Enzyme From Extremophile Holds Promise For Industrial Applications
For centuries chemists have looked for ways to synthesize or alter molecules. The countless reactions that were discovered have been essential to industrial development. But in four billion years, living organisms have found far more ways to alter their chemical environments. Enzymes, proteins produced by all living organisms, catalyze an incredible array of reactions under all manner of challenging circumstances.
One of nature's most amazing creations is extremophiles. These tiny organisms thrive in some of the harshest conditions on the planet. They survive in places devoid of nutrients other organisms rely on, or in environments poisonous to nearly any other life form. To survive, extremophiles must produce enzymes that function normally at extremes of temperature, pH, and salinity. This makes extremophile enzymes an interesting and potentially lucrative target for research.
One extremophile enzyme currently under scrutiny recently won researchers at the Idaho National Laboratory (INL) a 2004 R&D 100 Award, given by R&D Magazine. Vicki Thompson, a staff scientist at INL, and colleagues have found a potential use for an enzyme from an extremophile called Thermus brockianus, found in a geyser in Yellowstone National Park. The enzyme degrades hydrogen peroxide and could find use in treating waste from bleaching processes. "What's really special about this enzyme is that it loves high temperature and pH," says Thompson.
Hydrogen peroxide occurs in small quantities in most living organisms as a byproduct of various reactions. It can cause damage to cells at very low concentrations, so most organisms produce a type of enzyme called catalase which can degrade hydrogen peroxide to water and oxygen. T. brockianus is no exception, and its catalase loves the hot, basic conditions common in bleaching waste because the organism lives in geysers.
Hydrogen peroxide is increasingly being used as a less environmentally harmful alternative to chlorine bleach, primarily in paper and fabric bleaching. There are several methods for treating hydrogen peroxide waste, including commercially available catalase products. These catalases don't come from extremophiles, though, so they are rendered useless in just seconds by high temperature or pH. Manufacturers using catalase must choose to either pretreat their waste or purchase large amounts of catalase. Either option is an effective way to treat hydrogen peroxide waste, but both are quite expensive.
It isn't the first time that extremophile enzymes have been used to overcome problems of temperature. The most well-known use of extremophiles is the Taq DNA polymerase used in the polymerase chain reaction, or PCR, used to make many millions of copies of a specific segment of DNA.
There are several major hurdles to overcome in working with extremophiles. The first is finding them. The very definition of an extremophile means one must search strange and often secluded environments to get them. Hot springs, deserts, salt lakes, and even Antarctica are some of the places one must visit to look for these incredible organisms.
But even if it means going half way around the world, collecting extremophiles is easy when compared to the next challenge: isolating enzymes. A milliliter of water from a thermal pool may contain hundreds or thousands of different organisms, each one producing thousands of different enzymes. "When you go after an enzyme in an organism, its sort of like a needle in a haystack," says Thompson. So how do you find the needle?
Usually, crude extracts of proteins from the organisms are subjected to a series of tests to see how, and to what extent, they react with various chemicals. Often the search will be directed to find a specific function in an extremophile. But, as is so often the case in science, accidents and luck can be almost as important as directed research.
When the scientists at INL found the catalase enzyme, they were actually trying to find a way to detect lactic acid in waste streams from sugar beet processing. In the course of examining the bacteria, they added hydrogen peroxide, which Thompson calls a "classic microbiological test." They observed unusually vigorous bubbling in the sample, indicating exceptionally high catalase activity. This led the team to further, more careful investigations.
Finally, once an enzyme has been selected and rigorously tested to show its marketable function, it must be produced on a large scale so that it can be sold. Simply harvesting extremophiles from nature and extracting enzymes is impractical, if not impossible.
However, most enzymes can be easily expressed in a lab in other bacteria, often E. coli, which is easy to grow and can be made to produce quantities of enzyme much greater than the original organism produces. INL has yet to do this with the catalase, but it is the next step once they find the funding, Thompson says. Soon the catalase will join the ever growing list of extremophile enzymes making chemistry cheaper and cleaner.
Chris Wentz is a senior in the biochemistry department at the University of Washington.
Image at top:
INL intern Abbie Aiken measures the pH and temperature of a spring at the Lower Geyser Basin in Yellowstone National Park.