Genetic analysis places Loki squarely within the single-celled archaea. But it possesses an intriguing collection of genes that look as though they would be more at home in eukaryotes, rather like modern words dotting a medieval manuscript. In fact, Loki’s genetic machinery suggests that the organism might be able to engulf other cells, the first step in the creation of mitochondria. Even if Loki doesn’t solve the mystery of our ancient origins, its discovery shows just how much biological diversity remains to be unearthed. Perhaps the next discovery will be a eukaryote with no history of possessing mitochondria. Or perhaps it will be an archaeon with signs of a symbiotic bacterium living within.

2020-11-25: Viral nucleus origin?

A trove of giant viruses was recently sequenced from the very same deep-sea sediments where Lokiarchaeota were discovered. He hopes someone will test whether any of these viruses can infect archaea and, if so, whether they build viral factories similar to those made by the NCLDVs that infect eukaryotes. Demonstrating that would be “game over.”

2022-11-12: Syntropic eukaryogenesis

Today, at the microbial mats in the Atacama Desert and other sites throughout the world, scientists are investigating what the earliest eukaryotic cells may have looked like, the partnerships they may have struck up with other organisms, and how their molecular machinery might have functioned and evolved. Already, the discovery of the Asgards has solidified certain aspects of eukaryogenesis while raising new questions about others. “I think this is the most exciting development in biology right now. So much is being discovered and so many predictions are being met. Eukaryogenesis is arguably one of the most important events in the history of life, after the origin of life itself.” Many scientists have rallied behind the idea that the first eukaryotes evolved out of a syntrophy between an archaeal host and bacteria that somehow found their way inside to become the organelles, such as nuclei and mitochondria, that distinguish eukaryotes. The details of these relationships remain murky, but mitochondria provide the most tantalizing clues to their origin story. “There’s DNA in mitochondria that we can somewhat clearly connect or trace back to alphaproteobacteria”. There are contrasting hypotheses as to how the alphaproteobacterium would have gotten inside an archaeal host, however. In the eukaryogenesis version of the chicken-and-egg conundrum, scientists go back and forth on whether mitochondria would have been necessary to power the energetically expensive process of phagocytosis, or whether phagocytosis would have had to arise first as the means of ingesting the symbiotic partner. When it comes to the nucleus, the picture is much less clear. Hypotheses of its origin run the gamut from a bacterial endosymbiont within an amoeboid host to the remnants of a giant virus.

2023-06-19: Lokiarchaeota aren’t the the origin of eukaryotes, but are closely related.

Eukaryotes are placed as a well-nested clade within Asgard archaea and as a sister lineage to Hodarchaeales, a newly proposed order within Heimdallarchaeia, consistent with the 2 domain tree of life scenario. Using sophisticated gene tree and species tree reconciliation approaches, we show that analogous to the evolution of eukaryotic genomes, genome evolution in Asgard archaea involved significantly more gene duplication and fewer gene loss events compared with other archaea. Finally, we infer that the last common ancestor of Asgard archaea was probably a thermophilic chemolithotroph and that the lineage from which eukaryotes evolved adapted to mesophilic conditions and acquired the genetic potential to support a heterotrophic lifestyle.

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