Tough new bacteria lunches on pollutants
12 Dec 2001
Scientists at the US Department of Energy's Brookhaven National Laboratory have developed strains of bacteria able to live in harsh environments while and consume carbon-rich materials such as coal. The bacteria's digestive action is said to remove potentially harmful pollutants, and could be used to yield more-efficient, cleaner-burning coal.
'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 sulphur 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 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, the Brookhaven team has developed several strains of coal-adapted bacteria that can survive at temperatures up to 85 degrees centigrade, pressures up to 2,500 pounds per square inch and over wide ranges of pH and salinity. The bacteria can also survive 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 sulphur 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.
