The discovery of new archaea offers more clues on the development of eukaryotic cells

Asgard archaea in the tree of life (Image courtesy Eva Fernandez-Caceres)
Asgard archaea in the tree of life (Image courtesy Eva Fernandez-Caceres)

An article published in the journal “Nature” describes the discovery of new microorganisms that provide more information on the evolution of eukaryotic organisms, the ones formed by complex cells. The new species discovered are archaea that were called Thor, Odin and Heimdall, simpler organisms that however have some characteristics found only in eukaryotes and together with another archaea family called Loki whose discovery was announced in September 2015, form a group that was called the Asgard archaea.

The evolution from prokaryotic organisms made up of small and simple cells to eukaryotes, which includeplants, animals and fungi, is a problem still unsolved. Until a few years ago, genetic research on microorganisms were long and difficult but the steady progress in this area are helping biologists a lot. However, there’s the problem of finding interesting microorganisms when new species are discovered all the time, including many in the domain Archaea, included among prokaryotes.

Dr. Thijs Ettema of the Uppsala University, Sweden, had conducted the research that  studied the archaea called Loki or Lokiarchaeota, discovered in an ocean thermal spring. The scientist was also part of the team that conducted this new research and this time other archaea were searched in that spring, called Loki’s Castle, and in places such as the US Yellowstone National Park.

The research gave very interesting results with the discovery of other archaea that seem related in various ways to Loki and also show various characteristics typical of eukaryotes. The names of these new archaea are inspired by Norse mythology: Thor or Thorarchaeota, Odin or Odinarchaeota and Heimdall or Heimdallarchaeota.

Each of these archaea is different from the others enough that according to researchers is a different phylum. However, they’re united by the fact of having characteristic of eukaryotes so a superphylum was proposed called Asgard consisting of these four phyla.

These Archaea may be the closest relatives to animals among the microbes but the last common ancestor between archaea and eukaryotes may have lived about two billion years ago. After such a long time and all the changes that happened in the world it’s difficult to reconstruct the evolutionary processes that occurred in the species of that ancestor common to fork into those that became archaea and eukaryotes. For example, researchers are wondering why the Asgard archaea developed a cellular complexity with characteristics of eukaryotes prokaryotes while other prokaryotes haven’t.

The discovery of other possible missing links between prokaryotes and eukaryotes is an interesting step forward in the search for answers regarding the development of increasingly complex cells. The fact that some of these archaea live in rather extreme environments is a problem because it’s not possible to grow them in laboratory. Being able to do that would allow studying them much better to see how they develop and live.

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