Leave water in contact with metal for any length of time and you've got a problem. Slimy bacterial colonies, or biofilms, form on just about any surface under water and corrode metal surfaces. One kind of sulfate-reducing bacteria can cause pitting even on stainless steel. But researchers at the Electric Power Research Institute (EPRI) in Palo Alto, Calif., have found that certain bacteria actually inhibit corrosion. These "aerobic" species not only consume the oxygen that corrodes metal; they also secrete proteins that suppress bacterial growth.

These bacteria could form the basis of new corrosion-resistant coatings that would have a big advantage over conventional paints: if scratched, a bacteria-based coating could repair itself. EPRI is testing this method in a cooling-water system at the University of California at Irvine. If it works, EPRI plans to try to genetically engineer bacteria for corrosion protection. As the research arm of the electric utilities, EPRI has a strong financial incentive: corrosion costs the U.S. electric power industry $5-10 billion per year.