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Selenium speciation and partitioning within Burkholderia cepacia biofilms formed on α-Al2O3 surfaces |
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| Authors: | Alexis S Templeton Thomas P Trainor Gordon E Brown Jr |
| Institution: | 1 Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94035-2115, USA 2 Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60439, USA 3 Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA 4 Stanford Synchrotron Radiation Laboratory, SLAC, MS 99, 2575 Sand Hill Road, Menlo Park, CA 94025, USA |
| Abstract: | The distribution and speciation of Se within aerobic Burkholderia cepacia biofilms formed on α-Al2O3 (1-102) surfaces have been examined using grazing-angle X-ray spectroscopic techniques. We present quantitative information on the partitioning of 10−6 M to 10−3 M selenate and selenite between the biofilms and underlying alumina surfaces derived from long-period X-ray standing wave (XSW) data. Changes in the Se partitioning behavior over time are correlated with microbially induced reduction of Se(VI) and Se(IV) to Se(0), as observed from X-ray absorption near edge structure (XANES) spectroscopy.Selenite preferentially binds to the alumina surfaces, particularly at low Se], and is increasingly partitioned into the biofilms at higher Se]. When B. cepacia is metabolically active, B. cepacia rapidly reduces a fraction of the SeO32− to red elemental Se(0). In contrast, selenate is preferentially partitioned into the B. cepacia biofilms at all Se] tested due to a lower affinity for binding to the alumina surface. Rapid reduction of SeO42− by B. cepacia to Se(IV) and Se(0) subsequently results in a vertical segregation of Se species at the B. cepacia/α-Al2O3 interface. Elemental Se(0) accumulates within the biofilm with Se(VI), whereas Se(IV) intermediates preferentially sorb to the alumina surface.B. cepacia/α-Al2O3 samples incubated with SeO42− and SeO32− when the bacteria were metabolically active result in a significant reduction in the mobility of Se vs. X-ray treated biofilms. Remobilization experiments show that a large fraction of the insoluble Se(0) produced within the biofilm is retained during exchange with Se-free solutions. In addition, Se(IV) intermediates generated during Se(VI) reduction are preferentially bound to the alumina surface and do not fully desorb. In contrast, Se(VI) is rapidly and extensively remobilized. |
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