Asgard (archaea)

Asgard
Scientific classification
Domain: Archaea
Kingdom: Proteoarchaeota
Superphylum: Asgard
Katarzyna Zaremba-Niedzwiedzka et al. 2017
Phylum
  • "Lokiarchaeota" Spang et al. 2015
  • "Thorarchaeota" Seitz et al. 2016
  • "Odinarchaeota" Katarzyna Zaremba-Niedzwiedzka et al. 2017
  • "Heimdallarchaeota" Katarzyna Zaremba-Niedzwiedzka et al. 2017

Asgard is a proposed superphylum consisting of a group of uncultivated archaea that includes Lokiarchaeota, Thorarchaeota, Odinarchaeota, Heimdallarchaeota.[1] The Asgard superphylum represents the closest prokaryotic relatives of eukaryotes.[2]

Discovery

In the summer of 2010, sediments from a gravity core taken in the rift valley on the Knipovich ridge in the Arctic Ocean, near the so-called Loki's Castle hydrothermal vent site, were analysed. Specific sediment horizons, previously shown to contain high abundances of novel archaeal lineages were subjected to metagenomic analysis.[3][4]

In 2015, a Uppsala University-led team proposed the Lokiarchaeota phylum based on phylogenetic analyses using a set of highly conserved protein-coding genes.[5] Through a reference to the hydrothermal vent complex from which the first genome sample originated, the name refers to Loki, the Norse shape-shifting god.[6] The Loki of literature has been described as "a staggeringly complex, confusing, and ambivalent figure who has been the catalyst of countless unresolved scholarly controversies",[7] an analogy to the role of Lokiarchaeota in debates about the origin of eukaryotes.[5]

In 2016, a University of Texas-led team discovered Thorarchaeota from samples taken from the White Oak River in North Carolina, named in reference to Thor, another Norse god.[8]

Additional samples from Loki’s Castle, Yellowstone National Park, Aarhus Bay, an aquifer near the Colorado River, New Zealand's Radiata Pool, hydrothermal vents near Taketomi Island, and the White Oak River estuary led researchers to discover Odinarchaeota and Heimdallarchaeota[1], which, following the pattern of naming the archaea after Norse gods, were named for Odin and Heimdallr, respectively. Researchers therefore named the superphylum containing these microbes, Asgard, after the realm of the gods in Norse mythology.[1]

Classification

The phylogenetic relationship of this group is still under discussion. The relationship of the members is approximately as follows[2]:

Proteoarchaeota

TACK

 

Korarchaeota

 
 

 

Crenarchaeota

 
 

 

 

Aigarchaeota

 
 

Geoarchaeota

 
 
 

 

Thaumarchaeota

 
 

Bathyarchaeota

 
 
 
 
 
Asgard

 

 

Lokiarchaeota

 
 

Odinarchaeota

 
 

Thorarchaeota

 
 
 

 

Heimdallarchaeota

 
(+α─Proteobacteria)

Eukaryota

 
 
 
 

References

  1. 1 2 3 Zaremba-Niedzwiedzka, Katarzyna; Caceres, Eva F.; Saw, Jimmy H.; Bäckström, Disa; Juzokaite, Lina; Vancaester, Emmelien; Seitz, Kiley W.; Anantharaman, Karthik; Starnawski, Piotr (11 January 2017). "Asgard archaea illuminate the origin of eukaryotic cellular complexity". Nature. 541 (7637): 353–358. doi:10.1038/nature21031. ISSN 1476-4687.
  2. 1 2 Eme, Laura; Spang, Anja; Lombard, Jonathan; Stairs, Courtney W.; Ettema, Thijs J. G. (10 November 2017). "Archaea and the origin of eukaryotes". Nature Reviews Microbiology. 15 (12): 711–723. doi:10.1038/nrmicro.2017.133. ISSN 1740-1534.
  3. ↑ Jørgensen, Steffen Leth; Hannisdal, Bjarte; Lanzen, Anders; Baumberger, Tamara; Flesland, Kristin; Fonseca, Rita; Øvreås, Lise; Steen, Ida H; Thorseth, Ingunn H; Pedersen, Rolf B; Schleper, Christa (September 5, 2012). "Correlating microbial community profiles with geochemical data in highly stratified sediments from the Arctic Mid-Ocean Ridge". PNAS. 109 (42): E2846–E2855. doi:10.1073/pnas.1207574109. PMC 3479504. PMID 23027979.
  4. ↑ Jørgensen, Steffen Leth; Thorseth, Ingunn H; Pedersen, Rolf B; Baumberger, Tamara; Schleper, Christa (October 4, 2013). "Quantitative and phylogenetic study of the Deep Sea Archaeal Group in sediments of the Arctic mid-ocean spreading ridge". Frontiers in Microbiology. 4. doi:10.3389/fmicb.2013.00299.
  5. 1 2 Spang, Anja; Saw, Jimmy H.; Jørgensen, Steffen L.; Zaremba-Niedzwiedzka, Katarzyna; Martijn, Joran; Lind, Anders E.; Eijk, Roel van; Schleper, Christa; Guy, Lionel (May 2015). "Complex archaea that bridge the gap between prokaryotes and eukaryotes". Nature. 521 (7551): 173–179. doi:10.1038/nature14447. ISSN 1476-4687. PMC 4444528.
  6. ↑ Yong, Ed. "Break in the Search for the Origin of Complex Life". The Atlantic. Retrieved 2018-03-21.
  7. ↑ von Schnurbein, Stefanie (November 2000). "The Function of Loki in Snorri Sturluson's "Edda"". History of Religions. 40 (2): 109–124. doi:10.1086/463618.
  8. ↑ Seitz, Kiley W; Lazar, Cassandre S; Hinrichs, Kai-Uwe; Teske, Andreas P; Baker, Brett J (29 January 2016). "Genomic reconstruction of a novel, deeply branched sediment archaeal phylum with pathways for acetogenesis and sulfur reduction". The ISME Journal. 10 (7): 1696–1705. doi:10.1038/ismej.2015.233. ISSN 1751-7370.
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