Euryarchaeota | |
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Halobacterium sp. strain NRC-1, each cell about 5 µm in length. | |
Scientific classification | |
Domain: | Archaea |
Kingdom: | Euryarchaeota Woese, Kandler & Wheelis, 1990 [1] |
Phyla [2] | |
Synonyms | |
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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. They are separated from the other archaeans based mainly on rRNA sequences and their unique DNA polymerase. [4]
The Euryarchaeota are diverse in appearance and metabolic properties. The phylum contains organisms of a variety of shapes, including both rods and cocci. Euryarchaeota may appear either gram-positive or gram-negative depending on whether pseudomurein is present in the cell wall. [5] Euryarchaeota also demonstrate diverse lifestyles, including methanogens, halophiles, sulfate-reducers, and extreme thermophiles in each. [5] Others live in the ocean, suspended with plankton and bacteria. Although these marine euryarchaeota are difficult to culture and study in a lab, genomic sequencing suggests that they are motile heterotrophs. [6]
Though it was previously thought that euryarchaeota only lived in extreme environments (in terms of temperature, salt content and/or pH), a paper by Korzhenkov et al published in January 2019 showed that euryarchaeota also live in moderate environments, such as low-temperature acidic environments. In some cases, euryarchaeota outnumbered the bacteria present. [7] Euryarchaeota have also been found in other moderate environments such as water springs, marshlands, soil and rhizospheres. [8] Some euryarchaeota are highly adaptable; an order called Halobacteriales are usually found in extremely salty and sulfur-rich environments but can also grow in salt concentrations as low as that of seawater 2.5%. [8] In rhizospheres, the presence of euryarchaeota seems to be dependent on that of mycorrhizal fungi; a higher fungal population was correlated with higher euryarchaeotal frequency and diversity, while absence of mycorrihizal fungi was correlated with absence of euryarchaeota. [8]
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) [9] and National Center for Biotechnology Information (NCBI) [10]
16S rRNA based LTP_12_2021. [11] [12] [13] | Dombrowski et al. 2019, [14] Jordan et al. 2017 [15] and Cavalier-Smith2020. [16] | |||||||||
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Other phylogenetic analyzes have suggested that the archaea of the clade DPANN may also belong to Euryarchaeota and that they may even be a polyphyletic group occupying different phylogenetic positions within Euryarchaeota. It is also debated whether the phylum Altiarchaeota should be classified in DPANN or Euryarchaeota. [14] A cladogram summarizing this proposal is graphed below. [15] [16] The groups marked in quotes are lineages assigned to DPANN, but phylogenetically separated from the rest.
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A third phylogeny, 53 marker proteins based GTDB 08-RS214. [17] [18] [19]
| Euryarchaeota s.s. |
The Thermoproteota are prokaryotes that have been classified as a phylum of the Archaea domain. 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. Originally, they were separated from the other archaea based on rRNA sequences; other physiological features, such as lack of histones, have supported this division, although some crenarchaea were found to have histones. Until recently all cultured Thermoproteota had been thermophilic or hyperthermophilic organisms, some of which have the ability to grow at up to 113 °C. These organisms stain Gram negative and are morphologically diverse, having rod, cocci, filamentous and oddly-shaped cells.
The Korarchaeota is a proposed phylum within the Archaea. The name is derived from the Greek noun koros or kore, meaning young man or young woman, and the Greek adjective archaios which means ancient. They are also known as Xenarchaeota. The name is equivalent to Candidatus Korarchaeota, and they go by the name Xenarchaeota or Xenarchaea as well.
The Thermoprotei is a class of the Thermoproteota.
Archaeoglobus is a genus of the phylum Euryarchaeota. Archaeoglobus can be found in high-temperature oil fields where they may contribute to oil field souring.
In taxonomy, the Methanopyri are a class of the Euryarchaeota.
Halobacteriales are an order of the Halobacteria, found in water saturated or nearly saturated with salt. They are also called halophiles, though this name is also used for other organisms which live in somewhat less concentrated salt water. They are common in most environments where large amounts of salt, moisture, and organic material are available. Large blooms appear reddish, from the pigment bacteriorhodopsin. This pigment is used to absorb light, which provides energy to create ATP. Halobacteria also possess a second pigment, halorhodopsin, which pumps in chloride ions in response to photons, creating a voltage gradient and assisting in the production of energy from light. The process is unrelated to other forms of photosynthesis involving electron transport; however, and halobacteria are incapable of fixing carbon from carbon dioxide.
In taxonomy, the Thermoplasmata are a class of the Euryarchaeota.
In taxonomy, the Thermoplasmatales are an order of the Thermoplasmata. All are acidophiles, growing optimally at pH below 2. Picrophilus is currently the most acidophilic of all known organisms, being capable of growing at a pH of -0.06. Many of these organisms do not contain a cell wall, although this is not true in the case of Picrophilus. Most members of the Thermotoplasmata are thermophilic.
Haloarchaea are a class of prokaryotic organisms under the archaeal phylum Euryarchaeota, found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea rather than bacteria and are one of the largest groups. The name 'halobacteria' was assigned to this group of organisms before the existence of the domain Archaea was realized, and while valid according to taxonomic rules, should be updated. Halophilic archaea are generally referred to as haloarchaea to distinguish them from halophilic bacteria.
Methanococcus is a genus of coccoid methanogens of the family Methanococcaceae. They are all mesophiles, except the thermophilic M. thermolithotrophicus and the hyperthermophilic M. jannaschii. The latter was discovered at the base of a “white smoker” chimney at 21°N on the East Pacific Rise and it was the first archaeal genome to be completely sequenced, revealing many novel and eukaryote-like elements.
In the taxonomy of microorganisms, the Methanomicrobia are a class of the Euryarchaeota.
Methanococci is a class of methanogenic archaea in the phylum Euryarchaeota. They can be mesophilic, thermophilic or hyperthermophilic.
In taxonomy, the Methanococcales are an order of the Methanococci.
Methanocaldococcus formerly known as Methanococcus is a genus of coccoid methanogen archaea. They are all mesophiles, except the thermophilic M. thermolithotrophicus and the hyperthermophilic M. jannaschii. The latter was discovered at the base of a “white smoker” chimney at 21°N on the East Pacific Rise and it was the first archaean genome to be completely sequenced, revealing many novel and eukaryote-like elements.
In taxonomy, Metallosphaera is a genus of the Sulfolobaceae.
In taxonomy, Methanohalophilus is a genus of the Methanosarcinaceae.
Methanobacterium is a genus of the Methanobacteria class in the Archaea kingdom, which produce methane as a metabolic byproduct. Despite the name, this genus belongs not to the bacterial domain but the archaeal domain. Methanobacterium are nonmotile and live without oxygen, which is toxic to them, and they only inhabit anoxic environments.
Archaea is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotic. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this term has fallen out of use.
The eocyte hypothesis in evolutionary biology proposes that the eukaryotes originated from a group of prokaryotes called eocytes. After his team at the University of California, Los Angeles discovered eocytes in 1984, James A. Lake formulated the hypothesis as "eocyte tree" that proposed eukaryotes as part of archaea. Lake hypothesised the tree of life as having only two primary branches: prokaryotes, which include Bacteria and Archaea, and karyotes, that comprise Eukaryotes and eocytes. Parts of this early hypothesis were revived in a newer two-domain system of biological classification which named the primary domains as Archaea and Bacteria.
DPANN is a superphylum of Archaea first proposed in 2013. Many members show novel signs of horizontal gene transfer from other domains of life. They are known as nanoarchaea or ultra-small archaea due to their smaller size (nanometric) compared to other archaea.