extremophile extremophile an extremophile (from latin extremus meaning "extreme" and greek philiā (φιλία) meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments with conditions approaching or expanding the limits of what known life can adapt to, such as extreme temperature, radiation, salinity, or ph level. the bright colors of grand prismatic spring, yellowstone national park, are produced by thermophiles, a type of extremophile. since the definition of an extreme environment is relative to an arbitrarily defined standard, often an anthropocentric one, these organisms can be considered 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. the study of extremophiles has expanded human knowledge of the limits of life, and informs speculation about extraterrestrial life. extremophiles are also of interest because of their potential for bioremediation of environments made hazardous to humans due to pollution or contamination. 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 vents far under the ocean's surface. according to astrophysicist 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." some bacteria were found living in the cold and dark in a lake buried a half-mile deep under the ice in antarctica, and in the marianas trench, the deepest place in earth's oceans. expeditions of the international ocean discovery program found microorganisms in 120 °c sediment that is 1.2 km below seafloor in the nankai trough subduction zone. some microorganisms have been found thriving inside rocks up to 1,900 feet (580 m) below the sea floor under 8,500 feet (2,600 m) 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 composition, affecting their protein folding 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 420 °c (788 °f). limits of known life on earth factorenvironment / sourcelimitsexamples high temperaturesubmarine hydrothermal vents, oceanic crust110 °c (230 °f) to 121 °c (250 °f)pyrolobus fumarii, pyrococcus furiosus low temperatureice−20 °c (−4 °f) to −25 °c (−13 °f)rhodotorula glutinis alkaline systemssoda lakesph > 11psychrobacter, vibrio, arthrobacter, natronobacterium acidic systemsvolcanic springs, acid mine drainageph -0.06 to 1.0picrophilus ionizing radiationcosmic rays, x-rays, radioactive decay1,500 to 6,000 gy deinococcus radiodurans, rubrobacter, thermococcus gammatolerans uv radiationsunlight5,000 j/m2 high pressuremariana trench1,100 barpyrococcus sp. salinityhigh salt concentrationaw ~ 0.6halobacteriaceae, dunaliella salina desiccationatacama desert (chile), mcmurdo dry valleys (antarctica)~60% relative humiditychroococcidiopsis deep crustaccessed in some gold mineshalicephalobus mephisto, mylonchulus brachyurus, unidentified arthropods 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 might be a radioresistant xerophile, a psychrophile, and an oligotroph. polyextremophiles are well known for their ability to tolerate both high and low ph levels. terms microscopic image from the hypersaline lake tyrrell (salinity> 20% w/v), in which the eukaryotic chlorophyte, dunaliella salina, can be tentatively identified. dunaliella salina is grown commercially for the carotenoid, β-carotene, which is widely used as a natural food colorant as well as a precursor to vitamin a. alongside is the haloarchaeon, haloquadratum walsbyi, which has flat square-shaped cells with gas vesicles that allow flotation to the surface, most likely to acquire oxygen. acidophilean organism with optimal growth at ph levels of 3.0 or below. alkaliphilean organism with optimal growth at ph levels of 9.0 or above. anaerobean organism with optimal growth in the absence of molecular oxygen. two sub-types exist: facultative anaerobe and obligate anaerobe. 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.: capnophilean 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, a term that also includes organisms populating fissures, aquifers, and faults filled with groundwater in the deep subsurface. halophilean organism with optimal growth at a concentration of dissolved salts of 50 g/l (= 5% m/v) or above. hyperpiezophilean organism with optimal growth at hydrostatic pressures above 50 mpa (= 493 atm = 7,252 psi). hyperthermophilean organism with optimal growth at temperatures above 80 °c (176 °f). hypolithan organism that lives underneath rocks in cold deserts. metallotolerantcapable of tolerating high levels of dissolved heavy metals in solution, such as copper, cadmium, arsenic, and zinc. examples include ferroplasma sp., cupriavidus metallidurans and gfaj-1. oligotrophan organism with optimal growth in nutritionally limited environments. osmophilean organism with optimal growth in environments with a high sugar concentration. piezophilean organism with optimal growth in hydrostatic pressures above 10 mpa (= 99 atm = 1,450 psi). also referred to as barophile. polyextremophilea polyextremophile (faux ancient latin/greek for 'affection for many extremes') is an organism that qualifies as an extremophile under more than one category. psychrophile/cryophilean organism with optimal growth at temperatures of 15 °c (59 °f) or lower. radioresistantorganisms resistant to high levels of ionizing radiation, most commonly ultraviolet radiation. this category also includes organisms capable of resisting nuclear radiation. sulphophilean organism with optimal growth conditions in high concentrations of sulfur. an example would be sulfurovum epsilonproteobacteria, a sulfur-oxidizing bacteria that inhabits deep-water sulfur vents. thermophilean organism with optimal growth at temperatures above 45 °c (113 °f). xerophilean organism with optimal growth at water activity 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, chemistry, astronomy, solar physics, biology, molecular biology, ecology, planetary science, geography, and geology to investigate the possibility of life on other worlds and help recognize biospheres 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 are exposed to harmful uv radiation, low temperature, high salt concentration and low mineral concentration. these conditions are similar to those on mars. 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 involved a variety of bacteria including escherichia coli and paracoccus denitrificans 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). 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 cells is essential for successful growth under hypergravity. the research has implications on the feasibility of panspermia. 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 (dlr). on 29 april 2013, scientists at rensselaer polytechnic institute, funded by nasa, reported that, during spaceflight on the international space station, microbes 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". on 19 may 2014, scientists announced that numerous microbes, 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 microorganisms living half a mile below the ice of antarctica. in september 2015, scientists from 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 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 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, based on studies on the international space station. these findings support the notion of panspermia. bioremediation extremophiles can also be useful players in the bioremediation 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 were found 1.1 kilometers below water surface level and at concentrations as high as 183 μmol 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, 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 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