An article published in the journal “Nature” reports the results of a genetic study on the archaea Asgard that expands the genetic diversity of this group of microorganisms and concludes that the taxonomic order Hodarchaeales is the one most closely related to eukaryotes, the organisms that make up all forms of multicellular life on Earth. A team of researchers conducted a genetic analysis of Asgard archaea from samples collected at 11 locations around the world in a genomic research using state-of-the-art analysis techniques. The conclusion is that eukaryotes constitute a group within the Asgard archaea, from which they may have directly evolved.
The discovery of the Asgard archaea was announced in 2017 and aroused great interest among biologists due to the characteristics of these microorganisms, in various ways similar to those of eukaryotic cells. Since this discovery, various groups of researchers started studying what was proposed as a superphylum to try to solve some mysteries related to the evolution of eukaryotes from simpler organisms.
The results, with the discovery of various similarities between Asgard archaea and eukaryotes, are arriving and this new study even proposes to include eukaryotes within the taxonomic classification of the Asgard group. A superphylum was proposed for the Asgard and including eukaryotes within it would somehow demote them since they are currently considered a domain and therefore on the same level as archaea. The image (Courtesy University of Texas at Austin. All rights reserved) shows the structure of the various groups of archaea resulting from this study with eukaryotes as part of this taxonomic domain.
Taxonomic considerations could keep biologists busy for years given the developments in studies focusing on the Asgard archaea and their similarities to eukaryotes. The study published in “Nature” is based on a genomic analysis that among other things expands the diversity of the Asgard.
The analyzed genomes were collected in 11 places around the world. Previous studies indicate that they evolved over two billion years ago and diversified by adapting to very different environments ranging from deep seas to hot springs. So far, only two types of Asgard were successfully grown in the laboratory forcing interested researchers to harvest them in their natural environments.
This genomic study based on state-of-the-art genetic analysis techniques added 63 hitherto undescribed genomes to the Asgard group. According to reconstructions, their possible common ancestors lived in hot environments consuming carbon dioxide and chemicals. Their evolution and diversification also led to substantial metabolic changes with some descendants consuming carbon and living in colder environments, much like eukaryotes.
The Asgard archaea that were found most similar to eukaryotes are those of the taxonomic order Hodarchaeales, or simply Hod like the Norse god they were named after. In the new taxonomic reconstruction, the proposed superphylum Asgard includes the proposal of some phyla among which the Heimdallarchaeia which in turn includes two groups: the Asgard Hodarchaeales and the eukaryotes.
The metagenomic approach of the new genetic research, which combines the power of today’s computers with sophisticated software to the latest genetic analysis techniques, is leading to great results in understanding the evolution of life on Earth. In the case of archaea and eukaryotes, each new study offers new insights into the origins of eukaryotic cell complexity. It’s a complex work that must reconstruct a couple of billions of evolutionary history and discovering the kinships with the Asgard archaea allows to make significant progress.