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The term ‘extremophile’ applies to organisms that can survive in extreme environmental conditions such as in extremes of heat, cold or acidity. Most of the known extremophiles are microbes, including many bacteria. One recent exciting example of discovery of an extremophile bacteria is the identification of bacteria living in the cold and dark deep under the Antarctic ice, reported in the New York Times in 2013. These bacteria were found in water and sediment samples obtained by drilling down through a half-mile of ice into Lake Whillans. The presence of live bacteria was confirmed microscopically and by confirmation of presence of DNA and by measurement of adenosine triphosphate (ATP) levels. (http://www.nytimes.com/2013/02/07/science/living-bacteria-found-deep-under-antarctic-ice-scientists-say.html?_r=0)

Extremophile bacteria have proved useful in biotechnological applications. One famous example is the use of the heat-resistant enzyme Taq DNA polymerase in the process of polymerase chain reaction (PCR), a method first developed by Kary Mullis in 1983 that has transformed molecular biology and is used in processes from disease diagnosis to forensic science. A PCR reaction basically uses a single-stranded DNA template in the presence of a heat-stable DNA polymerase with an optimal catalytic activity at approximately 70[sup]0[/sup]C, nucleotides and DNA oligonucleotides (sequence-specific DNA primers). Most PCR methods use thermal cycling, which involves repeated cycles of heating and cooling in order to allow denaturing of the DNA template (approximately 95[sup]0[/sup]C), annealing of the primers (approximately 55[sup]0[/sup]C, depending on the primer sequences) and extension of the PCR product (approximately 72[sup]0[/sup]C), through a defined series of temperature steps. The most well-known of the heat resistant polymerases used is Taq DNA polymerase, derived from the extremophile Thermus aquaticus, a gram-negative bacterium that can tolerate high temperatures. It is a member of Deinococcus-Thermus group of thermophilic. T. aquaticus was first discovered in the Lower Geyser Basin of Yellowstone National Park but has since been found in other similar environments. Other naturally occurring heat-stable DNA polymerases that can be used include Pfu polymerase from Pyrococcus furiosus, which has a lower error rate than Taq polymerase and Vent polymerase (Tli polymerase) from Thermococcus litoralis, which has a half-life of approximately 7 h at 95[sup]0[/sup]C as opposed to approximately 1.6 h for Taq polymerase. All of these enzymes are derived from extremophile bacterial species that survive at extremes of heat in nature.