Complex archaea that bridge the gap between prokaryotes and eukaryotes

Complex archaea that bridge the gap between prokaryotes and eukaryotes

Archea

The origin of the eukaryotic cell remains one of the most contentious puzzles in modern biology. Recent studies have provided support for the emergence of the eukaryotic host cell from within the archaeal domain of life, but the identity and nature of the putative archaeal ancestor remain a subject of debate. Here we describe the discovery of ‘Lokiarchaeota’, a novel candidate archaeal phylum, which forms a monophyletic group with eukaryotes in phylogenomic analyses, and whose genomes encode an expanded repertoire of eukaryotic signature proteins that are suggestive of sophisticated membrane remodelling capabilities. Our results provide strong support for hypotheses in which the eukaryotic host evolved from a bona fide archaeon, and demonstrate that many components that underpin eukaryote-specific features were already present in that ancestor. This provided the host with a rich genomic ‘starter-kit’ to support the increase in the cellular and genomic complexity that is characteristic of eukaryotes.

In 1977, biochemist Dr Carl Woese and his colleagues at the University of Illinois described an entirely new group of organisms, the Archaea (originally found in extreme environments, such as hydrothermal vents and terrestrial hot springs).

The scientists were studying relationships among the prokaryotes using DNA sequences, and found that Archaea have distinct molecular characteristics separating them from bacteria as well as from eukaryotes. They proposed that life can be divided into three domains: Eukaryota, Eubacteria, and Archaebacteria.

Despite that archaeal cells were simple and small like bacteria, scientists found that Archaea were more closely related to organisms with complex cell types, a group collectively known as ‘eukaryotes.’ This observation has puzzled biologists for years.

Dr Guy, Dr Ettema and their colleagues from the University of Bergen, the University of Vienna, and Uppsala University, have described a new group of Archaea, named Lokiarchaeota, and identified it as a missing link in the origin of eukaryotes.

The name Lokiarchaeota is derived from the hostile environment close to where it was found, Loki’s Castle, a hydrothermal vent system located on the Mid-Atlantic Ridge between Greenland and Norway at a depth of 2,352 meters.

“The puzzle of the origin of the eukaryotic cell is extremely complicated, as many pieces are still missing. We hoped that Lokiarchaeota would reveal a few more pieces of the puzzle, but when we obtained the first results, we couldn’t believe our eyes. The data simply looked spectacular,” Dr Ettema explained.“Lokiarchaeota formed a well-supported group with the eukaryotes in our analyses,” Dr Guy added.

The scientists found that Lokiarchaeota shares many genes with eukaryotes, suggesting that cellular complexity emerged in an early stage in the evolution of eukaryotes.

“Our results provide strong support for hypotheses in which the eukaryotic host evolved from a bona fide archaeon, and demonstrate that many components that underpin eukaryote-specific features were already present in that ancestor,” the biologists said.

“This provided the host with a rich genomic ‘starter-kit’ to support the increase in the cellular and genomic complexity that is characteristic of eukaryotes.”

·                                 Anja Spang et al. Complex archaea that bridge the gap between prokaryotes and eukaryotes. Nature,

·                                 Anja Spang,

·                                 Jimmy H. Saw,

·                                 Steffen L. Jørgensen,

·                                 Katarzyna Zaremba-Niedzwiedzka,

·                                 Joran Martijn,

·                                 Anders E. Lind,

·                                 Roel van Eijk,

·                                 Christa Schleper,

·                                 Lionel Guy

·                                 & Thijs J. G. Ettema

·                                 Affiliations

·                                 Contributions

·                                 Corresponding authors

·                                  

 Nature2015

 With a Licence Creative Commons 4 International

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