January 24, 2002. Copyright 2001. Graphic News. All rights reserved.

PICTURE CAPTION TO PHOTO GN13365:

Picture shows psychrophilic bacteria. The small fluorescing dots and rods in the photomicrograph grow to high numbers in sea ice. Credit: David Thomas.
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Living on the extreme edge 

LONDON, January 24, Graphic News: A unique group of bacteria and microscopic plants and animals lives in the sea ice at the Earth's poles. These microbes have developed a complex set of survival techniques allowing them to thrive under conditions that would kill other creatures.

In research presented in the January 25 issue of the journal, Science, David Thomas at the University of Wales, and Gerhard Dieckmann at the Alfred Wegener Institute for Polar and Marine Research describe the physiological and metabolic characteristics that permit organisms in the Antarctic to live in the semi-solid matrix of frozen seawater they call home. These microbes are called ÒextremophilesÓ because they thrive under conditions that, from the human point of view, are clearly extreme. 

The survival tricks -- which help these organisms cope with extremely low temperatures, high salinities, low light, and other harsh environmental conditions -- have implications for understanding certain ecological effects of climate change and possibly the evolution of life elsewhere in the universe, as well as for industries ranging from biotechnology to cleaning agents and food processing, says Thomas.

Many organisms, including viruses, bacteria, algae, flatworms and small crustaceans are caught between ice crystals as they rise through the water when surface waters freeze in autumn. The most conspicuous microorganisms found in the ice are diatoms -- unicellular plants -- which live and grow by photosynthesising sunlight and nutrients in the water. Each diatom is protected by a strong, shell-like cell wall made of silica, the same material found in sand and used to make glass.

Of particular interest to Thomas and Dieckmann are the enzymes, the biological catalysts that help extremophiles to function in brutal circumstances. Like synthetic catalysts, enzymes, which are proteins, speed up chemical reactions without being altered themselves. 

The diatoms utilize psychrotropic enzymes, which work at extremely low temperatures, to produce proteins to protect the cell structure from potentially life-threatening stresses.

Biotech and other industries worldwide spend more than $2.5 billion annually on enzymes for applications ranging from the production of sweeteners to the genetic identification of criminals and the diagnosis of infectious and genetic diseases. But standard enzymes stop working when exposed to heat or other extremes, and so manufacturers that rely on them must often take special steps to protect the proteins during reactions or storage. 

By remaining active when other enzymes fail, enzymes from extremophiles -- called ÒextremozymesÓ -- can potentially eliminate the need for those added steps, thereby increasing efficiency and reducing costs. They can also form the basis of entirely new enzyme-based processes.

Whatever the reason for their greater activity, extremozymes have begun to make impressive inroads in industry. One of the most spectacular examples is Pfu polymerase, derived from the Òflaming fireballÓ bacteria, Pyrococcus furiosus, which grows best at 100 degrees Centigrade around deep-sea vents. Pfu polymerase is employed widely in Polymerase Chain Reaction (PCR) which is the basis for the forensic ÒDNA fingerprintingÓ that has secured convictions in many recent criminal trials. It is also used extensively in the medical diagnosis of HIV infection and in screening for genetic susceptibility to various diseases, including specific forms of cancer.

Among the other extremophiles now under increasing scrutiny are those that prefer highly acidic or basic conditions, known as acidophiles and alkaliphiles. The acid-tolerant extremozymes of acidophiles, also found around hydrothermal vents, have applications ranging from the synthesis of compounds in acidic solution to additives for animal feed which work in the stomachs of livestock. When added to feed, the enzymes improve the digestibility of inexpensive grains, thereby avoiding the need for more expensive food.

Alkaliphiles live in soils laden with carbonate and in so-called soda lakes, such as those found in Egypt, the Rift Valley of Africa and the western United States. Detergent makers in the U.S. and Japan use extremozymes in highly alkaline laundry detergents to ÒeatÓ protein and grease stains. They are also used to produce the ÒstonewashedÓ look in denim jeans. 

Many scientists believe that life as we know it might first have arisen three billion or so years ago in high-temperature environments, and that the first organisms on earth might therefore have been extremophiles. Such organisms would then have continued to exist on earth in the intervening period, finding refuges in the hot springs that continue to dot the earth. In addition, these thermophiles would have been the forerunners of all other life forms including, eventually, humans.
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Sources; Science, Scientific American, NASA