderophore design are described. Appendix 1 provides a comprehensive list of siderophore structures.
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            Upper ocean ecosystem dynamics and iron cycling in a global three-dimensional model

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              The biogeochemical cycle of iron in the ocean

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                Author and article information

                Journal
                Front Microbiol
                Front Microbiol
                Front. Microbio.
                Frontiers in Microbiology
                Frontiers Research Foundation
                1664-302X
                28 February 2012
                2012
                : 3
                : 69
                Affiliations
                [1] 1simpleOcean and Earth Science, National Oceanography Centre – Southampton, University of Southampton Southampton, UK
                [2] 2simpleBermuda Institute of Ocean Sciences St. George’s, Bermuda
                Author notes

                Edited by: Benjamin Twining, Bigelow Laboratory for Ocean Sciences, USA

                Reviewed by: Sylvia G. Sander, University of Otago, New Zealand; Alessandro Tagliabue, Council for Scientific and Industrial Research, South Africa

                *Correspondence: Martha Gledhill, Ocean and Earth Science, National Oceanography Centre – Southampton, University of Southampton, Southampton SO14 3ZH, UK. e-mail: martha@ 123456soton.ac.uk ; Kristen N. Buck, Bermuda Institute of Ocean Sciences, Ferry Reach, St. George’s GE 01, Bermuda. e-mail: kristen.buck@ 123456bios.edu

                Martha Gledhill and Kristen N. Buck have contributed equally to this work.

                This article was submitted to Frontiers in Microbiological Chemistry, a specialty of Frontiers in Microbiology.

                Article
                10.3389/fmicb.2012.00069
                3289268
                22403574
                37214bb7-8ec8-4062-98c8-347401f7b653
                Copyright © 2012 Gledhill and Buck.

                This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.

                History
                : 14 November 2011
                : 09 February 2012
                Page count
                Figures: 4, Tables: 2, Equations: 2, References: 149, Pages: 17, Words: 16429
                Categories
                Microbiology
                Review Article

                Microbiology & Virology
                exopolymeric substances,seawater,humic substances,ligands,nanoparticles,colloids,siderophores,speciation

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