Triple-element compound-specific stable isotope analysis of 1,2-dichloroethane for characterization of the underlying dehalogenation reaction in two Dehalococcoides mccartyi strains

Abstract

Chlorinated ethanes belong to the most common groundwater and soil contaminants. Of these, 1,2-dichloroethane (1,2-DCA) is an man-made, persistent and toxic contaminant, released due to improper waste treatment at versatile production sites. This study investigated the anaerobic transformation of 1,2-DCA by Dehalococcoides mccartyi strain 195 and strain BTF08 using triple-element compound-specific stable isotope analysis (CSIA) of carbon, chlorine and hydrogen for the first time. Isotope fractionation patterns for carbon (ε^C_BTF08 = -28.4 ± 3.7 ‰; ε^C₁₉₅ = -30.9 ± 3.6 ‰) and chlorine (ε^Cl_BTF08 = -4.6 ± 0.7 ‰; ε^Cl₁₉₅ = -4.2 ± 0.5 ‰) within both investigated D. mccartyi strains, as well as the dual-element analysis (Λ_BTF08 = 6.9 ± 1.2; Λ₁₉₅ = 7.1 ± 0.2), supported identical reaction mechanisms for dehalogenation of 1,2-DCA. Hydrogen isotope fractionation analysis revealed dihaloelimination as prevalent reaction mechanism. Vinyl chloride as major intermediate could be excluded by performing the experiment in deuterated aqueous media. Furthermore, evaluation of the derived apparent kinetic isotope effects (AKIE^C_BTF08 = 1.029/AKIE^C₁₉₅ = 1.031; AKIE^Cl_BTF08 = 1.005/AKIE^Cl₁₉₅ = 1.004) pointed towards simultaneous abstraction of both involved chlorine-substituents in a concerted matter. It was shown that D. mccartyi strain BTF08 and strain 195 are capable of complete, direct dihaloelimination of 1,2-DCA to ethene.

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