Abstract

Methane is the second most important greenhouse gas on earth. It is produced by methanogenic archaea, which play an important role in the global carbon cycle. Three main methanogenesis pathways are known: in the hydrogenotrophic pathway H₂ and carbon dioxide are used for methane production, whereas in the methylotrophic pathway small methylated carbon compounds like methanol and methylated amines are used. In the aceticlastic pathway, acetate is disproportionated to methane and carbon dioxide. However, next to these conventional substrates, further methanogenic substrates and pathways have been discovered. Several phylogenetically distinct methanogenic lineages (Methanosphaera, Methanimicrococcus, Methanomassiliicoccus, Methanonatronarchaeum) have evolved hydrogen-dependent methylotrophic methanogenesis without the ability to perform either hydrogenotrophic or methylotrophic methanogenesis. Genome analysis of the deep branching Methanonatronarchaeum revealed an interesting membrane-bound hydrogenase complex affiliated with the hardly described class 4 g of multisubunit hydrogenases possibly providing reducing equivalents for anabolism. Furthermore, methylated sulfur compounds such as methanethiol, dimethyl sulfide, and methylmercaptopropionate were described to be converted into adapted methylotrophic methanogenesis pathways of Methanosarcinales strains. Moreover, recently it has been shown that the methanogen Methermicoccus shengliensis can use methoxylated aromatic compounds in methanogenesis. Also, tertiary amines like choline (N,N,N-trimethylethanolamine) or betaine (N,N,N-trimethylglycine) have been described as substrates for methane production in Methanococcoides and Methanolobus strains. This review article will provide in-depth information on genome-guided metabolic reconstructions, physiology, and biochemistry of these unusual methanogenesis pathways.

Key points

• Newly discovered methanogenic substrates and pathways are reviewed for the first time.

• The review provides an in-depth analysis of unusual methanogenesis pathways.

• The hydrogenase complex of the deep branching Methanonatronarchaeum is analyzed.

中文翻译：

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一种从非常规底物产生目标甲烷的方法。

摘要

甲烷是地球上第二重要的温室气体。它由产甲烷的古细菌产生，在全球碳循环中起着重要作用。已知三种主要的甲烷生成途径：在氢营养途径中，H ₂和二氧化碳用于甲烷生产，而在甲基营养途径中，使用小的甲基化碳化合物，例如甲醇和甲基化胺。在乙破途径中，乙酸盐歧化为甲烷和二氧化碳。然而，除了这些常规底物，还发现了其他产甲烷底物和途径。几个不同系统发育谱系甲烷（Methanosphaera，Methanimicrococcus，Methanomassiliicoccus，Methanonatronarchaeum已进化出氢依赖性的甲基营养型甲烷生成，而没有能力进行氢营养型或甲基营养型甲烷生成。基因组分析的深分支甲烷八叠膜原菌揭示了一个有趣的膜结合的氢酶复合物，与难以描述的4 g类多亚基氢化酶有关，可能为合成代谢提供了减少的当量。此外，甲基化的硫化合物（例如甲硫醇，二甲基硫醚和巯基丙酸甲酯）已被描述为转化为甲烷八叠球菌菌株的甲基营养型甲烷生成途径。而且，最近已经显示产甲烷菌胜利力甲烷球菌可以在甲烷化反应中使用甲氧基化的芳香族化合物。另外，叔胺等胆碱（Ñ，Ñ，Ñ -trimethylethanolamine）或甜菜碱（Ñ，Ñ，Ñ -trimethylglycine）已经被描述为用于甲烷生产的基板Methanococcoides和Methanolobus菌株。这篇评论文章将提供有关这些异常甲烷生成途径的基因组指导的代谢重建，生理学和生物化学的深入信息。

关键点

•首次审查了新发现的产甲烷底物和途径。

•该评论深入分析了不寻常的甲烷生成途径。

•分析了深分支的甲烷八氢古菌的氢化酶复合物。