Complete reductive dechlorination of chloroethenes to ethene and isolation of Dehalococcoides sp. strain BAV1

The chlorinated solvents tetrachloroethene (PCE) and trichloroethene (TCE) are among the most pervasive groundwater contaminants due to their widespread use as organic solvents and degreasing agents. Natural biotic and abiotic processes acting on PCE and TCE at contaminated sites lead to the accumulation of dichloroethenes (DCEs) and vinyl chloride (VC), causing DCEs and VC to become ubiquitous groundwater pollutants in the United States and worldwide. VC was detected in at least 496 of the 1,430 National Priority List (NPL) sites identified by the U.S. Environmental Protection Agency (EPA). VC is toxic and carcinogenic, and hence is a priority drinking water pollutant. Noticeably, VC frequently accumulates during the degradation of polychlorinated ethenes in anoxic and reduced environments. Thus, an anaerobic process that leads to complete detoxification would be most effective to achieve in situ remediation. Substantial information is available that describes bacteria capable of utilizing polychlorinated ethenes as metabolic electron acceptors; however, the populations isolated so far are incapable of dechlorinating VC metabolically. To shed light on the microbiology involved in the final dechlorination step and to support future field applications, isolating organisms that efficiently reduce VC to ethene and characterizing their physiologies and phylogenies are priority goals.; In order to evaluate the most promising electron donors to stimulate complete reductive dechlorination to the nontoxic product ethene, a study was conducted with Bachman microcosms and dechlorinating enrichment cultures. Experimental results revealed that either acetate alone or H₂ alone can be sufficient to promote complete reductive dechlorination of VC to the benign product ethene.; After more than 30 consecutive transfers of the VC-dechlorinating Bachman enrichment culture, focus was placed on characterizing the physiology and phylogeny of the dechlorinating population(s). The enrichment culture dechlorinated VC to ethene at rates up to 54 μmol liter−1 day −1 with pyruvate as the source of reducing equivalents at temperatures between 22–30°C. DCEs were also dechlorinated by the VC-enrichment culture; however, this enriched culture could only cometabolize PCE and TCE to cis-DCE. 16S rRNA gene-based tools identified the dechlorinating population as a Dehalococcoides population, and Dehalococcoides-targeted quantitative real-time PCR confirmed VC-dependent growth of this organism. (Abstract shortened by UMI.)...