The Call of the Slime

9 April 1998 8:00 pm

Scientists have discovered a chemical rallying cry that some bacteria use to congregate and form biofilms, tough colonies that resist antibiotics and disinfectants. The finding, reported in tomorrow's Science, could lead to new and safer ways to disperse such films.

Known in the vernacular as slime, biofilms infect everything from catheters to contact lenses. They foul water pipes and, as dental plaque, corrode teeth. By developing mushroom-shaped pillars with thick coatings, biofilms protect themselves against antibiotics and biocides (Science, 27 September 1996, p. 1795). Researchers at Montana State University in Bozeman, the University of Iowa in Iowa City, and the University of Rochester in Rochester, New York, wanted to know what triggers pillar formation by Pseudomonas aeruginosa, a biofilm that infects the lungs of cystic fibrosis patients and is the leading cause of hospital-acquired infections.

The team zeroed in on homoserine lactones (HSL), chemicals known to be involved in cell-to-cell communication in solitary bacteria that prompts them to produce, for instance, bacterial toxins. When the researchers knocked out the gene for one type of HSL, called 3OC12-HSL, the mutant grew into continuous, orderly sheets that were easily dissolved by a detergent. However, when 3OC12-HSL was added back to the mutant bacteria, they grew into a biofilm that resisted the suds. When 3OC12-HSL attaches to a surface receptor, the team found, it switches on genes needed for biofilm development in a two-step process. Discovering this role "means we have a key to turn off biofilm development," says microbiologist David Davies of Montana State University, who headed the study. His team is creating and testing chemical 3OC12-HSL analogs that turn off genes for biofilm development.

The findings have "considerable significance because they could offer a new, environmentally benign way to disrupt biofilms," says molecular geneticist John Geiger at the Olin Corporation, a manufacturer of industrial biocides in Cheshire, Connecticut. "If you could prevent biofilm formation on surfaces by pouring in analogs of HSL, it would be a tremendous help," he says. Even the most well-studied biofilm--dental plaque--could be treated with HSL analogs to prevent gum disease, says Geiger.

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