Extremophile
Encyclopedia
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
that thrives in physically or geochemically extreme conditions
Extreme environment
An extreme environment exhibits extreme conditions which are challenging to most life forms. These may be extremely high or low ranges of temperature, radiation, pressure, acidity, alkalinity, air, water, salt, sugar, carbon dioxide, sulphur, petroleum and many others.An extreme environment is one...
that are detrimental to most life on Earth
Life on Earth
Life on Earth: A Natural History by David Attenborough is a television natural history series made by the BBC in association with Warner Bros. and Reiner Moritz Productions...
. In contrast, organisms that live in more moderate environments may be termed mesophile
Mesophile
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 25 and 40 °C...
s or neutrophile
Neutrophile
A neutrophile is an organism that thrives in neutral pH environments....
s. The category name is unfortunate as it calls for subjective judgements of two issues - firstly, the degree of deviation from 'normal' justifying the use of 'extreme', and secondly, whether the organism prefers the environment or merely tolerates it.
In the 1980s and 1990s, biologists found that microbial life has an amazing flexibility for surviving in extreme environments - niches that are extraordinarily hot, or acidic, for example - that would be completely inhospitable to complex organisms. Some scientists even concluded that life may have begun on Earth in hydrothermal vent
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...
s far under the ocean's surface. According to astrophysicist Dr. Steinn Sigurdsson, "There are viable bacterial spores that have been found that are 40 million years old on Earth - and we know they're very hardened to radiation."
Most known extremophiles are microbes. The domain Archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
contains renowned examples, but extremophiles are present in numerous and diverse gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
tic lineages of both bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and archaeans. Furthermore, it is erroneous to use the term extremophile to encompass all archaeans, as some are mesophilic
Mesophile
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 25 and 40 °C...
. Neither are all extremophiles unicellular; protostome
Protostome
Protostomia are a clade of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers...
animals found in similar environments include the Pompeii worm
Pompeii worm
Alvinella pompejana, , is a species of deep-sea polychaete worm...
, the psychrophilic
Psychrophile
Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −15°C to +10°C. Temperatures as low as −15°C are found in pockets of very salty water surrounded by sea ice. They can be contrasted with thermophiles, which...
Grylloblattodea (insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s), Antarctic krill
Antarctic krill
Antarctic krill, Euphausia superba, is a species of krill found in the Antarctic waters of the Southern Ocean. It is a shrimp-like crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 individual animals per cubic metre...
(a crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
) and Tardigrades (water bears).
Types
There are many different 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. For example, organisms living inside hot rocks deep under Earth's surface are both thermophilic and barophilic.Acidophile
Acidophile (organisms)
Acidophilic organisms are those that thrive under highly acidic conditions . These organisms can be found in different branches of the tree of life, including Archaea, Bacteria, and Eukaryotes...
: An organism with optimal growth at pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
levels of 3 or below
Alkaliphile
Alkaliphile
Alkaliphiles are microbes classified as extremophiles that thrive in alkaline environments with a pH of 9 to 11 such as playa lakes and carbonate-rich soils...
: An organism with optimal growth at pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
levels of 9 or above
Anaerobe: An organism that does not require oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
for growth such as Spinoloricus Cinzia
Cryptoendolith: An organism that lives in microscopic spaces within rocks, such as pores between aggregate grains; these may also be called Endolith
Endolith
An endolith is an organism that lives inside rock, coral, animal shells, or in the pores between mineral grains of a rock. Many are extremophiles, living in places previously thought inhospitable to life...
, a term that also includes organisms populating fissures, aquifers, and faults filled with groundwater in the deep subsurface.
Halophile
Halophile
Halophiles are extremophile organisms that thrive in environments with very high concentrations of salt. The name comes from the Greek for "salt-loving". While the term is perhaps most often applied to some halophiles classified into the Archaea domain, there are also bacterial halophiles and some...
: An organism requiring at least 0.2M concentrations of salt (NaCl
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
) for growth
Hyperthermophile
Hyperthermophile
A hyperthermophile is an organism that thrives in extremely hot environments— from 60 degrees C upwards. An optimal temperature for the existence of hyperthermophiles is above 80°C . Hyperthermophiles are a subset of extremophiles, micro-organisms within the domain Archaea, although some bacteria...
: An organism that can thrive at temperatures between 80–122 °C, such as those found in hydrothermal systems
Hypolith
Hypolith
In Arctic and Antarctic ecology, a hypolith is a photosynthetic organism that livesunderneath rocks in climatically extreme deserts such as Cornwallis Island and Devon Island in the Canadian high Arctic. The community itself is the hypolithon....
: An organism that lives underneath rocks in cold deserts
Lithoautotroph
Lithoautotroph
A lithoautotroph is a microbe which derives energy from reduced compounds of mineral origin. They may also be referred to as chemolithoautotrophs, a type of lithotrophs, reflecting their autotrophic metabolic pathways. Lithoautotrophs are exclusively microbes; macrofauna do not possess the...
: An organism (usually bacteria) whose sole source of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
is carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and exergonic inorganic oxidation (chemolithotrophs) such as Nitrosomonas europaea; these organisms are capable of deriving energy from reduced mineral compounds like pyrites, and are active in geochemical cycling and the weathering of parent bedrock to form soil
Metallotolerant: capable of tolerating high levels of dissolved heavy metals in solution, such as copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
, arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
, and zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
; examples include Ferroplasma
Ferroplasma
In taxonomy, Ferroplasma is a genus of the Ferroplasmaceae.The genus Ferroplasma consists solely of F. acidophilum, an acidophilic iron-oxidizing member of the Euryarchaeota. Unlike other members of the Thermoplasmata F.acidophilum is a mesophile with a temperature optimum of approximately 35°C, at...
sp. and Cupriavidus metallidurans
Cupriavidus metallidurans
Cupriavidus metallidurans strain CH34, is a non-spore-forming bacillus which is adapted to survive several forms of heavy metal stress. Therefore, it is an ideal subject to study heavy metal disturbance of cellular processes...
Oligotroph
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...
: An organism capable of growth in nutritionally limited environments
Osmophile
Osmophile
Osmophilic organisms are microorganisms adapted to environments with high osmotic pressures, such as high sugar concentrations. Osmophiles are similar to halophillic organisms because a critical aspect of both types of environment is their low water activity, aW...
: An organism capable of growth in environments with a high sugar concentration
Piezophile
Piezophile
A piezophile is an organism which thrives at high pressures, such as deep sea bacteria or archaea. They are generally found on ocean floors, where pressure often exceeds 380 atm . Some have been found at the bottom of the Pacific Ocean where the maximum pressure is roughly 117 MPa...
: An organism that lives optimally at high hydrostatic pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
; common in the deep terrestrial subsurface, as well as in oceanic trench
Oceanic trench
The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor....
es
Polyextremophile
Polyextremophile
A polyextremophile is an organism which combines several extremophilic features. For example, a polyextremophile living at the summit of a mountain in the Atacama Desert might be a radioresistant xerophile, a psychrophile, and an oligotroph...
: An organism that qualifies as an extremophile under more than one category
Psychrophile
Psychrophile
Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −15°C to +10°C. Temperatures as low as −15°C are found in pockets of very salty water surrounded by sea ice. They can be contrasted with thermophiles, which...
/Cryophile: An organism capable of survival, growth or reproduction at temperatures of -15 °C or lower for extended periods; common in cold soils, permafrost, polar ice, cold ocean water, and in or under alpine snowpack
Radioresistant: Organisms resistant to high levels of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
, most commonly ultraviolet radiation, but also including organisms capable of resisting nuclear radiation
Thermophile
Thermophile
A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122 °C . Many thermophiles are archaea...
: An organism that can thrive at temperatures between 60–80 °C
Thermoacidophile
Thermoacidophile
A thermoacidophile is an extreme archeon which thrives in acidous, sulfur rich, high temperature environments....
: Combination of thermophile
Thermophile
A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122 °C . Many thermophiles are archaea...
and acidophile
Acidophile (organisms)
Acidophilic organisms are those that thrive under highly acidic conditions . These organisms can be found in different branches of the tree of life, including Archaea, Bacteria, and Eukaryotes...
that prefer temperatures of 70–80 °C and pH between 2 and 3
Xerophile
Xerophile
Xerophiles are extremophilic organisms that can grow and reproduce in conditions with a low availability of water, also known as water activity. Water activity is a measure of the amount of water within a substrate that an organism can use to support sexual growth. Xerophiles are often said to...
: An organism that can grow in extremely dry, desiccating conditions; this type is exemplified by the soil microbes of the Atacama Desert
Atacama Desert
The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...
In astrobiology
AstrobiologyAstrobiology
Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This interdisciplinary field encompasses the search for habitable environments in our Solar System and habitable planets outside our Solar System, the search for evidence of prebiotic chemistry,...
is the field concerned with forming theories, such as panspermia, about the distribution, nature, and future of life in the universe. In it, microbial ecologists, astronomers, planetary scientists, geochemists, philosophers, and explorers cooperate constructively to guide the search for life on other planets. Astrobiologists are particularly interested in studying extremophiles, as many organisms of this type are capable of surviving in environments similar to those known to exist on other planets. For example, Mars may have regions in its deep subsurface permafrost that could harbor endolith
Endolith
An endolith is an organism that lives inside rock, coral, animal shells, or in the pores between mineral grains of a rock. Many are extremophiles, living in places previously thought inhospitable to life...
communities. The subsurface water ocean of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
's moon Europa
Europa (moon)
Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
may harbor life, especially at hypothesized hydrothermal vents at the ocean floor.
Recent research carried out on extremophile
Extremophile
An extremophile is an organism that thrives in physically or geochemically extreme conditions that are detrimental to most life on Earth. In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles...
s in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
involved a variety of bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
including Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
and Paracoccus denitrificans
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 the possible ancestor of the eukaryotic mitochondrion .-Description:...
being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an ultracentrifuge
Ultracentrifuge
The ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 2,000,000 g . There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge...
at high speeds corresponding to 403,627 times "g" (the normal accelaration due to gravity). Paracoccus denitrificans was one of the bacteria which displayed not only survival but also robust cellular growth under these conditions of hyperaccelaration which are usually found only in cosmic environments, such as on very massive stars or in the shock waves of supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
s. Analysis showed that the small size of prokaryotic cells is essential for successful growth under hypergravity
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...
. The research has implications on the feasibility of panspermia.
Examples
Microbial life lives in the liquid asphaltAsphalt
Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...
lake Pitch Lake
Pitch Lake
The Pitch Lake is the largest natural deposit of asphalt in the world, located at La Brea in southwest Trinidad, within the Siparia Regional Corporation. The lake covers about 40 ha and is reported to be 75 m deep....
. Research indicates that extremophiles inhabit the asphalt lake in populations ranging between 106 to 107 cells/gram.
Industrial uses
The thermoalkaliphilic catalaseCatalase
Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...
, 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
Aspergillus niger
Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food...
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.