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Evolutionary biology
One of the three domains of living organisms: Archaea, Bacteria and Eukaryota. While Archaea are single-celled, they are unlike bacteria given their independent evolutionary history. Archaea differ from Eukaryota in their ribosomal structure and the presence—in some—of introns in the genome, as well as other features (e.g., different membrane composition).
Molecular biology
Archaea are of interest in biotechnology as they have unique biochemical features (e.g., enzymes of theromophiles, such as Taq polymerase, the “workhorse” enzyme of PCR) and are extremely stable at high temperatures. Archaea include metabolic oddities (e.g., extreme halophiles, which live in extremely salty environments), methanogens (which produce methane) and sulphur-dependant extreme thermophiles (which can live in extremely hot environments).

Archaea phyla
• Crenarchaeota
• Euryarchaeota
• Korarchaeota
• Nanoarchaeota
• Thaumarchaeota (recently proposed)


A group of microorganisms that thrive in the absence of oxygen, produce methane, and live only in bodies of highly concentrated salt water, or in the acidic waters of sulfur springs, at temperatures near 80° Celsius and pH levels as low as 2.


one of the three primary groupings (DOMAINS) of ORGANISMS, according to some classification schemes, based on genetic structures and sequences. See CLASSIFICATION. Members of the Archaea are PROKARYOTES and include the extreme HALOPHILES, the thermoacidophiles (organisms that normally grow at high temperatures in acidic environments; see also THERMOPHILIC), and the METHANOGENS.

They differ in a number of ways from other BACTERIA, for example in the structure of their MEMBRANE LIPIDS, TRANSFER RNA molecules and CELL WALL, and in their sensitivity to ANTIBIOTICS. The Archaea is a very diverse group organized into two KINGDOMS, the CRENARCHAEOTA and the EURYARCHAEOTA. It was initially considered to represent the most ancient group of organisms still living. This is reflected in the name, from the Greek archaios, meaning ancient.


prokaryotic organisms, distinct from eubacteria, which are found in association with high temperatures or salinity, or are methanogenic. None are pathogens.
References in periodicals archive ?
Actually, Russell and Martin say, this crucial evolutionary leap may have happened in two different ways that correspond to what subsequently became archaebacteria and eubacteria.
Compare those same enzymes with archaebacteria and it drops to 31 or 32 or 33, way back further in time.
Eubacteria and archaebacteria in the culture fluids were identified by DNA extraction, polymerase chain reaction (PCR) amplification, denaturing gradient gel electrophoresis (DGGE) analysis and sequencing.
ELLINGTON: The membrane lipids in the cyclophilic Archaebacteria seem to accumulate ring structures.
The structure of a domaincommon to archaebacteria and the homocystinuria disease protein.
Evolutionary relationship of archaebacteria, eubacteria and eukaryotes inferred from phylogenetic trees of duplicated genes.
To do so, they analyzed the biochemical personalities of the progenote's own descendants -- today's archaebacteria and eubacteria (the two kingdoms of bacteria) and the eukaryotes (organisms whose cells have defined nuclei), which include animals and plants.
Protein Phylogenetics snd Signature Sequences: A Reappraisal of Evolutionary Relationship Among Archaebacteria, Eubacteria, and Eukaryotes.
At stake is the survival of a popular classification scheme in which members of the diverse class Archaebacteria are dubbed the progenitors of all modern life.
One concerns vacuolar ATPases which, like informational molecules, reveal an affinity between Archaebacteria and eukaryotes (4), and these proteins function in the eukaryotic endomembrane system.
That is one reason why, at one time, I did accept Archaebacteria as a separate kingdom rather than just as an infrakingdom.