Many subsurface environments across the United States are contaminated from past xenobiotic discharges, much of it too deep and extensive for conventional methods of remediation. Bacteria might be the best option available for the bioremediation of deep subsurface contamination because of their potential to travel to distant contaminated locations, and their ability through metabolic activities to potentially detoxify or limit the further migration of contaminants. However, relatively little is known about the transport capabilities of injected microorganisms into the subsurface, nor their ability to colonize, survive and grow once they reach locations of distant contamination. A basic understanding of both processes is therefore necessary to design strategies for the use of bacteria in remediation of subsurface environments.; My dissertation research project consisted of two studies related to the ecology of bacteria in subsurface environments. The first study involved analysis of the microbial community diversity of shale and sandstone rocks located 200 meters below Cerro Negro, New Mexico. The objective was to increase our understanding of the microbial ecology of deep subsurface environments typical of many contaminated sites. The second involved studies of short-term temporal transport of bacteria, in laboratory column experiments and in situ injection experiments at a field site in Oyster, Virginia. The objectives were to develop methods of accurately monitoring bacterial transport and to determine the factors that control transport of bacteria in subsurface environments.; In the study of the ecology of the deep subsurface shale/sandstone interface at Cerro Negro, we found that the geochemistry of a site alone is not adequate to predict the types of organisms present. We found a predominance of organisms capable of Fe(III) reduction in an environment where sulfate reducing microbes were expected to dominate based on the geochemistry of the site. Therefore the design of remediation strategies must account for the Fe(III) reducing bacteria. In the Oyster transport study, we were able to demonstrate the in situ transport of adherence-deficient microbes, and their subsequent attachment and growth in aquifer sediments, demonstrating that bioremediation using injected microorganisms was feasible for subsurface contamination.
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