Characterization of an anaerobic microbial community in a TCE-contaminated aquifer and the degradation of TCE by Pantoea agglomerans

A fractured basalt aquifer at the Idaho National Engineering and Environmental Laboratory-Test Area North (INEEL-TAN) in southeast Idaho is the site of a nearly two-mile long trichloroethylene (TCE) contaminant plume. As part of an effort to evaluate the feasibility of applying bioremediation techniques at TAN, organisms potentially responsible for naturally attenuating or remediating the site were identified. Culture-based and molecular biology methods were used to investigate planktonic and attached anaerobic subsurface microbial communities. Many organisms were identified representing twenty-two different genera, ten by culture-based methods and twelve by direct identification using molecular biology methods. These results confirmed the presence of a diverse eubacteria community within this oligotrophic, but contaminated subsurface system. One of the identified organisms, Pantoea agglomerans, was capable of partially degrading 0.2 mM of PCE or 0.5 mM of TCE in about 7 days. Many attempts were made to achieve complete degradation of TCE by adjusting the medium. Although some increases in TCE degradation were observed, most of the increases were not significantly different from the baseline performance. We were unable to ascertain why only partial TCE degradation occurred.; Molecular biology techniques were used to observe changes in the microbial community during a field scale application of enhanced in situ bioremediation of a TCE contaminated groundwater plume located INEEL-TAN. Dramatic shifts in the dominant microbial species following sodium lactate injection into the TCE plume were observed and were attributed to the onset of reducing conditions, which were induced by the presence of lactate and its fermentation products (propionate and acetate). Although reductive dehalogenation of TCE was observed during the in-situ study, none of the organisms identified have been documented as capable of reductive dechlorination.