Essential Information & explanations, latest texts & monographs on
Archaea.
Archaea
Archaea
Scientific classification
Domain*:Archaea
Phyla* & classes
Crenarchaeota
Euryarchaeota
Halobacteria
Methanobacteria
Methanococci
Methanopyri
Archeoglobi
Thermoplasmata
Thermococci
Korarchaeota
Nanoarchaeota
* Or kingdom (see text)
The Archaea are one of the three major groups of living organisms, together with the bacteria and eukaryotes. They are prokaryotes, like bacteria, and were originally included among them. Their separate identity was discovered in the late 1970s by Dr. Carl Woese at the University of Illinois by genetic comparison. Originally they were termed the Archaebacteria, and the other prokaryotes the Eubacteria, but now there is a growing tendency to restrict the term bacteria to the latter and the names have adjusted accordingly. The Archaea may be treated as a single kingdom or as a domain, in which case the subgroups may be ranked as kingdoms.
Archaea differ from the true bacteria in many important respects, as well as from the eukaryotes. These differences include:
- wall structures and chemistry (lack of peptidoglycan and Gram staining)
- lipidic membrane structure (their lipid bilayers consist of branched chain hydrocarbons linked by ether linkages to glycerol)
- metabolism (methanogens, sulfate reducers...)
Many Archaea live in extreme environments, including water whose temperature exceeds that of boiling water, like geysers, very salty, acid or alkaline water or black smokers. They are very diverse, both in morphology and physiology. Some are single-celled, while others form filaments or aggregates. They may be spherical, rod-shaped, spiral, lobed. Their size varies in diameter from 0.1 to more than 15 µm (filaments up to 200 µm).
They show a great diversity in multiplication modes, which may be by binary fission, budding or fragmentation.
For a nutrional point of view, they range from being chemolithoautotrophic to organotrophic. Physiologically, they can be aerobic, facultatively anaerobic, or stricly anaerobic. Some are mesophiles, others hyperthermophiles (may live over 100°C). Though most of them live in high-temperature, anaerobic, hypersaline environment, some have also been found in cold places. They are mostly found in aquatic and terrestrial habitats, but a few have been found in animal digestive systems. The environmental conditions archaea prefer and their unusual biochemistry make them usually harmless to organisms belonging to the other two domains. No case of infection of a human with archaea has been reported so far.
There are two main groups of Archaea, the Crenarchaeota and Euryarchaeota. The Korarchaeota have been described from RNA samples, but the actual organisms remain unknown, and the Nanoarchaeota are known from a single species discovered in 2002, Nanoarchaeum equitum. The Archaea appear to be close relatives of the eukaryotes, and some work has suggested that the Euryarchaeota may be closer to them than the Crenarchaeota, though more recent studies support their monophyly. Woese argued that the Bacteria, Archaea, and eukaryotes all diverged separately from an ancestral progenote, but this has little support, and a few authors consider the Archaea and eukaryotes highly derived Bacteria (making that kingdom paraphyletic).
See also: extremophile -- phylogeny -- rRNA
External links
The above article is adapted from from Wikipedia All Wikipedia article text is available under the terms of the GNU Free Documentation License
The Surprising Archaea: Discovering Another Domain of Life by John L. Howland
Bergey's Manual of Systematic Bacteriology Volume 1: The Archaea and the Deeply Branching and Phototrophic Bacteria by George Garrity
Bergey's Manual of Systematic Bacteriology (Vol 1) : The Archaea, Cyanobacteria, Phototrophs by J.G. Holt
Methanogens (Archaea: A Laboratory Manual) by F.T. Robb
Respiration in Archaea and Bacteria: Diversity of Prokaryotic Electron Carriers by Davide Zannoni
Bergey's Manual of Systematic Bacteriology: The Archaea and the Deeply Branching and Phototrophic Bacteria (Bergey's Manual of Systematic Bacteriology, 3) by David R. Boone
Archaea: A Laboratory Manual by F.T. Robb
Thermophiles (Archaea: A Laboratory Manual) by F. T. Robb
Bergey's Manual of Systematic Bacteriology: The Archaea and the Deeply Branching and Phototrophic Bacteria (Bergey's Manual of Systematic Bacteriology, 2) by David R. Boone
Halophiles (Archaea: A Laboratory Manual) by S. Dassarma
The Biochemistry of Archaea (Archaebactera) by D.J. Kushner
Molecular Biology of Archaea by Felicitas Pfeifer
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