অতিজীবী বা EXTREMOPHILE এর বিস্ময়কর জগতঃ Whats your ideal environment? Sunny, 72 degrees Fahrenheit (22 degrees Celsius) and a light breeze? How about living in nearly boiling water thats so acidic it eats through metal? Or residing in a muddy, oxygenless soup far saltier than any ocean? If youre an extremophile, that might sound perfect. Extremophiles are organisms that live in extreme environments. The name, first used in 1974 in a paper by a scientist named R.D. MacElroy, literally means extreme-loving. These hardy creatures are remarkable not only because of the environments in which they live, but also because many of them couldnt survive in supposedly normal, moderate environments. For example, the microorganism Ferroplasma aci¬diphilum ¬needs a large amount of iron to survive, quantities that would kill most other life forms. Like other extremophiles, F. acidiphilum may recall an ancient time on Earth when most organisms lived in harsh conditions similar to those now favored by some extremophiles, whether in deep-sea vents, geysers or nuclear waste. Extremophiles arent just bacteria . They come from all three branches of the three domain classification system: Archaea, Eubacteria and Eukaroyta. So extremophiles are a diverse group, and some surprising candidates -- yeast, for example -- qualify for membership. Theyre also not always referred to strictly as extremophiles. For example, a halophile is so named because it thrives in a very salty environment. The discovery of extremophiles, beginning in the 1960s, has caused scientists to reassess how life began on Earth. Numerous types of bacteria have been found deep underground, an area previously considered a dead zone (because of lack of sunlight) but now seen as a clue to lifes origins. In fact, the majority of the planets bacteria live underground . These specialized, rock-dwelling extremophiles are called endoliths (all underground bacteria are endoliths, but some endoliths are nonbacterial organisms). Scientists speculate that endoliths may absorb nutrients moving through rock veins or subsist on inorganic rock matter. Some endoliths may be genetically similar to the earliest forms of life that developed around 3.8 billion years ago. For comparison, Earth is about 4.5 billion years old, and multicellular organisms developed relatively recently compared to unicellular, microbial life Terms Used to Describe Extremophiles Most terms used to describe extremophiles are generally straightforward. They are a combination of the suffix phile, meaning lover of, and a prefix specific to their environment. For example, acidophiles are organisms that love (phile) acid (acido). • Acidophile: An organism that grows best at acidic (low) pH values. • Alkaliphile: An organism that grows best at high pH values. • Anaerobe: An organism that can grow in the absence of oxygen. • Endolith: An organism that lives inside rock or in the pores between mineral grains. • Halophile: An organism requiring high concentrations of salt for growth.Methanogen: An organism that produces methane from the reaction of hydrogen and carbon dioxide, member of the Archaea. Oligotroph: An organism with optimal growth in nutrient limited conditions. • Psychrophile: An organism with optimal growth at temperature 15 °C or lower. • Thermophile: An organism with optimal growth at temperature 40 °C or higher. o Hyperthermophile: An organism with optimal growth at temperature 80 °C or higher. • Toxitolerant: An organism able to withstand high levels of damaging elements (e.g., pools of benzene, nuclear waste). . When studies of biological organisms in hot springs began in the 1960s, scientists thought that the life of thermophilic bacteria could not be sustained in temperatures above about 55 °C (131 °F). Soon, however, it was discovered that many bacteria in different springs not only survived, but also thrived in higher temperatures. In 1969, Thomas D. Brock and Hudson Freeze ofIndiana University reported a new species of thermophilic bacterium which they named Thermus aquaticus. The bacterium was first discovered in the Lower Geyser Basin of Yellowstone National Park, and has since been found in similar thermal habitats around the world. DNA polymerase (Taq pol) DNA polymerase was first isolated from T. aquaticus in 1976. The first advantage found for this thermostable (temperature optimum 80°C) DNA polymerase was that it could be isolated in a purer form (free of other enzyme contaminants) than could the DNA polymerase from other sources. Later, Kary Mullis and other investigators at Cetus Corporation discovered this enzyme could be used in the polymerase chain reaction (PCR) process for amplifying short segments of DNA, eliminating the need to add enzyme after every cycle of thermal denaturation of the DNA. The enzyme was also cloned, sequenced, modified and produced in large quantities for commercial sale. In 1989 Science magazine named Taq polymerase as its first Molecule of the Year. In 1993, Dr. Mullis was awarded the Nobel Prize for his work with PCR.
Posted on: Sun, 21 Sep 2014 16:59:11 +0000
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