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An extremophile (from Latin extremus 'extreme' and Ancient Greek φιλία (philía) 'love') is an organism that is able to live or even thrive in extreme environments, such as extreme temperature (hot or cold), pressure, radiation, salinity, or pH level.

Extremophiles are mainly species of microorganisms – bacteria and chiefly archaea, but also include some eukaryotes such as some fungi, and tardigrades. 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. 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.

In the 1980s and 1990s, biologists found that microbial life can survive in extreme environments—niches that are acidic, extraordinarily hot, or with irregular air pressure for example—that would be inhospitable to complex organisms. 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 Mariana Trench, the deepest place in Earth's oceans. Expeditions of the International Ocean Discovery Program found microorganisms in 120 °C (248 °F) sediment that is 1.2 km (0.75 mi) 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.

Acidophile: an organism with optimal growth at high acidity – pH levels of 3.0 or below. Alkaliphile: an organism with optimal growth at low acidity – pH levels of 9.0 or above. Osmophile: an organism with optimal growth in environments with a high sugar concentration. Sulphophile: an organism with optimal growth conditions in high concentrations of sulfur.

Astrobiologists are interested in 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. 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. 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". In September 2015, scientists from CNR-National Research Council of Italy reported that S. soflataricus survived under Martian radiation at a wavelength that was considered lethal to most bacteria. In June 2016, scientists from Brigham Young University reported that endospores of Bacillus subtilis were able to survive high speed impacts up to 299±28 m/s, extreme shock, and extreme deceleration. This is the first study which reported that bacteria can survive in such high-velocity impact. 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.

Quick Facts

• Extremophiles have continued to thrive in the most extreme conditions, making them one of the most abundant lifeforms.
• Extremophiles are also of interest because of their potential for bioremediation of environments made hazardous to humans due to pollution or contamination.
• The study of extremophiles has expanded human knowledge of the limits of life, and informs speculation about extraterrestrial life.
• Extremophiles are mainly species of microorganisms – bacteria and chiefly archaea, but also include some eukaryotes such as some fungi, and tardigrades.
• 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.

Source material: Wikipedia - "Extremophile". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.