The discovery of Asgard archaea, phylogenetically closer to eukaryotes than other archaea, together with improved knowledge of microbial ecology, impose new constraints on emerging models for the origin of the eukaryotic cell (eukaryogenesis). Long-held views are metamorphosing in favour of symbiogenetic models based on metabolic interactions between archaea and bacteria. These include the classical Searcy's and Hydrogen hypothesis, and the more recent Reverse Flow and Entangle-Engulf-Endogenize models. Two decades ago, we put forward the Syntrophy hypothesis for the origin of eukaryotes based on a tripartite metabolic symbiosis involving a methanogenic archaeon (future nucleus), a fermentative myxobacterial-like deltaproteobacterium (future eukaryotic cytoplasm) and a metabolically versatile methanotrophic alphaproteobacterium (future mitochondrion). A refined version later proposed the evolution of the endomembrane and nuclear membrane system by invagination of the deltaproteobacterial membrane. Here, we adapt the Syntrophy hypothesis to contemporary knowledge, shifting from the original hydrogen and methane-transfer-based symbiosis (HM Syntrophy) to a tripartite hydrogen and sulfur-transfer-based model (HS Syntrophy). We propose a sensible ecological scenario for eukaryogenesis in which eukaryotes originated in early Proterozoic microbial mats from the endosymbiosis of a hydrogen-producing Asgard archaeon within a complex sulfate-reducing deltaproteobacterium. Mitochondria evolved from versatile, facultatively aerobic, sulfide-oxidizing and, potentially, anoxygenic photosynthesizing alphaproteobacterial endosymbionts that recycled sulfur in the consortium. The HS Syntrophy hypothesis accounts for (endo)membrane, nucleus and metabolic evolution in a realistic ecological context. We compare and contrast the HS Syntrophy hypothesis to other models of eukaryogenesis, notably in terms of the mode and tempo of eukaryotic trait evolution, and discuss several model predictions and how these can be tested.

中文翻译：

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重新讨论了真核生物起源的同养型假说。

与其他古细菌相比，系统发育上更接近真核生物的阿斯加德古细菌的发现，加上对微生物生态学知识的提高，对新兴的真核细胞起源（真核生物）模型施加了新的限制。长久以来的观点正在变形，有利于基于古细菌和细菌之间代谢相互作用的共生模型。其中包括经典的Searcy和氢假说，以及最新的逆流和缠结-内生化模型。二十年前，我们基于涉及产甲烷菌的古细菌（未来核）的三方代谢共生，提出了真核生物起源的同质化假说，发酵的类黏细菌三角洲变形杆菌（未来的真核细胞质）和具有代谢功能的甲烷营养型α变形杆菌（未来的线粒体）。一个改进的版本随后提出了通过三角洲变形菌膜的内陷来进化内膜和核膜系统。在这里，我们将“同质共生”假说调整为当代知识，从最初的基于氢和甲烷转移的共生关系（HM Syntrophy）转变为基于三方氢和硫转移的共生模型（HS Syntrophy）。我们为真核生物提出了一个明智的生态场景，其中真核生物起源于复杂的硫酸盐还原型三角洲细菌内产氢的阿斯加德古细菌内生共生的早期元古代微生物垫。线粒体从多功能，兼性有氧，硫化物氧化和潜在的产氧性光合作用的α蛋白细菌内共生体，它们在联盟中回收了硫。HS Syntrophy假说解释了现实生态环境中的（内）膜，核和代谢演变。我们比较并比较了HS同养异能假说与其他真核发生模型，特别是在真核性状进化的方式和速度方面，并讨论了几种模型预测以及如何对其进行检验。