Question

Describe the major groups of the phylum Euryachaeota and highlight their medical and economic importance

Answer 1

Euryarchaeota  is a phylum of archaea. It is one of two phyla of archaea, the other being crenarchaeota.[5] 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 122º C.

The phylum Euryachaeota are divided into 8 classes. they are Methanomicrobia,Archaeoglobi,Halobacteria,Methanobacteria,Methanococci/Methanothermea, Methanopyri,Thermococcoi/Protoarchaea and Thermoplasmata

Methanogenic Euryarchaeota: Methanobacteria, Methanococci, Methanopyri, and Methanomicrobia

Methanogens are euryarchaeal species that are capable of producing methane, using a process referred to as methanogenesis. As opposed to Haloarchaea, methanogens are obligate anaerobes, requiring strict anoxic techniques to culture them. Habitats of methanogens include anoxic sediments, such as marshes and swamps; lake sediments, such as rice paddy fields; animal digestive tracts,

The class Methanobacteria consists of five genera that include rod-shaped, lancet-shaped, or coccoid methanogens that reduce CO2 or methyl compounds with H2, formate, or secondary alcohols as electron donors. They are nonmotile and contain cell walls made of psuedopeptidoglycan. Methanobacteria are widely distributed in nature, and are found in anaerobic habitats such as aquatic sediments, soil, anaerobic sewage digesters, and the gastrointestinal tracts of animals.

The class Methanococci includes cells that are cocci or coccoid in shape, and contain protein cell walls. All species of Methanococci are strict anaerobes, and obtain energy by the reduction of CO2 to methane. Genera range from mesophilic (e.g., Methanococcus) to thermophilic (e.g., Methanothermococcus) to hyperthermophilic (e.g., Methanocaldococcus), and some species are mobile due to tufts of flagella.

Members of the class Methanomicrobia include a variety of cell shapes, including cocci, coccoid, rods, and sheathed rods. Most cells in this class have cells walls made of protein, and some cells are surrounded by a sheath. Most Methanomicrobia form methane by the reduction of carbon dioxide using a variety of electron donors, and all species are obligate anaerobes. Methanomicrobia can be found in a variety of habitats, including aquatic sediments, anaerobic sewage digesters, and the gastrointestinal tracts of animals.

The class Methanopyri consists of a single genus, Methanopyrus. Cells of this genus are rodshaped and contain cell walls made of psuedopeptidoglycan. Methanopyrus are hyperthermophilic and grow between 84 and 110°C, with optimal growth at 98°C. These cells grow chemoautotrophically by the conversion of CO2 and H2 to methane. Phylogenetic 16S rRNA studies have shown that Methanopyrus kandleri represents a very deep branch-off within Euryarchaeota, and is seemingly unrelated to any other methanogen.

Themophilic Euryarchaeota: Thermoplasmata This class consists of one order (Thermoplasmatales) and three families (Thermoplasma, Picrophilus, and Ferroplasma). Thermoplasma and Ferroplasma are the only representatives of Archaea that do not contain a cell wall.Species of Thermoplasma are obligate thermoacidophiles, with optimal growth achieved at 60°C and pH 2.Thermoplasma are facultative anaerobes, and obligate heterotrophs, using elemental sulfur for respiration. Species may be found in self-heating coal refuse piles and in acidic solfatara fields. Members of the family Picrophilus are the most acidophilic organisms known thus far.34, 35 Cells in this family are irregular cocci 1 to 1.5 µm in diameter and contain S-layer cell wall.

Picrophilus are thermophilic and hyperacidophilic, growing at temperatures between 47 and 60°C and pH ranges from below 0 to 3.5.17 Their ability to grow at pH values at and below zero and at high temperatures has shifted the physico-chemical boundaries at which life was considered to exist. Ferroplasma is the only member of this class that is not thermophilic, and has been identified at Iron Mountain in northern California.

It can grow where the temperature is between 15°C and 47°C, with an optimum temperature of 35°C, and where the pH is between 1.3 and 2.2, with an optimum pH of 1.7.36 The cells are pleomorphic and lack a cell wall. Unlike other families in this class, Ferroplasma are autotrophic, oxidizing ferrous iron as the sole energy source and fixing inorganic carbon as the sole carbon source.

Hyperthermophilic Euryarchaeota: Archaeoglobi and Thermococci

The class Archaeoglobi is composed of a single family and three genera: Archaeoglobus, Ferroglobus, and Geoglobus. Archaeoglobi are regular to irregular cocci occurring singly or in pairs. Species of this class are strictly anaerobic and hyperthermophilic, growing optimally at 80°C and at neutral pH. These cells exhibit blue-green fluorescence at 420 nm. Organisms in the genus Archaeoglobus are autotrophic and/or organotrophic and reduce sulfate or sulfite for respiration. Species of Ferroglobus grow by oxidation of Fe(II), S2-, and H2, whereas Geoglobus grow anaerobically in the presence of acetate and ferric iron.

Members of the class Thermococci are spherical and sometimes pleomorphic, and are about 1 µm in diameter. The cells often occur as diplococci or as clusters of up to 30 cells, and contain an S-layer cell wall. Thermococci are strictly anaerobic hyperthermophilic heterotrophs that generally perform sulfur respiration. Optimal growth temperatures for the type genus Thermococcus range from 75 to 88°C. Thermococcus releases strong-smelling sulfur-based products such as mercaptans. Species of Thermococcus have been isolated from submarine solfataras, including deep-sea hydrothermal vents.

Halophilic Euryarchaeota: Class Halobacteria Halobacteria, sometimes referred to as haloarchaea, is a class of Archaea composed of 27 genera that grow under extreme salinity. Salt requirements of these species range from 1.5 to 5.2 M NaCl, although most strains grow best at 3.5 to 4.5 M NaCl, at or near the saturation point of salt (36% (wt/ vol) salts). To maintain the osmolarity of these cells in their high-salt environment, halobacterial species accumulate up to 5 M intracellular levels of KCl to counterbalance the high extracellular salt concentration. As a result, the entire intracellular machinery, including enzymes and structural proteins, must be adapted to high salt levels, although these mechanisms are not entirely understood.

The proteins of all haloarchaeal species have a very low isoelectric point and the genomes contain high GC contents that are well above 60%.30 Some species of halobacteria are motile by means of tufts of flagella, although many species are nonmotile.Halobacteria are largely aerobic or facultative anaerobes. Halobacteria come in a wide variety of shapes, including rods, cocci, and a multitude of pleomorphic forms.The lack of turgor pressure within haloarchaeal cells enables the cells to tolerate the formation of corners and, as such, some species are triangular or square.Cell envelopes of coccoid haloarchaea are stable in the absence of salt but noncoccoid species maintain their integrity only in the presence of high concentrations of NaCl or KCl. The surface of the cell envelope of noncoccoid species has a hexagonal pattern due to the regular packing of glycoprotein subunits that are held together only in the presence of salt. Species of Halobacteria are the primary inhabitants of salt lakes, inland seas, and evaporating

Economic Importance

Because they have enzymes that can function at high temperatures, considerable effort is being made to exploit the archaea for commercial processes such as providing enzymes to be added to detergents (maintain their activity at high temperatures and pH) and an enzyme to covert corn starch into dextrins. Archaea may also be enlisted to aid in cleaning up contaminated sites, e.g., petroleum spills

The main technical application of methanogens is the production of biogas by digestion of organic substrates. It is estimated that up to 25% of the bioenergy used could be produced using the biogas process until 2020