Characterization of microbial communities associated with anaerobic reductive dechlorination of polychlorinated biphenyls in river sediments

Microbial anaerobic dechlorination renders polychlorinated biphenyls (PCBs) less toxic and more biodegradable. Microbial communities from two PCB contaminated river sediments, the Grasse River (NY) and the Hudson River (NY) sediments were studied to compare their dechlorination activities and other biogeochemical properties associated with reductive dechlorination of PCBs. To (1) test the hypothesis that changes in nutrient amendment may alter microbial dechlorination activities, and (2) characterize the population diversity of dechlorinator communities, 40-ppm 2,4,5-trichlorobiphenyl (BZ-29) spiked (nutrient amended) river sediment microcosms, and 16S rDNA clone libraries were studied in this research.; Although current analytical methods did not distinguish these two river sediments by most of their nutrient contents or their total aerobic heterotroph population size, the sediment microcosms from the Grasse River and the Hudson River had distinct soil characteristics, gas production activities, and PCB dechlorination rates. In no nutrient amendment, clay-like Grasse River sediment microcosms, the production of methane and carbon dioxide was very active, but the dechlorination did not occur until after a lag period, during which a substantial mount of carbon dioxide and methane had been accumulated in the headspace. Dechlorination of 4o-ppm BZ-29 took place approximately after seven to 12 weeks of anaerobic incubation in Grasse River sediment microcosms without any nutrient amendment. Conversely, the no nutrient amendment, granular and rocky Hudson River sediment microcosms anaerobically dechlorinated PCBs at a relatively faster rate, which could be detected within seven weeks of incubation. No production of methane or any considerable amount of carbon dioxide was found in the headspace of these Hudson River sediment microcosms.; All nutrient amendment types tested in this study resulted in an enhancement of dechlorination in Grasse River sediment microcosms. In Hudson River sediment microcosms, however, enhanced dechlorination was observed in samples amended with organic phosphate (P), organic carbon (F: formic acid and acetate), nitrogen plus organic carbon (NF), organic phosphate plus carbon (PF), and all three nutrient (NPF) amendments; while inhibition in dechlorination of BZ-29 was found in Hudson River sediment microcosms amended with nitrogen alone (N), or nitrogen plus phosphate (NP). These results suggested that (1) both Grasse River and Hudson River sediments examined in this study were likely to be carbon-poor sediments, and (2) PCB-dechlorinators could possibly metabolize nitrogen and thus bypass (the necessity of) PCB-dechlorination.