Domain Archaea PDF

Domain Achaea  The domain Archaea is named for the Archaean eon, the period of geological history when life first spread across Earth. In the Archaean, high temperatures and an atmosphere devoid of O2 and thick in toxic gases enveloped Earth. Archaea were once thought to be remnants of thi...

Domain Achaea  The domain Archaea is named for the Archaean eon, the period of geological history when life first spread across Earth. In the Archaean, high temperatures and an atmosphere devoid of O2 and thick in toxic gases enveloped Earth. Archaea were once thought to be remnants of this forgotten age since many Archaea live in extreme environments such as volcanic systems or salt ponds. While Archaea and Bacteria are both single-celled organisms with prokaryotic cell structure , these domains are highly differentiated both genetically and physiologically. Archaea share more features with Eukarya than with Bacteria. Indeed, it is likely that archaeal cells contributed fundamentally to the origin of the domain Eukarya.  The Archaea are nearly as diverse as the Bacteria, but the vast majority of Archaea have thus far proven difficult to grow in culture. To date, most well-characterized species of Archaea come from only two phyla: the Euryarchaeota and the Crenarchaeota In addition, several species have been isolated from the phylum Thaumarchaeota. By contrast, the phyla Korarchaeota and Nanoarchaeota are represented only by strains grown in coculture or studied using enrichment techniques  Common traits of all Archaea include ether-linked lipids, a lack of peptidoglycan in cell walls, and structurally complex RNA polymerases that resemble those of Eukarya Archaea can be chemoorganotrophs or chemolithotrophs, they can be respiratory or fermentative, and they can be aerobic or anaerobic using a wide diversity of electron donors and acceptors  Broader taxonomic sampling of archaeal diversity has allowed the clustering of several archaeal phyla into larger taxonomic groups that are now referred to as superphyla. Currently, there are three named superphyla recognized: Asgard, DPANN and TACK. DPANN and TACK Archaea were originally named based on the phyla present in them: DPANN referring to the Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanohaloarchaeota and Nanoarchaeota; TACK to the Thaumarchaeota, Aigarchaeota, Crenarchaeota and Korarchaeota. These superphyla now include several additional phyla Features unusual in Archaea Methane production, for example, is a unique characteristic of Archaea called methanogens Methanogenesis evolved very early within the archaeal domain, and all well-characterized methanogens belong to the phylum Euryarchaeota. Methanogenesis is a globally important process that has produced virtually all of the natural gas on Earth and has a significant effect on climate because methane is a strong “greenhouse gas”  Methanogens are important in a wide range of anoxic habitats including freshwater sediments, wetlands, rice paddies, wastewater treatment plants, geothermal systems, the subsurface of the Earth’s crust, and within the guts of many animals.  Methanopyrus, a Hyperthermophilic Methanogen Methanopyrus , the only genus in the order Methanopyrales, is a rod- shaped hyperthermophilic methanogen that shares phenotypic properties with both the hyperthermophiles and the methanogens. Methanopyrus was isolated from hot sediments near submarine hydrothermal vents and from the walls of “black smoker” hydrothermal vent chimneys. Methanopyrus produces CH4 only from H2 + CO2 and grows rapidly for an autotrophic organism(generation time ,1 h at 100degree C). In special pressurized vessels, growth of one strain of Methanopyrus has been recorded at 122 degree C, the highest temperature yet shown to support microbial growth  Archaea are also well known for containing many examples of extremophiles including hyperthermophiles (organisms with growth temperature optima above 80degree C) halophiles, acidophiles, psychrophiles The north arm of Great Salt Lake, Utah Euryarchaeota Euryarchaeota comprise a large and physiologically diverse group of Archaea. This phylum includes methanogens as well as many genera of extremely halophilic (salt-loving) Archaea. As a study in physiological contrasts, these two groups are remarkable: Methanogens are the strictest of anaerobes while extreme halophiles are primarily obligate aerobes. An organism is considered an extreme halophile if it requires 1.5 M (about 9%) or more sodium chloride (NaCl) for growth. Most species of extreme halophiles require 2–4 M NaCl (12–23%) for optimal growth and can grow at salinities as high as 5.5 M NaCl (32%, the limit of saturation for NaCl), although some species grow very slowly at this salinity.  Extremely halophilic Archaea, often given the nickname “haloarchaea,” are a diverse group that inhabits environments high in salt. These include naturally salty environments, such as solar salt evaporation ponds Marine salterns (enclosed basins filled with seawater left to evaporate, eventually yielding solar sea salt and salt lakes) Artificial saline habitats such as the surfaces of heavily salted foods, for example, certain fish and meats  Archaea are not the only microorganisms present. The eukaryotic alga Dunaliella is the major, if not the sole, oxygenic phototroph in most salt lakes. In highly alkaline soda lakes where Dunaliella is absent, anoxygenic phototrophic purple bacteria of the genera Ectothiorhodospira and Halorhodospira ( Section 15.4) predominate  Haloarchaea stain gram-negatively, reproduce by binary fission, and do not form spores. Cells of the various cultured genera are rod-shaped, cocci, or cup-shaped, but even cells that form squares are known Contain gas vesicle Obilgate aerobes Few strains of extreme halophiles are weakly motile by archaella, but most halophiles lack archaella  Other Archaea contains thermophilic and extremely acidophilic genera: Thermoplasma, Ferroplasma, and Picrophilus. These organisms are among the most acidophilic of all known microbes, with Picrophilus being capable of growth even below pH 0. Cell wall–less Thermoplasma, Ferroplasma organism phenotypically similar to the mycoplasmas