Dual C–Cl isotope fractionation offers potential to assess biodegradation of 1,2-dichloropropane and 1,2,3-trichloropropane by Dehalogenimonas cultures

Abstract

1,2-dichloropropane (1,2-DCP) and 1,2,3-trichloropropane (1,2,3-TCP) are hazardous chemicals frequently detected in groundwater near agricultural zones due to their historical use in chlorinated fumigant formulations. In this study, we show that the organohalide-respiring bacterium <em style="color:black">Dehalogenimonas alkenigignens</em><span style="color:black"> strain BRE15M can grow during the dihaloelimination of </span>1,2-DCP and 1,2,3-TCP to propene and allyl chloride, respectively. Our work also provides the first application of dual isotope approach to investigate the anaerobic reductive dechlorination of 1,2-DCP and 1,2,3-TCP. Stable carbon and chlorine isotope fractionation values for 1,2-DCP (Ɛ_C= -13.6 ± 1.4 ‰ and Ɛ_Cl= -27.4 ± 5.2 ‰) and 1,2,3-TCP (Ɛ_C= -3.8 ± 0.6 ‰ and Ɛ_Cl= -0.8 ± 0.5 ‰) were obtained resulting in distinct dual isotope slopes (Λ_12DCP= 0.5 ± 0.1, Λ_123TCP= 4 ± 2). However direct comparison of Λ_C-Cl among different substrates is not possible and investigation of the C and Cl apparent kinetic isotope effects lead to the hypothesis that <em>concerted </em>dichloroelimination mechanism is more likely for both compounds. In fact, whole cell activity assays using cells suspensions of the <em>Dehalogenimonas</em>-containing culture grown with 1,2-DCP and methyl viologen as electron donor suggest that the same set of reductive dehalogenases was involved in the transformation of 1,2-DCP and 1,2,3-TCP. This study opens the door to the application of isotope techniques for evaluating biodegradation of 1,2-DCP and 1,2,3-TCP, which often co-occur in groundwaters near agricultural fields.