Asgard Archaea Hint at Eukaryotic Origins

A newly discovered superphylum of archaea may be related to a microbe that engulfed a bacterium to give rise to complex eukaryotic life.

By | January 18, 2017

WIKIMEDIA, JIM PEACOOne key step in the origins of eukaryotic life likely involved a single, large archaeon engulfing a smaller bacterium. The symbiotic relationship between the microbes flourished, researchers have proposed, giving rise to modern mitochondria and chloroplasts that share striking similarities with their aerobic and photosynthetic predecessors, respectively. But scientists have long searched for the archaeon behind the initial engulfing.

According to a study published January 11 in Nature, this archaeon may have been related to the Asgard archaea—a pantheon of microbes named for Norse gods, including Lokiarchaeota, Thorarchaeota, Odinarchaeota, and Heimdallarchaeota.

“The things we thought made a eukaryote a eukaryote, we’re now finding in these new archaea,” coauthor Brett Baker, an assistant professor at the University of Texas Marine Science Institute, said in a press release. “We’re essentially rewriting the textbook on basic biology.”

In 2015, coauthor Thijs Ettema of Uppsala University in Sweden discovered a new type of microbe and named it Lokiarchaeota. Shortly thereafter, a separate team discovered a similar microbe and named it Thorarchaeota. In both cases, the researchers noted the similarities between these archaea and eukaryotic cells. 

See “Prokaryotic Microbes with Eukaryote-like Genes Found

For the present study, Ettema and colleagues reconstructed the phylogenetic group from which these two microbes likely originated, and reported two new groups also named for Norse gods, Odinarchaeota and Heimdallarchaeota. They then named the superphylum that contains all these groups “Asgard,” home of the Norse gods.

Their analysis suggests that Asgard archaea are similar to eukaryotes in several key ways. Asgard genomes are enriched for proteins once thought specific to eukaryotes, for instance, including genes that code for eukaryotic membrane-trafficking and vesicle biogenesis. The findings suggest that the archaeon that gave rise to eukaryotic cells may well have been closely related to Asgard archaea.

“I am convinced that [further study] will reveal more important clues about how complex cells evolved,” Ettema said in the press release. “Ultimately our microbial ancestry will be uncovered.”

Meantime, Ettema’s team will continue to search for more archaea within the Asgard superphylum.  “There’s around 50 more Asgardian gods,” he told The Atlantic. “We’re good to go for the next few years.”

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