Extremophile

Most animals live in conditions where the temperature is between 4°C and 40°C (39°F-104°F), the pH (which measures acidity and alkalinity) is between 5 and 9, and oxygen is abundant. Some animals, called extremophiles, live in conditions that are outside these ranges. The term "extremophile" is given to micro-organisms that live in extreme environments. These environments range from hot springs to sea ice to brine lakes to deep-ocean hydrothermal (hot water) vents. Each of these environments has conditions that are considered punishing or even unbearable for most animals. However, extremophiles thrive under these conditions. Extremophiles may also provide a glimpse of what the earliest forms of life looked like.

Extremophiles are part of a new kingdom of animals called Archae. The members of this kingdom look like bacteria and were considered a phylum in the Kingdom Monera. In the late-twentieth century, however, scientistsseparated the Archae from other bacteria based on their genetic and biochemical makeup.

Extremophiles are loosely grouped into categories on the basis of where they live. Thermophiles are found living in temperature extremes. Some thermophiles are found in hot springs with water temperatures that approach boiling. The hydrothermal vents along the midoceanic ridges support extremophiles that not only tolerate high temperatures and acidic conditions but also metabolize, or process, hydrogen sulfide, which is poisonous to most animals. At the other extreme, some extremophiles thrive in very cold conditions. These are found in sea ice and on glaciers.

Other examples of extreme environments include natural salt lakes such as the Dead Sea and Great Salt Lake. The extremophiles living there are called halophiles. Still other extremophiles live in highly acidic or highly alkaline environments. Acidophiles thrive in environments with a pH less than 5 while alkaliphiles live in environments with a pH greater than 9. Acidophiles are found in places such as hydrothermal vents while alkaliphiles are found in soda lakes such as are found in Egypt and the western United States. A final major group of extremophiles are the methanogens. They are found living in places with little oxygen, such as swamps and the intestinal tracts of animals. Methanogens do not use oxygen to metabolize their food and they produce methane gas as a waste product.

Scientists have known about extremophiles for more than forty years. Most scientists considered them curiosities in the animal kingdom. Scientists became interested in extremophiles because of their enzymes. Because extremophiles live in extreme conditions, their enzymes must also work under these conditions. Enzymes extracted from extremophiles have grown into a multibillion dollar industry. The enzymes are used in industrial and medical applications that range from making stone-washed jeans to creating artificial sweeteners to conducting genetic tests.

The enzyme-based process known as PCR is used to amplify DNA for genetic identification or genetic testing for disease and conditions. The enzyme reactions used in the procedure occur slowly at room temperatures. By using enzymes from a thermophile, the reactions are performed at a much higher temperature and so at a faster rate.

In recent years, scientists have began searching extreme environments on earth in hope of discovering clues for finding extraterrestrial life. As scientists searched extreme environments, they found more and more kinds of extremophiles. Many environments that scientists had in the past considered sterile were discovered to be the home of many different organisms. Some scientists came to believe that the total mass of all extremophiles on Earth exceeded the mass of all humans on Earth.

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Taylor, Michael Ray. Dark Life. New York: Scribners, 1999.

Madigan, Michael T., and Barry L. Marrs. "Extremophiles. " Scientific American. <http://www.sciam.com/0497issue/ 0497marrs.html>.

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