Zhao Siyan, Ding Chang, He Jianzhong
Department of Civil and Environmental Engineering, National University of Singapore, Singapore, 117576, Singapore.
PLoS One. 2015 Apr 2;10(3):e0119507. doi: 10.1371/journal.pone.0119507. eCollection 2015.
1,1,2-trichloroethane (1,1,2-TCA) has become a common groundwater pollutant due to historically extensive utilization, improper disposal, as well as from incomplete dechlorination of 1,1,2,2-tetrachloroethane. Currently, limited information is available on microbial detoxification of 1,1,2-TCA. Desulfitobacterium sp. strain PR, which was isolated from an anaerobic bioreactor maintained to dechlorinate chloroethenes/ethanes, exhibited the capacity to dechlorinate 1,1,1-trichloroethane and chloroform. In this study, the dechlorinating ability of strain PR was further explored. Strain PR showed the capability to dechlorinate 1,1,2-TCA (~1.12 mM) predominantly to 1,2-dichloroethane (1,2-DCA) and chloroethane, and to trace amounts of vinyl chloride and ethene within 20 days. Strain PR coupled growth with dechlorination of 1,1,2-TCA to 1,2-DCA, while no cell growth was observed with dechlorination of 1,2-DCA to chloroethane. Later, through transcriptomic and enzymatic analysis, the reductive dehalogenase CtrA, which was previously reported to be responsible for 1,1,1-trichloroethane and chloroform dechlorination, was identified as the 1,1,2-TCA reductive dehalogenase. Since trichloroethene (TCE) is usually co-contaminated with 1,1,2-TCA, a co-culture containing Dehalococcoides mccartyi strain 11a capable of detoxifying TCE and 1,2-DCA and strain PR was established. Interestingly, this co-culture dechlorinated 1,1,2-TCA and TCE to the non-toxic end-product ethene within 48 days without chloroethane production. This novel pathway avoids production of the carcinogenic intermediate dechlorination product vinyl chloride, providing a more environmentally friendly strategy to treat 1,1,2-TCA.
1,1,2-三氯乙烷（1,1,2-TCA）由于历史上的广泛使用、不当处置以及1,1,2,2-四氯乙烷的不完全脱氯，已成为一种常见的地下水污染物。目前，关于1,1,2-TCA微生物解毒的信息有限。从维持氯乙烯/乙烷脱氯的厌氧生物反应器中分离出的脱硫脱硫弧菌属菌株PR，表现出对1,1,1-三氯乙烷和氯仿的脱氯能力。在本研究中，进一步探索了菌株PR的脱氯能力。菌株PR能够在20天内将1,1,2-TCA（约1.12 mM）主要脱氯为1,2-二氯乙烷（1,2-DCA）和氯乙烷，并产生痕量的氯乙烯和乙烯。菌株PR将1,1,2-TCA脱氯为1,2-DCA的过程与生长耦合，而将1,2-DCA脱氯为氯乙烷的过程未观察到细胞生长。后来，通过转录组学和酶分析，先前报道负责1,1,1-三氯乙烷和氯仿脱氯的还原脱卤酶CtrA被鉴定为1,1,2-TCA还原脱卤酶。由于三氯乙烯（TCE）通常与1,1,2-TCA共同污染，建立了一种共培养体系，其中包含能够解毒TCE和1,2-DCA的麦氏脱卤球菌属菌株11a和菌株PR。有趣的是，这种共培养体系在48天内将1,1,2-TCA和TCE脱氯为无毒终产物乙烯，且不产生氯乙烷。这种新途径避免了致癌中间脱氯产物氯乙烯的产生，为处理1,1,2-TCA提供了一种更环保的策略。
