Strange, tentacled archaea microbe may resemble ancestor of complex life

Amazing stuff! The story of the origin of life on earth is not written yet not by a long shot! I think, we are still scratching only the surface! 😊

"By growing an unusual tentacled microbe in the lab, microbiologists may have taken a ... step toward resolving the earliest branches on the tree of life and unraveling one of its great mysteries: how the complex cells that make up the human body—and all plants, animals, and many single-celled organisms—first came to be. Such microbes, called Asgard archaea, have previously been cultured—once—but the advance reported today in Nature marks the first time they’ve been grown in high enough concentrations to study their innards in detail. ...
The resulting electron microscopy images reveal complex internal structures suggestive of those in our own cells, adding support to the still controversial idea that ancient Asgard-like microbes may have been the key ancestor of complex cells. ...
The idea that Asgard-like archaea might be the ancestors of eukaryotes came about in 2015 when ... discovered eukaryoticlike genes in strange archaea from sediment samples ...
But in 2019, ... team cultured the first Asgard microbe ... and reported that its genome also had eukaryotic genes.
Additional evidence came earlier this year [2022] when ... isolated enough of two other Asgard species ... 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 ...
but it took 12 years of trial and error to culture the first Asgard, and the second one described today wasn’t much easier. .. [a] 7-year project. ..."

From the abstract:

"Asgard archaea are considered to be the closest known relatives of eukaryotes. Their genomes contain hundreds of eukaryotic signature proteins (ESPs), which inspired hypotheses on the evolution of the eukaryotic cell. A role of ESPs in the formation of an elaborate cytoskeleton and complex cellular structures has been postulated, but never visualized. Here we describe a highly enriched culture of ‘Candidatus Lokiarchaeum ossiferum’, a member of the Asgard phylum, which thrives anaerobically at 20 °C on organic carbon sources. It divides every 7–14 days, reaches cell densities of up to 5 × 107 cells per ml and has a significantly larger genome compared with the single previously cultivated Asgard strain. ESPs represent 5% of its protein-coding genes, including four actin homologues. We imaged the enrichment culture using cryo-electron tomography, identifying ‘Ca. L. ossiferum’ cells on the basis of characteristic expansion segments of their ribosomes. Cells exhibited coccoid cell bodies and a network of branched protrusions with frequent constrictions. The cell envelope consists of a single membrane and complex surface structures. A long-range cytoskeleton extends throughout the cell bodies, protrusions and constrictions. The twisted double-stranded architecture of the filaments is consistent with F-actin. Immunostaining indicates that the filaments comprise Lokiactin—one of the most highly conserved ESPs in Asgard archaea. We propose that a complex actin-based cytoskeleton predated the emergence of the first eukaryotes and was a crucial feature in the evolution of the Asgard phylum by scaffolding elaborate cellular structures."

Strange, tentacled microbe may resemble ancestor of complex life | Science | AAAS: Detailed internal images of second Asgard microbe reveal components similar to plant and animal cells

Actin cytoskeleton and complex cell architecture in an Asgard archaeon (open access)

Fig. 4: Complex and variable architecture of ‘Ca. L. ossiferum’ cells.