Worlds of David Darling
Encyclopedia of Science
   
Home > Encyclopedia of Science

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. Image credit: NOAA
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).

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


Related categories

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