A toxin at the heart of Lyme disease?

Although scientists recently sequenced all the genes of Borrelia burgdorferi, they're still struggling to explain how this spiral-shaped bacterium causes the varied symptoms of Lyme disease. Beginning as a simple rash, Lyme disease can go on to cause fatigue, paralysis of the face and limbs, headaches, and even behavioral changes. Sam T. Donta of Boston University School of Medicine and his colleagues now report that the microbe may produce a nerve cell toxin similar to ones made by the bacteria that cause botulism and cholera.

The initial computer-aided scan of the B. burgdorferi genome did not reveal obvious nerve-cell toxins, but such searches are notoriously unreliable, notes Donta's colleague Mark J. Cartwright. Consequently, the researchers used strands of the DNA of known bacterial toxins to fish out similar genetic sequences within the Lyme bacterium. They found a gene for a possible toxin and showed that its protein induces cells to become rounder, apparently by altering their internal skeleton.

Eventually, nearly 40 percent of cells exposed to this protein die, reports Cartwright. The next task is to prove that the bacterium actually secretes the toxin during an infection, he says.