Mussel muzzled; bacterial toxin may control pest. (This Week).

Daniel P. Molloy has been trying to get rid of an unwelcome guest for more than a decade. He may finally have found a solution: a bacterial toxin that can kill the uninvited caller.

No need to alert the homicide squad. The focus of Molloy's wrath is the lowly invertebrate Dreissena polymorpha, better known as the zebra mussel.

After entering North America more than a decade ago, probably in the ballast water of a ship from Europe, these mussels have proliferated rapidly in waters of eastern Canada and the United States. In doing so, they've driven out native mussels, altered the ecology of freshwater lakes and streams, and blocked the water-carrying pipes of power plants and many other industrial facilities (SN: 5/4/91, p. 282).

Since 1991, Molloy, a researcher at the New York State Museum in Albany, has led an effort to identify predators, parasites, and infectious microbes that can kill zebra mussels. At last week's American Society for Microbiology meeting in Salt Lake City, he and his colleagues presented evidence that a common soil bacterium, Pseudomonas fluorescens, makes a toxin that slays the nonnative mussels.

The bacterium destroys a digestive gland within the mussels, leading to their death. Because even dead Pseudomonas cells kill zebra mussels, Molloy suspects that the bacterium contains a toxin within its cell walls. He and his colleagues are now working to identify and purify the toxin.

In small-scale trials, they've shown that the bacterium can eliminate zebra mussels in pipes at a hydropower facility. "We've gotten a 95 percent kill," Molloy says.

He and his colleagues also conducted preliminary tests indicating that the microbe doesn't harm untargeted species, including fish and native mussels. A major challenge, admits Molloy, will be to find a way to produce enough of the bacterium or its toxin economically.

Nevertheless, he suggests that the bacterial toxin could offer industrial facilities an alternative to traditional zebra mussel-control methods. Currently, plants depend upon chlorine, nonspecific chemical molluscicides, or mechanical cleaning of pipes. While chlorine is effective and cheap, environmental regulations on its use may become stricter in the coming years, notes Charles R. O'Neill of New York Sea Grant in Brockport.

O'Neill calls Molloy's discovery "exciting" and notes that chlorine and other nonspecific toxic chemicals aren't a realistic option for lakes and rivers clogged with zebra mussels. "Right now, anything that you would use to kill zebra mussels would nuke the entire water body," he says.

P. fluorescens may offer scientists trying to fight the mussels "another arrow in the quiver," says O'Neill.

The results by Molloy and his colleagues are "extremely promising," notes zebra mussel specialist Andrew Miller of the U.S. Army Corps of Engineers in Vicksburg, Miss. "They certainly need to do a lot more work," he cautions. "Whatever we come up with in the laboratory has got to be inexpensive and easy to apply. And we have to be sure it doesn't cause any other damage."