An artist impression on the evolution of complex cells © Blair Lyons, Stroma Studios

Thor and Loki microbes hold clues to origin of life

An elusive group of microbes with names inspired by old Norse mythology shed more light on the origin of multicellular life.

Avengers fans will know Asgard as the home to the Norse gods Thor and Loki, but thanks to a new study it also lends its legendary name to an elusive group of microbes that shed more light on the origins of life on Earth.

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The godly group are all single-celled organisms, technically called archaea or ‘ancient things’. Archaea were only discovered in 1977 and form one of the three domains of life alongside bacteria and eukaryotes.

The eukaryotes make up all visible life, including us, but it remains a mystery how we multicellular organisms evolved from archaea and bacteria. “The evolution of complex cell types has been a long and complicated process, it’s poorly understood,” says Thijs Ettema, who worked on the study published in Nature this week.

The dominant theory is that a co-operative relationship developed, in which a group of archaea engulfed bacterial cells, gaining some evolutionary advantage in the process. This study gives support to that theory, “we identified a new archaeal group that is related to the host cell from which eukaryotic cells evolved,” says Ettema.

The identification of this new group, known as the Asgard archaea, represents another missing link between single-celled organisms and complex life. It follows the description in 2015 of the genome of the deep-sea archaeon Loki at a hydrothermal vent.

“We named these new archaea Thor, Odin and Heimdall after the Norse gods” says Eva Fernandez-Caceres, who was also part of the study team. “These new groups are found in environments all over the world, not only in the deep sea like Loki,” she said.

The genetic evidence seems to show a strong evolutionary link between eukaryotes and organisms related to the Asgard archaea. “[They] share many genes thought to be unique to eukaryotes” says team member Anja Spang “several that are involved in giving eukaryotic cells their complex character.”

Loki and the other godly archaea were discovered from genetic material isolated from the environment. Archaea are found everywhere, but notably in extreme environments where other life cannot survive, such as volcanic pools and the hydrothermal vent where Loki was found.


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