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Photochemical cycling of iron in the surface ocean mediated by microbial iron(iii)-binding ligands

Nature volume 413, pages 409–413 (2001)Cite this article

Abstract

Iron is a limiting nutrient for primary production in large areas of the oceans1,2,3,4. Dissolved iron(iii) in the upper oceans occurs almost entirely in the form of complexes with strong organic ligands5,6,7 presumed to be of biological origin8,9. Although the importance of organic ligands to aquatic iron cycling is becoming clear, the mechanism by which they are involved in this process remains uncertain. Here we report observations of photochemical reactions involving Fe(iii) bound to siderophores—high-affinity iron(iii) ligands produced by bacteria to facilitate iron acquisition10,11,12. We show that photolysis of Fe(iii)–siderophore complexes leads to the formation of lower-affinity Fe(iii) ligands and the reduction of Fe(iii), increasing the availability of siderophore-bound iron for uptake by planktonic assemblages. These photochemical reactions are mediated by the α-hydroxy acid moiety, a group which has generally been found to be present in the marine siderophores that have been characterized13,14,15. We suggest that Fe(iii)-binding ligands can enhance the photolytic production of reactive iron species in the euphotic zone and so influence iron availability in aquatic systems.

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Figure 1: Schematic representation of the photochemical reaction of Fe(iii)–aquachelin complexes.
Figure 2: Tandem mass spectrometry and UV–visible spectrophotometry of the Fe(iii)–aquachelin peptide photoproduct.
Figure 3: Rate of iron(ii) production during photolysis of Fe(iii)–aquachelin C in natural sunlight, as determined via absorption of the ferrous tris(BPDS) complex at 536 nm.
Figure 4: Biological uptake of iron from photolysed Fe(iii)–aquachelin complexes, and diagram of siderophore-mediated photochemical iron cycling.

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Acknowledgements

This work was supported by the NSF/DOE Environmental Molecular Science Institute (A.B. and K.W.B.), the National Institutes of Health (A.B.) and the University of California President's postdoctoral fellowship program (K.B.).

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Author notes

  1. K. Barbeau

    Present address: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, 92093, USA

Authors and Affiliations

  1. Department of Chemistry and Biochemistry, University of California, Santa Barbara, 93106, California, USA

    K. Barbeau & A. Butler

  2. Institute of Marine Sciences, University of California, Santa Cruz, 95064, California, USA

    E. L. Rue & K. W. Bruland

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  1. K. Barbeau
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  3. K. W. Bruland
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Correspondence to A. Butler.

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Barbeau, K., Rue, E., Bruland, K. et al. Photochemical cycling of iron in the surface ocean mediated by microbial iron(iii)-binding ligands. Nature 413, 409–413 (2001). https://doi.org/10.1038/35096545

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