Shedding light on the origin of complex life forms
How did the complex organisms on Earth arise? This is one of the big open questions in biology. A collaboration between the working groups of Christa Schleper at the University of Vienna and Martin Pilhofer at ETH Zurich ...
This member of the Asgard archaea exhibits unique cellular characteristics and may represent an evolutionary "missing link" to more complex life forms such as animals and plants. The study was recently published in the journal Nature.
All life forms on earth are divided into three major domains: eukaryotes, bacteria and archaea. Eukaryotes include the groups of animals, plants and fungi. Their cells are usually much larger and, at first glance, more complex than the cells of bacteria and archaea. The genetic material of eukaryotes, for example, is packaged in a cell nucleus and the cells also have a large number of other compartments.
Cell shape and transport within the eukaryotic cell are also based on an extensive cytoskeleton. But how did the evolutionary leap to such complex eukaryotic cells come about?
Most current models assume that archaea and bacteria played a central role in the evolution of eukaryotes. A eukaryotic primordial 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 group of the so-called "Asgard archaea", which in the tree of life represent the closest relatives of eukaryotes. The first images of Asgard cells were published in 2020 from enrichment cultures by a Japanese group.
Cryo-electron tomography provided insight into the cellular structure of a newly cultured Asgard archaeon illustrated here. Remarkable are the extensive actin cytoskeleton filaments (orange) in the cell bodies and cell protrusions, as well as the unique cell envelope (blue). Credit: Margot Riggi, The Animation Lab, University of Utah
Scanning electron micrograph of a Lokiarchaeum ossiferum cell showing the long and complex cell protrusions. Credit: Thiago Rodrigues-Oliveira, Univ. Wien
One of the currently most popular evolutionary theories assumes that eukaryotes (including animals, plants and fungi) arose from the fusion of an Asgard archaeon with a bacterium. Credit: Florian Wollweber, ETH Zürich