Abstract Methane generated by microorganisms is most often depleted in the doubly substituted isotopologue 12 CH2D2 relative to the stochastic reference distribution. To constrain the controls on depleted Δ 12 CH 2 D 2 values, we experimentally isolated the root cause with microorganisms that produce methane from methylphosphonate via the C-P lyase pathway. This mechanism of methane production preserves the three hydrogens from methylphosphonate and adds one hydrogen from water. When maintaining the same methylphosphonate source, but varying the D/H composition of growth medium water, we observed significant shifts in methane Δ 12 CH 2 D 2 values, but little to no change in Δ 13 CH 3 D values. We reproduced these observations with a model that considers only the combinatorial isotope effect. The variation in Δ 12 CH 2 D 2 values of product methane resulted from the differences in D/H between reactants water and methylphosphonate. This work validates the hypothesis that combinatorial effects can strongly influence methane Δ 12 CH 2 D 2 values, and must be considered for low temperature, abiotic or biotic systems where methane hydrogen is derived from multiple reservoirs.

中文翻译：

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组合同位素效应导致微生物甲烷中的低表观 Δ12CH2D2

摘要 微生物产生的甲烷通常在双取代同位素体 12 CH2D2 中相对于随机参考分布耗尽。为了限制对耗尽的 Δ 12 CH 2 D 2 值的控制，我们用通过 CP 裂解酶途径从甲基膦酸盐产生甲烷的微生物通过实验分离了根本原因。这种甲烷生产机制保留了甲基膦酸酯的三个氢，并从水中添加了一个氢。当保持相同的甲基膦酸盐来源，但改变生长培养基水的 D/H 组成时，我们观察到甲烷 Δ 12 CH 2 D 2 值发生显着变化，但 Δ 13 CH 3 D 值几乎没有变化。我们使用仅考虑组合同位素效应的模型重现了这些观察结果。产物甲烷的Δ 12 CH 2 D 2 值的变化是由反应物水和甲基膦酸酯之间的D/H差异引起的。这项工作验证了组合效应可以强烈影响甲烷 Δ 12 CH 2 D 2 值的假设，并且必须考虑低温、非生物或生物系统，其中甲烷氢来自多个储层。