The genomes of the Asgard superphylum of Archaea hold clues pertaining to the nature of the host cell that acquired the mitochondrion at the origin of eukaryotes1-4. Representatives of the Asgard candidate phylum Candidatus Lokiarchaeota (Lokiarchaeon) have the capacity for acetogenesis and fermentation5-7, but how their metabolic activity responds to environmental conditions is poorly understood. Here, we show that in anoxic Namibian shelf sediments, Lokiarchaeon gene expression levels are higher than those of bacterial phyla and increase with depth below the seafloor. Lokiarchaeon gene expression was significantly different across a hypoxic-sulfidic redox gradient, whereby genes involved in growth, fermentation and H2-dependent carbon fixation had the highest expression under the most reducing (sulfidic) conditions. Quantitative stable isotope probing revealed that anaerobic utilization of CO2 and diatomaceous extracellular polymeric substances by Lokiarchaeon was higher than the bacterial average, consistent with higher expression of Lokiarchaeon genes, including those involved in transport and fermentation of sugars and amino acids. The quantitative stable isotope probing and gene expression data demonstrate homoacetogenic activity of Candidatus Lokiarchaeota, whereby fermentative H2 production from organic substrates is coupled with the Wood-Ljungdahl carbon fixation pathway8. The high energetic efficiency provided by homoacetogenesis8 helps to explain the elevated metabolic activity of Lokiarchaeon in this anoxic, energy-limited setting.

中文翻译：

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代谢活动分析表明 Lokiarchaeon 在硫化海洋沉积物中表现出同质乙酸生成。

古细菌 Asgard superphylum 的基因组包含有关在真核生物 1-4 起源处获得线粒体的宿主细胞性质的线索。Asgard 候选门 Candidatus Lokiarchaeota (Lokiarchaeon) 的代表具有产乙酸和发酵的能力 5-7，但它们的代谢活动如何对环境条件做出反应却知之甚少。在这里，我们表明在缺氧的纳米比亚大陆架沉积物中，Lokiarchaeon 基因表达水平高于细菌门，并随着海底以下深度的增加而增加。Lokiarchaeon 基因表达在缺氧 - 硫化物氧化还原梯度中显着不同，其中涉及生长、发酵和 H2 依赖性碳固定的基因在最还原（硫化物）条件下具有最高表达。定量稳定同位素探测表明，Lokiarchaeon 对 CO2 和硅藻胞外聚合物的厌氧利用高于细菌平均值，这与 Lokiarchaeon 基因的高表达一致，包括参与糖和氨基酸运输和发酵的基因。定量稳定同位素探测和基因表达数据证明了 Candidatus Lokiarchaeota 的同型产乙酸活性，由此有机底物的发酵 H2 生产与 Wood-Ljungdahl 碳固定途径相结合。homoacetogenesis8 提供的高能量效率有助于解释 Lokiarchaeon 在这种缺氧、能量有限的环境中代谢活动升高。