Complete Detoxification of Vinyl Chloride by an Anaerobic Enrichment Culture and Identification of the Reductively Dechlorinating Population as a Dehalococcoides Species

Abstract

ABSTRACT A major obstacle in the implementation of the reductive dechlorination process at chloroethene-contaminated sites is the accumulation of the intermediate vinyl chloride (VC), a proven human carcinogen. To shed light on the microbiology involved in the final critical dechlorination step, a sediment-free, nonmethanogenic, VC-dechlorinating enrichment culture was derived from tetrachloroethene (PCE)-to-ethene-dechlorinating microcosms established with material from the chloroethene-contaminated Bachman Road site aquifer in Oscoda, Mich. After 40 consecutive transfers in defined, reduced mineral salts medium amended with VC, the culture lost the ability to use PCE and trichloroethene (TCE) as metabolic electron acceptors. PCE and TCE dechlorination occurred in the presence of VC, presumably in a cometabolic process. Enrichment cultures supplied with lactate or pyruvate as electron donor dechlorinated VC to ethene at rates up to 54 μ mol liter −1 day −1 , and dichloroethenes (DCEs) were dechlorinated at about 50% of this rate. The half-saturation constant ( K S ) for VC was 5.8 μ M, which was about one-third lower than the concentrations determined for cis -DCE and trans -DCE. Similar VC dechlorination rates were observed at temperatures between 22 and 30°C, and negligible dechlorination occurred at 4 and 35°C. Reductive dechlorination in medium amended with ampicillin was strictly dependent on H 2 as electron donor. VC-dechlorinating cultures consumed H 2 to threshold concentrations of 0.12 ppm by volume. 16S rRNA gene-based tools identified a Dehalococcoides population, and Dehalococcoides -targeted quantitative real-time PCR confirmed VC-dependent growth of this population. These findings demonstrate that Dehalococcoides populations exist that use DCEs and VC but not PCE or TCE as metabolic electron acceptors.