Aerial image of Grand Prismatic Spring (view from the south)

An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...

that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

, or

pH level In chemistry, pH (), historically denoting "potential of hydrogen" (or "power of hydrogen"), is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of ions) are me ...

. These organisms are ecologically dominant in the evolutionary history of the planet. Some spores and cocooned bacteria samples have been dormant for more than 40 million years, extremophiles have continued to thrive in the most extreme conditions, making them one of the most abundant lifeforms.

Characteristics

Diversity of extreme environments on Earth

In the 1980s and 1990s, biologists found that microbial life has great flexibility for surviving in extreme environments—niches that are acidic, extraordinarily hot or within irregular air pressure for example—that would be completely inhospitable to complex organisms. Some scientists even concluded that life may have begun on Earth in

hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspo ...

s far under the ocean's surface. According to astrophysicist Steinn Sigurdsson, "There are viable

bacterial spores An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., ...

that have been found that are 40 million years old on Earth—and we know they're very hardened to

." Some

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

were found living in the cold and dark in a lake buried a half-mile deep under the ice in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

, and in the

Marianas Trench The Mariana Trench is an oceanic trench located in the western Pacific Ocean, about east of the Mariana Islands; it is the deepest oceanic trench on Earth. It is crescent-shaped and measures about in length and in width. The maximum known ...

, the deepest place in Earth's oceans. Expeditions of the

International Ocean Discovery Program The International Ocean Discovery Program (IODP) is an international marine research collaboration dedicated to advancing scientific understanding of the Earth through drilling, coring, and monitoring the subseafloor. The research enabled by IODP ...

found microorganisms in 120 °C sediment that is 1.2 km below seafloor in the

Nankai Trough The is a submarine trough located south of the Nankaidō region of Japan's island of Honshu, extending approximately offshore. The underlying fault, the ''Nankai megathrust,'' is the source of the devastating Nankai megathrust earthquakes, wh ...

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

zone. Some microorganisms have been found thriving inside rocks up to below the sea floor under of ocean off the coast of the northwestern United States. According to one of the researchers, "You can find microbes everywhere—they're extremely adaptable to conditions, and survive wherever they are." A key to extremophile adaptation is their

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

composition, affecting their

protein folding Protein folding is the physical process by which a protein chain is translated to its native three-dimensional structure, typically a "folded" conformation by which the protein becomes biologically functional. Via an expeditious and reproduc ...

ability under particular conditions. Studying extreme environments on Earth can help researchers understand the limits of habitability on other worlds. Tom Gheysens from Ghent University in Belgium and some of his colleagues have presented research findings that show spores from a species of Bacillus bacteria survived and were still viable after being heated to temperatures of .

Classifications

There are many classes of extremophiles that range all around the globe; each corresponding to the way its environmental niche differs from mesophilic conditions. These classifications are not exclusive. Many extremophiles fall under multiple categories and are classified as polyextremophiles. For example, organisms living inside hot rocks deep under Earth's surface are thermophilic and piezophilic such as ''Thermococcus barophilus''. A polyextremophile living at the summit of a mountain in the

Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in th ...

might be a radioresistant

xerophile A xerophile () is an extremophilic organism that can grow and reproduce in conditions with a low availability of water, also known as water activity. Water activity (aw) is measured as the humidity above a substance relative to the humidity above ...

, a

psychrophile Psychrophiles or cryophiles (adj. ''psychrophilic'' or ''cryophilic'') are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from to . They have an optimal growth temperature at . They are found in ...

, and an

oligotroph An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...

. Polyextremophiles are well known for their ability to tolerate both high and low pH levels.

Terms

Microorganisms from the hypersaline Lake Tyrrell

; Acidophile:An organism with optimal growth at pH levels of 3.0 or below. ;

Alkaliphile Alkaliphiles are a class of extremophilic microbes capable of survival in alkaline ( pH roughly 8.5–11) environments, growing optimally around a pH of 10. These bacteria can be further categorized as obligate alkaliphiles (those that require hig ...

:An organism with optimal growth at pH levels of 9.0 or above. ;

Anaerobe An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenate ...

:An organism with optimal growth in the absence of

molecular oxygen There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are ...

. Two sub-types exist:

facultative anaerobe A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are '' Staphylococ ...

and

obligate anaerobe Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environme ...

. A ''facultative'' anaerobe can tolerate anoxic and oxic conditions whilst an ''obligate'' anaerobe will die in the presence of even low levels of molecular oxygen.: ; Capnophile:An organism with optimal growth conditions in high concentrations of carbon dioxide. An example would be '' Mannheimia succiniciproducens,'' a bacterium that inhabits a ruminant animal's digestive system. ; ; Cryptoendolith :An organism that lives in microscopic spaces within rocks, such as pores between aggregate grains. These may also be called

endolith An endolith or endolithic is an organism ( archaeon, bacterium, fungus, lichen, algae or amoeba) that is able to acquire the necessary resources for growth in the inner part of a rock, mineral, coral, animal shells, or in the pores between min ...

, a term that also includes organisms populating fissures,

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...

s, and faults filled with groundwater in the deep subsurface. ;

Halophile The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...

:An organism with optimal growth at a concentration of dissolved salts of 50 g/L (= 5% m/v) or above. ; Hyperpiezophile:An organism with optimal growth at

hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body " fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an i ...

s above 50 MPa (= 493 atm = 7,252 psi). ;

Hyperthermophile A hyperthermophile is an organism that thrives in extremely hot environments—from 60 °C (140 °F) upwards. An optimal temperature for the existence of hyperthermophiles is often above 80 °C (176 °F). Hyperthermophiles are often within the doma ...

:An organism with optimal growth at temperatures above . ; Hypolith:An organism that lives underneath rocks in cold deserts. ; Metallotolerant:Capable of tolerating high levels of dissolved heavy metals in solution, such as

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

cadmium Cadmium is a chemical element with the Symbol (chemistry), symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Li ...

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...

, and

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

. Examples include '' Ferroplasma sp.,'' '' Cupriavidus metallidurans'' and GFAJ-1. ;

Oligotroph An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...

:An organism with optimal growth in nutritionally limited environments. ;

Osmophile An osmophile is a microorganism adapted to environments with high osmotic pressures, such as high sugar concentrations. Osmophiles are similar to halophiles (salt-loving organisms) in that a critical aspect of both types of environment is their low ...

:An organism with optimal growth in environments with a high sugar concentration. ;

Piezophile A piezophile (from Greek "piezo-" for pressure and "-phile" for loving) is an organism with optimal growth under high hydrostatic pressure i.e. an organism that has its maximum rate of growth at a hydrostatic pressure equal to or above 10 MPa (= 99 ...

:An organism with optimal growth in

s above 10 MPa (= 99 atm = 1,450 psi). Also referred to as barophile. ; Polyextremophile:A polyextremophile (faux Ancient Latin/Greek for 'affection for many extremes') is an organism that qualifies as an extremophile under more than one category. ;

Psychrophile Psychrophiles or cryophiles (adj. ''psychrophilic'' or ''cryophilic'') are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from to . They have an optimal growth temperature at . They are found in ...

/Cryophile:An organism with optimal growth at temperatures of or lower. ; Radioresistant:Organisms resistant to high levels of

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

, most commonly ultraviolet radiation. This category also includes organisms capable of resisting nuclear radiation. ;Sulphophile: An organism with optimal growth conditions in high concentrations of

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

. An example would be ''

Sulfurovum Epsilonproteobacteria ''Sulfurovum'' is a genus within the ''Campylobacterota Campylobacterota are a phylum of bacteria. All species of this phylum are Gram-negative. The Campylobacterota consist of few known genera, mainly the curved to spirilloid ''Wolinella'' s ...

'', a sulfur-oxidizing bacteria that inhabits deep-water sulfur vents. ;

Thermophile A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...

: An organism with optimal growth at temperatures above . ;

Xerophile A xerophile () is an extremophilic organism that can grow and reproduce in conditions with a low availability of water, also known as water activity. Water activity (aw) is measured as the humidity above a substance relative to the humidity above ...

: An organism with optimal growth at

water activity Water activity (''aw'') is the partial vapor pressure of water in a solution divided by the standard state partial vapor pressure of water. In the field of food science, the standard state is most often defined as pure water at the same tempe ...

below 0.8.

In astrobiology

Astrobiology Astrobiology, and the related field of exobiology, is an interdisciplinary scientific field that studies the origins, early evolution, distribution, and future of life in the universe. Astrobiology is the multidisciplinary field that invest ...

is the multidisciplinary field that investigates the deterministic conditions and contingent events with which life arises, distributes, and evolves in the universe.

makes use of

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...

astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...

, solar physics,

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...

molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

planetary science Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), celestial bodies (such as moons, asteroids, comets) and planetary systems (in particular those of the Solar System) and the processes of their ...

geography Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, an ...

, and

geology Geology () is a branch of natural science concerned with Earth and other Astronomical object, astronomical objects, the features or rock (geology), rocks of which it is composed, and the processes by which they change over time. Modern geology ...

to investigate the possibility of life on other worlds and help recognize

biosphere The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also ...

s that might be different from that on Earth. Astrobiologists are particularly interested in studying extremophiles, as it allows them to map what is known about the limits of life on Earth to potential extraterrestrial environments For example, analogous deserts of

are exposed to harmful

UV radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiatio ...

, low temperature, high salt concentration and low mineral concentration. These conditions are similar to those on

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. Therefore, finding viable microbes in the subsurface of Antarctica suggests that there may be microbes surviving in endolithic communities and living under the Martian surface. Research indicates it is unlikely that Martian microbes exist on the surface or at shallow depths, but may be found at subsurface depths of around 100 meters. Recent research carried out on extremophiles in

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...

involved a variety of

including ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

'' and ''

Paracoccus denitrificans ''Paracoccus denitrificans'', is a coccoid bacterium known for its nitrate reducing properties, its ability to replicate under conditions of hypergravity and for being a relative of the eukaryotic mitochondrion (endosymbiotic theory). Descripti ...

'' being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an ultracentrifuge at high speeds corresponding to 403,627 g (i.e. 403,627 times the gravity experienced on Earth). ''

'' was one of the bacteria which displayed not only survival but also robust cellular growth under these conditions of hyperacceleration which are usually found only in cosmic environments, such as on very massive stars or in the shock waves of

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...

s. Analysis showed that the small size of prokaryotic cells is essential for successful growth under

hypergravity Hypergravity is defined as the condition where the force of gravity exceeds that on the surface of the Earth. This is expressed as being greater than 1 '' g''. Hypergravity conditions are created on Earth for research on human physiology in a ...

. The research has implications on the feasibility of

panspermia Panspermia () is the hypothesis, first proposed in the 5th century BCE by the Greek philosopher Anaxagoras, that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, and planetoids, as well as by spacec ...

. On 26 April 2012, scientists reported that

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.adaptation capacity of photosynthetic activity within the simulation time of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the

German Aerospace Center The German Aerospace Center (german: Deutsches Zentrum für Luft- und Raumfahrt e.V., abbreviated DLR, literally ''German Center for Air- and Space-flight'') is the national center for aerospace, energy and transportation research of Germany ...

(DLR). On 29 April 2013, scientists at

Rensselaer Polytechnic Institute Rensselaer Polytechnic Institute () (RPI) is a private research university in Troy, New York, with an additional campus in Hartford, Connecticut. A third campus in Groton, Connecticut closed in 2018. RPI was established in 1824 by Stephen Van ...

, funded by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

, reported that, during

spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in ...

on the

International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...

microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

seem to adapt to the space environment in ways "not observed on Earth" and in ways that "can lead to increases in growth and

virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...

". On 19 May 2014, scientists announced that numerous

, like '' Tersicoccus phoenicis'', may be resistant to methods usually used in spacecraft assembly clean rooms. It's not currently known if such resistant microbes could have withstood space travel and are present on the ''Curiosity'' rover now on the planet Mars. On 20 August 2014, scientists confirmed the existence of

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...

s living half a mile below the ice of

. In September 2015, scientists fro
CNR-National Research Council
of Italy reported that ''S.soflataricus'' was able to survive under Martian radiation at a wavelength that was considered extremely lethal to most bacteria. This discovery is significant because it indicates that not only bacterial spores, but also growing cells can be remarkably resistant to strong UV radiation. In June 2016, scientists from Brigham Young University conclusively reported that

endospore An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., n ...

s of ''

Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus ...

'' were able to survive high speed impacts up to 299±28 m/s, extreme shock, and extreme deceleration. They pointed out that this feature might allow endospores to survive and to be transferred between planets by traveling within meteorites or by experiencing atmosphere disruption. Moreover, they suggested that the landing of spacecraft may also result in interplanetary spore transfer, given that spores can survive high-velocity impact while ejected from the spacecraft onto the planet surface. This is the first study which reported that bacteria can survive in such high-velocity impact. However, the lethal impact speed is unknown, and further experiments should be done by introducing higher-velocity impact to bacterial endospores. In August 2020 scientists reported that bacteria that feed on air discovered 2017 in Antarctica are likely not limited to Antarctica after discovering the two genes previously linked to their "atmospheric chemosynthesis" in soil of two other similar cold desert sites, which provides further information on this

carbon sink A carbon sink is anything, natural or otherwise, that accumulates and stores some carbon-containing chemical compound for an indefinite period and thereby removes carbon dioxide () from the atmosphere. Globally, the two most important carbon si ...

and further strengthens the extremophile evidence that supports the potential existence of microbial life on alien planets. The same month, scientists reported that bacteria from Earth, particularly '' Deinococcus radiodurans'', were found to survive for three years in

outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...

, based on studies on the

. These findings support the notion of

Text and images are available under
Creative Commons Attribution 4.0 International License

Bioremediation

Extremophiles can also be useful players in the

bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...

of contaminated sites as some species are capable of biodegradation under conditions too extreme for classic bioremediation candidate species. Anthropogenic activity causes the release of pollutants that may potentially settle in extreme environments as is the case with tailings and sediment released from deep-sea mining activity. While most bacteria would be crushed by the pressure in these environments, piezophiles can tolerate these depths and can metabolize pollutants of concern if they possess bioremediation potential.

Hydrocarbons

There are multiple potential destinations for hydrocarbons after an oil spill has settled and currents routinely deposit them in extreme environments. Methane bubbles resulting from the

Deepwater Horizon oil spill The ''Deepwater Horizon'' oil spill (also referred to as the "BP oil spill") was an industrial disaster that began on 20 April 2010 off of the coast of the United States in the Gulf of Mexico on the BP-operated Macondo Prospect, considere ...

were found 1.1 kilometers below water surface level and at concentrations as high as 183 ''μ''mol per kilogram. The combination of low temperatures and high pressures in this environment result in low microbial activity. However, bacteria that are present including species of ''

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able t ...

'', ''

Aeromonas ''Aeromonas'' is a genus of Gram-negative, facultative anaerobic, rod-shaped bacteria that morphologically resemble members of the family Enterobacteriaceae. Most of the 14 described species have been associated with human diseases. The most imp ...

'' and ''

Vibrio ''Vibrio'' is a genus of Gram-negative bacteria, possessing a curved-rod (comma) shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Being highly salt tolerant and unable to survive ...

'' were found to be capable of bioremediation, albeit at a tenth of the speed they would perform at sea level pressure.

Polycyclic Aromatic Hydrocarbons A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...

increase in solubility and bioavailability with increasing temperature. Thermophilic ''

Thermus ''Thermus'' is a genus of thermophilic bacteria. It is one of several bacteria belonging to the '' Deinococcota'' phylum. ''Thermus'' species can be distinguished from other genera in the family ''Thermaceae'' as well as all other bacteria by ...

'' and ''

Bacillus ''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum '' Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacill ...

'' species have demonstrated higher gene expression for the alkane mono-oxygenase ''

alkB AlkB (Alkylation B) is a protein found in E. coli, induced during an adaptive response and involved in the direct reversal of alkylation damage.Errol C.Friedberg, Graham c. Walker, Wolfram Siede, Richard D. Wood, Roger A. schultz, Tom Ellenberge ...

'' at temperatures exceeding 60 °C. The expression of this gene is a crucial precursor to the bioremediation process. Fungi that have been genetically modified with cold-adapted enzymes to tolerate differing pH levels and temperatures have been shown to be effective at remediating hydrocarbon contamination in freezing conditions in the Antarctic.

Metals

'' Acidithiubacillus ferroxidans'' has been shown to be effective in remediating mercury in acidic soil due to its ''merA'' gene making it mercury resistant. Industrial effluent contain high levels of metals that can be detrimental to both human and ecosystem health. In extreme heat environments the extremophile '' Geobacillus thermodenitrificans'' has been shown to effectively manage the concentration of these metals within twelve hours of introduction. Some acidophilic microorganisms are effective at metal remediation in acidic environments due to proteins found in their periplasm, not present in any mesophilic organisms, allowing them to protect themselves from high proton concentrations.

Rice paddies A paddy field is a flooded field of arable land used for growing semiaquatic crops, most notably rice and taro. It originates from the Neolithic rice-farming cultures of the Yangtze River basin in southern China, associated with pre-Au ...

are highly oxidative environments that can produce high levels of lead or cadmium. '' Deinococcus radiodurans'' are resistant to the harsh conditions of the environment and are therefore candidate species for limiting the extent of contamination of these metals. Some bacteria are known to also use

rare earth elements The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...

on their biological processes for example

Methylacidiphilum fumariolicum ''Methylacidiphilum fumariolicum '' is an autotrophic bacterium first described in 2007 growing on volcanic pools near Naples, Italy. It grows in mud at temperatures between 50 °C and 60 °C and an acidic pH of 2–5. It is able to ox ...

Methylorubrum extorquens ''Methylorubrum extorquens'' is a Gram-negative bacterium. ''Methylorubrum'' species often appear pink, and are classified as pink-pigmented facultative methylotrophs, or PPFMs. The wild type has been known to use both methane and multiple carb ...

and

Methylobacterium radiotolerans Methylobacterium radiotolerans is a radiation-tolerating Gram-negative bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of p ...

are known to be able to use

lanthanides The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and ytt ...

as cofactors to increase their

methanol dehydrogenase In enzymology, a methanol dehydrogenase is an enzyme that catalyzes the chemical reaction: :methanol \rightleftharpoons formaldehyde + 2 electrons + 2H+ How the electrons are captured and transported depends upon the kind of methanol dehydrogenas ...

activity.

Acid mine drainage

Acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines or coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weathering ...

is a major environmental concern associated with many metal mines. One of the most productive methods of its remediation is through the introduction of the extremophile organism ''

Thiobacillus ferrooxidans ''Acidithiobacillus'' is a genus of the '' Acidithiobacillia'' in the "Pseudomonadota". The genus includes acidophilic organisms capable of iron and/or sulfur oxidation. Like all ''"Pseudomonadota"'', ''Acidithiobacillus'' spp. are Gram-negative. ...

.''

Radioactive materials

Any bacteria capable of inhabiting radioactive mediums can be classified as an extremophile. Radioresistant organisms are therefore critical in the bioremediation of radionuclides. Uranium is particularly challenging to contain when released into an environment and very harmful to both human and ecosystem health. The NANOBINDERS project is equipping bacteria that can survive in uranium rich environments with gene sequences that enable proteins to bind to uranium in mining effluent, making it more convenient to collect and dispose of. Some examples are ''

Shewanella putrefaciens ''Shewanella putrefaciens'' is a Gram-negative pleomorphic bacterium. It has been isolated from marine environments, as well as from anaerobic sandstone in the Morrison Formation in New Mexico. ''S. putrefaciens'' is also a facultative anaerobe ...

'', '' Geobacter metallireducens'' and some strains of ''

Burkholderia fungorum Paraburkholderia fungorum (P. fungorum) is a Gram-negative species of bacteria. that has been commonly used as a beneficial microorganism in agriculture as an agent for biocontrol and bioremediation. ''Paraburkholderia fungorum'' is Some of its ...

.'' Radiotrophic fungus, which use radiation as an energy source have been found inside and around the

Chernobyl Nuclear Power Plant The Chernobyl Nuclear Power Plant (ChNPP; ; ), is a nuclear power plant undergoing decommissioning. ChNPP is located near the abandoned city of Pripyat in northern Ukraine northwest of the city of Chernobyl, from the Belarus–Ukraine borde ...

. Radioresistance has also been observed in certain species of macroscopic lifeforms. The lethal dose required to kill up to 50% of a tortoise population is 40,000 roentgens, compared to only 800 roentgens needed to kill 50% of a human population. In experiments exposing

lepidopteran Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described specie ...

insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...

gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

, significant DNA damage was detected only at 20 Gy and higher doses, in contrast with human cells that showed similar damage at only 2 Gy.

Examples and recent findings

New sub-types of -philes are identified frequently and the sub-category list for extremophiles is always growing. For example, microbial life lives in the liquid

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...

lake,

Pitch Lake The Pitch Lake is the largest natural deposit of asphalt in the world, estimated to contain 10 million tons. It is located in La Brea in southwest Trinidad, within the Siparia Regional Corporation. The lake covers about 100 acres (0.405 squ ...

. Research indicates that extremophiles inhabit the asphalt lake in populations ranging between 10⁶ to 10⁷ cells/gram. Likewise, until recently

boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the '' boron group'' it has t ...

tolerance was unknown but a strong borophile was discovered in bacteria. With the recent isolation of ''

Bacillus boroniphilus ''Bacillus boroniphilus'' is a species of highly boron-tolerant bacterium, hence its name. It is Gram-positive, motile Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability ...

'', borophiles came into discussion. Studying these borophiles may help illuminate the mechanisms of both boron toxicity and boron deficiency. In July 2019, a scientific study of Kidd Mine in Canada discovered

sulfur-breathing organisms Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as termi ...

which live 7900 feet below the surface, and which breathe sulfur in order to survive. These organisms are also remarkable due to eating rocks such as pyrite as their regular food source.

Biotechnology

The thermoalkaliphilic

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting t ...

, which initiates the breakdown of hydrogen peroxide into oxygen and water, was isolated from an organism, ''

Thermus brockianus ''Thermus'' is a genus of thermophilic bacteria. It is one of several bacteria belonging to the ''Deinococcota'' phylum. ''Thermus'' species can be distinguished from other genera in the family ''Thermaceae'' as well as all other bacteria by ...

'', found in

Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowst ...

Idaho National Laboratory Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...

researchers. The catalase operates over a temperature range from 30 °C to over 94 °C and a pH range from 6–10. This catalase is extremely stable compared to other catalases at high temperatures and pH. In a comparative study, the ''T. brockianus'' catalase exhibited a half life of 15 days at 80 °C and pH 10 while a catalase derived from ''

Aspergillus niger ''Aspergillus niger'' is a mold classified within the ''Nigri'' section of the ''Aspergillus'' genus. The ''Aspergillus'' genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on de ...

'' had a half life of 15 seconds under the same conditions. The catalase will have applications for removal of hydrogen peroxide in industrial processes such as pulp and paper bleaching, textile bleaching, food pasteurization, and surface decontamination of food packaging. DNA modifying enzymes such as '' Taq'' DNA polymerase and some ''

'' enzymes used in clinical diagnostics and starch liquefaction are produced commercially by several biotechnology companies.

DNA transfer

Over 65 prokaryotic species are known to be naturally competent for genetic transformation, the ability to transfer DNA from one cell to another cell followed by integration of the donor DNA into the recipient cell's chromosome. Several extremophiles are able to carry out species-specific DNA transfer, as described below. However, it is not yet clear how common such a capability is among extremophiles. The bacterium '' Deinococcus radiodurans'' is one of the most radioresistant organisms known. This bacterium can also survive cold, dehydration, vacuum and acid and is thus known as a polyextremophile. ''D. radiodurans'' is competent to perform genetic transformation. Recipient cells are able to repair DNA damage in donor transforming DNA that had been UV irradiated as efficiently as they repair cellular DNA when the cells themselves are irradiated. The extreme

thermophilic A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...

bacterium ''

Thermus thermophilus ''Thermus thermophilus'' is a Gram-negative bacterium used in a range of biotechnological applications, including as a model organism for genetic manipulation, structural genomics, and systems biology. The bacterium is extremely thermophilic, ...

'' and other related ''Thermus'' species are also capable of genetic transformation. '' Halobacterium volcanii'', an extreme halophilic ( saline tolerant) archaeon, is capable of natural genetic transformation. Cytoplasmic bridges are formed between cells that appear to be used for DNA transfer from one cell to another in either direction. '' Sulfolobus solfataricus'' and '' Sulfolobus acidocaldarius'' are hyperthermophilic archaea. Exposure of these organisms to the DNA damaging agents UV irradiation, bleomycin or mitomycin C induces species-specific cellular aggregation. UV-induced cellular aggregation of ''S. acidocaldarius'' mediates chromosomal marker exchange with high frequency. Recombination rates exceed those of uninduced cultures by up to three orders of magnitude. Frols et al. and Ajon et al. hypothesized that cellular aggregation enhances species-specific DNA transfer between ''Sulfolobus'' cells in order to repair damaged DNA by means of homologous recombination. Van Wolferen et al. noted that this DNA exchange process may be crucial under DNA damaging conditions such as high temperatures. It has also been suggested that DNA transfer in ''Sulfolobus'' may be an early form of sexual interaction similar to the more well-studied bacterial transformation systems that involve species-specific DNA transfer leading to homologous recombinational repair of DNA damage (and see

Transformation (genetics) In molecular biology and genetics, transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane(s). For transformation to t ...

). Extracellular membrane vesicles (MVs) might be involved in DNA transfer between different hyperthermophilic archaeal species. It has been shown that both

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...

s and viral

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...

s can be transferred via MVs. Notably, a horizontal plasmid transfer has been documented between hyperthermophilic ''

Thermococcus In taxonomy, ''Thermococcus'' is a genus of thermophilic Archaea in the family the Thermococcaceae. Members of the genus ''Thermococcus'' are typically irregularly shaped coccoid species, ranging in size from 0.6 to 2.0 μm in diameter. Some ...

'' and ''

Methanocaldococcus ''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 discov ...

'' species, respectively belonging to the orders ''Thermococcales'' and ''Methanococcales''.

References

External links

Extreme Environments - Science Education Resource CenterExtremophile Research

The Research Center of Extremophiles

* ttp://extremophiles.org/ The International Society for Extremophilesbr>Idaho National Laboratory

* ttps://deepcarbon.net/feature/how-hot-is-too-hot#.V9Fp-4WASfE/ T-Limit Expedition {{Portal bar, Astronomy, Biology Environmental microbiology Astrobiology Bacteria Ecology Geomicrobiology Microbial growth and nutrition

Characteristics

Classifications

Terms

In astrobiology

Bioremediation

Hydrocarbons

Metals

Acid mine drainage

Radioactive materials

Examples and recent findings

Biotechnology

DNA transfer

See also

References

Further reading

External links