Researchers develop ‘missing link’ microorganism – ScienceDaily

How did complex organisms on Earth arise? This is one of the big open questions in biology. Collaboration between the working groups of Christa Schleper of the University of Vienna and Martin Pilhofer of ETH Zurich brings one step closer to the answer. The researchers were able to breed a special archaeon and characterize it more precisely using microscopic methods. This member of the Asgard archaea exhibits unique cellular features and may represent an evolutionary “missing link” of more complex life forms such as animals and plants. The research was recently published in the journalism. Nature.

All life forms on Earth are divided into three main domains: eukaryotes, bacteria, and archaea. Eukaryotes include groups of animals, plants, and fungi. Its cells are usually much larger and at first glance more complex than bacterial and archaeal cells. For example, the genetic material of eukaryotes is packaged in a cell nucleus, and cells also have numerous other compartments. Cell shape and transport within the eukaryotic cell are also based on an extensive cytoskeleton. So how did the evolutionary leap towards such complex eukaryotic cells take place?

Most existing models assume that archaea and bacteria played a central role in the evolution of eukaryotes. A eukaryotic primitive cell is believed to have evolved from a close symbiosis between archaea and bacteria about two billion years ago. In 2015, genomic studies of deep-sea environmental samples discovered the so-called “Asgard archaea” group, which represents the closest relatives of eukaryotes in the tree of life. The first images of Asgard cells were released in 2020 by a Japanese group from enrichment cultures.

Asgard archaea grown from marine sediments

Christa Schleper’s working group at the University of Vienna has now, for the first time, succeeded in growing a representative of this group at higher concentrations. She comes from marine sediments on the Piran coast of Slovenia, but is also a resident of Vienna, for example, in coastal sediments of the Danube river. Due to its growth to high cell densities, this representative is particularly well studied. “Getting this highly sensitive organism in stable culture in the laboratory was a very difficult and demanding task,” says Thiago Rodrigues-Oliveira, postdoc in the Archaea working group at the University of Vienna, one of the first authors of the study.

Asgard archaea have a complex cell shape with an extensive cytoskeleton.

The remarkable success of the Viennese group in breeding a highly enriched representative of Asgard finally led to a more detailed study of cells by microscopy. ETH researchers in Martin Pilhofer’s group used a modern cryo-electron microscope to take pictures of shock-frozen cells. “This method provides a three-dimensional view of the internal cellular structures,” explains Pilhofer. “Cells consist of round cell bodies with thin, sometimes very long cell extensions. These tentacle-like structures sometimes seem to connect different cell bodies together,” says Florian Wollweber, who has been watching the cells for months under the microscope. Cells also contain an extensive network of actin filaments thought to be unique to eukaryotic cells. This suggests that extensive cytoskeletal structures arose in archaea before the first eukaryotes appeared, fueling evolutionary theories around this important and magnificent event in the history of life.

Future predictions through new model organism

“Our new organism, Lokiarchaeum ossiferum“It took six long years to get a stable and highly enriched culture, but now we can use that experience to do a lot of biochemical studies,” says microbiologist Christa Schleper. and to breed other Asgard archaea.” Additionally, scientists can now use new imaging methods developed at ETH to probe, for example, the close interactions between Asgard archaea and their bacterial partners. Fundamental cell biological processes such as cell division are shedding light on the evolutionary origins of these mechanisms in eukaryotes. may be examined in the future.

This text is similarly published by ETH Zurich. See:

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