Archaea are a major division of microorganisms. Like bacteria, Archaea are single-celled organisms lacking nuclei and are therefore prokaryotes, classified as belonging to kingdom Monera in the traditional six-kingdom taxonomy. Although there is still uncertainty in the approximate phylogeny of the groups, Archaea, Eukaryota and Bacteria are the fundamental classifications in what is called the three-domain system. They were originally described in extreme environments, but have since been found in all types of habitat.
Individual archaeans range from 0.1 μm to over 15 μm in diameter, and some form aggregates or filaments up to 200 μm in length. They occur in various shapes, such as spherical, rod-shape, spiral, lobed, or rectangular. Archaea have no murein in their cell walls. Recently, a species of flat, square archaean that lives in hypersaline pools has been discovered
Archaea exhibit a variety of different types of metabolism. Of note, the halobacteria can use light to produce ATP, although no Archaea conduct photosynthesis with an electron transport chain, as occurs in other groups. Rather light-activated ion pumps like bacteriorhodopsin and halorhodopsin play a role in generating ion gradients, whose energy then leads to production of ATP.
Archaea can reproduce using binary and multiple fission, fragmentation, and budding
2007-03-14 10:26:46
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