Expanded Asgard archaea shed new light on the origin of eukaryotes and support a 2-domain tree of life

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 seven 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 Asgard archaea. Here, we describe five novel phylum-level Asgard archaeal lineages, tentatively named Tyr-, Sigyn-, Freyr-, Hoder- and Balderarchaeota. Comprehensive phylogenomic analyses supported a new Asgard lineage Tyrarchaeota was identified as a deeper branching lineage cluster with the eukaryotic nuclear host lineage than Heimdallarchaeota that were previously considered as the closest archaeal relatives of eukaryotes. Metabolic reconstruction of Tyrarchaeota suggests a mixotrophic lifestyle of this archaea, capable of peptides and amino acids utilization while having the potential using the Wood-Ljungdahl pathway for carbon fixation and acetogenesis. This study largely expands the Asgard superphylum, provides additional evidences to support the 2-domain life tree thus sheds new light on the evolution and geochemical functions of the Asgard archaea.