Lokiarchaeota: Biologists Discover `Missing Link` Microorganism

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Lokiarchaeota: Biologists Discover
‘Missing Link’ Microorganism
May 7, 2015 by Sci-News.com
Published in
Biology
Tagged as
Archaea
Bacteria
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A team of biologists, co-led by Dr Lionel Guy and Dr Thijs J. G. Ettema from
Uppsala University in Sweden, has discovered a new group of
microorganisms that represents an intermediate form in-between the
simple cells of bacteria and the complex cell types of eukaryotes.
Eukaryote
Lokiarchaeota
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This false-color image shows a cell of thermophilic methanogenic archaea. Image credit: University of
California Museum of Paleontology.
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).
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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.
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“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.”
The details of the discovery are published in the journal Nature.
_____
Anja Spang et al. Complex archaea that bridge the gap between prokaryotes
and eukaryotes. Nature, published online May 06, 2015; doi:
10.1038/nature14447
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