A group of microbes discovered recently in the sediments of a hydrothermal field could belong to the line from which we have evolved.
Our Earth dates from about 4.5 billion years, and the life soon after. For a long time, the living beings have belonged to two domains: bacteria and arches, microscopic monocells.
It was a status quo for at least 1.7 billion years, then very different eukaryotes joined. The eukaryotes have a larger genome, a nucleus and organelles delimited by membranes.
Eucaryotes could have been created by highly unlikely fusion between members of the other two domains: a bacterium has found its place in an archeon and has become a permanent part of its host, providing it with a profitable source of energy and pathways of evolution previously inaccessible.
Until 2015, the archeon was little known. A team from the University of Uppsala collected sediment samples from the "Loki Castle", a field of hydrothermal vents located between Greenland and Norway, between Iceland and Svalbard, at a depth of 2,300 meters, on the Arctic Ocean Ridge.
DNA analysis in the sample allowed to identify a new archeon called Lokiarcheota, a living relative of all eukaryotes.
Some have been found in Yellowstone National Park, a hot spring in New Zealand, or deep sea vents near a Japanese island.
Four major groups, Lokiarchaeota, Thorarchaeota, Odinarchaeota, and Heimdallarcheota, have been distinguished for the moment, referring to the northern gods (Loki, Thor, Odin, Heimdall) living in the mythological Kingdom of Asgard.
The Nordic pantheon gathers some 50 Asgardian gods ... the next discoveries will draw their particular names without problems.
The debate about the origin of eukaryotes remains entire, ... if Asgardian microbes possess genes supposedly unique to eukaryotes, they are not nevertheless eukaryotes themselves.
Moreover, if their DNA has been found, we still have no idea of their appearance. It is crucial to see the functioning of cells, but they remain either difficult to access in deep ocean sediments, or present in poor quantities in shallow environments.
Yellowstone National Park - Midway geyser basin / Grand Prismatic pool - another "nest" to archeon - photo © Bernard Duyck
- The Atlantic - A Break in the Search for the Origin of Complex Life - link
- For Science - Lokiarchaeon, a missing link between archaea and eukaryotes? - link
- CNRS The Journal - The metagenomic revolution - by JP Braly - link
- Nature communications - Discovery of a Black Smoker at the Arctic Mid-Ocean Ridge by Rolf B.Pederse & al - link