USU team finds microbes that eat carcinogens, cleaning soil cheaply and naturally

By Doan Nguyen

March 4, 2005 | Microbes isolated by USU researchers in a wood-treatment facility actually eat carcinogens, raising the significant possibility of cleaning contaminated soil cheaply, effectively and naturally.

The microbes, known as mycobacterium isolates, look upon the cancer-causing agents as eagerly "as we look at pizza," investigator Ron Sims said.

Sims, biological and irrigation engineering department head at Utah State University, said that while other microbes nearby ate plants, decaying vegetation and simpler chemicals, the organisms found in Libby, Mont., remarkably consume carcinogens as their main food source.

The discovery could affect the cleanup of dangerous chemicals, essentially allowing a natural process to render them harmless in soil.

The USU team conducted microbiological tests examining characteristics of three microbes at the contaminated site. Sims and biology professors Charles Miller, Ann Anderson and Joanne Hughes concluded that the microbes were mycobacteria, which they isolated from millions of organisms in the soil. Two other kinds of mycobacterium from the Arkansas Toxicology Center was discovered by Carl Cerniglia, Sims said.

An underground water system near the site was polluted when creosote, a wood preservative fluid, seeped into the soil. The fluid is highly toxic because of its polycyclic aromatic hydrocarbons, or PAHs. Sims said the townspeople stopped drinking the water before their possible exposure to the chemical carcinogens. PAHs can cause cancer in humans when consistently consumed, inhaled or placed in contact with skin. Sims said the same PAH compounds are in cigarettes.

"You don't need a lot of carcinogens to get sick. What happens is the rain dilutes the chemicals out, making it less concentrated, but the problem is when people get exposed to it day after day of drinking water," Sims said.

Mycobacterium organisms have adapted to extreme environments -- in this case they are carcinogenic compounds toxic to humans. This adaptation is similar to the way organisms found in Yellowstone National Park's hot springs have adapted to extreme environments of heat, Sims said.

After writing up proposals to clean up the site in 1991, Sims and graduate students brought back soil samples from the site to USU for analyzing. The group, mostly focusing on the chemistry of the soil, discovered a decrease in carcinogens.

At that time, Sims appointed Brian Issa, an undergraduate biology student, to conduct a side experiment looking at the soil's microbiology.

As a result of lab tests, Issa recognized the microbes might have been degrading carcinogens, said Sims.

"I was interested in knowing what was breaking [the carcinogens] down and if any microorganisms were resistant to their toxic effects," Issa said.

Because of the diversity of organisms in the soil, Issa said he thought that it was "entirely possible that some were chewing up these compounds."

Issa's research hypothesis in 1998-99 led to what is known today.

Issa said the ability of the organisms were significant because PAHs are toxic and very resistant to degradation. Pyrene (one PAH compound) is one of the hardest contaminants to degrade because it is composed of multiple benzene rings tightly bonded together, he said.

"Whether or not we could isolate them was another matter," Issa said. "When we did, we were then faced with the question of what they were." Issa did some basic testing to narrow the identity of the bacteria to mycobacterium. The results were consistent with other studies that had been done, he said.

The next step was to do genetic work to "characterize these critters" and to see if he had found something new. Unfortunately, Issa had neither the time nor the focus to take the project any further, he said.

"I currently work as a city planner in Oregon, focusing on environmental planning around wetlands and storm water issues," said the former student, who now has his master's degree from the University of Oregon in community and regional planning.

Long after Issa left USU, Sims' research team decided to take another look at Issa's project with more of a biological focus.

"The past 10 to 12 years have resulted in identifying these organisms," Sims said. The research has included biology, bio-engineering and environmental engineering students going for bachelor's, master's or doctoral degrees. In the past, groups have taken soil samples from many sites in Florida, Mississippi, Oklahoma, Canada and the Netherlands.

Today, most biology researchers are examining frozen samples from sites never visited, Sims said. There are thousands of wood-treatment sites in the world. Researchers are interested in knowing which sites have the mycobacterium.

The purpose of this project is to restore the contaminated soil so that it can serve society. Sims said the Libby site couldn't be used to grow crops nor have people living there because of its dangers.

"We are working on sustainability," Sims said.

Bioremediation is better for the soil than using chemical or physical remediation. Using the latter can "hurt" the soil, he said. The use of heat or incineration will create unwanted ash when trying to remove carcinogens in soils. Sims said using of chemicals for remediation can destroy the "good" organisms in the soil that allow it to sustain the growth of plants.

"Bioremediation is using nature," Sims said. "Left over is clean soil." As long as the carcinogens are in the soil the mycobacterium will eat the toxic chemicals.

The bioremediation research project is supported by $1.5 million from the U.S. Department of Energy, however, bioremediation costs are usually 10 times cheaper than attempting to clean soils around the world by chemical and physical means.

USU researchers will soon find the length of each chromosome in the organism's DNA and how many genes are in the organism. A "gene probe" will be done to find out the part of the organism's genetic makeup, which specifically breaks down the cancer causing compounds.

"We know they do it, but we only see the result," Sims said.

"Understanding the genetics of these organisms will help us understand how they work," Sims said. Right now, researchers know that mycobacterium degrade carcinogens, but not exactly how they do.

The genes and base pairs of the mycobacterium are to be matched with those in the GenBank, a reserve of gene sequences. The matched set of genes will allow researches to find sites that have mycobacterium.

USU researchers are running a gene probe on soils from Russia. The USU research group is working with the Russian Federation to find out if the Tartar Stan region has the organism.

"We have now made up a small piece of the gene probe. And we will know in one month if these organisms are similar," Sims said.

Further steps to projects will be figuring out how to make mycobacterium grow faster in their environment to efficiently clean soil.

Sims wants the research to improve the environment and protect people's health.

"Unlike doctors who treat patients with cancer, we work on trying to prevent the cancerous chemicals from getting into people's bodies," he said.

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