Life at High Temperatures
by Thomas D. Brock
The thermophilic bacteria that live in the Yellowstone hot springs have been the foundation of impressive developments in medicine and biotechnology. The unique thermostable enzymes of these bacteria are finding wide industrial and medical use, and have become the basis of a multimillion dollar industry!
When researchers began to study the biology of Yellowstone hot springs in the 1960s, the presence of these hyperthermophilic bacteria was not suspected. The upper temperature limit for life was thought to be around 73 degrees C (163 degrees F), which was actually the limit for photosynthetic organisms such as cyanobacteria. The preferred temperature for thermophilic bacteria was considered even lower, around 55 degrees C (131 degrees F). Because of the known effects of heat on biological structures such as proteins and DNA, it was thought that life at higher temperatures would be impossible. In fact, biochemists have known for over 100 years that enzymes (key cellular proteins) are destroyed by boiling.
However, field observations in Yellowstone showed that in certain springs bacteria existed at much higher temperatures. Although these springs were rather small and not especially conspicuous among the impressive geysers and giant hot pools of the Yellowstone thermal basins, they were impressive microbial culture systems and turned out to be of great scientific and intellectual interest. It turns out that the enzymes of Yellowstone thermophiles are very tolerant of heat and are active even at boiling water temperatures.
We know now that dozens of kinds of bacteria live in these high temperature systems. The first such bacterium discovered, and one that has proved of special significance for biotechnology, is called Thermus aquaticus.
The outflow channel this small spring has mats of orange-colored cyanobacteria where it has cooled below 73 degrees C (163 degrees F). However, in the whitish areas at higher temperature, long stringy masses of Thermus aquaticus can be seen upon close examination (photo below).
Thermus aquaticus in the outflow
channel of the spring shown above
The large spring above, near Great Fountain Geyser, was the source of the culture of Thermus aquaticus that is used to make Taq polymerase, a key constituent of the polymerase chain reaction. At the time of the discovery, this spring was hotter than it is today, and its outflow was 70 degrees C (158 degrees F), the optimum temperature of Thermus aquaticus. A sample of the microbial mat at the point of outflow was used to prepare the initial culture. Once the culture was available in the laboratory, a large amount of research could be readily done. The culture obtained was later deposited in the American Type Culture Collection, making it available to any researcher. Scientists from the Cetus Company obtained the culture from this source and purified the enzyme Taq polymerase using conventional biochemical techniques.
Thermus aquaticus under the microscope. Left: light microscope, showing the typical long, slender rods. Right: The cell structure seen under the electron microscope is similar to that of many bacteria that live at conventional temperatures. There is nothing that would tell us that this is a highly unusual bacterium. The lighter areas in the center contain the DNA of the cell.
Although Yellowstone has been justly famous for its wildlife, it is now becoming famous for the incredibly small, amazingly versatile microbes that are found in such profusion here, and which are so rare elsewhere. Even other volcanic areas, such as Iceland, Japan, and New Zealand, do not have the riches that we find in Yellowstone. The main reason for this is that Yellowstone thermal features have been protected from destruction. In the other major thermal areas of the world (Iceland, Italy, Japan, and New Zealand) geothermal power developments and health spas have taken over and destroyed the natural thermal features. It is for this reason that scientists from foreign countries come to Yellowstone: they know that the thermal features here are intact for all to see and explore.
It is important to emphasize that microbial research in Yellowstone has no effect on the thermal features. The biotechnologist simply removes extremely small samples and takes them to the laboratory, where all further research is carried out.
Yellowstone may have a billion dollar potential for the
industry. And with proper management as a Park, Yellowstone will be
for future generations of research scientists.
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