Thermus aquaticus, a bacterial thermophile Source: Govt of
Canada An extremophile is an organism adapted to unusual limits
of one or more abiotic factors in the environment. Some of the
extreme conditions are temperature, pH, high salinity, high
levels of radiation and high pressure. Note that some of these
factors, such as temperature and pH, have two extrema. Most
extremophiles are micro-organisms such as bacteria and archaea,
since higher organisms generally are less adaptive to wide
variations from the norm in environmental conditions. Upper
limits of existence for carbon based lifeforms appear to be
about 150 degrees Celsius, based upon inherent thermal
stabilities of amino acids and polypeptides essential to DNA
manufacture. In some cases extremophile metabolism thrives on
the exotic variation in environmental conditions; in other
situations, there is adaptive behavior such as metabolic
diapause (cryptobiosis) or desiccation (endosphore formation).
Extremophiles are thought to have been some of the earl