Expanding Asgard members in the domain of Archaea sheds new light on the origin of eukaryotes

Abstract

The hypothesis that eukaryotes originated from within the domain Archaea has been strongly supported by recent phylogenomic analyses placing Heimdallarchaeota from the Asgard superphylum as the closest known archaeal sister-group to eukaryotes. At present, only six phyla are described in the Asgard superphylum, which limits our understanding of the relationship between eukaryotes and archaea, as well as the evolution and ecological functions of the Asgard archaea. Here, we describe five previously unknown phylum-level Asgard archaeal lineages, tentatively named Tyr-, Sigyn-, Freyr-, Njord-and Balderarchaeota.Comprehensive phylogenomic analyses further supported the origin of eukaryotes within Archaea and a new Asgard lineage Njordarchaeota was supposed as the known closest branch with the eukaryotic nuclear host lineage. Metabolic reconstruction suggests that the Asgard archaea described here have potential to fix inorganic carbon via the Wood-Ljungdahl pathway and degrade organic matters except Njordarchaeota, which may possess a heterotrophic lifestyle with capability of peptides and amino acids utilization. Additionally, the Ack/Pta pathway for homoacetogenesis and de novo anaerobic cobalamin biosynthesis pathway were found in Balderarchaeota and Tyrarchaeota, respectively. This study largely expands the Asgard superphylum, provides additional evidences to support the 2-domain life tree and sheds new light on the evolution of eukaryotes.

Looking through the Lens of the Ribosome Biogenesis Evolutionary History: Possible Implications for Archaeal Phylogeny and Eukaryogenesis

“…Intriguingly, the tRNA Ala is located next to the 23S rRNA, in a similar fashion normally found in Euryarchaeota. To our surprise, unlinked rRNA genes are not restricted to Lokiarchaeota, as do found in Heimdallarchaeota, Wukongarchaeota, Njordarchaeota, and other recently described Asgard archaea we could examine ( Zaremba-Niedzwiedzka et al 2017 ; Liu et al 2021 ; Xie et al 2021 ; Wu et al 2022 ) (see fig. 2 C and supplementary information, Supplementary Material online).…”

“…Moreover, the linked rRNA genes organization of Odinarchaea LCB_4 and unlinked rRNA genes organization in Heimdallarchaeota have been recently confirmed by long-read sequencing ( Tamarit et al 2021 ; Wu et al 2022 ). Finally, the unlinked rRNA genes organization observed in Wukongarchaeota, Njordarchaeota (see supplementary information, Supplementary Material online) were obtained from independent metagenomic analyses ( Liu et al 2021 ; Xie et al 2021 ).…”

“…To our knowledge, most existing phylogeny analyses placing the eukaryotic lineage within the Asgard archaea, suggest a closer association of eukaryotes to Asgard possessing unlinked rRNA genes. They either occur as a sister group or within the Heimdallarchaeota–Gerdarchaeota–Kariarchaeota–Hodarchaeota–Wukongarchaeota–Njordarchaeota clades ( Zaremba-Niedzwiedzka et al 2017 ; Liu et al 2021 ; Xie et al 2021 ). A less well-supported phylogenetic hypothesis placed the eukaryotic lineage as a sister group to the Asgard and TACK superphyla ( Liu et al 2021 ).…”

The expanding Asgard archaea and their elusive relationships with Eukarya

“…S1 in Da Cunha et al 5 ). This raises the possibility that the variable positions of 13 and Xie et al 14 , respectively, and in grey new lineages not present in these publications corresponding to the Sifarchaea 12 , the Jordarchaeia 16 and Asgard Lake Cootharaba 16 . The schema was designed combining the trees of all these publications.…”

Editorial: Ecology, Metabolism and Evolution of Archaea-Perspectives From Proceedings of the International Workshop on Geo-Omics of Archaea

“…The emerging view is that archaea are prominent members of all terrestrial and marine communities (DeLong) and play central roles in global carbon and nitrogen cycles in the ocean and on land (Hatzenpichler, 2012;Spang et al, 2017;Yu et al, 2018;Evans et al, 2019;Qin et al, 2020;Zhang et al, 2020). Recent environmental genomics on uncultured asgard archaea (Eme et al, 2017;Spang et al, 2017;van der Gulik et al, 2017;Zhou et al, 2018;Liu et al, 2021;Xie et al, 2021) and the isolation of co-cultures of the microscopically characterized obligate symbiotic archeaon Candidatus Prometheoarchaeum syntrophicum (Imachi et al, 2020) has led to exciting insights into the role of the Archaea in eukaryogenesis. However, most archaea remain uncultivated (Zhang et al, 2015;Spang et al, 2017;Rinke et al, 2021) and therefore the world of the Archaea remains an exciting frontier in biology.…”