In situ biostimulation of uranium reducing microorganisms at the Old Rifle UMTRA site (Colorado)

Bioremediation is a promising strategy for cleaning up heavy metal and radionuclide contamination. Nutrient or electron donor amendment is an increasingly accepted practice used to stimulate the growth of microorganisms capable of immobilizing dissolved uranium in situ, but there is scant understanding of the systematic effects of nutrient addition on indigenous microbial populations or the progress of the bioremediation. Successful implementation of metal and radionuclide bioremediation in heterogeneous environments requires an understanding of the complex microbial and geochemical interactions that influence the redox speciation and mobility of toxic metals. The major challenge in microbial ecology and biogeochemistry is to connect observed biogeochemical processes to the microbial populations responsible for carrying them out. This thesis thus investigated the effects of electron donor addition to indigenous microbial populations actively involved in uranium bioremediation. Stable Isotope Probing (SIP) technique for environmental application was developed and established. A microcosm study was designed in parallel to a field biostimulation test at the Old Rifle, UMTRA site.; In the microcosm study that simulated Rifle in situ biostimulation of uranium reducing organisms, the microbial community dynamics were analyzed quantitatively and qualitatively using Phospholipid Fatty-acid Analysis (PLFA) and Denaturing Gradient Gel Electrophoresis (DGGE) analysis combined with SIP, which was modified to accommodate low biomass environmental samples. The microcosms consisted of sediment and groundwater from the Rifle, Colorado UMTRA site and activated carbon bead microbial traps (Biosep beads). 13C labeled acetate amended and non-amended microcosms were compared. Lipid analyses showed a significant biomass increase with acetate amendment, specifically monounsaturated PLFA. The data also demonstrated a community shift in acetate-amended microcosms, mirroring the observation of DGGE analysis. The bacterial community in non-amended microcosms showed notable differences from those amended with acetate. beta-proteobacterial sequences dominated the non-amended community. Furthermore, 13C DNA analysis indicated that acetate treatment encouraged the growth of Gram-negative microorganisms such as Pseudomonas, Geobacter, and sulfate reducing bacteria (SRB). (Abstract shortened by UMI.)...