Bacteria live in many extreme environments in which humans cannot survive. Some bacteria, known as extremophiles, have evolved enzymes or cellular mechanisms to live only in extreme conditions such as high heat, high or low pH, high pressure, or high salinity.
Bacteria that live in hot environments above 45 degrees C are known as thermophiles. These bacteria are typically found only in geothermally active areas on Earth, such as the hot springs at Yellowstone National Park. A subset of the thermophile classification is hyperthermophile, which requires an optimal temperature of 80 degrees C.
Also known as cryophiles, psychrophilic bacteria live in extremely cold temperatures as low as -15 degrees C. These bacteria are present in glaciers, arctic soil and sea ice.
Bacteria that thrive at pH below 2.0 are considered acidophilic. Most of these bacteria have evolved methods to efficiently pump protons out of the cell to retain a near-neutral pH inside. Acidophiles can be found in acid mine runoff and in our intestinal tracts.
Bacteria that live in alkaline conditions, usually between pH 8.5 and 11, are known as alkaliphiles. These bacteria have evolved specific mechanisms to acidify within the cell or function optimally at high pH. You can find alkaliphiles naturally in soda lakes.
Also known as barophiles, these bacteria are found in high-pressure conditions, usually on the ocean floor or in geothermal vents. Due to evolutionary adaptation, piezophiles can thrive in situations with pressures as much as 1000 times greater than atmospheric pressure.
Halophiles are salt-loving bacteria that can be found in the Dead Sea, Great Salt Lake and man-made evaporation ponds. Some of these bacteria can survive in sodium concentrations up to 10 times the salinity of seawater.
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