The aim of this study was to evaluate and optimize the detection of Dehalococcoides, the only group of bacteria reported so far that reductively dechlorinates tetrachloroethene to ethene. Samples were taken from microcosms and groundwater of two tetra- and trichloroethene-contaminated sites differing significantly in their pollutant profiles. At the Killisfeld site, cis-1,2-dichloroethene, vinyl chloride and ethene are detected in the plume indicating complete reductive dechlorination. At the Frankenthal site, cis-1,2-dichloroethene is predominating and ethene is not detected. The sensitivity of Dehalococcoides detection by 16S-PCR (polymerase chain reaction) in groundwater was increased by optimizing the DNA-extraction and the protocols for direct and nested PCR. Direct PCR made the visualization of Dehalococcoides growth during complete degradation of tetrachloroethene in microcosms possible. With nested PCR Dehalococcoides were detected in all seven groundwater samples taken in the plume from the Killisfeld site, but not in any of eleven samples taken at the Frankenthal site. Thus, 16S-PCR detection of Dehalococcoides represents a quick and easy means to assess the potential of complete reductive dechlorination in microcosms and field samples.

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