Geologists Study Mobility Of Bacteria, Heavy Metals In Water

Virginia Tech researchers are looking at the mobility of bacteria and of heavy metals in surface and ground water. Geosciences professor Michael Hochella Jr. will present recent findings at the Geological Sciences of America national meeting in Salt Lake City Oct. 16-19.

How do we understand when bacteria, moving in the groundwater, will attach itself to a mineral surface? What are the sticking efficiencies of bacteria on minerals? If they are high, there is a good chance it will be bound by minerals. If they are low, the bacteria will bounce off. "That is a frequent theme with toxins," said Hochella. "How mobile are they? Will they stick on surfaces or transport through water or air? Mobility is not good.

"Geologists are now becoming microbiologists in order to discover how biosystems affect geosystems," he said. "We study bacteria and other microorganisms in sophisticated ways. Geoscience Ph.D. students take courses in microbiology and biochemistry and apply biotools to geosystems."

Doctoral student Tracy (Cail) Bank did her dissertation research on the sticking efficiencies of Enterococcus faecalis bacteria, which causes opportunistic urinary tract infections and wound infections, and is becoming antibiotic resistant. "We also picked it for this research because it is spherical," Hochella said.

Bank attached a single bacterial cell as the tip of a cantilever in an atomic force microscope, lowered it to a mineral surface in water, and measured the exceptionally small approach and adhesion forces present. She used a mathematical model (the interaction force boundary layer model) to determine the sticking efficiencies. Thus, she has provided for the first time a direct measurement of how likely those cells are to stick to those surfaces.

She used a silica glass surface, which mimics quartz, the single most common mineral in the curst of the earth, and the principal mineral in sandstones. "Water flowing through sandstone is a common occurrence," Hochella said.

Bank altered the pH of the water and discovered significant differences in stickiness as a result. As the water went from neutral to slightly acidic, the sticking efficiencies increased dramatically.

Bank's research with E. faecalis took several years. She now works at the environmental sciences division of Oak Ridge National Lab. "It is up to others to test other minerals," Hochella said.

He also will describe transmission electron microscope techniques used to study nanoparticles in surface water, groundwater, and drinking water and to determine the role of such particles in transporting heavy metals. Hochella discovered nanoparticles binding heavy metals in the course of his research on transport of such metals from the Clark Fork Superfund Complex in Montana.

Additional information about Hochella's work can be found at http://www.geol.vt.edu/profs/mfh/mfh-r.html

This article originally appeared in the 10/01/2005 issue of Environmental Protection.

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