This paper aims to inform about extremophiles and their current and future applications.
Extremophiles
Anaerobes:
These extremophiles have the capability to grow without the presence of oxygen. These may be found in the rumen of cattle, in the gut, soil and other places. Clostridium spp. is an example of such extremophiles.
Thermophiles:
These are organisms may be found in high temperature that may range from 40°C to 70°C. that are heat stable are essential for the survival of these organisms. The enzymes in these organisms denature at higher temperatures. These proteins are more densely packed to exclude internal water so the less water that is present the higher the temperature that the organism can withstand (3). These proteins are also more hydrophobic, have more salt bridges and have more saturated and longer chained (28). Thermophilic have ether-linked, branched chain fatty acids that are more hydrophobic still. (28)
Hyperthermophiles:
These organisms are thermophiles that can withstand even higher temperatures. These temperatures may range between 60°C to 113°C (3).
Psychrophiles:
These organisms live and reproduce best at low temperatures in the range of -10 to 20°C. Psychrophiles are found in the Arctic and Antarctic oceans, which remain frozen for much of the year. These organisms have that are adapted to function at lower temperatures and they denatured at moderate temperatures. They also exhibit polyunsaturated in their (5). Psychrotolerant organisms also come under the category of psychrophiles. These are organisms that can tolerate cold environments, but grow slowly.
If the water within a cell is frozen, this will most likely be lethal. Some mechanisms for survival of these psychrophiles are to avoid freezing, (by producing special proteins called antifreeze proteins which can lower the freezing point of water by 9 - 18°C) (5), changes in the structure of a cell's proteins, mainly the enzymes, so they can allow the organisms to function at lower temperatures and also the fluidity of cell membranes decreases with low temperature. Because of this, organisms are able to get used to the cold environments by simply increasing the ratio of unsaturated to saturated fatty acids therefore retaining the required flexibility of membranes.
Halophiles:
Organisms that live, grow, and multiply in highly saline environments. Extreme halophiles inhabit water that is up to 10 times more saline than ordinary seawater including that found in the Great Salt Lake in Utah, Owens Lake in California and the Dead Sea (11). They are mostly , have specialized , and have special pigmentation for photosynthesis, and for protection (11). To prevent a mass departure of water from the cell, halophiles make up for the high salt in the environment by accumulating compounds like potassium. This allows a balance of salts inside and outside of the cell preventing water from flowing outward as would be the case if lower salt levels existed within the cells (16).
Acidophiles:
These organisms live, grow and multiply in acidic conditions, such as sulphuric pools, where the pH values are in the range 1 to 5. Because high intracellular acidity levels would destroy essential molecules, such as DNA, acidophiles have evolved the ability to pump hydrogen ions out of their cells at a constant high rate. The result is a mildly acidic internal pH of about 6.5 compared with a typical external pH of about 2.
Several algae, such as the unicellular red alga Cyanidium caldarium and the green alga Dunaliella acidophila, are exceptional acidophiles both of which can live below pH 1. Three fungi, Acontium cylatium, Cephalosporium sp., and Trichosporon cerebriae, grow near pH 0. Another species, Ferroplasma acidarmanus, has been found growing at pH 0 in acid mine drainage in Iron Mountain in California. These polyextremophiles (tolerant to multiple environmental extremes) thrive in a brew of sulphuric acid and high levels of copper, arsenic, cadmium, and zinc with only a and no .
Alkaliphiles:
Organisms that live and reproduce in highly environments, such as soda lakes and -rich soils, where the values range from about 9 to 11. Alkaliphiles maintain a mildly alkaline intracellular pH of about 8 among surroundings of a much higher pH by continuously pumping hydrogen ions across their into their (22).
Xerophiles:
Organisms that live and reproduce in dry conditions where humidity is low. These bacteria must have mechanisms that prevent water from the cells from escaping and evaporating in the atmosphere. They must be able to retain their water.
Endoliths:
These are organisms that live inside rock and thousands of different species are known. Endoliths have been found inhabiting the Earth's crust at depths up to nearly 3 km. Many are that manufacture their own organic compounds from inorganic chemicals in the rock. Other varieties of endolith feed on the organics produced by the autotrophs. The lowest depth in the Earths crust has not yet been determined. The main problem the organisms face at increasing depth is not so much the high pressure but the rising temperature. For oceanic crust, where the temperature rises about 15°C per km of depth, a tolerance of 110°C (for hyperthermophiles) would allow microbial life to extend down to about 7 km below the seafloor. For continental crust, where the temperature rise is faster, a 110°C threshold would allow life to continue at depths of up to 4 km.
Table 1: Summary of extremophiles.
Current applications of extremophiles
Application of these extremophiles is a common thing. From laundry detergent to medicine, food, industrial and a lot of other uses.
From a commercial point of view, enzymes from extremophiles have made the most impact so far. As an example, alkaline proteases, derived from alkaliphilic species, constitute an important group of enzymes that find applications primarily as protein-degrading additives in detergents. Given the robust nature of alkaliphiles, these enzymes can be subjected to harsh environments, including high temperature, high pH, surfactants, bleach chemicals, and chelating agents, where applications of many other enzymes are restricted because of their low activity or stability. In molecular biology, DNA polymerases have been isolated from hyperthermophiles for use in the PCR. The thermostable polymerase enzymes, such as Taq polymerase, must withstand the alternating cycles of heating and cooling which are parts of the PCR process for the target DNA to replicate. Sales of Taq DNA polymerase in Europe alone reached US$26 million in 1991 and worldwide sales of PCR enzymes are estimated to be in the range of US$50–100 million (27).
Apart from heat stable polymerases used in PCR, thermo and hyperthermophiles have useful lipases and proteases that are heat stable for hot water use in laundry detergents. Amylases are used in baking soda; these can with stand high temperatures and still function while being cooked. Bacteriorhodopsin, a pigment from halophiles, used in photosynthesis is light sensitive and is used in optical switches. Also cell extracts along with γ-Linoleic acid and β-carotene from halophiles are used for health foods, dietary supplements, food colouring and feedstock. Psychrophiles, along with thermophiles, have lipases; amylases and proteases that are used in laundry detergents except these are cold loving and therefore are used in cold machine washes. Polyunsaturated fatty acids are used as food additives and ice nucleating proteins are used in the creation of fake snow we would see on the Australian mountains at some times of the year. These same proteins are also used to make ice cream. Acidophiles and alkaliphiles produce products that are used in waste management, detergents, chemicals, food applications and a variety of other things.
Table 2: A summary of extremophiles and some of their products and applications.
Carl R Woese, University of Illinois at Urbana-Champaign, USA
Future applications of extremophiles
One cannot predict what might happen in the future. Countless opportunities exist in the application of extremophiles to our everyday life. More time and research is needed, but a lot of opportunities exist. For example, trehalose is a non-reducing disaccharide and has been shown to stabilize enzymes, vaccines, antibodies and hormones and is also used in the food industry as a preservative and moisture retainer. Currently trehalose is produced at 45°C by two enzymes from a non-extremophile. Through a few reactions, dextrin is converted to trehalose. With the use of thermophilic enzymes, viscosity and sterility would not be a problem and so the production of trehalose will be improved (9). Bacteriorhodopsin, the photosynthetic pigment in halo bacteria, may one day be used in eye operations, namely in the retina. Because it is sensitive to light it may assist the retinal function to improve eyesight (26).
Psychrophiles may be introduced into summer crops and the psychrophilic enzymes may allow for the crops to survive through winter therefore doubling the yield. Xerophilc bacteria may be placed into plants and allow them to grow in the desert, making the desert a tropical wonderland instead of a lifeless, dry and uninhabitable place. There are countless other ideas that need to be explored but this is difficult as extemophiles need special conditions to grow and these are expensive to reproduce in a laboratory.
Conclusion
Many extremophiles have been isolated and some of the purified enzymes have potential for current and future applications. Even with the extensive research that has gone into studying these enzymes and organisms, applications remain limited mainly to the difficulties associated with large-scale production because of their extreme nature.
Extremophiles may very well change life and the Earth, as we know it, from eradication of disease and hunger to life in places we never thought possible. All this may one day come to be but until then we have got to keep trying.
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