HR: 1340h
AN: B33A-0857    [Abstracts]
TI: Comparative Effects of Electron Transfer Mediators on the Bioreduction of Fe(III) Oxide
AU: * O'Loughlin, E J
EM: oloughlin@anl.gov
AF: Argonne National Laboratory, Biosciences Division, Building 203 Room E-154, 9700 S. Cass Avenue, Argonne, IL 60439, United States
AB: The transfer of electrons from microbes to sparingly-soluble, extracellular electron acceptors such as Fe(III) oxides can occur via direct contact with the mineral surface, by dissolution of the mineral facilitated by exogenous or endogenous ligands and subsequent reduction of the dissolved Fe(III) ligand complex, and by facilitated electron transfer involving endogenous or exogenous electron transfer mediators (ETMs, also commonly referred to as electron shuttles) that are reduced by the microbes and then subsequently diffuse away from the cell and transfer electrons to the Fe(III) mineral surface, regenerating the oxidized form of the ETM. This study examines the effects of a series of compounds representing major classes of natural and synthetic organic ETMs (including low molecular-mass quinones, humic substances, phenazines, phenoxazines, phenothiazines, and indigo derivatives) on the bioreduction of lepidocrocite (γ-FeOOH) by the dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens CN32. S. putrefaciens CN32 was able to reduce lepidocrocite in the absence of exogenous ETMs; however, relative to the control, all of the synthetic ETMs examined in this study enhanced the bioreduction of lepidocrocite. The extent of the enhanced bioreduction increased with decreasing reduction potential of the given ETM redox couple. However, the addition of Suwannee River fulvic acid, humic acid, or unfractionated NOM (10 mg organic C L^-1) resulted in, at best, a minimal enhancement of lepidocrocite bioreduction relative to the control that did not contain any added exdogenous ETM. These results suggest that the relative contribution of humic substances to microbially mediated Fe(III) reduction may be minimal in low-carbon environments such as oligotrophic lakes and typical groundwaters.
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 0461 Metals
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0471 Oxidation/reduction reactions (4851)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting