Alleviating Chlorinated Alkane Inhibition on Dehalococcoides to Achieve Detoxification of Chlorinated Aliphatic Cocontaminants

Cocontamination by multiple chlorinated solvents is a prevalent issue in groundwater, presenting a formidable challenge for effective remediation. Despite the recognition of this issue, a comprehensive assessment of microbial detoxification processes involving chloroethenes and associated cocontaminants, along with the underpinning microbiome, remains absent. Moreover, strategies to mitigate the inhibitory effects of cocontaminants have not been reported. Here, we revealed that chloroform exhibited the most potent inhibitory effects, followed by 1,1,1-trichloroethane and 1,1,2-trichloroethane, on dechlorination of dichloroethenes (DCEs) in Dehalococcoides-containing consortia. The observed inhibition could be attributed to suppression of biosynthesis and enzymatic activity of reductive dehalogenases and growth of Dehalococcoides. Notably, cocontaminants more profoundly inhibited Dehalococcoides populations harboring the vcrA gene than those possessing the tceA gene, thereby explaining the accumulation of vinyl chloride under cocontaminant stress. Nonetheless, we successfully ameliorated cocontaminant inhibition by augmentation with Desulfitobacterium sp. strain PR owing to its ability to attenuate cocontaminants, resulting in concurrent detoxification of DCEs, trichloroethanes, and chloroform. Microbial community analyses demonstrated obvious alterations in taxonomic composition, structure, and assembly of the dechlorinating microbiome in the presence of cocontaminants, and introduction of strain PR reshaped the dechlorinating microbiome to be similar to its original state in the absence of cocontaminants. Altogether, these findings contribute to developing bioremediation technologies to clean up challenging sites polluted with multiple chlorinated solvents.