Extremophile
An extremophile (from Latin extremus meaning "extreme" and Greek philiā (φιλία) meaning "love") is an organism that thrives in and may even require physically or geochemically extreme conditions that are detrimental to the majority of life on Earth. (In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles.)
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 vents far under the ocean's surface.[1]
Most known extremophiles are microbes. The domain Archaea contains renowned examples, but extremophiles are present in numerous and diverse genetic lineages of both bacteria and archaeans. Furthermore, it is erroneous to use the term extremophile to encompass all archaeans, as some are mesophilic. Neither are all extremophiles unicellular; protostome animals found in similar environments include the Pompeii worm, the psychrophilic Grylloblattodea (insects), Antarctic krill (a crustacean), and the "water bear".
Extremophiles are also thought to be the last organisms that will remain on Earth when the oceans will have vaporized.[2]
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Types
There are many different classes of extremophiles, 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
- An organism with optimal growth at pH levels of 3 or below
- Alkaliphile
- An organism with optimal growth at pH levels of 9 or above
- Endolith
- An organism that lives in microscopic spaces within rocks, such as pores between aggregate grains; these may also be called cryptoendoliths, a term that also includes organisms populating fissures, aquifers, and faults filled with groundwater in the deep subsurface.
- Halophile
- An organism requiring at least 0.2M concentrations of salt (NaCl) for growth[3]
- Hyperthermophile
- An organism that can thrive at temperatures between 80–122 °C, such as those found in hydrothermal systems
- Hypolith
- An organism that lives underneath rocks in cold deserts
- Lithoautotroph
- An organism (usually bacteria) whose sole source of carbon is carbon dioxide 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, cadmium, arsenic, and zinc; examples include Ferroplasma sp. and Ralstonia metallidurans
- Oligotroph
- An organism capable of growth in nutritionally limited environments
- Osmophile
- An organism capable of growth in environments with a high sugar concentration
- Piezophile
- An organism that lives optimally at high hydrostatic pressure; common in the deep terrestrial subsurface, as well as in oceanic trenches
- Polyextremophile
- An organism that qualifies as an extremophile under more than one category
- Psychrophile/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, most commonly ultraviolet radiation, but also including organisms capable of resisting nuclear radiation
- Thermophile
- An organism that can thrive at temperatures between 60–80 °C
- Thermoacidophile
- Combination of thermophile and acidophile that prefer temperatures of 70–80 °C and pH between 2 and 3
- Xerophile
- An organism that can grow in extremely dry, desiccating conditions; this type is exemplified by the soil microbes of the Atacama Desert
In astrobiology
Astrobiology 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 communities. The subsurface water ocean of Jupiter's moon Europa may harbor life, especially at hypothesized hydrothermal vents at the ocean floor.
Examples
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.[4][5]
Industrial Applications
The thermoalkaliphilic catalyst, 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 catalyst operates over a temperature range from 30°C to over 94°C and a pH range from 6-10. This catalyst is extremely stable compared to other catalysts at high temperatures and pH. In a comparative study, the T. brockianus catalyst exhibited a half life of 15 days at 80°C and pH 10 while a catalyst derived from Aspergillus niger had a half life of 15 seconds under the same conditions. The catalyst 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.[6]
References
- ↑ "Mars Exploration - Press kit" (PDF). NASA. June 2003. http://marsrovers.jpl.nasa.gov/newsroom/merlaunch.pdf. Retrieved 2009-07-14.
- ↑ Smil, V. The Earth's Biosphere: Evolution, Dynamics, and Change,p. 269
- ↑ Cavicchioli, R. & Thomas, T. 2000. Extremophiles. In: J. Lederberg. (ed.) Encyclopedia of Microbiology, Second Edition, Vol. 2, pp. 317–337. Academic Press, San Diego.
- ↑ Microbial Life Found in Hydrocarbon Lake. the physics arXiv blog 15 April 2010.
- ↑ Schulze-Makuch, Haque, Antonio, Ali, Hosein, Song, Yang, Zaikova, Beckles, Guinan, Lehto, Hallam. Microbial Life in a Liquid Asphalt Desert.
- ↑ https://inlportal.inl.gov/portal/server.pt/community/idaho_national_laboratory_biological_systems/352/bioenergy_and_industrial_microbiology/2660
- Wilson, Z. E. and Brimble, M. A. (January 2009). "Molecules derived from the extremes of life". Nat. Prod. Rep. 26 (1): 44–71. doi:10.1039/b800164m. PMID 19374122.
- Rossi M et al. (July 2003). "Extremophiles 2002". J Bacteriol. 185 (13): 3683–9. doi:10.1128/JB.185.13.3683-3689.2003. PMID 12813059.
- Satyanarayana, T.; Raghukumar, C.; Shivaji, S. (July 2005). "Extremophilic microbes: Diversity and perspectives". Current Science 89 (1): 78–90. http://hdl.handle.net/2264/330.
External links
- Extremophile Research
- Eukaryotes in extreme environments
- The Research Center of Extremophiles
- DaveDarling's Encyclopedia of Astrobiology, Astronomy, and Spaceflight
- The International Society for Extremophiles
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