Asgard is a recently discovered archaeal superphylum, closely linked to the emergence of eukaryotes. Among Asgard archaea, Lokiarchaeota are abundant in marine sediments, but their in situ activities are largely unknown except for Candidatus ‘Prometheoarchaeum syntrophicum’. Here, we tracked the activity of Lokiarchaeota in incubations with Helgoland mud area sediments (North Sea) by stable isotope probing (SIP) with organic polymers, ¹³C-labelled inorganic carbon, fermentation intermediates and proteins. Within the active archaea, we detected members of the Lokiarchaeota class Loki-3, which appeared to mixotrophically participate in the degradation of lignin and humic acids while assimilating CO₂, or heterotrophically used lactate. In contrast, members of the Lokiarchaeota class Loki-2 utilized protein and inorganic carbon, and degraded bacterial biomass formed in incubations. Metagenomic analysis revealed pathways for lactate degradation, and involvement in aromatic compound degradation in Loki-3, while the less globally distributed Loki-2 instead rely on protein degradation. We conclude that Lokiarchaeotal subgroups vary in their metabolic capabilities despite overlaps in their genomic equipment, and suggest that these subgroups occupy different ecologic niches in marine sediments.

Asgard 是最近发现的古细菌超门，与真核生物的出现密切相关。在 Asgard 古细菌中，Lokiarchaeota 在海洋沉积物中含量丰富，但除了Candidatus 'Prometheoarchaeum syntrophicum' 外，它们的原位活动在很大程度上是未知的。^{在这里，我们通过使用有机聚合物、 13} C 标记的无机碳、发酵中间体和蛋白质的稳定同位素探测 (SIP) 来跟踪 Lokiarchaeota 在与 Helgoland 泥区沉积物（北海）孵育中的活动。在活跃的古生菌中，我们检测到 Lokiarchaeota 类 Loki-3 的成员，它们似乎混合营养地参与木质素和腐殖酸的降解，同时同化 CO ₂，或异养使用的乳酸。相比之下，Lokiarchaeota 类 Loki-2 的成员利用蛋白质和无机碳，以及在孵化中形成的降解细菌生物量。宏基因组分析揭示了 Loki-3 中乳酸降解的途径，以及参与芳香族化合物降解，而全球分布较少的 Loki-2 则依赖于蛋白质降解。我们得出结论，尽管基因组设备重叠，但 Lokiarchaeotal 亚群的代谢能力有所不同，并表明这些亚群在海洋沉积物中占据不同的生态位。