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  • Full Terms & Conditions of access and use can be found athttp://www.tandfonline.com/action/journalInformation?journalCode=ugmb20

    Download by: [Penn State University] Date: 17 February 2016, At: 13:12

    Geomicrobiology Journal

    ISSN: 0149-0451 (Print) 1521-0529 (Online) Journal homepage: http://www.tandfonline.com/loi/ugmb20

    Interactions between Fe(III)-oxides and Fe(III)-phyllosilicates during microbial reduction 1:Synthetic sediments

    T. Wu, R.K. Kukkadapu, A.M. Griffin, C.A. Gorski, H. Konishi, H. Xu & E.E.Roden

    To cite this article: T. Wu, R.K. Kukkadapu, A.M. Griffin, C.A. Gorski, H. Konishi, H.Xu & E.E. Roden (2015): Interactions between Fe(III)-oxides and Fe(III)-phyllosilicatesduring microbial reduction 1: Synthetic sediments, Geomicrobiology Journal, DOI:10.1080/01490451.2015.1117546

    To link to this article: http://dx.doi.org/10.1080/01490451.2015.1117546

    Accepted author version posted online: 15Dec 2015.

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  • ACCEPTED MANUSCRIPT

    ACCEPTED MANUSCRIPT 1

    Interactions between Fe(III)-oxides and Fe(III)-phyllosilicates during microbial

    reduction 1: Synthetic sediments

    T. Wu1, R.K. Kukkadapu

    2, A.M. Griffin

    3, C.A. Gorski

    3, H. Konishi

    1, H. Xu

    1 and E.E. Roden

    1*

    1University of Wisconsin, Department of Geoscience, 1215 W. Dayton Street, Madison, WI

    53707

    2 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory,

    Richland, WA 99354

    3Pennsylvania State University, Department of Civil and Environmental Engineering, 231F

    Sackett Building, University Park, PA 16802

    *Address correspondence to Eric E. Roden, University of Wisconsin, Department of Geoscience,

    Madison, WI 53706; E-mail eroden@geology.wisc.edu

    Abstract

    Fe(III)-oxides and Fe(III)-bearing phyllosilicates are the two major iron sources utilized as

    electron acceptors by dissimilatory iron-reducing bacteria (DIRB) in anoxic soils and sediments.

    Although there have been many studies of microbial Fe(III)-oxide and Fe(III)-phyllosilicate

    reduction with both natural and specimen materials, no controlled experimental information is

    available on the interaction between these two phases when both are available for microbial

    reduction. In this study, the model DIRB Geobacter sulfurreducens was used to examine the

    pathways of Fe(III) reduction in Fe(III)-oxide stripped subsurface sediment that was coated with

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    different amounts of synthetic high surface area goethite. Cryogenic (12K) 57

    Fe Mssbauer

    spectroscopy was used to determine changes in the relative abundances of Fe(III)-oxide, Fe(III)-

    phyllosilicate, and phyllosilicate-associated Fe(II) (Fe(II)-phyllosilicate) in bioreduced samples.

    Analogous Mssbauer analyses were performed on samples from abiotic Fe(II) sorption

    experiments in which sediments were exposed to a quantity of exogenous soluble Fe(II)

    (FeCl22H2O) comparable to the amount of Fe(II) produced during microbial reduction. A Fe

    partitioning model was developed to analyze the fate of Fe(II) and assess the potential for abiotic

    Fe(II)-catalyzed reduction of Fe(III)-phyllosilicates. The microbial reduction experiments

    indicated that although reduction of Fe(III)-oxide accounted for virtually all of the observed bulk

    Fe(III) reduction activity, there was no significant abiotic electron transfer between oxide-

    derived Fe(II) and Fe(III)-phyllosilicatesilicates, with 26-87% of biogenic Fe(II) appearing as

    sorbed Fe(II) in the Fe(II)-phyllosilicate pool. In contrast, the abiotic Fe(II) sorption experiments

    showed that 41 and 24% of the added Fe(II) engaged in electron transfer to Fe(III)-phyllosilicate

    surfaces in synthetic goethite-coated and uncoated sediment. Differences in the rate of Fe(II)

    addition and system redox potential may account for the microbial and abiotic reaction systems.

    Our experiments provide new insight into pathways for Fe(III) reduction in mixed Fe(III)-

    oxide/Fe(III)-phyllosilicate assemblages, and provide key mechanistic insight for interpreting

    microbial reduction experiments and field data from complex natural soils and sediments.

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    Introduction

    Iron (Fe) redox cycling plays a major role in the biogeochemistry of soils, sediments, and

    aquifers (Schmidt et al., 2010). Fe(III) reduction is driven by dissimilatory iron-reducing bacteria

    (DIRB), which couple the reduction of various types of Fe(III) mineral phases to organic carbon

    and hydrogen oxidation (Lovley et al., 2004). Microbial Fe(III) reduction influences numerous

    important environmental processes including carbon and energy flow and the mobility of

    nutrients and toxic heavy metals (e.g. Roden and Wetzel, 1996; Roden and Edmonds, 1997;

    Thamdrup, 2000; Islam et al., 2004; Dubinsky et al., 2010).

    Insoluble Fe(III)-oxide minerals are common sources of Fe(III) for DIRB in soils and

    sediments (Cornell and Schwertmann, 1996). Various mineralogical properties such as surface

    area, crystallinity, and mineral aggregation influence the rate and extent of Fe(III) oxide

    reduction (Roden and Zachara, 1996; Zachara et al., 1998; Roden, 2003, 2006b; Cutting et al.,

    2009). In addition, sorption of biogenic Fe(II) to the surface of non-reacted Fe(III)-oxide and

    DIRB cell surfaces may limit the extent of oxide reduction (Roden and Urrutia, 2002b).

    Advective removal of aqueous Fe(II) as well as the presence of aqueous and solid-phase Fe(II)

    chelators can stimulate microbial Fe(III)-oxide reduction by preventing or delaying Fe(II)

    sorption to oxide and DIRB cell surfaces (Roden and Urrutia, 1999b; Urrutia et al., 1999; Roden

    et al., 2000).

    It is also known that DIRB can reduce structural Fe(III) in phyllosilicate minerals, e.g.

    nontronite and other types of smectites (Kostka et al., 1996; Stucki and Kostka, 2006; Dong et al.,

    2009; Stucki, 2011). The rate and extent of microbial reduction of Fe(III)-phyllosilicatesilicate

    (referred to hereafter as Fe(III)-phyllosilicate) are primarily controlled by the properties of the

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    phyllosilicates. The site of Fe(III) in the phyllosilicate structure can affect its susceptibility to

    microbial reduction (Jaisi et al., 2005a). Furthermore, there have been several studies revealing

    that mineralogical factors strongly influenced microbial reduction of model phyllosilicates. For

    example, the extent of microbial reduction was positively correlated to the proportion of smectite

    in illite-smectite mixed interlayer minerals (Bishop et al., 2011; Liu et al., 2012; Zhang et al.,

    2012). Phyllosilicate thermodynamic properties also may exert a primary control on Fe(III)-

    phyllosilicate reduction microbial clay reduction: Luan et al. (Luan et al., 2014; Luan et al.,

    2015a; Luan et al., 2015b) recently showed that DIRB can only reduce structural Fe(III) in

    phyllosilicates to a set reduction potential, after which reduction is no longer thermodynamically

    favorable.

    While the studies mentioned above have investigated numerous key aspects of the

    microbial reduction of Fe(III)-oxides or Fe(III)-phyllosilicate by DIRB, comparatively few have

    examined the controls on Fe(III)-oxide and Fe(III)-phyllosilicate reduction when both phases are

    present. Recent Mssbauer spectroscopic studies have shown that absorbed Fe(II) can react with

    model Fe(III)-phyllosilicate mineral (NAu-1 and NAu-2 nontronite) surfaces, resulting in partial

    reduction of the phyllosilicate and the formation of Fe(III) oxide phases such as lepidocrocite or

    goethite (Schafer et al., 2011; Neumann et al., 2013). These findings have important implications

    for interpretation of Fe(III)-phyllosilicate reduction in soils and sediments where Fe(III)-oxides

    are also available for microbial reduction: Fe(II) produced from Fe(III)-oxide reduction could

    abiotically reduce Fe(III)-phyllosilicate surfaces, with the oxide-derived Fe functi

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