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A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. All prokaryotes are unicellular and are classified into bacteria and archaea. Many eukaryotes are multicellular, but many are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.8–4.0 billion years ago.
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from 20 to 45 °C. The term is mainly applied to microorganisms. Organisms that prefer extreme environments are known as extremophiles. Mesophiles have diverse classifications, belonging to two domains: Bacteria, Archaea, and to kingdom Fungi of domain Eucarya. Mesophiles belonging to the domain Bacteria can either be gram-positive or gram-negative. Oxygen requirements for mesophiles can be aerobic or anaerobic. There are three basic shapes of mesophiles: coccus, bacillus, and spiral.
Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. They are common in wetlands, where they are responsible for marsh gas, and in the digestive tracts of animals such as ruminants and many humans, where they are responsible for the methane content of belching in ruminants and flatulence in humans. In marine sediments, the biological production of methane, also termed methanogenesis, is generally confined to where sulfates are depleted, below the top layers. Moreover, methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments. Others are extremophiles, found in environments such as hot springs and submarine hydrothermal vents as well as in the "solid" rock of Earth's crust, kilometers below the surface.
Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C to +10 °C. They are found in places that are permanently cold, such as the polar regions and the deep sea. They can be contrasted with thermophiles, which are organisms that thrive at unusually high temperatures, and mesophiles at intermediate temperatures. Psychrophile is Greek for 'cold-loving', from ψυχρός.
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, Methanopyrus is a genus of the Methanopyraceae.
Belgica antarctica, the Antarctic midge, is a species of flightless midge, endemic to the continent of Antarctica. At 2–6 mm (0.079–0.24 in) long, it is the largest purely terrestrial animal native to the continent. It also has the smallest known insect genome as of 2014, with only 99 million base pairs of nucleotides. It is the only insect that can survive year-round in Antarctica.
Methanogenium boonei is a methanogenic archaean. Cells are non-motile irregular cocci 1.0-2.5 μm in diameter. This mesophile grows optimally at 19.4 °C, pH6.4-7.8, salinity 0.3-0.5M Na+. It was first isolated from Skan Bay, Alaska.
In taxonomy, Methanocorpusculum is a genus of microbes within the family Methanocorpusculaceae. The species within Methanocorpusculum were first isolated from biodisgester wastewater and activated sludge from anaerobic digestors. In nature, they live in freshwater environments. Unlike most other methanogenic archaea, they do not require high temperatures or extreme salt concentrations to live and grow.
In taxonomy, Methanofollis is a genus of the Methanomicrobiaceae.
A prokaryote is a unicellular organism that lacks a nuclear membrane-enclosed nucleus. The word prokaryote comes from the Greek πρό and κάρυον. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria and Archaea. Organisms with nuclei are placed in a third domain, Eukaryota. In the study of the origins of life, prokaryotes are thought to have arisen before eukaryotes.
Archaea constitute a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this term has fallen out of use.
Thermococcus celer is a Gram-negative, spherical-shaped archaeon of the genus Thermococcus. The discovery of T. celer played an important role in rerooting the tree of life when T. celer was found to be more closely related to methanogenic Archaea than to other phenotypically similar thermophilic species. T. celer was the first archaeon discovered to house a circularized genome. Several type strains of T. celer have been identified: Vu13, ATCC 35543, and DSM 2476.
Leucosporidium frigidum is a species of yeast that belongs to the genus of fungi Leucosporidium, and the family Leucosporidiaceae.
Methanogenium marinum is a psychrophilic, H2-using methanogen from Skan Bay, Alaska. Its cells are highly irregular, non-motile coccoids, occurring singly. AK-1 is its type strain.
Methanococcoides burtonii is a methylotrophic methanogenic archaeon first isolated from Ace Lake, Antarctica. Its type strain is DSM 6242.
Deinococcus frigens is a species of low temperature and drought-tolerating, UV-resistant bacteria from Antarctica. It is Gram-positive, non-motile and coccoid-shaped. Its type strain is AA-692. Individual Deinococcus frigens range in size from 0.9-2.0 μm and colonies appear orange or pink in color. Liquid-grown cells viewed using phase-contrast light microscopy and transmission electron microscopy on agar-coated slides show that isolated D. frigens appear to produce buds. Comparison of the genomes of Deiococcus radiodurans and D. frigens have predicted that no flagellar assembly exists in D. frigens.
Galdieria sulphuraria is an extremophilic unicellular species of red algae. It is the type species of the genus Galdieria. It is known for its broad metabolic capacities, including photosynthesis and heterotrophic growth on over 50 different extracellular carbon sources. The members of the class Cyanidiophyceae are among the most acidophilic known photosynthetic organisms, and the growth conditions of G. sulphuraria – pH between 0 and 4, and temperatures up to 56 °C – are among the most extreme known for eukaryotes. Analysis of its genome suggests that its thermoacidophilic adaptations derive from horizontal gene transfer from archaea and bacteria, another rarity among eukaryotes.
Notothenia coriiceps, also known as the black rockcod, Antarctic yellowbelly rockcod, or Antarctic bullhead notothen, is a species of marine ray-finned fish, belonging to the family Nototheniidae, the notothens or cod icefishes. It is widely spread around the Antarctic continent. Like other Antarctic notothenioid fishes, N. coriiceps evolved in the stable, ice-cold environment of the Southern Ocean. It is not currently targeted by commercial fisheries.
References
- ↑ Franzmann, P. D.; Liu, Y.; Balkwill, D. L.; Aldrich, H. C.; Conway De Macario, E.; Boone, D. R. (1997). "Methanogenium frigidum sp. nov., a Psychrophilic, H2-Using Methanogen from Ace Lake, Antarctica". International Journal of Systematic Bacteriology. 47 (4): 1068–1072. doi: 10.1099/00207713-47-4-1068 . ISSN 0020-7713. PMID 9336907.
- 1 2 Asim K. Bej; Jackie Aislabie; Ronald M. Atlas (2009). Polar Microbiology: The Ecology, Biodiversity and Bioremediation Potential of Microorganisms in Extremely Cold Environments. CRC Press. pp. 52–53, 103, 121. ISBN 978-1420083880 . Retrieved 2016-09-05.
- ↑ Saunders, N.F.W.; Thomas, T.; Curmi, P.M.G.; Mattick, J.S.; et al. (2003). "Mechanisms of thermal adaptation revealed from the genomes of the Antarctic Archaea Methanogenium frigidum and Methanococcoides burtonii". Genome Research. 13 (7): 1580–1588. doi:10.1101/Gr.1180903. PMC 403754 . PMID 12805271 . Retrieved 2016-08-03.
