Sustained detoxification of 1,2-dichloroethane to ethylene by a symbiotic consortium containing Dehalococcoides species

1,2-Dichloroethane (1,2-DCA) is a ubiquitous volatile halogenated organic pollutant in groundwater and soil, which poses a serious threat to the ecosystem and human health. Microbial reductive dechlorination has been recognized as an environmentally-friendly strategy for the remediation of sites contaminated with 1,2-DCA. In this study, we obtained an anaerobic microbiota derived from 1,2-DCA contaminated groundwater, which was able to sustainably convert 1,2-DCA into non-toxic ethylene with an average dechlorination rate of 30.70 +/- 11.06 mu M d-1 (N = 6). The microbial community profile demonstrated that the relative abundance of Dehalo-coccoides species increased from 0.53 +/- 0.08% to 44.68 +/- 3.61% in parallel with the dechlorination of 1,2-DCA. Quantitative PCR results showed that the Dehalococcoides species 16S rRNA gene increased from 2.40 +/- 1.71 x 108 copies center dot mL-1 culture to 4.07 +/- 2.45 x 108 copies center dot mL-1 culture after dechlorinating 110.69 +/- 30.61 mu mol of 1,2-DCA with a growth yield of 1.55 +/- 0.93 x 108 cells per mu mol Cl- released (N = 6), suggesting that Deha-lococcoides species used 1,2-DCA for organohalide respiration to maintain cell growth. Notably, the relative abundances of Methanobacterium sp. (p = 0.0618) and Desulfovibrio sp. (p = 0.0001995) also increased signifi-cantly during the dechlorination of 1,2-DCA and were clustered in the same module with Dehalococcoides species in the co-occurrence network. These results hinted that Dehalococcoides species, the obligate organohalide-respiring bacterium, exhibited potential symbiotic relationships with Methanobacterium and Desulfovibrio spe -cies. This study illustrates the importance of microbial interactions within functional microbiota and provides a promising microbial resource for in situ bioremediation in sites contaminated with 1,2-DCA.