Scientists Awarded Patent For Coal-Purifying Bacteria

"These bacteria can convert ordinary coal to an environmentally attractive resource," said chemist Mow Lin. He and retired natural products chemist Eugene Premuzic were recently awarded U.S. Patent No. 6,294,351 for this work.

Coal is one of Earth's most abundant fossil fuels. But burning it presents a variety of environmental problems, including the release of atmosphere-polluting sulfur and nitrogen oxides, and leftover ash containing toxic metals. While other scientists have attempted to use bacteria to remove these impurities, most microbes are unable to survive the harsh conditions present when processing coal, such as high pressure, heat, and acidity.

Lin and Premuzic, who have previously developed bacterial strains that digest oil, decided to start with bacteria naturally adapted to extreme conditions and see if they could change the microbes' diet. The bacteria were isolated from geothermal locations in the South Pacific and North America.

Using a technique called "challenge biosynthesis nutritional stressing," the scientists first cultured the bacteria in a medium containing small amounts of crude oil, supplemented with other nutrients. The bacteria that were able to survive in the presence of oil ("the fittest") were then transferred to a new culture medium, this time with a higher concentration of oil and lower levels of other nutrients. This process was repeated in sequential steps, gradually increasing the oil content and eliminating the other nutrients, until the survivors were bacteria that could use oil as their only food source.

The scientists then used the same process to gradually wean the oil-eating bacteria off oil while giving them increasing levels of coal. "Essentially, we are forcing the bacteria to adapt to the new food source," said Lin.

By gradually altering other environmental variables such as temperature and acidity in a similar fashion, the Brookhaven team has developed several strains of coal-adapted bacteria that can survive under a variety of extreme conditions -- for example, at temperatures up to 85°C (185°F), pressures up to 2,500 pounds per square inch, over wide ranges of pH and salinity, and in the presence of toxic metals (up to 10 percent by weight). The strains include newly evolved members of the species Leptospirillum ferrooxidans and Thiobacillus ferrooxidans, as well as a variety of mixed cultures.

When combined with a slurry of coal, these new microbes break down the coal's complex molecules to form simpler ones, and concurrently remove sulfur and heavy-metal contaminants. The resulting cleaner coal can be burned or converted to liquid or gaseous fuel much more efficiently than untreated coal, while producing fewer environmentally undesirable by-products.

"The best results can be achieved by using a combination of the newly-adapted organisms, wherein each is very efficient at degrading one or more of the desired sites within the complex structure of coal," said Lin. "This mixed-culture approach permits us to tailor the microbial package to transform different types of coal and other carbon-containing materials."

###

This work was funded by the U.S. Department of Energy, which supports basic research in a variety of scientific fields. Support from the Assistant Secretary for Fossil Energy more than 10 years ago led to an original patent on the oil-eating microbes. More recently, the department's Office of Fossil Energy provided support for a university student assisting in this work.

To see a web version of this news release, with pictures, go to: http://www.bnl.gov/bnlweb/pubaf/pr/2001/bnlpr121201.htm

The U.S. Department of Energy's Brookhaven National Laboratory (http://www.bnl.gov) conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.