Structure and Function of Metal- and Nitrate-reducing Microbial Communities in the FRC Subsurface
The overall goal of this study is to evaluate structure-function relationships of sedimentary microbial communities likely to regulate U(VI) reduction and immobilization in the subsurface of Area 2 at the Field Research Center (FRC), Oak Ridge, TN. Microcosm experiments were conducted under near in situ conditions with FRC subsurface materials cocontaminated with high levels of U(VI) and nitrate. The activity, abundance, and community composition of microorganisms was determined in microcosm samples, stimulated with ethanol or glucose, and compared to those from sediment cores and unamended controls. Activity was assessed by monitoring terminal electron accepting processes (TEAPs; nitrate, sulfate, uranium, and iron reduction) as well as electron donor utilization. Microbial functional groups, nitrate- and iron(III)-reducing bacteria, were enumerated during the nitrate- and metal-reduction phases of the incubation and in sediment core samples using a most probable number (MPN) serial dilution assay. U(VI) and Fe(III) were reduced concurrently in the glucose but not the ethanol treatments. In ethanol-amended microcosms, U(VI) was reduced during a 4-day lag phase between nitrate- and Fe(III)-reduction phases. Biostimulation resulted in 3 to 5 orders of magnitude higher counts of Fe(III)-reducing bacteria, whereas populations of nitrate-reducers were enhanced by 1 to 3 orders of magnitude. One to 2 orders of magnitude more Fe(III)-reducers were observed in ethanol- as compared to glucose-amended treatments in parallel with enhanced U(VI) removal in ethanol treatments. Cultivatable Fe(III)-reducing bacteria in the ethanol treatments were dominated by Geobacter sp. while those cultured on glucose were dominated by fermentative organisms, i.e., Tolumonas sp. Currently, carbon substrate utilization is being examined through HPLC analysis of microcosm porewaters. In addition, changes in the overall microbial community composition are being assessed using cultivation-independent techniques, including fluorescence in situ hybridization (FISH), terminal restriction fragment length polymorphism analysis (T-RFLP) and cloning/sequencing of structural and functional genes. Our results indicate that the microbially-catalyzed mechanism of U(VI) reduction is electron donor dependent and that more effective U(VI) removal is achieved in parallel with an enrichment of Geobacter sp. upon treatment with ethanol.
- Research Organization:
- Department of Oceanography, Florida State University, Tallahassee, FL; Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ
- Sponsoring Organization:
- USDOE Office of Science (SC)
- OSTI ID:
- 894678
- Report Number(s):
- CONF-ERSP2006-52; TRN: US200702%%195
- Resource Relation:
- Conference: Annual Environmental Remediation Sciences Program PI Meeting, April 3-5, 2006, Warrenton, VA
- Country of Publication:
- United States
- Language:
- English
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