Heimdallarchaeia
| Heimdallarchaeia | |
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| CARD-FISH imaging from Lake Techirghiol | |
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| Class: | "Candidatus Heimdallarchaeia" Zaremba-Niedzwiedzka et al., 2017
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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]
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]
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.[8]
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][9] 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.[8]
| Eme et al., 2023.[10] | Zhang et al., 2025.[11] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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See also
References
- ^ a b c d Zaremba-Niedzwiedzka, Katarzyna; Caceres, Eva F.; Saw, Jimmy H.; Bäckström, Disa; Juzokaite, Lina; Vancaester, Emmelien; Seitz, Kiley W.; Anantharaman, Karthik; Starnawski, Piotr; Kjeldsen, Kasper U.; Stott, Matthew B.; Nunoura, Takuro; Banfield, Jillian F.; Schramm, Andreas; Baker, Brett J.; Spang, Anja; Ettema, Thijs J. G. (2017). "Asgard archaea illuminate the origin of eukaryotic cellular complexity". Nature. 541 (7637): 353–358. doi:10.1038/nature21031. PMID 28077874.
- ^ Coskun, Ömer K.; Geiß, Martin; Almendinger, Moritz; Hinzke, Timo; Kleiner, Manuel; Teske, Andreas; Spang, Anja; Ettema, Thijs J. G.; Wünsch, Ulrike J.; Rodrigues-Oliveira, Thiago; Ettema, Thijs J. G. (2020). "Visualization of Lokiarchaeia and Heimdallarchaeia (Asgardarchaeota) by Fluorescence In Situ Hybridization and Catalyzed Reporter Deposition (CARD-FISH)". mSphere. 5 (4): e00686-20. doi:10.1128/msphere.00686-20. PMC 7392546. PMID 32727863.
- ^ Spang, Anja; Eme, Laura; Saw, Jimmy H.; Caceres, Eva F.; Zaremba-Niedzwiedzka, Katarzyna; Lombard, Jonathan; Guy, Lionel; Ettema, Thijs J. G. (2018). "Asgard archaea are the closest prokaryotic relatives of eukaryotes". PLOS Genetics. 14 (3) e1007080. doi:10.1371/journal.pgen.1007080. PMC 5875740. PMID 29596421.
- ^ Oren, A.; Göker, M. (2023). "Candidatus list no. 5. Lists of names of prokaryotic Candidatus taxa". International Journal of Systematic and Evolutionary Microbiology. 73: 5821. doi:10.1099/ijsem.0.005821.
- ^ Liu, Yang; Makarova, Kira S.; Huang, Wen-Chih; Wolf, Yuri I.; Nikolskaya, Anastasia N.; Zhang, Xinxin; Cai, Mingwei; Zhang, Cheng-Jie; Xu, Wen; Luo, Zhe (2021). "Expanded diversity of Asgard archaea and their relationships with eukaryotes". Nature. 593 (7860): 553–557. doi:10.1038/s41586-021-03494-3. PMC 11165668. PMID 33911286.
- ^ Wen, Jun; Zhang, Ying; Zhou, Hong; Lian, Chao; Sun, Wenjun (2024). "Metagenomic insights into Heimdallarchaeia clades from the deep-sea cold seep and hydrothermal vent". Environmental Microbiome. 19 (1) 43: 44. doi:10.1186/s40793-024-00585-2. PMC 11193907. PMID 38909236.
- ^ Eme, Laura; Tamarit, Daniel; Caceres, Eva F.; Stairs, Courtney W.; Anda, Valerie De; Schön, Max E.; Seitz, Kiley W.; Dombrowski, Nina; Lewis, William H.; Homa, Felix; Saw, Jimmy H.; Lombard, Jonathan; Nunoura, Takuro; Moore, K. R.; Ettema, Thijs J. G. (2023). "Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes". Nature. 618 (7967): 992–999. doi:10.1038/s41586-023-06186-2. PMC 10307638. PMID 37316666.
- ^ a b Chi, H.; Jung, H.; Bhatt, S.; Bhatt, A.; Bhatt, H.; et al. (2021). "Heimdallarchaea encodes profilin with eukaryotic-like actin regulation and polyproline binding". Communications Biology. 4: 1024. doi:10.1038/s42003-021-02543-x.
- ^ "Asgard (archaea)". Wikipedia.
- ^ Eme, Laura; Tamarit, Daniel; Caceres, Eva F.; Stairs, Courtney W.; De Anda, Valerie; Schön, Max E.; Seitz, Kiley W.; Dombrowski, Nina; Lewis, William H.; Homa, Felix; Saw, Jimmy H.; Lombard, Jonathan; Nunoura, Takuro; Li, Wen-Jun; Hua, Zheng-Shuang; Chen, Lin-Xing; Banfield, Jillian F.; St John, Emily; Reysenbach, Anna-Louise; Stott, Matthew B.; Schramm, Andreas; Kjeldsen, Kasper U.; Teske, Andreas P.; Baker, Brett J.; Ettema, Thijs J. G. (2023-06-14). "Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes". Nature. 618: 992–999. doi:10.1038/s41586-023-06186-2.
- ^ Zhang, Jiawei; Feng, Xiaoyuan; Li, Meng; Liu, Yang; Liu, Min; Hou, Li-Jun; Dong, Hong-Po (2025-05-07). "Deep origin of eukaryotes outside Heimdallarchaeia within Asgardarchaeota". Nature. 642: 990–998. doi:10.1038/s41586-025-08955-7.