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Archaea were initially classified as bacteria, receiving the name archaebacteria (/ ˌ ɑːr k i b æ k ˈ t ɪər i ə /, in the Archaebacteria kingdom), but this term has fallen out of use. [5] Archaeal cells have unique properties separating them from Bacteria and Eukaryota. Archaea are further divided into multiple recognized phyla.
Euryarchaeota (from Ancient Greek εὐρύς eurús, "broad, wide") is a kingdom of archaea. [3] Euryarchaeota are highly diverse and include methanogens, which produce methane and are often found in intestines; halobacteria, which survive extreme concentrations of salt; and some extremely thermophilic aerobes and anaerobes, which generally live at temperatures between 41 and 122 °C.
Haloterrigena turkmenica is in the domain of Archaea. [1] Archaea are identified as being separate from bacteria and eukaryotes based on ribosomal RNA analysis and certain defining characteristics that separate the three domains of life as described by Woese in 1990. [6]
The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
According to the domain system, the tree of life consists of either three domains, Archaea, Bacteria, and Eukarya, [1] or two domains, Archaea and Bacteria, with Eukarya included in Archaea. [3] [4] In the three-domain model, the first two are prokaryotes, single-celled microorganisms without a membrane-bound nucleus.
Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission , fragmentation , or budding ; unlike bacteria and eukaryotes, no known species forms spores .
The defining feature of eukaryotes is that their cells have a well-defined, membrane-bound nuclei, distinguishing them from prokaryotes that lack such a structure. Eukaryotic cells have a variety of internal membrane-bound structures, called organelles , and a cytoskeleton which defines the cell's organization and shape.
As is the case for other archaea, methanogens lack peptidoglycan, a polymer that is found in the cell walls of bacteria. [15] Instead, some methanogens have a cell wall formed by pseudopeptidoglycan (also known as pseudomurein). Other methanogens have a paracrystalline protein array (S-layer) that fits together like a jigsaw puzzle. [5]