Cleaning Up With Bugs

By Dana Bauer

Angela Fisher walks briskly down the hallway of the Kappe Environmental Laboratories gently shaking a tube of thick pink liquid. “These are my bugs,” she says grinning.

Suspended in the solution are Shewanella putrefaciens, an iron-reducing bacteria. Fisher, a master’s student in environmental engineering, studies how “bugs” like S. putrefaciens interact with iron and natural organic material in soils. Her research is part of the Department of Energy’s NABIR (natural and accelerated bioremediation research) program. NABIR researchers from around the country are exploring ways to use microorganisms to clean up more than 120 DOE nuclear waste sites.

“Heavy metals such as zinc, lead, and chromium, and radionuclides such as strontium, technetium, and uranium were dumped onto the ground,” says Fisher. “The metals have percolated through the soil and could contaminate water supplies. Some may already be polluted.”

Fisher is trying to understand the process by which natural organic materials help bacteria reduce iron in the soil. In an iron-reducing environment, the metals and radionuclides, which stick to the iron in the soil, could be immobilized or changed into less-hazardous forms.

“Angela’s master’s work doesn’t involve the contaminants,” says Rich Royer, a post-doctoral research associate who works with Fisher in the Kappe Labs. “But she’s laying the groundwork for the other researchers in our group.”

“I’m looking at how the bacteria function in the soil,” says Fisher. To do so, she uses a model system of iron-reducing bacteria, iron oxide, and natural organic material. “I work in an anaerobic chamber to try to mimic the oxygen-free conditions in which the bacteria live,” Fisher thrusts her arms into the long gloves built into the plastic sheath covering the chamber. Her gloved arms protrude over the lab bench inside the chamber. “As soon as I put my arms in here my nose itches,” she says, as she pipettes the pink bacterial suspension into a deep red-orange solution of iron oxide.

“These bacteria can ‘breathe’ iron, allowing them to function in a groundwater environment,” explains Royer. In this case, “breathing” iron means reducing it from the Ferric form, Fe3+, to the Ferrous form, Fe2+.

The third component of Fisher’s model system is natural organic material — substances that are left over from the decay of plants and animals. “The natural organic material can act as an intermediate in iron reduction,” explains Royer. “The bacteria react with the organic material, then the organic material reacts with the iron. Certain functional groups act as catalysts, speeding up the reduction reactions. So far we’ve looked at seven different natural materials.”

Fisher and Royer are working with Jie Chen, a collaborator from the Oak Ridge National Laboratory in Tennessee, to study the mechanisms by which natural organic materials accelerate iron reduction. Fisher picks up an inch-high tube filled with fine reddish powder that Chen has brought with her. “They tell me it’s more valuable than gold because it’s so hard to purify,” she says. “It has to be purified because there are so many components in the material that would give us too many variables.” The purification process involves removing inorganic materials, then separating the remaining organic material into three classes: humic acid, fulvic acid, and humin.

Researchers think that natural organic materials have several possible functions: one of them is to shuttle electrons from the bacteria to the surface of the iron oxide, enhancing the rate of iron reduction. “We’re trying to isolate each function and figure out which mechanisms are important,” explains Royer.

“In nature it could take years for these reactions to take place and for the contaminants to be converted into less-hazardous forms,” says Fisher.

“Perhaps we could add something to the soil that will make the bacteria work faster,” says Royer. “People are talking about cheap ways to add natural organic materials to groundwater systems to stimulate iron reduction.”

But, Royer adds, “no one really has any magic additive yet.”

Angela Fisher received her master’s in environmental engineering in December 2000; afisher@psu.edu. She was a second place winner in the engineering category at the 2000 Graduate Exhibition. Her adviser is William Burgos, Ph.D., assistant professor of civil and environmental engineering, 216 Sackett Building, University Park, PA 16802; 814-863-0578; bburgos@psu.edu. Richard Royer, Ph.D., is a post-doctoral research associate in Burgos’ lab; rar126@psu.edu. Their research is funded by the Department of Energy’s NABIR program: www.lbl.gov/NABIR.