Today's Microbiologists Put Microbes To Work In Cleanup

When the Exxon Valdez ran aground in March 1989, spilling millions of gallons of crude oil into Alaska's Prince William Sound, it precipitated one of the largest bioremediation projects ever undertaken. A team of scientists from Exxon Corp., the Environmental Protection Agency, and the state of Alaska infused the contaminated beaches with nutrients to speed the growth of native oil-eating microbes, accelerating their metabolism of oil. Exxon and EPA cleaned miles of beaches, and they generated a wealth of information for those looking at new ways to clean up hazardous wastes. Many other companies are also turning to the use of microorganisms, particularly bacteria, in environmental applications such as bioremediation and producing clean fuels. Biological treatment of hazardous wastes--using bacteria to break down these wastes into compounds with reduced toxicity--is appealing because it is a lower-cost alternative to technologies like incineration or extraction of the hazardous material from contaminated soil or water. The fact that EPA is now favorably viewing bioremediation as an alternative to more conventional technologies has encour- aged companies to support research in this area. Bioremediation will be a widely discussed topic at the American Society of Microbiology's general meeting, to be held at the New Orleans Convention Center May 26-30. About 10,000 microbiologists are expected to attend the meeting, which will feature 2,600 presentations, including 316 seminars, symposia, and roundtables covering environmental, food, and clinical microbiology. Meeting highlights: President's Forum: "Biological Warfare: An Old Problem and Future Concerns" (Thursday, May 28; Sheraton New Orleans) Recent Progress in In Situ Bioremediation (Thursday, May 28; convention center) Microbial Ecology: Groundwater and Subsurface (Thursday, May 28; convention center) Scaleup: Interface Between Microbiologists and Biochemical Engineers (Saturday, May 30; convention center) "Bioremediation has become a hot field," says Bailey Ward, a microbiologist at the University of Mississippi. "And it's not just a hot field, it's also biologically interesting." The biodegradation of such hazardous substances as petroleum hydrocarbons (oil, gasoline, and diesel fuel), polychlorinated biphenyls (PCBs), and solvents like benzene and trichloroethene does not occur quickly in nature. So, for many bioremediation projects, the goal is to speed up the growth of microbes that are native to the contaminated area by adding such nutrients as nitrogen, phosphorus, and trace elements. Increasing the bacterial growth rate also accelerates the rate at which they degrade the hazardous substance. This approach, successful with the Exxon Valdez oil spill, is considered by many researchers as the method of choice. The bacteria are already adapted to the environmental conditions at the site and can often rapidly develop the ability to metabolize the toxic material. Adding a bacterial fertilizer to boost growth and decomposition of petroleum appears to have few adverse ecological effects, since the end products are carbon dioxide, water, and biomass, according to a 1991 study from the Office of Technology Assessment. Accessibility A Problem One problem facing scientists and bacteria alike is the accessibility of the hazardous substance. Oil and many environmental pollutants are not freely soluble in water and can therefore linger in inaccessible places--the nooks and crannies along the inside of a well, for example. Ward is studying ways to remove residual oil from wells using biosurfactants, substances naturally produced by bacteria that emulsify the hydrophobic compounds, making them more accessible to other treatments. "Biosurfactants produced by bacteria can be used to emulsify and disperse hydrophobic pollutants," says Ward. "This can be applied to oil spill cleanup by using a variety of organisms that produce biosurfac-tants to first mobilize the oil, making it more bioaccessible to either the same organisms or other [oil-degrading] microbes." A major focus of EPA's 10-year-old Superfund program is the remediation of soil and water contam- inated with toxic chlorinated solvents, such as trichlorethylene--the legacy of spills, leaking tanks, or poor disposal techniques. Even a spill of only a few gallons of chlorinated solvents can contaminate many square miles of groundwater, according to Cornell University microbiologist William Jewell. The General Electric Co., at its Fort Edward, N.Y., plant--which under previously lax environmental regulations legally dumped tons of PCBs into the Hudson River in upstate New York--first began looking at indigenous anaerobic bacteria in the early 1980s as a means to detoxify stretches of the Hudson polluted with PCBs. Since that time, bacteria and fungi that can detoxify even these highly chlorinated PCBs have been isolated from contaminated sites. Once again, the bulk of the research has been dedicated to finding better ways to help indigenous bacteria do their jobs faster and more thoroughly. But because toxic waste sites seldom contain only one type of contaminant, biochemical engineer David Kosson and his colleagues at Rutgers University in New Brunswick, N.J., are looking at ways to clean up sites that contain a variety of toxic chemicals, using many types of bacteria. While large numbers of organisms have been isolated that will degrade specific types of compounds, Kosson will attempt to determine the optimum growing conditions and types of compounds degraded by a wide spectrum of bacteria and use them to clean up old defense industry sites and military bases. Although degradation of toxic compounds can occur in situ, researchers have found that the process, especially for contaminated groundwater, can be vastly accelerated by placing the waste and bacteria together in a "bioreactor." For groundwater cleanup, the bioreactor approach overcomes the problem of delivering the microorganisms deep underground and then providing air and fertilizer to enhance their growth. Cornell's Jewell has created a bioreactor that uses a two-tank system, in which the bacteria are attached to small granules on a film to prevent them from being washed away by the flow of the contaminated water. Anaerobic bacteria in the first tank strip the chlorine atoms off of the solvents, yielding vinyl chloride, a volatile and highly toxic substance. The water then passes to a second tank, where methane is pumped in as a food source for anaerobic bacteria, which oxidize the vinyl chloride molecules, simplifying their consumption by the microbes. The end products of this process are carbon dioxide, water, and chloride ions. Jewell's bioreactor, which is small enough to throw into a pickup truck and transport to waste sites, will be moving to pilot scale later this year. A growing number of researchers are looking at bacteria that can remediate inorganic substances, especially heavy metals. Microbiologist Derek Lovley of the United States Geological Survey in Reston, Va., has isolated an anaerobic bacterium that survives in a high uranium environment. The bacterium oxidizes the soluble form of uranium into an insoluble form that precipitates out of solution. Lovley and his coworkers are designing bioreactors containing the bacterium to specifically precipitate uranium from contaminated water and soil. "Uranium in a large volume is concentrated into a compact solid using this process," Lovley says. "This helps minimize waste disposal problems." Results of experiments using this approach with other radioactive metals, like plutonium and technetium, also look promising, he says. Proactive Approach Not all uses of microbes are remedial; some are proactive. At Southern Illinois University in Carbondale, microbiologists Brian Klubek and David Clark are studying the desulfurization of coal. Klubek studies the dynamics of bacterial growth, such as effects of altering nutrients and temperature on bacterial growth and metabolism, while Clark characterizes the genes that degrade thiophene--an organic sulfur-containing compound. Removing sulfur from coal before it is burned prevents sulfur dioxide from being released into the atmosphere, contributing to acid rain. Both inorganic and organic forms of sulfur are found in coal, but the organic is especially difficult to remove because it is bound to the carbon in the coal and cannot be leached out. To deal with this problem, Klubek has isolated strains of naturally occurring soil bacteria from abandoned strip mines that can degrade organic sulfur. Clark is studying the genes found in E. coli mutants that are responsible for degradation of thiophene. Clark and Klubek then hope to insert these genes into a host bacterium--a super bug--that will then contain genes for the degradation of both organic and inorganic sulfur. "Once we know what we are dealing with, we can take the genes out of soil bacteria, put them into a host bacterium, and get a broad spectrum of activity in an organism with a rapid growth rate," says Klubek. And Ward hopes these types of studies can be extended to remove organic nitrogen from coal, also a contributor to acid rain. "We should be able to find organisms that clip out the [organic] nitrogen," he says. However, many scientists are reluctant to use bioengineered microbes because of the present strong opposition from citizens' groups and environmental groups, which question the safety of releasing genetically altered bacteria or plants into the environment. Federal regulators have approved small-scale field tests of genetically engineered organisms in agricultural applications, but none involving the large-scale release of microorganisms into the environment for bioremediation purposes. Studies In Microcosm Tamar Barkay, a microbiologist with EPA's Environmental Research Laboratory in Gulf Breeze, Fla., works with both natural and recombinant bacteria to break down mercury, which can accumulate in its highly toxic organic form in fish. Barkay uses systems called microcosms to test bacteria for their methylmercury-degrading capabilities in the laboratory. The most successful of the systems are then taken to the field. But Barkay is quick to point out that the bioengineered bacteria are studied in microcosm only, and are not intended for use in the field. "It is difficult to get the necessary [state, local, and federal] permits to use engineered bacteria in the field," says Barkay. "Very extensive environmental assessment documentation is required." Moreover, many researchers feel that given the political complications, it is not worth the trouble of using recombinant organisms, when naturally occurring bacteria can already do the job well. For instance, the University of Mississippi's Ward has isolated bioemulsifiers from hydrocarbon-polluted sites in Canada, Holland, Texas, and the California coast. "If you use naturally occurring microbes, there are no problems with federal regulations about recombinant organisms," he says. Holly Ahern teaches microbiology at the State University of New York, Albany.

Today's Microbiologists Put Microbes To Work In Cleanup

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