Heimdallarchaeia
Class of archaea related to eukaryotes
From Wikipedia, the free encyclopedia
Heimdallarchaeia (also known as "Candidatus Heimdallarchaeota") is a class of archaea within the phylum Asgardarchaeota. Heimdallarchaeia is considered the closest known archaeal relative of eukaryotes, making it a focus of research into eukaryogenesis.[1] Knowledge of the group derives from metagenome-assembled genomes (MAGs) and environmental sequencing. Heimdallarchaeia has been visualized in Lake Techirghiol using FISH.[2]
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| CARD-FISH imaging from Lake Techirghiol | |
| Scientific classification (Candidatus) | |
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| Class: | "Candidatus Heimdallarchaeia" Zaremba-Niedzwiedzka et al., 2017 |
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Discovery
Heimdallarchaeia was described in 2017 by Uppsala University researchers, alongside three other new archaeal lineages, Odinarchaeia, Thorarchaeia, and Lokiarchaeia, establishing the Asgard superphylum.[1] The genomic sequences were recovered from metagenomic samples collected at multiple sites, including sediments from Loki's Castle hydrothermal vent. The class is named after Heimdall, the Norse god who guards the Bifrost bridge between realms.
Two of three original Lokiarchaeum metagenome bins from the 2015 study by Spang et al. (designated Loki2 and Loki3) were subsequently reclassified as "Heimdallarchaeote LC_2" and "Heimdallarchaeote LC_3".[3]
Taxonomy and classification
Heimdallarchaeia holds Candidatus status because no member has been isolated in pure culture, meaning the group cannot be formally described under the International Code of Nomenclature of Prokaryotes.[4] The original publication proposed it at the phylum level as "Candidatus Heimdallarchaeota", but subsequent taxonomic revisions reclassified it as a class within the phylum Asgardarchaeota.[5] Within the Genome Taxonomy Database, several orders are recognised within Heimdallarchaeia, including Hodarchaeales, Heimdallarchaeales, Kariarchaeales, and the informally designated Gerdarchaeales.[6] The placement of a further lineage, Njordarchaeales, within Heimdallarchaeia is uncertain, as some associate it more closely with TACK.[7]
| Eme et al., 2023.[8] | Zhang et al., 2025.[9] | GTDB release 11-RS232 (15th April 2026).[10][11][12] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Eukaryotic proteins
Like other Asgard archaea, Heimdallarchaeia encode numerous eukaryotic signature proteins, including homologues of ESCRT and proteins involved in the ubiquitin modifier system.[1] Among all Asgard lineages, Heimdallarchaeia encode the highest count of signature proteins, with 31 identified (compared to 28 for Lokiarchaeia, 25 for Thorarchaeia and Odinarchaeia) from a reference set of 38 eukaryote-specific protein families.[13]
The 2017 description reported that Heimdallarchaeia possess histones with N-terminal tails resembling eukaryotic core histone tails, at the time thought to be unique to eukaryotes.[1][14] Structural characterisation of a profilin encoded by Heimdallarchaeota LC3 demonstrated that it adopts a canonical profilin fold, binds polyproline motifs, and that its activity is regulated by phosphoinositides, closely paralleling the behaviour of eukaryotic profilins.[13]