Dehalococcoides ethenogenesStrain 195 Reductively Dechlorinates Diverse Chlorinated Aromatic Pollutants

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Abstract
Dehalococcoides ethenogenes strain 195 dechlorinates tetrachloroethene to vinyl chloride and ethene, and its genome has been found to contain up to 17 putative dehalogenase gene homologues, suggesting diverse dehalogenation ability. We amended pure or mixed cultures containing D. ethenogenes strain 195 with 1,2,3,4-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3-dichlorodibenzo-p-dioxin, 1,2,3,4-tetrachloro-dibenzofuran, 2,3,4,5,6-pentachlorobiphenyl, 1,2,3,4-tetrachloronaphthalene, various chlorobenzenes, or a mixture of 2-, 3-, and 4-chlorophenol to determine the dehalogenation ability. D. ethenogenes strain 195 dechlorinated 1,2,3,4-tetrachlorodibenzo-p-dioxin to a mixture of 1,2,4-trichlorodibenzo-p-dioxin and 1,3-dichlorodibenzo-p-dioxin. 2,3,4,5,6- Pentachlorobiphenyl was dechlorinated to 2,3,4,6- and/or 2,3,5,6-tetrachlorobiphenyl and 2,4,6-trichlorobiphenyl. 1,2,3,4-Tetrachloronaphthalene was dechlorinated primarily to an unidentified dichloro-naphthalene congener. The predominant end products from hexachlorobenzene dechlorination were 1,2,3,5-tetrachloro-benzene and 1,3,5-trichlorobenzene. We did not detect dechlorination daughter products from monochlorophenols, 2,3-dichlorodibenzo-p-dioxin or 2,3,7,8- tetrachlorodibenzo-p-dioxin. D. ethenogenes strain 195 has the ability to dechlorinate many different types of chlorinated aromatic compounds, in addition to its known chloroethene respiratory electron acceptors. Remediation of sediments contaminated with aromatic halogenated organic pollutants such as polychlorinated biphenyls and polychlorinated dibenzo-p-dioxins could require billions of dollars in the coming years. Harnessing microorganisms such as Dehalococcoides spp. that detoxify these compounds via removal of halogens may lead to cost-effective biotechnological approaches for remediation.