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Research Highlights

February 2008

Stop that Slime!

Researchers learn more about halting bacterial secretion that fouls filters

The scanning electron microscope shows the rod-shaped bacteria wrapped in puffy coats (top) and after BisBAL stopped the production of the slime coating (bottom). The round dots in the background are the holes in the filtration membrane. Enlarged View

Results: A new discovery, from scientists at Pacific Northwest National Laboratory and the University of Houston, may stop water treatment filter plugs by preventing a bacterial slime that fouls the filter. Ninety-five percent fewer extracellular polymeric substances, or slime, were secreted when the bacteria Brevundimonas diminuta was treated with bismuth-3-dimercapto-1-propanol, known as BisBAL, over 5 days.

Why it matters: The slime coating around bacteria can plug the microscopic pores in water filers. Clearing or replacing the filters adds cost and creates waste. “If you could reduce cost, in theory you could produce more clean water,” said PNNL’s Kevin Rosso, a scientist on the team.

Methods: The team selected the chalk white Brevundimonas diminuta because it is commonly used to test water filter efficiency. The team then mixed the rod-shaped cells with 12 microMolar solution of BisBAL and examined the consequences over 5 days using sophisticated instruments available at the U.S. Department of Energy’s Environmental Molecular Sciences Laboratory, a national scientific user facility, at PNNL.

Using Fourier-transform infrared spectroscopy (FTIR), the team gained detailed insights into production of the EPS polysaccharides and proteins with and without BisBAL. The FTIR results suggest that the BisBAL is inhibiting the addition of a specific group of atoms to a carbohydrate involved in the EPS production. Also, FTIR revealed that the structure of the cells does not vary substantially when BisBAL is added, but the amount of proteins, polysaccharides, and peptides that ooze onto the surface does.

Atomic force microscopy and scanning electron microscopy were then employed to visualize EPS expression. The images obtained from these instruments clearly show changes consistent with the loss of the slimy coating.

Next steps: Having discovered that BisBAL treatment can stop the production of EPS, the researchers are delving into the bacteria’s proteomics and genomics to develop a fundamental understanding of what is happening.

“This may not be the end-all solution, but it is a step in the right direction,” said Rosso.

Acknowledgments: The National Science Foundation CAREER Program and the Texas Hazardous Waste Research Center funded this research.

Citation: Badireddy, AR, S Chellam, S Yanina, P Gassman, and K Rosso. 2008. “Bismuth Dimercaptopropanol (BisBAL) Inhibits the Expression of Extracellular Polysaccharides and Proteins by Brevundimonas diminuta: Implications for Membrane Microfiltration,” Biotechnology and Bioengineering, DOI: 10.1002/bit.21615. An image from this article graced the cover of the February 15, 2008, issue.

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