Archaebacteria

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Archaebacteria

Archaebacteria (ärˌkēbăktĭrˈēə), diverse group of bacteria (prokaryotes), sometimes called the archaea and considered a major group unto themselves. Archaebacteria are contrasted with the Eubacteria, from which they differ biochemically in the arrangement of the bases in their ribosomal RNA and in the composition of their plasma membranes and cell walls. There are three major known groups of Archaebacteria: methanogens, halophiles, and thermophiles. The methanogens are anaerobic bacteria that produce methane. They are found in sewage treatment plants, bogs, and the intestinal tracts of ruminants. Ancient methanogens are the source of natural gas. Halophiles are bacteria that thrive in high salt concentrations such as those found in salt lakes or pools of sea water. Thermophiles are the heat-loving bacteria found near hydrothermal vents and hot springs. Many thermophiles are chemosynthetic (see chemosynthesis), using dissolved sulfur or other elements as their energy source and iron as a means of respiration. Archaebacteria emerged at least 3.5 billion years ago and live in environments that resemble conditions existing when the earth was young.
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Archaebacteria

A group of prokaryotic organisms that are more closely related to eukaryotes than bacteria. Based on comparative analyses of small subunit ribosomal ribonucleic acid (rRNA) sequences and selected protein sequences, the three primary lines of descent from the common ancestor are the Archaea (archaebacteria), the Bacteria, and the Eucarya (eukaryotes). Although the Archaea look like Bacteria cytologically (they are both prokaryotes), they are not closely related to them.

The Archaea can be divided into two evolutionary lineages on the basis of rRNA sequence comparisons, the Crenarchaeotae and the Euryarchaeotae. The crenarchaeotes are organisms that grow at high temperatures (thermophiles) and metabolize elemental sulfur. Most are strict anaerobes that reduce sulfur to hydrogen sulfide (sulfidogens), but a few can grow aerobically and oxidize sulfur to sulfuric acid. The euryarchaeotes have a number of different phenotypes. Thermococcus and Pyrococcus are sulfidogens like many crenarchaeotes. Archaeoglobus reduces sulfate to sulfide. Thermoplasma grows under acidic conditions aerobically or anaerobically (as a sulfidogen). Many euryarchaeotes are methane-producing anaerobes (methanogens) and some grow aerobically in the presence of very high concentrations of salt (halophiles). See Methanogenesis (bacteria)

The thermophilic archaea are found in high-temperature environments around the world. They have been isolated from soils and shallow marine sediments heated by nearby volcanoes and from deep-sea hydrothermal vents. Some are used as a source for heat-stable enzymes useful for industrial applications. The methanogenic archaea inhabit the digestive tracts of animals (especially ruminants like cows), sewage sludge digesters, swamps (where they produce marsh gas), and sediments of marine and fresh-water environments. They are of interest commercially because of their ability to produce methane from municipal garbage and some industrial wastes. Halophilic archaea live in the Great Salt Lake, the Dead Sea, alkaline salt lakes of Africa, and salt-preserved fish and animal hides. They are also commonly found in pools used to evaporate seawater to obtain salt.

The discovery of the Archaea caused a major revision in the understanding of evolutionary history. It had previously been thought that all prokaryotes belonged to one evolutionary lineage. Since their cellular organization is simpler, prokaryotes were assumed to be ancestors of eukaryotes. The discovery of the relationship of the Archaea to the Eucarya revealed that prokaryotes do not comprise a monophyletic group since they can be divided into two distinct lineages. Although the three descended from a common ancestor, modern eukaryotes may have arisen from fusions of bacterial and archaeal endosymbionts with ancestral eukaryotes. Chloroplasts and mitochondria arose from free-living bacteria which became endosymbionts. The discovery of the Archaea has also given microbiologists a better picture of the common ancestor. The deepest-branching eukaryotes (like Giardia) are strict anaerobes that lack mitochondria, and they diverged much later than the deepest-branching bacteria and archaea. The earliest archaea and bacteria (Thermotoga and Aquifex) are also anaerobes and are also extreme thermophiles. Therefore the common ancestor of these groups was probably also an extremely thermophilic anaerobe. Therefore, it is possible that life may have arisen in a relatively hot environment, perhaps like that found in deep-sea hydrothermal vents. See Bacteria, Eukaryotae, Prokaryotae

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

archaebacteria

[‚ar·kē·bak′tir·ē·ə]
(microbiology)
A group of unusual prokaryotic organisms that microscopically resemble true bacteria but differ biochemically and genetically, and form a distinct evolutionary group; some occur widely in oxygen-free environments and produce methane, while others are found in extreme salty or acidic conditions or grow at high temperatures.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The archaea group lack nuclei and membrane-bound organelles.
Hilpert et al [39] found that archaea were insensitive to many antibiotics that inhibit eubacteria and eukaryotes, such as those inhibiting the synthesis or cross-linkage of the peptide subunit of murein or those suppressing RNA synthesis.
That said, the broad distribution of the new lineage of microbes in Yellowstone's thermal features suggests similar habitats played an important role in the evolution of archaea back in the day.
Di HJ, Cameron KC, Shen JP, Winefield CS, O'Callaghan M, Bowatte S (2009) Nitrification driven by bacteria and not archaea in nitrogen rich grassland soils.
Archaea in the Degradation of Organics in Hypersaline Environments
Out of a total of about 2,000 superfamilies of folds, the team found one that was exclusive to archaea and the viruses that infect archaea, 29 shared only by bacteria and the viruses that infect them, and 37 that are exclusive to eukaryotes and their viruses.
These structures revel that eukaryotic and archaea primase have unrelated polymerases fold, showing, however, a high conservation level and a three dimension arrangement of aspartate residues (Guilliam et al., 2015).
They found that Archaea (pronounced ar-KEY-uh) were most abundant in subjects younger than 12 and older than 60.
That is, the biocides kill some types of bacteria, thus enabling other bacteria and archaea to prosper--species that somehow find a way to survive in water that is, on average, four times saltier than the ocean, and under pressures that typically are hundreds of times higher than on the surface of the Earth.
"The three major domains of life are bacteria, archaea and eukaryotes," Edgcomb explained.
These data sources - and many others - were compiled to create the inventory in the IU study, which pulls together 20,376 sampling efforts on bacteria, archaea and microscopic fungi and 14,862 sampling efforts on communities of trees, birds and mammals.