extremophiles
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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 ...
that is able to live (or in some cases thrive) in
extreme environments An extreme environment is a habitat that is considered very hard to survive in due to its considerably extreme conditions such as temperature, accessibility to different energy sources or under high pressure. For an area to be considered an extrem ...
, 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 measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...
, radiation, salinity, 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

In the 1980s and 1990s, biologists found that
microbial life 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 ...
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 vents 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 radiation." 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 among ...
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 contine ...
, 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, w ...
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, the ...
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 a ...
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 Radioresistance is the level of ionizing radiation that organisms are able to withstand. Ionizing-radiation-resistant organisms (IRRO) were defined as organisms for which the dose of acute ionizing radiation (IR) required to achieve 90% reducti ...
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

;
Acidophile Acidophiles or acidophilic organisms are those that thrive under highly acidic conditions (usually at pH 5.0 or below). These organisms can be found in different branches of the tree of life, including Archaea, Bacteria,Becker, A.Types of Bacteria ...
: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 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 '' Staphylococc ...
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 Capnophiles are microorganisms that thrive in the presence of high concentrations of carbon dioxide (). Some capnophiles may have a metabolic requirement for carbon dioxide, while others merely compete more successfully for resources under these ...
: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 endolith or endolithic is an organism (Archaea, archaeon, bacterium, fungus, lichen, algae or amoeboid, amoeba) that is able to acquire the necessary resources for growth in the inner part of a Rock (geology), rock, mineral, coral, animal she ...
: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 characteris ...
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 imm ...
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 In Arctic and Antarctic ecology, a hypolith is a photosynthetic organism, and an extremophile, that lives underneath rocks in climatically extreme deserts such as Cornwallis Island and Devon Island in the Canadian high Arctic. The community it ...
:An organism that lives underneath rocks in
cold desert The desert climate or arid climate (in the Köppen climate classification ''BWh'' and ''BWk''), is a dry climate sub-type in which there is a severe excess of evaporation over precipitation. The typically bald, rocky, or sandy surfaces in desert ...
s. ; 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 pinkis ...
,
cadmium Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
,
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, ...
, 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 ''Ferroplasma'' is a genus of Archaea that belong to the family Ferroplasmaceae. Members of the ''Ferroplasma'' are typically acidophillic, pleomorphic, irregularly shaped cocci. The archaean family Ferroplasmaceae was first described in the ea ...
sp.,'' ''
Cupriavidus metallidurans ''Cupriavidus metallidurans'' is a non-spore-forming, Gram-negative bacterium which is adapted to survive several forms of heavy metal stress. As a model and industrial system It is an ideal subject to study heavy metal disturbance of cell ...
'' and
GFAJ-1 GFAJ-1 is a strain of rod-shaped bacteria in the family Halomonadaceae. It is an extremophile that was isolated from the hypersaline and alkaline Mono Lake in eastern California by geobiologist Felisa Wolfe-Simon, a NASA research fellow in resi ...
. ;
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
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 imm ...
s above 10 MPa (= 99 atm = 1,450 psi). Also referred to as
barophile 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 ...
. ; 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 Radioresistance is the level of ionizing radiation that organisms are able to withstand. Ionizing-radiation-resistant organisms (IRRO) were defined as organisms for which the dose of acute ionizing radiation (IR) required to achieve 90% reducti ...
:Organisms resistant to high levels of ionizing radiation, most commonly ultraviolet radiation. This category also includes organisms capable of resisting
nuclear 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 ...
. ;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 formula ...
. An example would be '' Sulfurovum Epsilonproteobacteria'', 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 is the multidisciplinary field that investigates the deterministic conditions and contingent events with which life arises, distributes, and evolves in the universe. Astrobiology 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 r ...
, chemistry,
astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
,
solar physics Solar physics is the branch of astrophysics that specializes in the study of the Sun. It deals with detailed measurements that are possible only for our closest star. It intersects with many disciplines of pure physics, astrophysics, and compu ...
,
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 i ...
,
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 physi ...
,
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 overlaps wi ...
, planetary science,
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 objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
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
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 contine ...
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 radiation i ...
, 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 north ...
involved a variety of
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 among ...
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 ''Escher ...
'' and '' Paracoccus denitrificans'' being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an
ultracentrifuge An ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as (approx. ). There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge. Both cla ...
at high speeds corresponding to 403,627 g (i.e. 403,627 times the gravity experienced on Earth). '' Paracoccus denitrificans'' 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 supernovas. Analysis showed that the small size of
prokaryotic cell A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
s 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 survived and showed remarkable results on the 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, 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, succeeding t ...
, 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 o ...
on the
International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
,
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 Space environment is a branch of astronautics, aerospace engineering and space physics that seeks to understand and address conditions existing in space that affect the design and operation of spacecraft. A related subject, space weather, deals ...
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
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 ...
, 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 olde ...
s living half a mile below the ice of
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 contine ...
. 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 endospores 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 ''Deinococcus radiodurans'' is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world' ...
'', 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
International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
. These findings support the notion 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 ...
. 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'' and ''Vibrio'' were found to be capable of bioremediation, albeit at a tenth of the speed they would perform at sea level pressure. Polycyclic aromatic hydrocarbon, Polycyclic Aromatic Hydrocarbons increase in solubility and bioavailability with increasing temperature. Thermophilic ''Thermus'' and ''Bacillus'' species have demonstrated higher gene expression for the alkane mono-oxygenase ''alkB'' 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. Paddy field, Rice paddies are highly oxidative environments that can produce high levels of lead or cadmium. ''
Deinococcus radiodurans ''Deinococcus radiodurans'' is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world' ...
'' 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 element, rare earth elements on their biological processes for example Methylacidiphilum fumariolicum, Methylorubrum extorquens and Methylobacterium radiotolerans are known to be able to use Lanthanide#Biological effects, lanthanides as cofactors to increase their methanol dehydrogenase activity.


Acid mine drainage

Acid mine drainage 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.''


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'', ''Geobacter metallireducens'' and some strains of ''Burkholderia fungorum.'' Radiotrophic fungus, which use radiation as an energy source have been found inside and around the Chernobyl Nuclear Power Plant. 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 insects to gamma radiation, significant DNA damage was detected only at 20 gray (unit), 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 lake, Pitch Lake. Research indicates that extremophiles inhabit the asphalt lake in populations ranging between 106 to 107 cells/gram. Likewise, until recently boron tolerance was unknown but a strong borophile was discovered in bacteria. With the recent isolation of ''Bacillus boroniphilus'', 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 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, which initiates the breakdown of hydrogen peroxide into oxygen and water, was isolated from an organism, ''Thermus brockianus'', found in Yellowstone National Park by Idaho National Laboratory 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'' 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 polymerase, Taq'' DNA polymerase and some ''Bacillus'' 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 ''Deinococcus radiodurans'' is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world' ...
'' 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 Transformation (genetics), 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 thermophile, thermophilic bacterium ''Thermus thermophilus'' and other related ''Thermus'' species are also capable of genetic transformation. ''Halobacterium volcanii'', an extreme halophilic (salinity, 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)). Extracellular membrane vesicles (MVs) might be involved in DNA transfer between different hyperthermophilic archaeal species. It has been shown that both plasmids and viral genomes can be transferred via MVs. Notably, a horizontal plasmid transfer has been documented between hyperthermophilic ''Thermococcus'' and ''Methanocaldococcus'' species, respectively belonging to the orders ''Thermococcales'' and ''Methanococcales''.


See also

* Dissimilatory metal-reducing microorganisms * Extremotroph * List of microorganisms tested in outer space * Mesophile – Organism that grows best in moderate temperatures * Neutrophile – Organism that grows best in a neutral pH level * RISE project * Tardigrade


References


Further reading

* * * *


External links


Extreme Environments - Science Education Resource CenterExtremophile Research

The Research Center of Extremophiles


*[http://extremophiles.org/ The International Society for Extremophiles]
Idaho National Laboratory


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