Katarzyna Zaremba-Niedzwiedzka et al. 2017
Asgard or Asgardarchaeota is a proposed superphylum consisting of a group of uncultivated archaea that includes Lokiarchaeota, Thorarchaeota, Odinarchaeota, Heimdallarchaeota. The Asgard superphylum represents the closest prokaryotic relatives of eukaryotes.
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.
In 2015, an Uppsala University-led team proposed the Lokiarchaeota phylum based on phylogenetic analyses using a set of highly conserved protein-coding genes. 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. 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", an analogy to the role of Lokiarchaeota in debates about the origin of eukaryotes.
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, Japan and the White Oak River estuary in the United States led researchers to discover Odinarchaeota and Heimdallarchaeota, 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.
The phylogenetic relationship of this group is still under discussion. The relationship of the members is approximately as follows:
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