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|Asgard archaea form a well-supported group with the eukaryotes in the tree of life. Credit: Eva Fernandez-Caceres|
“The evolution of complex cell types has been a long and complicated process that is poorly understood. By using new methods to obtain genome data from microbes that cannot be grown in the laboratory, we identified a new archaeal group that is related to the host cell from which eukaryotic cells evolved. These are very exciting times,” says Thijs Ettema at the Department of Cell and Molecular Biology, Uppsala University, who lead the scientific team that carried out the study.
“These organisms are our closest microbial relatives, and we know next to nothing about them. Current methods allow us to take a first genetic sneak peek. It is really exciting!” says Thijs Ettema.
“Our findings are based on analysis of genetic material that was directly obtained from the environment. We have actually never seen these cells,” says Jimmy Saw, researcher at the Department of Cell and Molecular Biology, Uppsala University, and co-lead author of the paper.
“We named these new archaea Thor, Odin and Heimdall after the Norse gods, and together with Loki, they form the Asgard archaea. Interestingly, these new groups are found in various environments all over the world, and not only in the deep sea, as Loki. So far they are most abundant in sediments,” says Eva Fernandez-Caceres, co-lead author from Uppsala University.
“Asgard archaea form a well-supported group with the eukaryotes in the tree of life. This indicates that they share a common ancestry,” says Kasia Zaremba-Niedzwiedzka, another co-lead author involved in the study from Uppsala University. “This part of the study was rather complicated, and we would clearly benefit from having more data. This is not the end of the story, rather the opposite!”
“We found that Asgard archaea share many genes uniquely with eukaryotes, including several genes that are involved in the formation of structures that give eukaryotic cells their complex character. Such genes had thus far only been found in eukaryotes, indicating that these archaea were somehow primed to become complex. However, the picture is far from being clear on exactly how this could have happened,” says Anja Spang, researcher at the Department of Cell and Molecular Biology, Uppsala University.
“It would be great if we could isolate or grow Asgard cells, and study them under the microscope. I am convinced that this will reveal more important clues about how complex cells evolved. Ultimately our microbial ancestry will be uncovered,” concludes Thijs Ettema.