HR: 11:50h
AN: B12A-07    [Abstracts]
TI: Influence of Arsenic on the Reduction of Lepidocrocite and Hydroxycarbonate Green Rust 1 Into Ferrous-Carbonate Hydroxide by Shewanella putrefaciens
AU: * Ona-Nguema, G
EM: onanguem@stanford.edu; georges.ona-nguema@impmc.jussieu.fr
AF: Surface & Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, 367 Panama Street, Stanford, CA 94305-2115, United States
AU: * Ona-Nguema, G
EM: onanguem@stanford.edu; georges.ona-nguema@impmc.jussieu.fr
AF: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR7590, CNRS, Universités Paris 6&7, IPGP, 140, rue de Lourmel, Paris, 75015, France
AU: Morin, G
EM: guillaume.morin@impmc.jussieu.fr
AF: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR7590, CNRS, Universités Paris 6&7, IPGP, 140, rue de Lourmel, Paris, 75015, France
AU: Wang, Y
EM: yuheng@impmc.jussieu.fr
AF: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR7590, CNRS, Universités Paris 6&7, IPGP, 140, rue de Lourmel, Paris, 75015, France
AU: Juillot, F
EM: farid.juillot@impmc.jussieu.fr
AF: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR7590, CNRS, Universités Paris 6&7, IPGP, 140, rue de Lourmel, Paris, 75015, France
AU: Abdelmoula, M
EM: mustapha.abdelmoula@lcpme.cnrs-nancy.fr
AF: Laboratoire de Chimie Physique et Microbiologie pour l'Environnement (LCPME), UMR 7564 CNRS, Université Nancy 1, 405, rue de Vandœuvre, Villers-lès-Nanc, 54600, France
AU: Ruby, C
EM: christian.ruby@lcpme.cnrs-nancy.fr
AF: Laboratoire de Chimie Physique et Microbiologie pour l'Environnement (LCPME), UMR 7564 CNRS, Université Nancy 1, 405, rue de Vandœuvre, Villers-lès-Nanc, 54600, France
AU: Guyot, F
EM: guyot@impmc.jussieu.fr
AF: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR7590, CNRS, Universités Paris 6&7, IPGP, 140, rue de Lourmel, Paris, 75015, France
AU: Calas, G
EM: georges.calas@impmc.jussieu.fr
AF: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR7590, CNRS, Universités Paris 6&7, IPGP, 140, rue de Lourmel, Paris, 75015, France
AU: Brown, G
EM: gordon@pangea.stanford.edu
AF: Surface & Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, 367 Panama Street, Stanford, CA 94305-2115, United States
AU: Brown, G
EM: gordon@pangea.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, SLAC, MS 69, 2575 Sand Hill Road, Menlo Park, CA 94025, United States
AB: Shewanella putrefaciens, an iron-respiring bacterium, is capable of reducing As(V) to As(III) when HAs(V)O₄^2- is the sole electron acceptor, or when it is adsorbed on the surface of lepidocrocite (γ-FeOOH), a common well-crystallized hydromorphic soil mineral. Cultures in which lepidocrocite was used as the sole electron acceptor (i.e., pure lepidocrocite and As(III)-adsorbed lepidocrocite) led to the formation of biogenic hydroxycarbonate green rust 1 (GR1) prior to precipitation of ferrous-carbonate hydroxide (FCH). However, the presence of As(III) slowed down the biotransformation of hydroxycarbonate GR1 into FCH, leading to the co-occurrence of both phases after 22-month of aging. In contrast, when the electron acceptor was As(V)- bearing lepidocrocite, XRD analysis revealed FCH to be the dominant reaction product; no green rust formation was observed in this case. Arsenic K-edge XANES spectroscopy indicated that all As(V) (K-edge(max) = 11875.0eV) was reduced to As(III) (K-edge(max) = 11871.3eV), suggesting the presence of As(III) either on the surface of FCH, and/or in another ferrous-containing solid phase. Mössbauer analysis of the 22-month aged biogenic sample obtained from the bioreduction of As(III)-adsorbed lepidocrocite revealed the presence of FCH (80%) and GR (20%). In contrast, Mössbauer spectra of white biogenic solid phases resulting from the bioreduction of As(V)-adsorbed lepidocrocite and of pure lepidocrocite were characterized by ferrous iron doublets. These spectra indicate that the white biogenic sample without arsenic contains 100% Fe(II) assigned to FCH, while the white biogenic As(III)-Fe(II)-containing reaction products consists of 87% FCH and of 13% of another ferrous phase, probably an As(III)-Fe(II)-containing compound. These results show for the first time bacterial reduction of stoichiometric hydroxycarbonate green rust 1.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
DE: 0489 Trace element cycling (4875)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting