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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.
Like all archaea, Thermoproteus possesses unique membrane lipids, which are ether-linked glycerol derivatives of 20 or 40 carbon branched lipids. The lipids' unsaturations are generally conjugated (as opposed to the unconjugation found in Bacteria and Eukaryota).
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.
The tree of life. Two domains of life are Bacteria (top branches) and Archaea (bottom branches, including eukaryotes). The two-domain system is a biological classification by which all organisms in the tree of life are classified into two domains, Bacteria and Archaea.
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.
Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea. [16] This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus. [ 13 ]
The Thermoproteota are prokaryotes that have been classified as a phylum of the domain Archaea. [2] [3] [4] Initially, the Thermoproteota were thought to be sulfur-dependent extremophiles but recent studies have identified characteristic Thermoproteota environmental rRNA indicating the organisms may be the most abundant archaea in the marine environment. [5]
Detailed phylogenetic and comparative analyses of genome sequences from members of the class Haloarchaea has led to division of this class into three orders, Halobacteriales, Haloferacales and Natrialbales, which can be reliably distinguished from each other as well as all other archaea/bacteria through molecular signatures known as conserved signature indels (CSIs). [7]