Life at High Temperatures

Water environments with temperatures up to and above boiling are commonly found in association with geothermal activity. At temperatures above 60°C, only bacteria are found. Bacteria with temperature optima over the range 65° to 105°C have been obtained in pure culture and are the object of many research projects. The upper temperature limit for life in liquid water has not yet been defined, but is likely to be somewhere between 110° and 200°C, since amino acids and nucleotides are destroyed at temperatures over 200°C. Because bacteria capable of growth at high temperatures are found in many phylogenetic groups, it is likely that the ability to grow at high temperature had a polyphyletic origin. The macromolecules of these organisms are inherently more stable to heat than those of conventional organisms, but only small changes in sequence can lead to increases in thermostability. Because of their unique properties, thermophilic organisms and their enzymes have many potential biotechnological uses, and extensive research on industrial applications is under way.