Reductive Dehalogenation of Trichloromethane by Two Different Dehalobacter restrictus Strains Reveal Opposing Dual Element Isotope Effects

Trichloromethane (TCM) is a frequently detected and persistent groundwater contaminant. Recent studies have reported that two closely related Dehalobacter strains (UNSWDHB and CF) transform TCM to dichloromethane, with inconsistent carbon isotope effects (e13CUNSWDHB = −4.3 ± 0.45‰; e13CCF = −27.5 ± 0.9‰). This study uses dual element compound specific isotope analysis (C; Cl) to explore the underlying differences. TCM transformation experiments using strain CF revealed pronounced normal carbon and chlorine isotope effects (e13CCF = −27.9 ± 1.7‰; e37ClCF = −4.2 ± 0.2‰). In contrast, small carbon and unprecedented inverse chlorine isotope effects were observed for strain UNSWDHB (e13CUNSWDHB = −3.1 ± 0.5‰; e37ClUNSWDHB = 2.5 ± 0.3‰) leading to opposing dual element isotope slopes (λCF = 6.64 ± 0.14 vs λUNSWDHB = −1.20 ± 0.18). Isotope effects of strain CF were identical to experiments with TCM and Vitamin B12 (e13CVitamin B12 = −26.0 ± 0.9‰, e37ClVitamin B12 = −4.0 ± 0.2‰, λVitamin B12 = 6.46 ± 0.20). Comp...