Of the six known autotrophic pathways, the Wood-Ljungdahl pathway (WL) is the only one present in both the acetate producing Bacteria (homoacetogens) and the methane producing Archaea (hydrogenotrophic methanogens), and it has been suggested that WL is one of the oldest metabolic pathways. However, only the so-called carbonyl branch is shared by Archaea and Bacteria, while the methyl branch is different, both in the number of reactions and enzymes, which are not homologous among them. In this work we show that some parts of the methyl branch of archaeal Wood-Ljungdahl pathway (MBWL) are present in bacteria as well as in non-methanogen archaea, although the tangled evolutionary history of MBWL cannot be traced back to the Last Common Ancestor. We have also analyzed the different variants of methanogenesis (hydrogenotrophic, acetoclastic and methylotrophic pathways), and concluded that each of these pathways, and every different enzyme or subunit (in the case of multimeric enzymes), has their own intricate evolutionary history. Our study supports the scenario of hydrogenotrophic methanogenesis being older than the other variants, albeit not old enough to be present in the last archaeal common ancestor.

中文翻译：

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生命早期的甲烷生成：古老而不是原始的。

在六种已知的自养途径中，Wood-Ljungdahl途径（WL）是产乙酸的细菌（均生乙酸原）和产甲烷的古细菌（氢营养型产甲烷菌）中唯一的一种，并且有人认为WL是一种自养途径。最古老的代谢途径。然而，古细菌和细菌仅共享所谓的羰基分支，而在反应和酶的数目上，甲基分支是不同的，它们之间不是同源的。在这项工作中，我们表明细菌和非甲烷原古细菌中存在着古细菌Wood-Ljungdahl途径（MBWL）的甲基分支的某些部分，尽管MBWL纠结的进化历史不能追溯到最后的祖先。我们还分析了甲烷生成的不同变体（氢营养，乙酰碎裂和甲基营养型途径），并得出结论，这些途径中的每一个以及每种不同的酶或亚基（在多聚酶的情况下）都有其自己复杂的进化历史。我们的研究支持氢营养型甲烷生成比其他变体更老的场景，尽管它的年龄不足以出现在最后的古细菌共同祖先中。