1,1,1-Trichloroethane and 1,1-Dichloroethane Reductive Dechlorination Kinetics and Co-Contaminant Effects in a Dehalobacter-Containing Mixed Culture

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Abstract

1,1,1-Trichloroethane (1,1,1-TCA) is a common groundwater contaminant that can be reductively dechlorinated to 1,1-dichloroethane (1,1-DCA) and monochloroethane, and can support the growth of certain dehalorespiring strains of Dehalobacter We used reductive dehalogenase cell-free extract assays (with reduced methyl viologen) and whole cell suspension dechlorination assays (with hydrogen) and a Dehalobacter-containing enrichment culture to explore the kinetics of l,1,1-TCA and 1,1-DCA reductive dechlorination in the presence of the common co-contaminants trichloroethene (TCE), cis-dichloroethene (cDCE), and vinyl chloride (VC). These chlorinated ethenes were most significant inhibitors of 1,1,1-TCA dechlorination in cell-free extracts, indicating direct effects on the reductive dehalogenase enzyme(s). The inhibition was present but less pronounced in whole cell suspension assays. None of the chlorinated ethenes inhibited 1,1-DCA dechlorination in cell-free extract assays, yet cDCE and particularly VC were inhibitors in whole cell assays, indicating an effect on Dehalobacter, but not on the dehalogenase enzyme(s). Marked differences in kinetic parameters for 1,1,1-TCA and 1,1-DCA, and an uncoupling of these two activities in cultures grown on 1,1-DCA compared to those grown on 1,1,1-TCA was strong evidence for the existence of distinct 1,1,1-TCA and 1,1-DCA reductive dehalogenase enzymes.

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