Evolution: origin of eukaryotes: Archaea candidate found (Evolution)

by David Turell @, Thursday, January 16, 2020, 00:24 (204 days ago) @ David Turell

Finally cultured:

https://arstechnica.com/science/2017/01/microbes-found-that-are-the-closest-living-rela...

"Last year, a hydrothermal vent in the Arctic named Loki's Castle yielded organisms that picked up the name Lokiarchaea. Now, researchers have used Lokiarchaea's genome to find a large group of related species that they are naming the Asgard superphylum. Genetically, these organisms are the closest relatives of complex cells. The relationship is so close that all organisms with complex cells may simply be one branch of this group.

***

"So, what sort of genes do the residents of Asgard have? Lots of things that we had thought were unique to eukaryotes. The proteins made from these genes do things like managing membranes internal to the cell, constructing a skeleton-like network of fibers within the cell, and shifting other proteins to specific locations within the cell. They also make specialized proteins that destroy defective proteins and repair damaged DNA.

"Given these findings, we shouldn't be surprised that a larger tree-building exercise grouped all eukaryotes with the Asgard archaea—hence the argument that there are only two domains of life. At this point, it's not possible to tell whether they are separate branches or if eukaryotes are an offshoot of a specific phylum, like Heimdallarchaeota.

"All of this, the authors argue, make the case that some of the basic features of eukaryotes existed before they swallowed a bacteria for energy production. And these same features still exist today in the archaea.

"That idea, they point out, isn't as radical as it once was. Far from being featureless, uniform collections of proteins and other molecules, we've begun to discover many examples of structure inside bacteria and archaea, from internal membranes to skeleton-like structures. It just appears that the Asgardians put together a more complete package—and the one that happened to produce eukaryotes.

"Obviously, we'd like to take a closer look at these organisms and get a better sense of their internals. But the prospects aren't great. Most of them are very rare in their environment, and the Odinarcheota seem to only be present in extreme high-temperature environments. And, aside from the fact that they only grow in environments that lack oxygen, we have no idea of the sort of conditions they do like. So, while we're sure they're out there, it may be a while before we can appreciate how they might have given rise to complex cells—and, ultimately, us."

Comment: thank goodness for Carl Woese who found Archaea. We appear to be direct descendants of these bugs, while bacteria are kept around to facilitate our lives


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