Zuckerberg Institute for Water Research, Department of Environmental Hydrology and Microbiology, Ben-Gurion University of the Negev, Sede Boqer Campus, 8499000, Israel.
Geological Survey of Israel, 32 Yesha'ayahu Leibowitz St, Jerusalem, 9692100, Israel.
Chemosphere. 2020 Mar;242:125130. doi: 10.1016/j.chemosphere.2019.125130. Epub 2019 Oct 18.
Identifying co-metabolic TCE oxidation in polluted groundwater is challenging due to lack of indicative by-products. This challenge may theoretically be resolved if the oxidation process can be characterized by a distinct dual isotope enrichment. In this work, we aimed to explore the carbon and chlorine isotope effects associated with TCE oxidation by a variety of oxygenases. These included pure strains and enrichment cultures of methane, toluene and ammonia oxidizers, as well as experiments with crude extracts. Isotope effects determined for TCE oxidation by toluene and ammonia oxidizers were mostly in line with expected values for epoxidation mechanism (ϵC -11.0 ± 0.7 to -24.8 ± 0.2‰ and ϵCl +0.9 ± 0.5 to +1.0 ± 0.4‰), whereas, the methanotrophs resulted in distinctively different isotope effects (ϵC -2.4 ± 0.4 to -3.4 ± 0.8‰ and ϵCl -1.8 ± 0.2 to -2.9 ± 0.9‰). It is suggested that in TCE oxidation by methanotrophs, substrate binding rather than bond cleavage is rate limiting, leading to this unexpected isotope effect. On the environmental level, our results imply that the oxidative process can be differentiated if catalyzed by toluene and ammonia oxidizers or by methanotrophs. Additionally, the oxidative process can be distinguished from the reductive one. However, using dual isotope analysis in the field may result in an under-estimation of the overall co-metabolic process if methanotrophs are to be excluded due to low isotope effects.
在污染地下水中识别共代谢 TCE 氧化具有挑战性，因为缺乏指示性的副产物。如果氧化过程可以通过独特的双同位素富集来表征，那么从理论上可以解决这一挑战。在这项工作中，我们旨在探索各种加氧酶与 TCE 氧化相关的碳和氯同位素效应。这些加氧酶包括甲烷、甲苯和氨氧化菌的纯菌株和富集培养物，以及粗提物实验。甲苯和氨氧化菌氧化 TCE 的同位素效应大多符合环氧化机制的预期值（εC-11.0±0.7 至-24.8±0.2‰和εCl+0.9±0.5 至+1.0±0.4‰），而甲烷氧化菌则产生了明显不同的同位素效应（εC-2.4±0.4 至-3.4±0.8‰和εCl-1.8±0.2 至-2.9±0.9‰）。建议在甲烷氧化菌氧化 TCE 时，是底物结合而不是键断裂限速，导致了这种意想不到的同位素效应。在环境水平上，我们的结果表明，如果由甲苯和氨氧化菌或甲烷氧化菌催化，氧化过程可以被区分。此外，可以将氧化过程与还原过程区分开来。然而，如果由于同位素效应较低而排除甲烷氧化菌，则在野外使用双同位素分析可能会低估总体共代谢过程。
