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Formation of Fe(III)-minerals by Fe(II)-oxidizing photoautotrophic bacteria

Kappler, Andreas and Newman, Dianne K. (2004) Formation of Fe(III)-minerals by Fe(II)-oxidizing photoautotrophic bacteria. Geochimica et Cosmochimica Acta, 68 (6). pp. 1217-1226. ISSN 0016-7037. doi:10.1016/j.gca.2003.09.006.

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It has been suggested that Fe(II)-oxidizing photoautotrophic bacteria may have catalyzed the precipitation of an ancient class of sedimentary deposits known as Banded Iron Formations. In order to evaluate this claim, it is necessary to define and understand this process at a molecular level so that putative Fe-isotope "biosignatures" in ancient rocks can be interpreted. In this report, we characterize the substrates and products of photoautotrophic Fe(II)-oxidation by three phylogenetically distinct Fe(II)-oxidizing bacteria. In every case, dissolved Fe(II) is used as the substrate for oxidation, and there is no evidence for active dissolution of poorly soluble Fe(II)-minerals by biogenic organic ligands. Poorly crystalline Fe(III) (hydr)oxide mineral phases are initially precipitated, and as they age, rapidly convert to the crystalline minerals goethite and lepidocrocite. Although the precipitates appear to associate with the cell wall, they do not cover it entirely, and precipitate-free cells represent a significant portion of the population in aged cultures. Citrate is occasionally detected at nanomolar concentrations in all culture fluids, whereas an unknown organic molecule is always present in two out of the three bacterial cultures. Whether these molecules are released by the cell to bind Fe(III) and prevent the cell from encrustation by Fe(III) (hydr)oxides is uncertain, but seems unlikely if we assume Fe(II)-oxidation occurs at the cell surface. In light of the energetic requirement the cell would face to produce ligands for this purpose, and given the local acidity metabolically generated in the microenvironment surrounding Fe(II)-oxidizing cells, our results suggest that Fe(III) is released in a dissolved form as an inorganic aqueous complex and/or as a colloidal aggregate prior to mineral precipitation. The implication of these results for the interpretation of Fe-isotope fractionation measured for this class of bacteria (Croal et al., 2004) is that equilibrium processes involving free biological ligands do not account for the observed fractionation.

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Newman, Dianne K.0000-0003-1647-1918
Additional Information:© 2004 Elsevier Ltd. Received June 5, 2003; accepted in revised form September 3, 2003. We thank B. Schink and F. Widdel for supplying the strains used in this study, C. Ma for assistance with the XRD and SEM, R. Mielke for taking the TEMs, N. Dalleska for assistance with the LC-MS and IC, and Laura Croal and Mariu Hernandez for many stimulating discussions and helpful comments. This work was supported by a post doctoral fellowship to A.K. from the German Research Foundation (Deutsche Forschungsgemeinschaft) and by grants to D.K.N. from the Packard Foundation. We would also like to thank anonymous reviewers for their constructive comments and suggestions.
Funding AgencyGrant Number
German Research Foundation (DFG)UNSPECIFIED
Packard FoundationUNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20130313-135113949
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Official Citation:Andreas Kappler, Dianne K Newman, Formation of Fe(III)-minerals by Fe(II)-oxidizing photoautotrophic bacteria, Geochimica et Cosmochimica Acta, Volume 68, Issue 6, 15 March 2004, Pages 1217-1226, ISSN 0016-7037, 10.1016/j.gca.2003.09.006.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37504
Deposited By: Tony Diaz
Deposited On:20 Mar 2013 16:34
Last Modified:09 Nov 2021 23:29

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