Tree of life gets a total makeover: Archaea to eukaryotes? (Introduction)

by David Turell , Tuesday, December 27, 2022, 18:15 (696 days ago) @ David Turell

More on Asgards:

https://www.livescience.com/asgard-archaea-striking-new-images

" Now, for the first time, scientists have grown a large enough quantity of these microbes in the lab to study their internal structure in detail,

"Researchers grew an organism called Lokiarchaeum ossiferum, which belongs to a group of microbes known as Asgard archaea, according to a new report, published Wednesday (Dec. 21) in the journal Nature(opens in new tab). Asgard archaea are thought by some scientists to be the closest evolutionary relatives of eukaryotes, cells that package their DNA in a protective bubble called a nucleus.

"On the evolutionary tree of life, Asgards often appear as a "sister" of eukaryotes or as their direct ancestor, Jan Löwe, leader of the Bacterial Cytoskeleton and other Molecular Machines research group at the Medical Research Council, wrote in a commentary about the new study. Asgards don't carry nuclei themselves, but they do contain a suite of genes and proteins that were once thought to be unique to eukaryotes. Researchers have a variety of theories as to how Asgards may have gained primitive nuclei and thus birthed the first complex cells, which later gave rise to plants, animals and humans.

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"Compared with other Asgards, L. ossiferum grows relatively fast, doubling its number of cells in seven to 14 days, Löwe noted. In comparison, P. syntrophicum replicates every 14 to 25 days. Note that the familiar bacterium Escherichia coli replicates every 20 minutes or so. (The slow growth of these archaea is one factor that makes them incredibly difficult to culture.)

"Gathered from mud in a canal on the coast of Piran, Slovenia, the L. ossiferum specimens have funky tentacles that extend from the body of each cell; odd bumps and bulges appear along the length of each appendage. These "surface protrusions" may support the idea that, at some point in evolutionary history, an Asgard grabbed a passing bacterium using similar extensions of its membrane and sucked the bacterium into its cell body, and this led to the development of the nucleus, Löwe wrote. The protrusions support the idea that such an interaction could have occurred, he explained.

"L. ossiferum also carries tiny, lollipop-like structures on its surface, which "look like they come from another planet," Thijs Ettema(opens in new tab), an environmental microbiologist at Wageningen University in the Netherlands who wasn't involved in the work, told Science. The microbe also contains structural filaments that closely resemble those seen in the cytoskeleton, or supporting scaffold, of eukaryotic cells, Löwe wrote.

More evidence:

https://www.science.org/content/article/strange-tentacled-microbe-may-resemble-ancestor...

"Additional evidence came earlier this year when Victoria Orphan, a geobiologist at the California Institute of Technology and her colleagues isolated enough of two other Asgard species—from rock collected from a hydrothermal vent in the Gulf of California—to sequence their complete genomes. The genes in those genomes bolstered the case that these genes really did arise in archaea. Moreover, the genomes harbored mobile pieces of DNA that contained bacterial genes involved in metabolism, suggesting these elements played a role in transferring genes among life’s major branches, Orphan and her colleagues reported on 13 January in Nature Microbiology.

"By comparing the proteins encoded by Asgard archaea and eukaryotes, researchers including Ettema, Baum, and Mohan Balasubramanian, a cellular microbiologist at the University of Warwick, recently connected the two domains in another way. They focused on the interacting protein complexes eukaryotic cells use to bend, cut up, and stitch together their membranes to link internal compartments. To that point, only two of those protein complexes had been found in archaea. But Asgard genomes contain instructions for making four of them, the team reported on 13 June in Nature Communications.

"After predicting the proteins’ structures, the group synthesized some of the molecules in the lab and showed they work similarly to the eukaryotic versions. To the scientists, that suggests this membrane-manipulating machinery predates the evolution of eukaryotes.

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"Its genome is larger and has more eukaryotic genes than the other cultured Asgard, and its DNA includes four genes for the protein actin, a key component of a eukaryotic cell’s internal skeleton, Schleper’s team reports. That skeleton extends throughout the cell and into the tentacles, and it varies from cell to cell, suggesting it’s capable of being rearranged. “We show that the ‘eukaryotic’ cytoskeleton—which is crucial for eukaryotes—was an invention within archaea, meaning it evolved before the emergence of the first eukaryotic cells,” Schleper explains.

“'This study further strengthens that our ancestor is archaea,” agrees Nobu’s collaborator, Hiroyuki Imachi, a microbiologist at the Japan Agency for Marine-Earth Science and Technology.

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"Some scientists now believe the most likely scenario for the emergence of eukaryotes, some 2 billion years after bacteria and archaea arose, is that an Asgard-like microbe enveloped an oxygen-using bacterium, turning it into an extra energy producer for its host. The archaea may have also acquired other bacteria to make the combined cell that comprise eukaryotes."

Comment: More evidence our ancestors are Archaea.