title: Size dependent microbial oxidation and reduction of magnetite nano- and micro-particles.
abstract: The ability for magnetite to act as a recyclable electron donor and acceptor for Fe-metabolizing bacteria has recently been shown. However, it remains poorly understood whether microbe-mineral interfacial electron transfer processes are limited by the redox capacity of the magnetite surface or that of whole particles. Here we examine this issue for the phototrophic Fe(II)-oxidizing bacteria Rhodopseudomonas palustris TIE-1 and the Fe(III)-reducing bacteria Geobacter sulfurreducens, comparing magnetite nanoparticles (d ≈ 12 nm) against microparticles (d ≈ 100-200 nm). By integrating surface-sensitive and bulk-sensitive measurement techniques we observed a particle surface that was enriched in Fe(II) with respect to a more oxidized core. This enables microbial Fe(II) oxidation to occur relatively easily at the surface of the mineral suggesting that the electron transfer is dependent upon particle size. However, microbial Fe(III) reduction proceeds via conduction of electrons into the particle interior, i.e. it can be considered as more of a bulk electron transfer process that is independent of particle size. The finding has potential implications on the ability of magnetite to be used for long range electron transport in soils and sediments.
authors: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, 72076, Tuebingen, Germany.
authors: James M
authors: JM
authors: Byrne
authors: Magnetic Spectroscopy Group, Diamond Light Source, Didcot, OX11 0DE, UK.|Williamson Research Centre for Molecular Environmental Science, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK.
authors: Gerrit
authors: G
authors: van der Laan
authors: Magnetic Spectroscopy Group, Diamond Light Source, Didcot, OX11 0DE, UK.
authors: Adriana I
authors: AI
authors: Figueroa
authors: Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors: Odeta
authors: O
authors: Qafoku
authors: Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors: Chongmin
authors: C
authors: Wang
authors: Pacific Northwest National Laboratory, Richland, WA 99352, USA.|School of Chemistry, The University of Manchester, M13 9PL, Manchester, UK.
authors: Carolyn I
authors: CI
authors: Pearce
authors: Institute for Rock Magnetism, University of Minnesota, 291 Shepherd Labs, 100 Union Street SE, MN 55455, Minneapolis, USA.
authors: Michael
authors: M
authors: Jackson
authors: Institute for Rock Magnetism, University of Minnesota, 291 Shepherd Labs, 100 Union Street SE, MN 55455, Minneapolis, USA.
authors: Joshua
authors: J
authors: Feinberg
authors: Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors: Kevin M
authors: KM
authors: Rosso
authors: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, 72076, Tuebingen, Germany.
authors: Andreas
authors: A
authors: Kappler
mesh_terms: D004579:Electron Transport; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D045302:Geobacter / Q000502:physiology*; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D058185:Magnetite Nanoparticles / Q000737:chemistry*; D008863:Microspheres; D008903:Minerals; D010084:Oxidation-Reduction; D010316:Particle Size; D012241:Rhodopseudomonas / Q000502:physiology*
chemical_list: D058185:Magnetite Nanoparticles; D008903:Minerals; D007501:Iron; D052203:Ferrosoferric Oxide