Chlorinated Alkanes Differentially Inhibit Dechlorination of Dichloroethene Isomers in Dehalococcoides: Mechanisms, Amelioration Strategy, and Microbial Ecological Insights

Co-contamination of chloroethenes with other chlorinated solvents is prevalent in the environment, however, there is a dearth of studies comprehensively evaluating the inhibition of different chlorinated solvents on microbial reductive dechlorination of dichloroethene (DCE) isomers and their influence on the underpinning microbial communities. Additionally, strategies to ameliorate co-contaminant inhibition have not been developed. This study found that chloroform, followed by 1,1,1-trichloroethane and 1,1,2-trichloroethane, exhibited the most detrimental inhibition on dechlorination of DCE isomers in Dehalococcoides-containing consortia. Interestingly, dechlorination of trans-DCE isomer was more susceptible to co-contaminant inhibition than cis-DCE, contributing as an alternative explanation to the more prevalence of the former at contaminated sites. The inhibition could be attributed to direct suppression on growth of Dehalococcoides and transcription of reductive dehalogenase genes (tceA and vcrA). Additionally, co-contaminants preferentially selected Dehalococcoides populations harboring tceA than vcrA. Microbial community analyses also demonstrated profound influence of co-contaminants on taxonomic composition, structure, and assembly of the entire dechlorinating communities. More importantly, augmentation with Desulfitobacterium sp. PR effectively ameliorated co-contaminant inhibition. Altogether, our findings contribute to better bioremediation of sites co-contaminated with multiple chlorinated solvents.