Jan. 8, 2002 BALTIMORE, Md. -- A first strain of bacterium that breaks down tough chlorine bonds of the pollutant PCBs, polychlorinated biphenyls, in estuarine sediment is reported in the current issue of the journal Environmental Microbiology by scientists with the University of Maryland Biotechnology (UMBI).
In experiments repeated many times on bottom sediments from Baltimore harbor, researchers of UMBI's Center of Marine Biotechnology (COMB) and the Medical University of South Carolina (MUSC), discovered the PCB-degrading bacterium using a rapid, DNA screening method.
For several decades, environmentalists and regulators have been challenged to deal with tons of banned PCBs in the environment, released by industries for over 70 years. "This first identification of a PCB-dechlorinating, anaerobic (without oxygen) bacterium is important for bioremediation efforts and for developing molecular probes to monitor PCB degrading where they are found," says Kevin Sowers, research microbiologist at COMB. The researchers linked PCB dechlorination directly to the growth of the bacterium. It appears to live off the compound.
Jennie Hunter-Cevera, UMBI president and environmental biotechnologist, adds, "This is a great example of how man-made pollution can be handled by microorganisms through their incredible ability to adapt." The report concludes that the UMBI method could be used to identify additional PCB-degrading microbes. Beginning in the 19th century, PCBs were made from petroleum as insulators for electrical equipment and other electronics. But, in 1979, the federal government banned them because of possible environment and human health hazards. However, all over the world, says Sowers, PCBs are still bound to bottom sediments of many rivers, harbors and bays. "Particles of PCBs persist after many years, because they don't dissolve well in water. They attach to sediment and get covered over," he says. "Unless there is some turnover, a lot of PCBs stay hidden." The hazardous pollutants can build up in fish and marine mammals, in which PCBs can reach thousands of times higher levels than in the water they live in, according to the U.S. Environmental Protection Agency.
The researchers chose a site near a former electrical power plant in Baltimore where levels of up to two parts PCB's per million in harbor sediments have been found. PCBs are found at many industrial sites.
The bacterium catalyzes dechlorination of PCBs. Until recently, few bacteria species had been described by scientists that "reduce" chlorinated organic molecules of any kind. Today several are known. However, the bacterium in UMBI/ MUSC study is the first found to break the chlorine bonds in the critical ortho position, say the researchers. The distinction raises hopes for the potential complete dechlorination of persistent molecules. "To develop bioremediation technology, this sort of discover is particularly exciting. It integrates modern tools of biotechnology and molecular screening with a keen understanding of microbial ecology," observes Hunter-Cevera. PCBs are either oily liquids or solids that are odorless, tasteless and nearly colorless. Before being banned, they freely entered the air, water and soil during their manufacture, use and disposal. Although often buried in anaerobic river and coastal mud, PCB contaminated particles get released when disturbed by natural currents and tides, burrowing activity of aquatic animals and dredging.
The University of Maryland Biotechnology Institute was mandated by the state of Maryland legislature in 1985 as "a new paradigm of state economic development in biotech-related sciences." With five major research and education centers across Maryland, UMBI is dedicated to advancing the frontiers of biotechnology. The names of the UMBI centers are the Center for Advanced Research in Biotechnology in Rockville; Center for Agricultural Biotechnology in College Park; and Center of Marine Biotechnology, Medical Biotechnology Center, and the Institute of Human Virology, all in Baltimore.
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