Reacción a "A Spanish study published in Nature reimagines the origin of our cells as a story of microbial alliances"

This is a really important paper. I know Toni Gabaldón's group well (no COI, met him at a meeting once and that is it), and they have a strong reputation in this area. The analyses look carefully done, and the consistency of the results across multiple datasets is reassuring. 

The conventional story of eukaryogenesis tends to center on a single symbiotic event: an Asgard archaeon takes up an alphaproteobacterium, that bacterium becomes the mitochondrion, and everything follows from there. What this work shows is that the reality was far messier and more interesting. The proto-eukaryotic lineage was acquiring genes from multiple unrelated bacterial groups over what was likely a very long period of time, and the mitochondrial endosymbiosis, while important, was just one episode in a much longer history of interactions. We tend to overweight the mitochondrion in how we think about eukaryotic origins, and this paper is a corrective to that. 

There's a beautiful logic to it, too. If the Asgard archaea was capable of establishing a symbiotic relationship with one bacterial lineage, internalizing much of its genome, there's no reason to expect that would be the only such interaction. These organisms were embedded in complex microbial communities, and the signatures of those ecological interactions are still legible in eukaryotic genomes billions of years later. It also raises the question of whether some of these genes came from earlier endosymbionts which were lost, perhaps prior to the start of the symbiosis leading to the mitochondrion. We tend to forget about ecology when looking through the long lens of ancient genomic reconstruction, and this work is a nice reminder that it mattered enormously.

The virus finding is particularly exciting. The idea that Nucleocytoviricota were shuttling genetic information between disparate lineages and into the proto-eukaryotic line reinforces a growing recognition that viruses play a critical role in long-term evolutionary dynamics. The boundaries between lineages (perhaps particularly for this lineage!), seem to be far more porous than we generally appreciate.

Taken together, the paper makes a compelling case that eukaryogenesis was not a phase transition crossed via a single event, but a gradual process of genetic assembly from a diverse microbial environment, and it shows us how much we still have to learn about how that process unfolded.