Stable carbon isotope enrichment factors for cis-1,2-dichloroethene and vinyl chloride reductive dechlorination by Dehalococcoides

Abstract

Compound-specific stable isotope analysis (CSIA) is a promising tool for monitoring in situ microbial activity, and enrichment factors (ε values) determined using CSIA can be employed to estimate compound transformation. Although ε values for some dechlorination reactions catalyzed by Dehalococcoides (Dhc) have been reported, reproducibility between independent experiments, variability between different Dhc strains, and congruency between pure and mixed cultures are unknown. In experiments conducted with pure cultures of Dhc sp. strain BAV1, ε values for 1,1-DCE, cis-DCE, trans-DCE, and VC were -5.1, -14.9, -20.8, and -23.2‰, respectively. The ε value for 1,1-DCE dechlorination was 48.9% higher than the value reported in a previous study, but ε values for other chlorinated ethenes were equal between independent experiments. For the dechlorination of cis-DCE and VC by Dhc strains BAV1, FL2, GT, and VS, average ε values were -18.4 and -23.2‰, respectively. cis-DCE and VC ε values determined in pure Dhc cultures with different reductive dehalogenase genes (e.g., vcrA vs bvcA) varied by less than 36.8 and 8.3%, respectively. In the BDI consortium, ε values for cis-DCE and VC dechlorination were -25.3‰ and -19.9‰, 31.6% higher and 15.3% lower, respectively, compared to the average ε value for Dhc pure cultures. As cis-DCE and VC ε values are all within the same order-of-magnitude and fractionation is always measured during Dhc dechlorination, CSIA may be a valuable approach for monitoring in situ cis-DCE and VC reductive dechlorination.