| Understanding the process of biodegradation of aromatic hydrocarbons in anaerobic aquifers requires an understanding of both the chemical and microbial factors of the environment. There are continuous interactions between these two factors. However, how the microbial community responds when anthropogenic pollutants enter a system or when exogenous electron acceptors are added for remediation is largely unknown. The objective of this dissertation research was to begin establishing links between the microbial populations and specific modifications of the environment. The unique aspect of these experiments was the attempt to link benzene, toluene, ethylbenzene and xylene (BTEX) degradation and nitrate-reduction, with changes in the microbial community composition.; Microcosms were used to study the chemical and microbial processes in a controllable laboratory environment. Both hydrocarbon amendment and electron acceptor availability altered the microbial community structure. However, the effects appeared to be dependent on the location that the sediment had originated from or on the conditions of the microcosm assembly. Comparison of the microbial communities from microcosms amended with toluene and/or nitrate with phylogenetic probes and chemical analyses showed that both toluene and nitrate stimulated microbial activity, but only the former has a significant effect on community structure at the phylum/subclass level.; In a second microcosm experiment, TEX degradation was detected only in microcosms amended with nitrate. A molecular community profile, generated by a combination of denaturant gradient gel electrophoresis and 16S rRNA gene sequencing, was identified in the microcosms amended with nitrate and nitrate + BTEX that was different from the microcosms amended only with BTEX. This nitrate specific profile presumably included organisms that were enriched by nitrate, and possibly those involved with TEX degradation.; Collectively, this research has demonstrated that microbial population changes do occur in sediment microcosms amended with nitrate or BTEX. Many of the microbial groups that were identified here were similar to organisms found at other anaerobic, contaminated, aquifer sites, indicating that some microbial populations may be indicative of environmental conditions at geographically distinct locations. These microbes would make good targets for monitoring the impacts of contamination and remediation on microbial communities in situ. |
