Abstract Details
| Parameters Controlling the Partitioning and Speciation of Trace Metal(loid)s at the Shewanella oneidensis MR-1 Biofilm/Mineral/Water Interface | |
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| Abstract ID | ENV-08 |
| Presenter | Yingge Wang |
| Presentation Type | Poster |
| Full Author List | Y. Wang (1) , A. Gelabert (1) , Y. Choi (2) , J. Ha (1) , J. Gescher (3) , J. R. Bargar (4) , J. Rogers (4) , P. J. Eng (2) , A. Spormann (3) , G. E. Brown Jr. (1,4) |
| Affiliations | (1) Department of Geological & Environmental Sciences, Stanford University, Stanford, CA 94305, USA (2) GSECARS, University of Chicago, Chicago, IL 60637, USA (3) Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA (4) Stanford Synchrotron Radiation Laboratory, SLAC, Menlo Park, CA 94025, USA |
| Category | Environmental Science |
| Abstract | Surface-attached microbial communities known as microbial biofilms are ubiquitous in natural environments. They are often present as coatings on mineral surfaces in soils and aquatic systems. Compared to bare mineral surfaces, these complex bacterial communities can induce significant changes in surface properties of minerals and sorption capacities for metal(loid) ions. However, such effects are still poorly understood at a molecular level due to the complex nature of these systems and the lack of appropriate tools to accurately probe such interfaces. In this study, long-period X-ray standing wave-florescence yield (XSW-FY) spectroscopy was used to measure in-situ partitioning of trace metal(loid) ions at S. oneidensis MR-1 biofilm-coated a-alumina (0001) and (1-102) and hematite (0001) single crystal surfaces as a function of metal concentration, exposure time, and pH. The competitive sorption effects among various metal ions were also probed by simultaneously exposing biofilm/mineral interfaces to different trace elements. To complement the in-situ XSW-FY measurements, grazing incidence X-ray adsorption fine structure (GI-XAFS) spectroscopic measurements at specific x-ray incidence angles were performed to probe ion speciation and local coordination environment at the mineral surfaces and in the biofilm. In addition, a number of surface characterization techniques including X-ray photoemission spectroscopy (XPS), X-ray reflectivity, atomic force microscopy (AFM), electrokinetic analyzer (EKA), and confocal laser scanning microscopy (CLSM) have been applied to study the properties of clean and biofilm-coated mineral surfaces.
S. oneidensis MR-1 biofilm, a facultative gram-negative bacterium, was grown on clean single crystal surfaces aerobically (10 days) and anaerobically (20 days) under flow-through conditions using minimal defined media and pyruvate as a carbon and energy source. Aqueous metal ions Pb(II) and Zn(II) XSW-FY partitioning profiles at biofilm coated hematite (0001) surfaces under aerobic conditions with concentrations ranging from 10e-4 M to 10e-7 M at pH 6.0 showed that metal ions are preferentially sorbed at mineral surfaces at low concentrations (≤ 10e-6 M) and are increasingly partitioned into biofilms at higher concentrations. However, most of As(V) sorbed at hematite (0001) surfaces for anaerobically grown S. oneidensis biofilm even at high concentration (10e-3 M) and various exposure times (3-40 hours) at pH 7.0. These results confirm that biofilms do not change the intrinsic reactivities of mineral surfaces; instead they provide more sorption sites for metal(loid) ions. Hematite (0001) was found to be the most reactive surface for metal sorption at these complex interfaces followed by a-alumina (1-102) and a-alumina (0001). Significant changes in metal ion XSW-FY profiles at different exposure times (30 minutes, 3 hours, and 20 hours) on fresh samples suggest the existence of diffusion limited processes occurring at the biofilm/mineral interface. Multiple metal ions partitioning at biofilm/mineral interfaces showed that at higher concentrations (>10e-5 M at pH 6.0 and 3 hours of exposure) there are no apparent competitive effects among Pb(II), Zn(II), and other metal ions including Cu(II), Co(II) and Ni(II). However, at lower metal concentrations (≤10e-6 M), longer exposure time (24 hours), and in the presence of additional metal ions, Zn(II) outcompete Pb(II) for metal oxide surface sites. GI-XAFS analysis of Pb(II) at S. oneidensis MR-1 biofilm-coated alumina surfaces indicate that carboxyl groups are responsible for Pb(II) complexation in the biofilm after 3 hours of exposure at pH 6, and no evidence of biomineralization has been found under the tested conditions. The results of this study will provide new insights about the factors controlling trace element partitioning and speciation at complex microbe-mineral interfaces and an improved understanding of the nature of local microenvironments created by the microbial biofilms at mineral surfaces. |
| Footnotes | |
| Funding Acknowledgement | NSF Grant CHE-0431425
Corning graduate fellowship |