Reductive Dehalogenation of Trichloromethane by Two Different Dehalobacter restrictus Strains Reveal Opposing Dual Element Isotope Effects
Reductive Dehalogenation of Trichloromethane by Two Different Dehalobacter restrictus Strains Reveal Opposing Dual Element Isotope Effects
复制标题
DOI：
10.1021/acs.est.8b03717
复制
发表时间：
2019-03-05
影响因子：
11.4
通讯作者：
Lee, Matthew
中科院分区：
文献类型：
--
作者：
Heckel, Benjamin;Phillips, Elizabeth;Lee, Matthew
三氯甲烷 (TCM) 是一种经常检测到的持久性地下水污染物。最近的研究报道，两种密切相关的脱盐杆菌菌株（UNSWWDHB 和 CF）将中药转化为二氯甲烷，但碳同位素效应不一致（e(13)C(UNSWWDHB) = -4.3 +/- 0.45 ppm；e13C(CF) = -27.5 +/- 0.9 ppm）。本研究使用双元素化合物特定同位素分析（C；Cl）来探索潜在的差异。使用 CF 菌株进行的 TCM 转化实验显示出明显的正常碳和氯同位素效应（e13C(CF) = -27.9 +/- 1.7 ppm；e37Cl(CF) = -4.2 +/- 0.2 ppm）。相比之下，菌株UNSWDHB (e13C(UNSWWDHB) = -3.1 +/- 0.5 ppm；e37Cl(UNSWWDB) = 2.5 +/- 0.3 ppm) 观察到小碳和前所未有的逆氯同位素效应，导致相反的双元素同位素斜率（?CF = 6.64 +/- 0.14 vs lambda(UNSWDHB) = -1.20 +/- 0.18）。 CF菌株的同位素效应与中药和维生素B12的实验相同（e13C（维生素B12）= -26.0 +/- 0.9 ppm，e37Cl（维生素 B12）= -4.0 +/- 0.2 ppm，lambda（维生素）（B12）= 6.46 +/- 0.20）。与之前报道的同位素效应相比，表明外层单电子转移或 S(N)2 是可能的潜在机制。使用菌株 UNSWWDHB 进行的细胞悬浮液和无细胞提取物实验均无法揭示还原性脱卤酶 (TmrA) 的内在 KIE，表明酶结合和/或向周质的传质是限速的。通过气体/水和气体/十六烷分配实验，排除了中药与细胞材料的非定向分子间相互作用作为反同位素效应的原因，表明特定的但未表征的相互作用必须在催化之前发生。
Trichloromethane (TCM) is a frequently detected and persistent groundwater contaminant. Recent studies have reported that two closely related Dehalobacter strains (UNSWDHB and CF) transform TCM to dichloromethane, with inconsistent carbon isotope effects (e(13)C(UNSWDHB) = -4.3 +/- 0.45 parts per thousand; e13C(CF) = -27.5 +/- 0.9 parts per thousand). This study uses dual element compound specific isotope analysis (C; Cl) to explore the underlying differences. TCM transformation experiments using strain CF revealed pronounced normal carbon and chlorine isotope effects (e13C(CF) = -27.9 +/- 1.7 parts per thousand; e37Cl(CF) = -4.2 +/- 0.2 parts per thousand). In contrast, small carbon and unprecedented inverse chlorine isotope effects were observed for strain UNSWDHB (e13C(UNSWDHB) = -3.1 +/- 0.5 parts per thousand; e37Cl(UNSWDHB) = 2.5 +/- 0.3 parts per thousand) leading to opposing dual element isotope slopes (?CF = 6.64 +/- 0.14 vs lambda(UNSWDHB) = -1.20 +/- 0.18). Isotope effects of strain CF were identical to experiments with TCM and Vitamin B12 (e13C(Vitamin B12) = -26.0 +/- 0.9 parts per thousand, e37Cl(Vitamin B12) = -4.0 +/- 0.2 parts per thousand, lambda(Vitamin) (B12) = 6.46 +/- 0.20). Comparison to previously reported isotope effects suggests outer-sphere-single-electron transfer or S(N)2 as possible underlying mechanisms. Cell suspension and cell free extract experiments with strain UNSWDHB were both unable to unmask the intrinsic KIE of the reductive dehalogenase (TmrA) suggesting that enzyme binding and/or mass-transfer into the periplasm were rate-limiting. Nondirected intermolecular interactions of TCM with cellular material were ruled out as reason for the inverse isotope effect by gas/water and gas/hexadecane partitioning experiments indicating specific, yet uncharacterized interactions must be operating prior to catalysis.