四氯乙烯（PCE）與三氯乙烯（TCE）是廣泛使用的工業溶劑，會持續存在於地下水與土壤中，對環境與健康造成嚴重風險。在這些氯代乙烯的生物整治中，脫鹵呼吸菌（organohalide-respiring bacteria， OHRB）—尤其是 Dehalococcoides spp. （Dhc）—透過還原性脫氯作用扮演關鍵角色。此過程由還原性脫鹵酶（reductive dehalogenases， RDases）所催化，其中許多仍缺乏充分的特性解析。大多數 Dehalococcoides 菌株會將 TCE 脫氯為順-1，2-二氯乙烯（cis-DCE），但優先產生反-1，2-二氯乙烯（trans-DCE）的菌株相當罕見，其潛在機制至今仍不明確。本研究利用來自受污染地下水的微宇宙（microcosm）分離並鑑定新穎的 trans-DCE 產生型 Dehalococcoides 菌株。首先，在厭氧還原性脫氯條件下富集具有 TCE 分解活性的微生物群落。分離後，利用氣相層析法確認其脫氯活性，結果顯示0.6 mM TCE可在14天內幾乎完全脫氯，且trans-DCE累積量達31.23 ± 1.35 μmol/bottle，並透過分子與基因體分析驗證菌株的純度與鑑定結果。限制酶片段長度多型性分析（RFLP）與次世代定序（NGS）確認了所分離菌株的純度。基因體分析顯示其具有獨特的 RDase 組成，共包含 21 個 RDase 基因，其中包括 1 個 pceA-like 基因、2 個 pcbA4-like 基因，以及數個未分類候選基因。根據系統發育、基因體與生理學分析，該新穎分離株被鑑定為 Dehalococcoides mccartyi 的成員，並命名為 strain SN。總體而言，本研究證實了一株可優先由 TCE 生成 trans-DCE 的 Dehalococcoides 菌株之存在及其獨特特性。這些發現增進了我們對與 trans-DCE 相關之脫氯途徑的理解，並有助於改善受污染場址生物整治的評估與最佳化。;Tetrachloroethene (PCE) and trichloroethene (TCE) are widely used industrial solvents that persist in groundwater and soil， posing serious environmental and health risks. In the bioremediation of these chlorinated ethenes， organohalide-respiring bacteria (OHRB)—particularly Dehalococcoides spp. (Dhc)—play a crucial role via reductive dechlorination. This process is catalyzed by reductive dehalogenases (RDases)， many of which remain poorly characterized. While most Dehalococcoides strains dechlorinate TCE to cis-1，2-dichloroethene (cis-DCE)， strains that preferentially produce trans-1，2-dichloroethene (trans-DCE) are rare， and their underlying mechanisms remain unclear. In this study， we used a microcosm derived from contaminated groundwater to isolate and characterize a novel trans–DCE–producing Dehalococcoides strain. Microbial communities with TCE-degrading activity were first enriched under anaerobic reductive dechlorination conditions. Following isolation， dechlorination activity was confirmed by gas chromatography， showing near-complete dechlorination of 0.6 mM TCE within 14 days and trans-DCE accumulation reaching 31.23 ± 1.35 μmol/bottle， while strain purity and identity were verified using molecular and genomic analyses. Restriction fragment length polymorphism (RFLP) and next-generation sequencing (NGS) confirmed the purity of the isolated strain. Genome analysis revealed a distinct RDase composition comprising 21 RDase genes， including one pceA-like gene， two pcbA4-like genes， and several unclassified candidates. Based on phylogenetic， genomic， and physiological analyses， the novel isolate was identified as a member of Dehalococcoides mccartyi and designated strain SN. Overall， this study demonstrates the existence and unique characteristics of a Dehalococcoides strain that preferentially generates trans-DCE from TCE. These findings advance our understanding of trans-DCE–associated dechlorination pathways and support the improved assessment and optimization of bioremediation at contaminated sites.
