In the 1980s and 1990s, biologists found that microbial life has great flexibility for surviving in extreme environments—niches that are acidic or extraordinarily hot, 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. 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.
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 barophilic such as Thermococcus barophilus. A polyextremophile living at the summit of a mountain in the Atacama Desert might be a radioresistantxerophile, a psychrophile, and an oligotroph. Polyextremophiles are well known for their ability to tolerate both high and low pH levels.
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.
Also referred to as barophile, is an organism that lives optimally at high pressures such as those deep in the ocean or underground; common in the deep terrestrial subsurface, as well as in oceanic trenches. Piezophilic organisms live under conditions of extreme pressure. High pressures can cause proteins to fold into themselves. Piezophiles have less large bulky amino acids that would take up space and prevent the other amino acids from coming close enough to create the reinforced area around the core of proteins.
A polyextremophile (faux Ancient Latin/Greek for 'affection for many extremes') is an organism that qualifies as an extremophile under more than one category.
An organism capable of survival, growth or reproduction at temperatures of −15 °C (5 °F) or lower for extended periods; common in cold soils, permafrost, polar ice, cold ocean water, and in or under alpine snowpack. Psychrophilic organisms live in environments at temperature below –15 °C. Low temperatures cause the kinetic energy and motion within proteins to slow, which prevents them from functioning properly. Cryophiles' proteins have adapted their amino acid composition to live in cold conditions and mitigate this threat. They have a high amount of glycine amino acids, the small size of which allows for more flexibility within the protein once it is folded. Psychrophiles also have a low concentration of charged amino acids, hydrophobic (non-polar) amino acids, and proline residues. The low amount of charged amino acids reduces the amount of interactions between them, while the reduced amount of hydrophobic (non-polar) amino acids allows the non-polar core of the protein to be smaller. Psychrophilic proteins have a small amount of proline amino acids because they cause a rigid structure. These adaptations allow psychrophilic proteins to be more flexible so they do not freeze under cold conditions.
An organism that can thrive at temperatures between 45–122 °C (113–252 °F). Normally high temperatures cause proteins to unfold and prevent them from functioning; thermophilic proteins have adapted their proteins to cope with these conditions. They have a higher amount of cysteine amino acids, which form disulfide bonds once the protein has folded. These disulfide bonds cause the protein to fold up tighter and become more rigid. They also have more charged amino acids, both positive and negative, that interact with each other to increase how rigid the protein is. When proteins become more rigid they are less likely to unfold due to high temperature. Even one extra disulfide bond can raise the temperature at which the protein folds by 6 °C. These adapted proteins allow thermophilic extremophiles to survive at high temperatures.
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 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.
On 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.
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.
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 DNA polymerase and some Bacillus enzymes used in clinical diagnostics and starch liquefaction are produced commercially by several biotechnology companies.
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 bacterium Thermus thermophilus 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)).
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.
^Marteinsson, VT; Birrien, JL; Reysenbach, AL; Vernet, M; Marie, D; Gambacorta, A; Messner, P; Sleytr, UB; Prieur, D (1999). "Thermococcus barophilus sp. nov., a new barophilic and hyperthermophilic archaeon isolated under high hydrostatic pressure from a deep-sea hydrothermal vent". International Journal of Systematic and Evolutionary Microbiology. 49 (2): 351–359. doi:10.1099/00207713-49-2-351. PMID10319455.
^Yadav, Ajar Nath; Verma, Priyanka; Kumar, Murugan; Pal, Kamal K.; Dey, Rinku; Gupta, Alka; Padaria, Jasdeep Chatrath; Gujar, Govind T.; Kumar, Sudheer (2014-05-31). "Diversity and phylogenetic profiling of niche-specific Bacilli from extreme environments of India". Annals of Microbiology. 65 (2): 611–629. doi:10.1007/s13213-014-0897-9. ISSN1590-4261.
^Cavicchioli, R. & Thomas, T. 2000. Extremophiles. In: J. Lederberg. (ed.) Encyclopedia of Microbiology, Second Edition, Vol. 2, pp. 317–337. Academic Press, San Diego.
^Wynn-Williams, D. A.; Newton, E. M.; Edwards, H. G. (2001). Exo-/astro-biology : proceedings of the first European workshop, 21 - 23 May 2001, ESRIN, Fracscati, Italy. Exo-/astro-Biology. 496. p. 226. Bibcode:2001ESASP.496..225W. ISBN978-92-9092-806-5.
^ abFröls, S; Ajon, M; Wagner, M; Teichmann, D; Zolghadr, B; Folea, M; Boekema, EJ; Driessen, AJ; Schleper, C; et al. (2008). "UV-inducible cellular aggregation of the hyperthermophilic archaeon Sulfolobus solfataricus is mediated by pili formation". Mol Microbiol. 70 (4): 938–52. doi:10.1111/j.1365-2958.2008.06459.x. PMID18990182.CS1 maint: Explicit use of et al. (link)
^ abcAjon, M; Fröls, S; van Wolferen, M; Stoecker, K; Teichmann, D; Driessen, AJ; Grogan, DW; Albers, SV; Schleper, C.; et al. (2011). "UV-inducible DNA exchange in hyperthermophilic archaea mediated by type IV pili". Mol Microbiol. 82 (4): 807–17. doi:10.1111/j.1365-2958.2011.07861.x. PMID21999488.CS1 maint: Explicit use of et al. (link)
^Van Wolferen, M; Ajon, M; Driessen, AJ; Albers, SV. (2013). "How hyperthermophiles adapt to change their lives: DNA exchange in extreme conditions". Extremophiles. 17 (4): 545–63. doi:10.1007/s00792-013-0552-6. PMID23712907.
^ abGaudin M, Krupovic M, Marguet E, Gauliard E, Cvirkaite-Krupovic V, Le Cam E, Oberto J, Forterre P; Krupovic; Marguet; Gauliard; Cvirkaite-Krupovic; Le Cam; Oberto; Forterre (2014). "Extracellular membrane vesicles harbouring viral genomes". Environ Microbiol. 16 (4): 1167–75. doi:10.1111/1462-2920.12235. PMID24034793.CS1 maint: Multiple names: authors list (link)
^Gaudin M, Gauliard E, Schouten S, Houel-Renault L, Lenormand P, Marguet E, Forterre P.; Gauliard; Schouten; Houel-Renault; Lenormand; Marguet; Forterre (2013). "Hyperthermophilic archaea produce membrane vesicles that can transfer DNA". Environ Microbiol Rep. 5 (1): 109–16. doi:10.1111/j.1758-2229.2012.00348.x. PMID23757139.CS1 maint: Multiple names: authors list (link)