Proposal of the reverse flow model for the origin of the eukaryotic cell based on comparative analyses of Asgard archaeal metabolism
Proposal of the reverse flow model for the origin of the eukaryotic cell based on comparative analyses of Asgard archaeal metabolism
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DOI：
10.1038/s41564-019-0406-9
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发表时间：
2019-04
影响因子：
28.3
通讯作者：
A. Spang;Courtney W. Stairs;Nina Dombrowski;Laura Eme;Jonathan Lombard;Eva F. Caceres;C. Greening
中科院分区：
文献类型：
--
作者：
A. Spang;Courtney W. Stairs;Nina Dombrowski;Laura Eme;Jonathan Lombard;Eva F. Caceres;C. Greening
真核生物的起源是进化生物学中一个未解之谜。目前的研究表明，真核生物是从宿主古细菌后裔和α变形菌内共生体的合并进化而来的。阿斯加德古菌的发现有助于阐明假定的古菌宿主的身份。阿斯加德古菌是一种被提出的古菌超门，包括Lokiarchaeota、Thorarchaeota、Odinarchaeota和Heimdallarchaeota，它被认为是真核生物最接近的古菌亲戚。虽然Lokiarchaeota被认为采用氢依赖的代谢，但对阿斯加德超级门其他成员的代谢潜力知之甚少。我们使用比较基因组学和系统遗传学来推断阿斯加德古菌的中心代谢途径，以便能够完善真核生物起源的当前模型。我们的分析表明，Thorarchaeota和Lokiarchaeota编码通过Wood-Ljungdahl途径固定碳和从有机基质中获得还原等量物所必需的蛋白质。相比之下，海姆达拉古菌lc2和LC3基因组编码的酶可能使有机底物氧化，使用硝酸盐或氧作为电子受体。heimdallarchaeumab125和dodinarchaeum2的基因库表明，这些生物可以通过将铁氧还蛋白再氧化偶联到呼吸质子还原来发酵有机底物并保存能量。总之，我们的基因组分析表明，Asgard代表主要是有机异养生物，具有可变的氢消耗和生产能力。在此基础上，我们提出了“逆向流动模型”，这是一种新的真核生物起源共生模型，涉及电子或氢从有机异养古细菌宿主流向细菌共生体。
The origin of eukaryotes represents an unresolved puzzle in evolutionary biology. Current research suggests that eukaryotes evolved from a merger between a host of archaeal descent and an alphaproteobacterial endosymbiont. The discovery of the Asgard archaea, a proposed archaeal superphylum that includes Lokiarchaeota, Thorarchaeota, Odinarchaeota and Heimdallarchaeota suggested to comprise the closest archaeal relatives of eukaryotes, has helped to elucidate the identity of the putative archaeal host. Whereas Lokiarchaeota are assumed to employ a hydrogen-dependent metabolism, little is known about the metabolic potential of other members of the Asgard superphylum. We infer the central metabolic pathways of Asgard archaea using comparative genomics and phylogenetics to be able to refine current models for the origin of eukaryotes. Our analyses indicate that Thorarchaeota and Lokiarchaeota encode proteins necessary for carbon fixation via the Wood–Ljungdahl pathway and for obtaining reducing equivalents from organic substrates. By contrast,HeimdallarchaeumLC2 and LC3 genomes encode enzymes potentially enabling the oxidation of organic substrates using nitrate or oxygen as electron acceptors. The gene repertoire ofHeimdallarchaeumAB125 andOdinarchaeumindicates that these organisms can ferment organic substrates and conserve energy by coupling ferredoxin reoxidation to respiratory proton reduction. Altogether, our genome analyses suggest that Asgard representatives are primarily organoheterotrophs with variable capacity for hydrogen consumption and production. On this basis, we propose the ‘reverse flow model’, an updated symbiogenetic model for the origin of eukaryotes that involves electron or hydrogen flow from an organoheterotrophic archaeal host to a bacterial symbiont.