Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A459

Modification of hematite surfaces during colonization by a dissimilatory

Fe(III) reducing bacterium under controlled hydrodynamic conditions G.G. GEESEY1, G. GONZALEZ-GIL2, J.E. AMONETTE3,

M.F. ROMINE3 AND Y.A. GORBY3

1Department of Microbiology, Montana State University, Bozeman, MT 59717-3520, USA (gill_g@erc.montana.edu)

2Swiss Federal Institute of Technology (ETH), Zurich, Institute of Terrestrial Ecology-Soil Biology, Grabenstrasse 3, CH-8952, Schlieren, Switzerland (gonzalez-gil@ito.unmw.ethz.ch)

3Pacific Northwest national Laboratory, P.O. Box 999, Richland, WA, USA (jim.amonette@pnl.gov, margie.romine@pnl.gov, yuri.gorby@pnl.gov) The influence of biofilm development by Fe(III)-reducing

bacteria on the structure and chemistry of specular hematite was evaluated under conditions that simulated saturated subsurface conditions to obtain a better understanding of biological transformations of minerals in subsurface environments. An open, hydrodynamically-controlled reactor described previously (1) was used to follow non-destructively in real time hematite surface colonization by cells of the dissimilatory iron reducing bacterium (DIRB) Shewanella oneidensis MR-1 when the hematite was the sole electron acceptor in the system.

Accumulation of cells on the hematite surface was accompanied by the release of soluble Fe(II) into the flowing aqueous phase when no precautions were taken to remove amorphous Fe(III) from the mineral surface before inoculation. No soluble Fe(II) was detectable in the aqueous phase during surface colonization when the mineral surface was treated with citrate-bicarbonate-dithionite (CBD) to remove amorphous Fe(III) before inoculation of the surface with cells. Hematite reduction by the surface-associated bacteria led to localized surface pitting and localized discrete areas where Fe(II) precipitation occurred. The cleavage plane of hematite left behind after bacterial Fe(III) reduction suggests that heterogeneous energetics of the mineral surface play a strong role in this bioprocess.

Dissolution, precipitation, and Fe(III) reduction in experimental systems

with nontronite (NAu-1) and Shewanella oneidensis MR-1

S.E. O’REILLY1, YOKO FURUKAWA1, BARRY BICKMORE2, JINWOOK KIM1, JAN WATKINS1,

AND STEVEN NEWELL 1

1Naval Research Laboratory, Seafloor Sciences Branch, Stennis Space Center, Mississippi 39529, USA (eoreilly@nrlssc.navy.mil)

2Department of Geology, Brigham Young University, Provo, UT 84602-4606 We investigated interactions between nontronite (NAu-1)

and facultative dissimilatory iron reducing bacteria (DIRB), Shewanella oneidensis, in aqueous environments using flow-through and batch experimental systems. The evolution of major structural components of NAu-1 (i.e., Fe, Al, and Si) were monitored along with an in-depth series of control experiments. Solid phase analyses included solid Fe speciation, morphology and crystal structure using atomic force microscopy (AFM) and transmission electron microscopy (TEM), as well as elemental compositions using TEM energy dispersive X-ray spectroscopy. The effluent solution analyses indicated that ≈ 9.35 % of Si and 0.18 % of Fe present in the original NAu-1 were transferred to and remained in solution during the seven-day flow experimental run, whereas the Al concentrations in aqueous solution remained below detection limits and batch experiments showed similar results. Up to 7 mol % of Fe in the original NAu-1 was reduced to Fe(II) and remained in solid. Control experiments showed that Si was found in solution regardless of the presence or absence of microbial Fe reduction activities. Ratios of Si, Al, and Fe in solution, released from the clay, were not stoichiometric to the clay, whereas crystal morphology observed with AFM suggested stoichiometric dissolution. Solid analysis using TEM showed the precipitation of siderite (FeCO3) in anaerobic, reduced systems, amorphous silica associated with bacteria cells (regardless of activity) and extracellular polymeric substances, amorphous aluminosilicates in both aerobic and Fe(III)-respiring systems, and Al and Si associated with bacterial cells. Bulk thermodynamic calculations confirmed that siderite precipitation is controlling the reduced, anaerobic system. The systems were undersaturated with respect to amorphous silica, amorphous aluminum hydroxide, and halloysite except for aerobic experiments.

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A460

Nanoscale environments associated with bioweathering of a

Mg-Fe-pyroxene K. BENZERARA1,2, T.-H. YOON1, N. MENGUY2,

F. GUYOT2, T. TYLISZCZAK3 AND G. E. BROWN, JR.1,4

1Surface & Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115

2Laboratoire de Minéralogie-Cristallographie, Universite Paris 7, Paris, France (benzerar@lmcp.jussieu.fr)

3Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA.

4Stanford Synchrotron Radiation Laboratory, SLAC, 2575 Sand Hill Road, Menlo Park, CA 94025, USA Microorganisms are believed to create microenvironments

leading to reaction products not predictable from equilibrium thermodynamics and to unique biomineral morphologies. Unambiguous evidence for such environments is, however, rare in natural samples. We characterize in this study the bioweathering products on a Fe-Mg-orthopyroxene reacted for 70 years under arid conditions in the presence of a filamentous microorganism. An electron transparent cross section of the interface between a single microorganism and an orthopyroxene grain was prepared with a focused ion beam-SEM system and was examined by scanning transmission x-ray microscopy and spectromicroscopy at the sub-40-nm scale, coupled with transmission electron microscopy. A 100 nm deep depression was observed in the orthopyroxene adjacent to the microorganism, suggesting enhanced dissolution of the pyroxene mediated by the microbe. Our measurements reveal an amorphous Al-rich layer beneath the microorganism, calcium carbonates of unique morphology intimately associated with polysaccharides adjacent to the microorganism, and regions surrounding the microorganism with different iron oxidation states. Our results confirm the presence of different microenvironments at this microorganism-mineral interface and provide unique nanometer-scale views of microbially controlled pyroxene weathering products.

Scanning electrochemcial microscopy (SECM) studies on microbial metal respiration using Pt/Hg amalgam

microelectrodes D. RUDOLPH1, D. BATES2, T. DICHRISTINA2,

B. MIZAIKOFF1 AND C. KRANZ1

1School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, U.S.A. (douglas.rudolph@chemistry.gatech.edu, boris.mizaikoff@chemistry.gatech.edu, christine.kranz@chemistry.gatech.edu)

2School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, U.S.A. (gt1281b@prism.gatech.edu, thomas.dichristina@biology.gatech.edu)

The bioavailability and in-situ detection of dissolved

chemical species such as Mn2+ and Fe2+ is attracting increasing interest for understanding the environmental and geological chemical reactions at the microbe-mineral interface. A versatile and promising tool for the investigation metal distributions at a microscopic scale is scanning electrochemical microscopy (SECM) in combination with square wave voltammetry (SWASV) performed at platinum/mercury amalgam microelectrodes [1].

In this contribution, we present the application of Pt/Hg amalgam electrodes in SECM detecting and imaging redox activity of iron-reducing proteins separated from shewanella species in native agarose gels. SECM enables for the first time a spatially resolved direct read-out of redox activity from proteins, which can not be easily stained. SECM approach curves to the gel were performed positioning the electrode in close proximity above the protein bands after calibration of the Pt/Hg microelectrodes in bulk solution for the targeted analytes (Fe2+, Mn2+). First SECM data on the determination of spatially resolved Mn2+ and Fe2+ concentrations produced by microbial protein bands in a gel buffered at mildly acidic conditions with Pt/Hg microdisk electrodes will be presented. Recently, we combined atomic force microscopy and electrochemical microscopy by integrating micro- and nanoelectrodes into an AFM cantilever [2], which will in future be applied to the determination of bacterial redox activity with high lateral resolution.

References [1] Rudolph D., Neuhuber S., Kranz C., Taillefert M., and

Mizaikoff B., (2004), Analyst 129, 443-448. [2] Kranz C., Friedbacher G., Mizaikoff B., Lugstein A.,

Smoliner J., and Bertagnolli E., (2001), Anal. Chem. 73, 2491-2500.

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A461

Nanoparticulate bacteriogenic manganese oxides: Environmental reactivity and stuctural chemistry

J.R. BARGAR1, C.C. FULLER2, S.M WEBB1, AND B.M. TEBO3

1Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Rd., Menlo Park, CA 94025, USA bargar@ssrl.slac.stanford.edu, samwebb@slac.stanford.edu)

2US Geological Survey, Water Resources Division, 345 Middlefield Rd, Menlo Park, CA 94025, USA (ccfuller@usgs.gov)

3Scripps Institute of Oceanography, La Jolla, CA 92037, USA (btebo@ucsd.edu) Bacteriogenic Mn oxides occur throughout (sub-)oxic

marine and freshwater environments. These reactive natural materials serve as the primary sinks and sources for Mn(II), which plays a major role in photosynthesis, and profoundly impact ground water chemistry via their ability to sequester metals, oxidize a variety of recalcitrant organic and inorganic compounds, and act as terminal electron acceptors for microbial respiration. We seek to understand the key factors that control the reactivity of these reactive materials in aquatic environments.

Mn oxide production by Bacillus sp., strain SG-1 has been studied in-situ in sea water, fresh water, and in the presence of metal contaminants using synchrotron-based wide-angle x-ray scattering (WAXS), X-ray absorption spectroscopy (XAS), and complementary techniques, and has been compared to Mn biooxides collected at field sites. Laboratory studies indicate the initial Mn oxide product is a sub-nanoparticulate hexagonal phyllomanganate, which is highly reactive and transforms to more stable secondary phases (including c-disordered birnessite and feitknechtite) in response to thermodynamic driving forces. Bacteriogenic Mn oxides from Pinal Creek, AZ and the Black Sea generally follow predictions based on our laboratory-based investigations. The bacteriogenically-derived Mn oxides can incorporate a surprisingly diverse number of metals into their structures, including copper(II), cobalt(II, III), zinc(II) and even uranium(VI). Thus, particle size, a propensity for mineralogic transformations, and a highly flexible solid-state structural chemistry appear to be fundamentally important to the interface between linked environmental cycles of Mn and other important elements.

Mössbauer spectroscopy of extracellular tabular magnetite

formed during microbial iron reduction

Y.-L. LI1, C. L. ZHANG1, H. VALI2, D. R. COLE3 AND T. J. PHELPS3

1Savannah River Ecology Laboratory and Univ. Georgia, Aiken, SC 29803, USA (Li@SREL.edu, zhang@srel.edu)

2Dept. Anatomy Cell Biol., McGill Univ., Montreal, QC, Canada H3A 2B2. (vali@eps.mcgill.ca)

3Oak Ridge Natl. Lab., Oak Ridge, TN 37831, USA (coledr@ornl.gov, phelpstj@ornl.gov) Mössbauer spectroscopy was employed to elucidate the

transformation processes of nano-scale iron oxides by Geobacter metallireducens strain GS-15. During dissimilatory iron reduction, the quadrupole splittings and line widths of Fe(III) decreased systematically and a structural ordering of the crystallographic sites of iron took place, consistent with mineralogical transformation from ferrihydrite to magnetite with lepidocrocite as an intermediate phase (Fig. 1). We propose a solid-state conversion mechanism for this transformation, which would allow magnetite to inherit the tabular- and lath-like morphologies of the lepidocrocite precursor. Results of this study suggest that unusual forms of magnetite can be formed by a unique combination of chemical and biological processes during reduction of iron oxides. The results also support our TEM observation of the tabular magnetite formed by the same bacterium (Vali et al. PNAS 101, 16121-16126, 2004).

0 .7 5

0 .8 0

0 .8 5

0 .9 0

0 .9 5

1 .0 0

0 .7 6

0 .8 0

0 .8 4

0 .8 8

0 .9 2

0 .9 6

1 .0 0

-8 - 6 - 4 - 2 0 2 4 6 8 1 00 .8 8

0 .9 0

0 .9 2

0 .9 4

0 .9 6

0 .9 8

1 .0 0

F e 3 +

0 H o u r a t R .T .

Abs

orpt

ion

F e r r ih y d r it e

F e 3 +

1 2 5 H o u r s a t R .T .

Abs

orpt

ion

L e p id o c r o c it e

F e 3 +

F e 2 .5 +

5 8 1 H o u r s a t R .T .

M a g n e t i t e

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A462

The fleeting (bio)availability of ferrihydrite

COLLEEN M. HANSEL AND SCOTT FENDORF Geological and Environmental Sciences, Stanford University,

Stanford, CA 94305, USA (hansel@stanford.edu) Within non-sulfidogenic, anaerobic sediments, the

majority of Fe reduction is thought to occur via bacterial Fe(III) respiration. Due to its high solubility and intrinsic reactivity, ferrihydrite (Fe(OH)3⋅nH2O) is considered the most bioavailable Fe (hydr)oxide for dissimilatory iron-reducing bacteria, allegedly resulting in the preservation of more crystalline phases within mature sediments. Here we illustrate that ferrihydrite may have a less significant role in both early and long-term microbial reduction and Fe phase transformations than currently deemed.

Reduction of ferrihydrite-coated sand under advective flow by Shewanella putrefaciens results in the secondary mineralization of ferrihydrite to goethite (α-FeOOH) and magnetite (Fe3O4). The mineralization of ferrihydrite occurs via a coupled biotic-abiotic reaction pathway such that bacterial-generated ferrous Fe reacts abiotically with the ferrihydrite surface. Conversion of ferrihydrite upon abiotic reaction with aqueous Fe(II), however, proceeds through a lepidocrocite (γ-FeOOH) precursor, ultimately resulting in the formation of goethite and magnetite. The residence time and extent of lepidocrocite precipitation, being a function of Fe(II) concentration and complexing ligand, dictates the ensuing secondary mineralization pathways.

Upon the onset of ferrihydrite reduction, a rapid pulse of Fe(II) generation and ferrihydrite conversion occurs followed by slower sustained rates consistent with those of more crystalline phases (e.g. goethite). Moreover, reduction of natural Fe(III)-coated sands by S. putrefaciens within minimal media under advective flow results in the preferential consumption of more recalcitrant Fe (hydr)oxide phases relative to ferrihydrite. Instead, ferrihydrite is converted to hematite (α-Fe2O3), most likely a consequence of sorbed and/or coprecipitated ions decreasing the solubility of ferrihydrite therefore favoring internal ordering to hematite rather than dissolution/ reprecipitation to lepidocrocite. Thus, the reactivity and reducibility of ferrihydrite is transient (i.e., conversion to lepidocrocite) and/or compromised (e.g. ion substitution) suggesting that the generation of Fe(II), ensuing secondary mineralization pathways, and subsequent reducing capacity of sediments will be controlled by more crystalline phases ultimately imposing limitations on the rates of microbial respiration.

Coupling biogeochemical Fe(III) oxide reduction and contaminant

transformation NICOLE B. TOBLER, THOMAS B. HOFSTETTER,

DANIELA FONTANA AND RENÉ P. SCHWARZENBACH Swiss Federal Institute of Environmental Science and

Technology (EAWAG) and Swiss Federal Institute of Technology (ETH), Dübendorf, Switzerland, (nicole.tobler@eawag.ch, thomas.hofstetter@eawag.ch, schwaba@eawag.ch) In anoxic environments, dissimilatory Fe(III) mineral

reduction may generate reactive, surface bound Fe(II) species, which are capable of reducing organic and inorganic conta-minants. Despite extensive studies on microbial strategies of Fe(III) mineral transformation and on abiotic contaminant reduction, respectively, only few studies addressed the environmentally relevant, coupled process. Current knowledge suggests that the bioavailability of Fe(III) minerals is inversely correlated with the reactivity of adsorbed Fe(II) species towards contaminant transformation. To this end, we examined the environmental conditions that favor the occurrence of the coupled process, e.g., the influence Fe(III) mineral type and Fe(II) surface concentration on the rates of nitroaromatic compound (NAC) reduction in suspensions of pure cultures of G. metallireducens.

We observed the highest rates of contaminant reduction in batch assays where two iron oxides were present simultaneously, i.e., amorphous ferrihydrite as microbial electron acceptor and lepidocrocite as sorbent for reactive Fe(II). Pseudo-first order rate constants of NAC reduction were almost identical to those obtained in abiotic reference experiments in the absence of microorganisms confirming that surface bound Fe(II) was the predominant reductant. In contrast, NAC reduction was up to two orders of magnitude slower when only ferrihydrite was present in the assays. Over the entire pH-range investigated (6.8 - 7.5) increasing reduction rate constants correlated well with the higher concentrations of adsorbed Fe(II). We found that in the presence of G. metallireducens, non-reactive Fe(II) species exist. Despite significant amounts of adsorbed Fe(II), no contaminant reduction was observed in the absence of dissolved Fe(II) suggesting that dissolved Fe(II) is essential for the regeneration of reactive Fe(II). Our results highlight that contaminant reduction in anoxic environments by Fe(II) species strongly depends on the phase distribution and bioavailability of Fe(III) minerals.

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A463

Green rust formation under anaerobic nitrate-dependent Fe(II)

oxiding conditions KARRIE A. WEBER1, JUERGEN THIEME2,

PHILIP LARESE-CASANOVA3, MICHELLE SCHERER3, LAURIE A. ACHENBACH4 AND JOHN D. COATES1

1University of California, Berkeley, CA 94720 2University of Goettingen, Goettingen, Germany 3University of Iowa, Iowa City, IA 52242 4Southern Illinois University, Carbondale, IL 62901

Recent studies have suggested that both oxidative and

reductive microbial Fe metabolisms result in the formation of a mixed valence, layered Fe(II)/Fe(III) hydroxide with anion interlayers known as green rust (GR), however, the extent of either process is unknown. Green rust is predominantly identified in hydromorphic soils and sediments. The contribution of anaerobic nitrate-dependent Fe(II) to iron redox cycling provides an ideal mechanism of GR formation given that microorganisms capable of this metabolism are ubiqitous. Given that nitrate-dependent Fe(II) oxidizing bacteria are ubiquitous as identified by most probable number enumeration, as high as 1.47 x 104 cells (g sediment)-1 in freshwater lake sediment, 2.04 x 103cells mL-1 in groundwater, and 1.17 x 103 cells (g sediment)-1 in subsurface sediment, and contributes to anaerobic iron redox cycling. Furthermore, a novel autotrophic, nitrate-dependent Fe(II)-oxidizing bacterium, Cosmobacter millennium strain 2002, yields a mixed phase Fe(II)/Fe(III) mineral phase, identified as green rust by Mössbauer spectroscopy and X-Ray diffraction. In contrast to the GR biogenically formed by Fe(III) reduction, the biogenic GR product formed via nitrate-dependent Fe(II) oxidation by C. millennium strain 2002 did not yield transformation products, i.e., magnetite. X-Ray fluorescence spectroscopy identified chloride and phosphate in association with the GR product. Furthermore, anion analysis of the GR by ion chromatography indicated that 6 mg SO4

2-, 32 mg Cl-, and 66 mg PO4

3- was associated with the oxidation of 111 mg Fe(II). These results suggest that GR(Cl-1) was formed. It is currently unknown whether phosphate is adsorped to the GR surface or intercalated into the interlayer. These results represent the first demonstration of the biogenic formation of green rust in significant quantities providing evidence for the biological mechanism for the production of GR(Cl-) in soils and sediments.

Coupling sulfide production and arsenic release in dynamic systems

ANDREW QUICKSALL, SAMANTHA SAALFIELD, CARL E. RENSHAW AND BENJAMIN C. BOSTICK

Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, USA (quicksall@dartmouth.edu, saalfield@dartmouth.edu; renshaw@dartmouth.edu; bbostick@dartmouth.edu)

Iron (hydr)oxides are a common constituent of clay-rich

soils to which toxic metals and metalloids readily adsorb. The influence of microbial populations on the speciation of such adsorbed metals and metalloids under reducing conditions is not well understood. Information of such processes will aide in the understanding of the mobility and retention of toxic metals and metalloids

We have examined arsenic remobilization in a series of column experiments using synthetic mineral suspensions and/or natural sediments from an uncontaminated, though arsenic-impacted, region of Cambodia. Here, we focus on arsenic release induced by the presence of dissolved sulfide production. As(III) and As(V) were adsorbed to ferrihydrite-coated sand within the columns and then reacted with a variety of solutions. These Fe-As systems were subjected to various flow rates, sulfide concentrations and microbial populations in replicate columns. Results indicate that arsenic and iron underwent considerable changes in speciation, and that arsenic mobility was significantly influenced by the presence of sulfide. At relatively high sulfide acitivities, iron reduction was observed without measurable arsenic release, while arsenic was released to a limited extent under conditions of slow flow and/or low sulfide activities. Changes in mineralogy were identified using X-ray absorption spectrosopy, and the mechanism of As retention also changed rapidly during sulfidization.

For Cambodian sediments, sulfate reduction also was stimulated in situ, and the results contrasted with sterilized controls. Community analysis, using 16S rDNA, was used to identify potential dominant microbial populations capable of reducing arsenic, iron and sulfur. Solid phase analysis using X-ray absorption methods also identified changes in mineralogy and to characterized As retention.

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A464

In-situ biological reduction of uranium within fractured saprolite

MATTHEW GINDER-VOGEL1, WEI-MIN WU2, BAOHUA GU3, JACK CARLEY3, JENNIFER NYMAN2,

CRAIG CRIDDLE2, PHIL JARDINE3 AND SCOTT FENDORF1

1Department of Geological and Environmental Science, Stanford University, Stanford, CA, USA

2Department of Civil and Environmental Engineering, Stanford University, Stanford, CA, USA

3Oak Ridge National Laboratory, Oak Ridge, TN, USA (gindervm@stanford.edu)

In-situ immobilization of heavy metals, such as uranium,

through biological reduction is a promising means for stabilizing contaminants within subsurface sediments. Species of U(VI) are highly mobile in groundwater systems while those of U(IV) are only sparingly soluble. Stimulation of biological uranium reduction at the field scale presents several challenges, including heterogeneous sediment mineralogy, a complex and evolving community of bacteria, and the presence of multiple electron donors and acceptors. The NABIR field research center at Oak Ridge National Laboratory is additionally complex owing to U concentrations of 1,000 ppm, pH values less than 3.4, and exceedlingly high concentrations of nitrate (> 0.1 M) and aluminum (> 0.01 M).

Here we present evidence of biological uranium reduction in a series of experiments of increasing complexity. First, uranium reduction was investigated in batch experiments using radionuclide-contaminated sediment from ORNL that were inoculated with a denitrifying bacterial community. Next, a packed column was used to mimic uranium reduction under field conditions. Finally, subsurface biological uranium reduction was stimulated at the field scale.

Successful stimulation of biological uranium reduction was accomplished in all experimental systems. However, even after long-term stimulation of biological activity, approximately 50% of uranium within the solid phase remained oxidized [U(VI)]. Furthermore, uranium(IV) was rapidly oxidized after the cessation of electron donor and exposure to air or other oxidants (NO3

-). These factors complicate the long-term immobilization of uranium through in-situ stimulation of biological activity.

Discerning geochemical and biogeochemical metal reduction

through gamma sterilization T.L. BANK1, P.M. JARDINE1, M. GINDER-VOGEL2,

S.E. FENDORF2 AND M.E. BALDWIN3

1Environmental Sciences Division, Oak Ridge National Lab, P.O. Box 2008, Oak Ridge, TN 37831-6038, USA (banktl@ornl.gov) (jardinepm@ornl.gov)

2Dept. of Geological and Environmental Sciences, Stanford Univ., Stanford, CA 94305-2115, USA (gindervm@pangaea.stanford.edu) (fendorf@stanford.edu)

3Nuclear Science and Technology Division, Oak Ridge National Lab, P.O. Box 2008, Oak Ridge, TN 37831-6227, USA (baldwinme@ornl.gov) The adsorption of U(VI) and Cr(VI) onto sterilized and

nonsterilized soil from the Oak Ridge Reservation was studied to distinguish biogeochemical versus geochemical effects on metal reduction. The Oak Ridge soil under investigation is a saprolite sequence of interbedded weathered shale and limestone with a pH near 7.6. Dried, crushed soil was sterilized using a Cobalt-60 source and a γ-ray dosage of 20kGy. Sterilization was greater than 99.99% successful.

U(VI) and Cr(VI) adsorption was studied through sterile and nonsterile batch shake reactions over a period of 3 days to 3 weeks. Absorption was studied over a U(VI) concentration range from 0.5-10 ppm and a Cr(VI) range from 0.5-50 ppm. Ethanol was used as an electron donor and an organic carbon source in all sterile and nonsterile experiments.

Results indicate that both U(VI) and Cr(VI) reduction decreases in sterilized reactions compared to the nonsterile soils. U(VI) adsorption coefficients (U kD) decrease by as much as 25% in sterile soils while Cr(VI) kD decrease up to 50%. The chemical environment and valence state of the adsorbed Cr and U species are being investigated by X-ray absorption spectroscopy (XAS). Investigations are underway to determine whether changes in metal adsorption are due to biogeochemical events or are caused by geochemical changes in the soil resulting from the sterilization technique.

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A465

Microbial transformation of iron oxide to sulfide species on steel

immersed in seawater JIZHOU DUAN1 AND BAORONG HOU2

1Department of Chemisry and Chemical Engineering, Ocean University of China, No.5 Yushan Road, Qingdao 266003, China (duanjz2002@yahoo.com.cn)

2Institute of Oceanology, Chinese Academy of Sciences, No. 7, Nanhai Road, Qingdao 266071, China

Iron oxides and sulfides on steel immersed in seawater

In the current study, rust samples were removed from the steel immersed in seawater in China and analysed with surface observation and element analysis, microbial cultivation and molecular ecology analysis methods. Global iron oxides and hexagonal iron sulfides could be found in the rust (Figure 1). Bacterial cells were also observed in the rust layer.

Fig.1 Glouble iron oxides and hexagonal iron sulfides presented in the rust

Disscussion The sulfate-reducing bacteria (SRB) in the rust have

presented a very high numbers. Especially, some culture mediums also appear pink color after longer incubation course, which indicates dissimilatory iron-reducing bacteria (DIRB) may participate in the mineralisation. The Fe(III) oxides may first reduced by DIRB as the electron acceptor, and further, the iron sulfide species were formed by biotic ferrous ion reacted with the sulfide produced by SRB. Further molecular biological analysis will reveal the ecology characteristics of rust. Conclusion

In the microbial community of rust in seawater, anaerobic DIRB and SRB may participate in the reduction of iron oxides and the formation of iron sulfide species.

References Hamilton W. A., (2003), Biofouling. 19: 65-76.

Rapid precipitation of amorphous silica and aluminum phases

in experimental systems with nontronite (NAu-1) and

Shewanella oneidensis MR-1 YOKO FURUKAWA AND S. ERIN O’REILLY

Naval Research Laboratory, Seafloor Sciences Branch, Stennis Space Center, Mississippi 39529 USA Rapid, microbially mediated formation of amorphous

silica and aluminosilicate phases at the expense of dissolving nontronite was studied in laboratory systems containing nontronite NAu-1, Shewanella oneidensis strain MR-1, and lean aqueous media. The systems were undersaturated with respect to amorphous silica and amorphous aluminum hydroxide throughout the durations of experiments. Experimental runs with dissolved O2 were initially undersaturated with respect to halloysite, a metastable clay mineral often associated with weathering products, but approached saturation during the seven-day runs. Runs in which S. oneidensis was forced to respire Fe(III) from NAu-1 remained undersaturated with respect to halloysite. Amorphous silica precipitation was confirmed in the immediate vicinity of bacterial cells and extracellular polymeric substances in all experimental systems that contained bacteria, whether the bacteria were respiring dissolved O2 or Fe(III) from NAu-1, or were heat-killed prior to the start of experimental runs. Amorphous aluminosilicates were found in both aerobic and Fe(III)-respiring systems. Neither amorphous Si nor aluminosilicates were observed in bacteria-free systems. Our results show that precipitation of amorphous silica and aluminosilicate phases can proceed rapidly in aqueous solutions that are not supersaturated with respect to these phases, and that the presence of bacteria is critical to the precipitation processes. We suggest that “reverse weathering,” the formation of authigenic clay minerals at the expense of dissolving clastic clays, may be more rapid and widespread than currently considered. In addition, our study proposes that the detection of silicified microfossils may not be limited to cherts and stromatolites.

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A466

Minerals and bacteria: Friends or foes?

E. HUTCHENS1, E. VALSAMI-JONES1, S. MCELDOWNEY2 AND ERIC OELKERS3

1The Natural History Museum, Cromwell Road, London SW7 5BD, UK (lilh@nhm.ac.uk; E.Valsami-Jones@nhm.ac.uk)

2University of Westminster, 115 New Cavendish Street, London W1M 8JS, UK (mceldows@westminster.ac.uk)

3Université Paul Sabatier, 38 rue des Trente-Six Ponts, Toulouse,France (oelkers@lmtg.obs-mip.fr) Microorganisms have been demonstrated to acquire

essential nutrients from dissolving minerals at the Earth’s surface and subsurface. There is evidence to suggest that mineral dissolution reactions are accelerated by the presence of heterotrophic bacteria. [1] However, the actual mechanism of microbial accelerated mineral dissolution has yet to be determined.

Dissolution experiments on feldspar and apatite in the presence of B. megaterium, a Gram-positive bacterium, were performed to establish the importance of metal uptake by cells, the impact of bacterial exoproducts on dissolution and the significance of bacterial adhesion to the mineral surfaces. Exopolysaccharides (EPS) and bacterial cells accumulated both, Al and Si. Al was rapidly adsorbed on the cell surface while Si accumulation was a slow process which suggests a possible internal uptake or a strong complexation on the cell surface. Exometabolites and EPS were shown to substantially enhance feldspar dissolution especially in conditions of nutrient limitation. The number of cells attaching to feldspar surfaces varied with type of mineral and growth conditions. We found no convincing evidence of enhanced dissolution induced by attached cells. In fact, a series of experiments performed with apatite, indicate that bacteria can accelerate mineral dissolution rates without their physical attachment to the mineral surfaces. The attachment of microbes on apatite crystals is found to actually limit microbial rate enhancement effects.

Reference [1] Hutchens, E., Valsami-Jones, E., McEldowney, S., Gaze,

W., McLean, J. (2003). Min. Mag., 67(7), 1157-1170.

Arsenic mobilization influenced by iron reduction and sulfidogenesis B. KOCAR, K. TUFANO, Y. MASUI, B. STEWART,

M. HERBEL AND S. FENDORF Dept. of Geological & Environmental Sciences, Stanford, CA

94305, USA (kocar@stanford.edu) Sulfidogenesis and iron reduction are ubiquitous processes

that occur in a variety of anaerobic environments that profoundly impact the cycling of arsenic. Of the iron (hydr)oxides, ferrihydrite possesses one of the highest capacities to retain arsenic and is globally distributed within soils and sediments. Upon dissimilatory iron reduction, ferrihydrite may transform to lower surface area minerals, such as goethite and magnetite, which decreases arsenic retention, thus enhancing its transport. Furthermore, interaction of ferrihydrite with dissolved sulfide may result in the dissociation of sorbed arsenic, followed by the repartitioning of As into reduced iron and/or sulfur solid phases. Here we examine the behavior of arsenate (As(V)) and arsenite (As(III)) in column systems containing ferrihydrite coated sand and bacteria capable of iron, sulfur, and/or arsenate reduction.

Greater quantities of pre-sorbed arsenite, rather than arsenate, eluted from abiotic columns during a one month period of time. In contrast, arsenite elution was attenuated in columns during periods of active iron reduction, suggesting the formation of reduced iron-arsenite solid phases within the columns. Furthermore, the abundance of reduced iron phases was diminished in iron reducing columns containing arsenate rather than arsenite, suggesting an As species dependent role in the transformation of iron (hydr)oxides during active iron reduction. Sulfide genesis mobilized arsenic through desorption mechanisms and possibly via the formation of soluble As-S species during the early stages of diagenesis. Progressive development into a sulfide dominated systems results in the repartitioning of arsenic into the solid phase.

Goldschmidt Conference Abstracts 2005 Microbial Mineral Transformations II

A467

Molecular study of microbial S oxidation in sulfidic sediments

S.L. ROGERS1 AND N. GREY2

1Cooperative Research Centre for Landscape Environments and Mineral Exploration/CSIRO Land & Water, Private Bag 2, Glen Osmond SA 5064, Australia. (steve.rogers@csiro.au)

2CSIRO Land & Water, Private Bag 2, Glen Osmond SA 5064, Australia. (naomi.grey@csiro.au)

Functional Molecular Tools An alternative approach to determining the relationship

between microbial activity and biogeochemical transformations is to target the ‘molecular genetic’ functional attributes of microbial populations (Rogers et al. 2002). We have developed a new generation of molecular biology techniques based on the direct extraction of nucleic acids from regolith samples to quantify functional gene presence and rates of gene expression. Results

In brief, DNA and mRNA were extracted from sulfidic sediments in the River Murray floodplain South Eastern Australia.. Oligonucleotide primers successfully amplified (using polymerase chain reaction [PCR] and reverse transcriptase PCR) soxB gene sequences in sediment DNA and mRNA extracts. The presence and rates of expression of the soxB gene was related to rates of S mineral oxidation reactions. This work forms part of a larger project assessing the impact of River Murray floodplain management on S oxidation/reduction mechanisms and acid sulfate soil formation (Lamontagne et al. 2004).

References Lamontagne, S., Hicks, W.S., Fitzpatrick, R.W. and Rogers S.

(2004). CRC LEME Open File Report 165, Perth WA. 63p.

Rogers S.L. Colloff M. & Gomez D. (2002). Abstracts. 13th Australian Nitrogen Fixation Conference September 24-27 Adelaide, South Australia.

Investigation of the geochemical relationships governing dissimilatory

bacterial reduction of U(VI) from solid uranyl mineral phases

CHRISTOPHER WEISENER1 , ADRIAN FORSYTH1, PETER BURNS2 AND DAVID FOWLE1

1GLIER, University of Windsor, Windsor, Ontario, Canada 2Department of Civil Engineering & Geological Sciences,

University of Notre Dame, Notre Dame, USA.

Hypothesis U(VI) mineral reactivity may differ systematically as a

function of mineral structure and chemical properties in the presence of bacteria. By measuring rates of microbial reductive corrosion for different minerals, and by comparing corrosion rates with quantifiable mineral properties (e.g. solubility, lattice structure, composition), it will be possible to assess the corrosion potential of a variety of U(VI) phases. Results

Preliminary XAFS results show of a shift in the U L3 edge energy for uranyl sulfate minerals to a reduced U species within the first 24 h and continues over 2 weeks (Fig 1.). Desulfovibrio desulfuricans appear to enhance U reduction in low nutrient media captalizing on nutrients derived from the mineral surface. Further reduction by Desulfovibrio desulfuricans occurs after 145 days characterized by an average U oxidation state of U(IV). Bulk XAFS structure shows the gradual development of uraninite as the principle phase.

Figure 1 Comparison of U (L3 edges) XANES and XAFS spectra. After a 145 day microbial exposure Na-zippeite contains features observed in uraninite. Conclusions

Desulfovibrio desulfuricans effect the U(VI)-phase reductive alteration of uranyl sulfate. This leads to changes in compositions and growth habits of the U(VI) protolith and biomineralization of a U(IV) secondary phase (uraninite). The mechanism along with additional solid phase characterization will be discussed.