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    extremophiles

    hydrothermal vent
    The first extremophile to have its genome sequenced was Methanococcus jannaschii, a microbe that lives near hydrothermal vents 2,600 meters below sea level, where temperatures approach the boiling point of water and the pressure is sufficient to crush an ordinary submarine
    Organisms that thrive in what, for most terrestrial life-forms, are intolerably hostile environments.1 The majority of known extremophiles are varieties of archaea and bacteria. They are classified, according to the conditions in which they exist, as thermophiles, hyperthermophiles, psychrophiles, halophiles, acidophiles, alkaliphiles, barophiles, and endoliths. These categories are not mutually exclusive, so that, for example, some endoliths are also thermophiles.

    The discovery of extremophiles points out the extraordinary adaptability of primitive life-forms and further raises the prospect of finding at least microbial life elsewhere in the Solar System and beyond.2 There is also growing support for the idea that extremophiles were among the earliest living things on Earth (see life, origin of)

    Chemoautotrophs, which obtain their energy from the oxidation of inorganic chemicals, might be particularly suited to alien environments. Thiobacillus, for example, makes a living by oxidizing sulfur to sulfuric acid, while other types oxidize hydrogen to water or nitrites to nitrates. Ferrobacillus is especially interesting because the energy won from oxidizing ferrous iron to ferric is very small, so that this organism must have evolved some ingenious way of boosting its low-grade energy input to the high levels needed to make essential chemicals such as adenosine triphosphate.

    Certain species can tolerate wide extremes of acidity and alkalinity. Thiobacillus will grow in solutions containing 3% sulfuric acid, while other types of bacteria have been found in the saturated brine of the Great Salt Lake in Utah and in an icy pool in Antarctica containing 33% calcium chloride.

    Some bacteria have survived enormous pressures, up to 10 tons/cm2, while low pressures appear to pose no threat to them at all, providing that liquid water is present. However, although some species of bacteria, such as Deinococcus radiodurans have been found growing in the radioactive cooling ponds where fuel cans from nuclear reactors are stored, they are not tolerant of highly ionizing radiation. For this reason alone, the notion of panspermia is not easy to uphold.


    Classification and examples of extremophiles

    Environmental parameter

    Type

    Definition

    Examples

    temperature

    hyperthermophile

    thermophile

    mesophile

    psychrophile

    growth >80°C

    growth 60-80°C

    15-60°C

    <15°C

    Pyrolobus fumarii, 113°C

    Synechococcus lividis

    Homo sapiens

    Psychrobacter, some insects

    radiation

    Deinococcus radiodurans

    pressure

    barophile

    piezophile

    Weight loving

    Pressure loving

    unknown

    For microbe, 130 MPa

    gravity

    hypergravity

    hypogravity

    >1g

    <1g

    None known

    None known

    vacuum

    		 

    tolerates vacuum (space devoid of matter)

    tardigrades, insects, microbes, seeds.

    desiccation

    xerophiles

    anhydrobiotic

    Artemia salina; nematodes, microbes, fungi, lichens

    salinity

    halophile

    Salt loving (2-5 M NaCl)

    Halobacteriacea, Dunaliella salina

    pH

    alkaliphile

     

    acidophile

    pH >9

     

    low pH loving

    Natronobacterium, Bacillus firmus OF4, Spirulina spp. (all pH 10.5)

    Cyanidium caldarium, Ferroplasma sp. (both pH 0)

    oxygen tension

    anaerobe

    microaerophil

    aerobe

    cannot tolerate O2

    tolerates some O2

    requires O2

    Methanococcus jannaschii

    Clostridium

    Homo sapiens

    chemical extremes

    gases

    metals

    Can tolerate high concentrations of metal (metalotolerant)

    Cyanidium caldarium (pure CO2)

    Ferroplasma acidarmanus(Cu, As, Cd, Zn); Ralstonia sp. CH34 (Zn, Co, Cd, Hg, Pb)




    References
    1. Gross, Michael. Life on the Edge: Amazing Creatures Thriving in Extreme Environments. New YorK: Plenum (1998).
    2. Seckbach, J. "Search for Life in the Universe with Terrestrial Microbes Which Thrive Under Extreme Conditions." In Cristiano Batalli Cosmovici, Stuart Bowyer, and Dan Wertheimer, eds., Astronomical and Biochemical Origins and the Search for Life in the Universe, p. 511. Milan: Editrice Compositori (1997).

    Related categories

       • EXTREMOPHILES
       • ORIGIN AND EVOLUTION OF LIFE
       • MICROBIOLOGY
       • ASTROBIOLOGY


    Archived news
    Ancient life thrives in deep (Feb 24, 2005)
    Life flourishes ar crushing depths (Feb 5, 2005)
    Mars-like bugs on Earth (Jan 18, 2002)
    Metabolically-active microbes found at the South Pole (Jul 7, 2000)


    External site
    Genome News Network: Extremophiles



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