James Byrne1, Nicole Klueglein1, Carolyn Pearce2, Erwin Appel3, Andreas Kappler1 1Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, 72076, Tuebingen, Germany 2School of Chemistry, The University of Manchester, M13 9PL, Manchester, UK 3Geophysics, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, 72076, Tuebingen, Germany Dissolved Fe(II) and various Fe(II) minerals can be used by Fe(II)-oxidizing bacteria as an electron donor, while Fe(III) present in the form of Fe(III)-complexes or Fe(III) minerals is used by Fe(III)-reducing bacteria as an electron acceptor for energy generation and growth. The mixed-valent iron oxide magnetite (Fe3O4) is often observed as a product of these microbial redox processes. However, despite the widespread abundance of magnetite in soils and sediments, the interaction of Fe(II)-oxidizing and Fe(III)-reducing bacteria with this mineral is not well studied. Here we present magnetic, mineralogical and spectroscopic data that shows that phototrophic and nitrate-reducing Fe(II)-oxidizing bacteria (Rhodopseudomonas palustris strain TIE-1 and Paracoccus denitrificans) can oxidize magnetite particles of different size and crystallinity, resulting in a significant decrease in magnetic susceptibility and stoichiometry (Fe(II)/Fe(III) ratio) to ca. 0.42, suggesting the use of magnetite as electron donor. Furthermore we show that this process can be reversed by Fe(III)-reducing bacteria (Geobacter sulfurreducens and Shewanella oneidensis MR-1) which re-reduce the magnetite to a reduced redox state, leading to increasing magnetic susceptibility and Fe(II)/Fe(III) ratio of up to ca. 0.52 suggesting the possible use of the mineral as an electron donor. This process is seen to be repeatable over several cycles of oxidation/reduction using the same magnetite. In summary these results show that iron ions bound in highly crystalline mineral magnetite are bioavailable for microbes for both electron stores and electron sinks under varying environmental conditions, making magnetite a potential “biogeobattery” during either day/night or oxic-anoxic redox cycles.

Biogeobattery: Redox cycling of Fe(II) and Fe(III) in magnetite by Fe-metabolizing bacteria

249th National Meeting (2015)

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