The biological production of methane is vital to the global carbon cycle and accounts for ca. 74% of total methane emissions. The organisms that facilitate this process, methanogenic archaea, belong to a large and phylogenetically diverse group that thrives in a wide range of anaerobic environments. Two main subgroups exist within methanogenic archaea: those with and those without cytochromes. Although a variety of metabolisms exist within this group, the reduction of growth substrates to methane using electrons from molecular hydrogen is, in a phylogenetic sense, the most widespread methanogenic pathway. Methanogens without cytochromes typically generate methane by the reduction of CO2 with electrons derived from H2, formate, or secondary alcohols, generating a transmembrane ion gradient for ATP production via an Na+-translocating methyltransferase (Mtr). These organisms also conserve energy with a novel flavin-based electron bifurcation mechanism, wherein the endergonic reduction of ferredoxin is facilitated by the exergonic reduction of a disulfide terminal electron acceptor coupled to either H2 or formate oxidation. Methanogens that utilize cytochromes have a broader substrate range, and can convert acetate and methylated compounds to methane, in addition to the ability to reduce CO2 Cytochrome-containing methanogens are able to supplement the ion motive force generated by Mtr with an H+-translocating electron transport system. In both groups, enzymes known as hydrogenases, which reversibly interconvert protons and electrons to molecular hydrogen, play a central role in the methanogenic process. This review discusses recent insight into methanogen metabolism and energy conservation mechanisms with a particular focus on the genus Methanosarcina.

中文翻译：

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产甲烷古菌，特别是甲烷菌属的甲烷中的能量守恒和加氢酶功能。

甲烷的生物生产对于全球碳循环至关重要，约占碳排放的一半。甲烷排放总量的74％。促成这一过程的生物是产甲烷菌，属于大型且系统发育多样的群体，它们在各种厌氧环境中都能繁衍生息。产甲烷古菌中存在两个主要亚群：有和没有细胞色素的亚群。尽管该组中存在各种新陈代谢，但从系统发育的角度来看，使用分子氢电子将生长底物还原为甲烷是最广泛的产甲烷途径。没有细胞色素的产甲烷菌通常会通过由H2，甲酸酯或仲醇衍生的电子将CO2还原来生成甲烷。通过Na +易位的甲基转移酶（Mtr）生成用于ATP的跨膜离子梯度。这些生物还通过一种基于黄素的新电子分叉机制来节约能量，其中铁氧还蛋白的二十碳五烯还原反应通过与H2或甲酸氧化偶联的二硫键电子受体的电子还原而得以促进。利用细胞色素的产甲烷菌具有更广泛的底物范围，并且除了具有减少二氧化碳的能力之外，还可以将乙酸盐和甲基化的化合物转化为甲烷。系统。在这两组中，称为氢化酶的酶可以将质子和电子可逆地相互转化为分子氢，在产甲烷过程中发挥重要作用。这篇评论讨论了对产甲烷菌代谢和能量守恒机制的最新见解，特别是甲烷菌属。