Dangerous beauty.
Brucella melitensis can infect both humans and animals, but scientists may have found its Achilles' heel.

Larry Stauffer, Oregon State Public Health Laboratory/CDC

Deadly in the Daylight

One of the most thoroughly studied and virulent kinds of bacteria has just revealed a surprising and potentially useful new trait. Brucella, which causes the sometimes fatal disease brucellosis in humans and farm animals, seems to depend on blue wavelengths of light--like those found in the sun's rays--for its survival. The finding should open up new ways of fighting the organism and its ilk.

Brucellosis is relatively rare in the United States, but epidemics periodically break out in many countries around the world. The bug can be transmitted to humans through contact with infected animals or by eating infected products such as milk or cheese. In the course of seeking new treatments for brucellosis, scientists discovered that Brucella contains a class of signaling proteins called LOVs. In plants, these proteins react to the presence of light, oxygen, or the voltage of a weak electrical current, hence the name. When activated, LOVs encourage plants to grow toward light, but their role in Brucella was unclear.

Now, researchers seem to have found the answer: When exposed to the blue wavelengths of sunlight, the LOVs in Brucella signal other proteins that tell the bacterium to reproduce at will. In lab experiments, the team compared samples shielded from blue light to controls illuminated normally. If the regular light was strong enough, Brucella grew rapidly and became infectious. When shielded from blue light, however, the bugs' reproductive rate dropped by more than 90%, the team reports in tomorrow's issue of Science. "We hardly expected anything so spectacular," says plant biologist and co-author Winslow Briggs of the Carnegie Institution of Washington in Stanford, California.

Isolating the function of LOV proteins in Brucella is a "very significant advance," says structural biologist Kevin Gardner of the University of Texas Southwestern Medical Center in Dallas. Molecular biologist Sean Crosson of the University of Chicago in Illinois agrees. The study shows for the first time "a remarkable connection between the light environment and the regulation of virulence in Brucella," he says.

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