A Dehalococcoides-dominated culture coupling reductive dechlorination of tetrachloroethene (PCE) to ethene to growth was enriched from a European field site for the first time. Microcosms were set up using groundwater from a chlorinated ethene-contaminated anaerobic aquifer in Bitterfeld (Germany). Active, lactate-amended microcosms capable of PCE dechlorination to ethene without the accumulation of intermediates were used for further enrichment. After three transfers on lactate as an electron donor and PCE as an electron acceptor, the enrichment was transferred to parallel cultures with one of the chlorinated ethenes as an electron acceptor and acetate and hydrogen as the carbon and energy source, respectively. After three more transfers, a highly purified culture was derived that was capable of dechlorinating PCE with hydrogen and acetate as the electron donor and carbon source, respectively. PCR, followed by denaturing gradient gel electrophoresis, cloning and sequencing revealed that this culture was dominated by a Dehalococcoides sp. belonging to the Pinellas group. Investigation of substrate specificity in the parallel cultures suggested the presence of a novel Dehalococcoides that can couple all dechlorination steps, from PCE to ethene, to energy conservation. Quantitative real-time PCR confirmed growth with PCE, cis-dichloroethene, 1,1-dichloroethene or vinyl chloride as electron acceptors. The culture was designated BTF08 due to its origin in Bitterfeld.

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The dechlorination rate in a flow-through porous matrix can be described by the species specific dechlorination rate observed in a liquid batch unless mass transport limitations prevail. This hypothesis was examined by comparing dechlorination rates in liquid batch with that in column experiments at various flow rates (3 -9 -12 cm d -1 ). Columns were loaded with an inoculated sand and eluted with a medium containing 1 mM trichloroethene (TCE) for 247 days. Dechlorination in the column treatments increased with decreasing flow rate, illustrating the effect of the longer residence time. Zero th order TCE or cis-DCE degradation rates were 4-7 fold larger in columns than in corresponding batch systems which could be explained by the higher measured Geobacter and Dehalococcoides numbers per unit pore volume in the columns. The microbial numbers also explained the variability in dechlorination rate among flow rate treatments marked by a large elution of the dechlorinating species' yield as flow increased. Stop flow events did not reveal mass transport limitations for dechlorination. We conclude that flow rate effects on reactive transport of TCE in this coarse sand are explained by residence time and by microbial transport and that mass transport limitations in this porous matrix are limited.

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