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Release: Embargoed until 4:00 p.m. EST Thursday, April 9

Scientists discover a secret of bacterial communication

IOWA CITY, Iowa -- The war against bacteria rages on, but a new battle plan has been drawn.

Bacteria existing together in a structure called biofilm are often more resistant to attack by antibiotics and the immune system than they are as individual cells.

This resistance presents a difficult problem for physicians, but recent research has revealed a way in which the biofilm fortress might be attacked. Dr. E.P. Greenberg, University of Iowa professor of microbiology and UI colleague, Matthew Parsek, together with investigators at Montana State University and the University of Rochester, have discovered a signal molecule released by bacteria called Pseudomonas aeruginosa that is essential for the development of biofilm. This finding is reported in the April 10 issue of the journal Science.

"This is basic research, but it leads us in two research directions," Greenberg says. "It may help us find a way to dislodge the biofilm, or it could lead to ways in which we could impair a biofilm, making it more sensitive to antibiotics."

Scientists are now learning that despite their reputation as rugged individualists, bacteria spend a considerable amount of time in communities. When a single, free-floating bacterium recognizes a surface, such as a rock in a stream or cell lining a blood vessel, it may attach to it. At first the bacterial cells multiply and spread across the surface, but when they reach a certain density, they build a complex biofilm structure with built-in water tunnels to carry nutrition into the cells and carry the waste out. Scientists call this process differentiation. The message that initiates differentiation has puzzled researchers for some time.

Greenberg and his colleagues discovered the chemical message that Pseudomonas aeruginosa uses to "tell" the community that it is time to build the biofilm structure. Pseudomonas aeruginosa, the organism that can infect catheters or medical implants, and causes lung infections in cystic fibrosis patients, secretes two signal molecules that accumulate as the number of bacteria on a surface increase. When the signal molecules reach a specific concentration they initiate various cell activities. Both turn on the genetic machinery that produces bacterial toxins, but only one is responsible for the cell-to-cell instructing the bacteria to build the biofilm. When the gene required for production of the signal was removed from the bacteria, the community did not differentiate into a normal biofilm. However, when the signal was added back by the investigators the biofilm structure developed as usual -- indicating that the signal molecule triggers biofilm development.

Currently, the researchers are working to determine if this finding for Pseudomonas aeruginosa can be generalized to other bacteria and, if so, how the information might be used to dislodge or impair the biofilms. The scientists hope that this finding will lead to the production of more effective antibiotics or novel therapeutic approaches to fight bacterial infections.