SELECTION FOR 'ICE RESISTANCE', ANTIFREEZE PROTEINS AND ICE OR HYDRATE INHIBITION

摘要

The tenacity of existence under extreme conditions has long been of interest. This, coupled with our curiosity about the evolution of life, has lead to studies on thermophiles, organisms that survive at temperatures near boiling. Such environments, in places such as thermal vents, are thought to mimic conditions found on the earth's surface some 4 billion years ago, although there is no compelling evidence to support this particular hypothesis. Nevertheless, these investigations inspired studies that have resulted in the discovery of a variety of gene products, such as thermophilic enzymes, which in turn, have allowed the development of new solutions for practical problems. For example, the discovery of a DNA polymerase from Thermus aquaticus (Taq polymerase) has facilitated the current revolution in genome analysis. Other extremophiles are resistant to pH extremes, salts, desiccation and pressure. Psychrophiles or psychrotolerant bacteria, which are hardy at low temperatures, have received comparatively less attention. However, there is some interest in prospecting for ice-associating proteins from psychrophiles that may find uses in the preservation of frozen products or for enzymes that are active at low temperatures. As a result, microbes with these characteristics have been sought at high altitudes, Arctic regions, glacial cores, ice accretions and in Antarctic lakes. Indeed, Antarctic expeditions have been mounted solely to identify bacteria with antifreeze proteins (AFPs), which bind to ice crystals and arrest their growth.