The compound, called DIP for its chemical abbreviation, had been previously found only in a recently discovered domain of microorganisms called archaea. This is the first time it has been found in bacteria. Researchers had theorized that the compound might play some role in making the bacteria stable in the face of extreme temperatures, but this proved not to be the case. Still, the discovery of the same compound in two distinct and separate branches on the tree of life will focus attention again on just how life survives and even flourishes in the extreme temperatures.
"Our question was whether or not the compound had any effect in stabilizing enzymes from the bacteria, and the answer was no, at least with the two types of enzymes we tested," said Dr. Michael Adams, also a member of the Center for Metalloenzyme Studies. "But because we know DIP is present in both archaea and bacteria, the study suggests it may well be involved in some way with life at high temperatures."
The research was published in the January issue of the journal Applied and Environmental Microbiology. Adams's co-authors were Vijai Ramakrishnan and Marc Verhagen of the department of biochemistry and molecular biology at UGA.
Organisms that thrive at extreme temperatures have fascinated scientists for decades, but only in recent years have business and industry realized how important and useful these enzymes can be. Adams and Dr. Robert Kelly of North Carolina State University pointed out in a 1995 article in Chemical and Engineering News that "thermophilic" or heat-loving microorganisms that grow at temperatures between 50 and 60 degrees centigrade have been known for years. But it was only in 1968 that a scientist isolated microorganisms from hot springs in Yellowstone National Park growing at temperatures of 70 degrees centigrade and higher. By the 1980s, researchers had discovered organisms on Italy's Volcano Island that flourished at 100 degrees centigrade or higher.
Enzymes that flourish at very high temperatures would be a boon to many industries. They would help eliminate the need for multi-step reactions and their unwanted side effects; help make food more palatable and healthful without the risk of bacterial contamination; and even help in the production of corn syrup, one of the most widely used food components in the world. High-temperature enzymes might also be used to enhance the flow of oil or gas in drilling operations.
In the past decade, scientists have found more than 20 genera of microorganisms that grow best at temperatures of 80 degrees centigrade or higher. Only two, however, are bacteria, Thermotoga and Aquifex. The rest belong to the domain called archaea. It was in the bacterium Thermotoga maritima that Adams discovered DIP.
"An intriguing question is how hyperthermophiles stabilize various molecules, particularly proteins, at extreme temperatures," said Adams. "Any significant insight into this problem obviously has many biotechnological ramifications."
Scientists already knew that the archeon Pyrococcus woesei and other archaea contained the compound DIP, and Adams wanted to see if it was present in the bacterium T. maritima as well. The idea Adams wanted to explore was the possible role DIP might play as a thermoprotectant, since it was in both domains.
Thus, T. maritima was grown with glucose as the carbon source in a 600-liter fermentor, and the team discovered the presence of DIP and isolated it. Further studies found that the compound had several unusual qualities. First, Adams and coworkers discovered that at high concentrations of sodium chloride, the DIP levels declined sharply. They also found that the concentration of DIP in the bacterium increased with growth temperature.
The UGA researchers used two proteins previously purified from T. maritima to test the effects of DIP. These enzymes, both containing iron and sulfur, are hydrogenase and pyruvate ferredoxin oxireductase.
The data showed that DIP is accumulated by T. maritima in response to both the external salt concentration and growth temperature, suggesting the compound may have a role in osmosis and potentially as a thermoprotectant. While further studies showed the compound probably has little role in thermostability, it may well be involved in osmosis.
"So far, DIP has been found only in hyperthermophilic organisms, though not all of them," said Adams. "We found that DIP does not have a general stabilizing effect on purified hyperthermophilic proteins, although the possibility that DIP has an effect on a specific group of proteins cannot be excluded."
The research was funded by grants from the U.S. Department of Energy and the National Science Foundation.
(Writers: The compound referred to as "DIP" in this news release is Di-myo-Inositol-1,1'-Phosphate.)