Psychrophiles are a class of extremophiles that has the ability to live in extremely low temperature conditions. As the name suggests, these are cold loving microbes that are commonly found in Polar region, and also in deep sea, mountains, glaciers, fresh and marine waters, polar and high alpine soils, all together constituting about three-fourth of the biosphere. True psychrophiles are those which have an optimum growth temperature below 15°C and cannot grow at a temperature beyond 20°C. Whereas psychrotolerant micro-organisms, (also known as psychrotrophs) are those which can live in cold conditions, but have a higher optimum growing temperature, much greater than 20°C. Psychrophiles became an important resource for bio prospecting because of their unique cold adaptations, which helped them to successfully live in such frigid living conditions.
Psychrophiles are successful in surviving such extreme living conditions by optimizing various basic cell processes like enzyme function, nutrient transport and cell membrane function. The most important of these adaptations, which has immense potential to be exploited, are the production of poly unsaturated fatty acid (PUFA) and cold active enzymes. The membranes and proteins in these microbes have a special property of increased structural flexibility that enhance the catalytic function and the presence of unsaturated fatty acids help in easy nutrient cell transportation, due to better fluidity. When temperature drops, psychrophiles produce cold shock or antifreeze proteins that enhance the activity of enzymes by improving enzyme kinetics and stabilizing microtubules. Psychrophilic enzymes have the advantage of having a low temperature optimum for activity with enhanced specific activity at low temperatures and rather high thermolability.
The useful applications of cold active enzymes are wide spread to a large number of industries like textile industry, food and dairy industry, brewing and wine industry, laundry, etc. Cold-active hydrolytic enzymes like lipases, proteases, cellulases and amylases can be used as an active agent in detergents applied for cold washing. This reduces energy consumption and prevents wear and tear of textile fibers. Industrial dehairing of skins and hides also uses psychrophilic proteases or keratinase at low temperatures saving energy and reducing undesirable effects of toxic chemicals. Other potential applications of psychrophilic enzymes, apart from these, are in processes such as the hydrolysis of lactose in milk using galactosidase, stone washing and bio polishing of textile products using cellulases, extraction and clearing fruit juices using pectinases, meat tenderization or taste improvement of refrigerated meat using proteases, betterment of bakery products using glycosidase (e.g. amylases, proteases and xylanases), softening of wool or cleaning of contact lenses using proteases.
Brewing and wine industries use other cold active enzymes as a better alternative to mesophilic enzymes. This can also work in cheese manufacturing and as animal feed supplements, etc. Both psychrophilic microorganisms and their enzymes such as oxidase, peroxidase, and catalase have been proposed as alternate options for the bioremediation of waste waters and solids that are polluted by hydrocarbons, oils and lipids. These enzymes can also be used as environmental biosensors (e.g. dehydrogenases) or in biotransformation (e.g. aminotransferases, methylases, and alanine racemase).
Psychrophiles are a good source of polyunsaturated fatty acids (PUFA), which can be extensively used in pharmaceutical industry for developing new therapeutic agents, because of the antibiotic properties of some microbes. The use of cold active enzymes in food industry reduces the risk of contamination and the flavor is not destroyed at high temperatures, and it conserves the nutritional quality of food. Diverse starch-modifying enzymes such as xylanases and proteases can be used to bring down the fermentation time of dough and improves its properties. In addition to this, cold-adapted lipases are preferred as flavor modifying enzymes in the mass production of fermented food, cheese manufacture, beer treatment, and for biotransformation reactions in chemical processes.
Cold-active β-galactosidases are helpful in removing lactose from refrigerated milk at low temperature so that it can be consumed by people who are allergic to lactose. Proteases from psychrophiles are also used widely in the food industry for the treatment of beer, in bakeries and in the fast maturing of cheese.
Enzymes have always been used as processing aids in various industries since many years. Enzymatic methods constitute an important and essential part in various treatment methods. The successful attempts of biotechnologists and microbiologists in searching novel products useful for mankind, has led to the discovery of psychrophilic enzymes, having vast potential in today's industry.
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