MR-1 bacterium protects metals, according to new study.

A new report on a series of experiments suggests that a bacterium may be used to protect metals in much the same way a paint or coating does. Researchers, led by Ph.D. candidate Esra Kus and Professor Florian Mansfeld at the University of Southern California's Viterbi School of Engineering, have written a study analyzing the ability of an organism called Shewanella oneidensis MR-1 (referred to as MR-1) to protect a number of metals.

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Scientists have long known that some bacteria can inhibit corrosion on metal surfaces, says Ms. Kus, who works in the Corrosion and Environmental Effects laboratory of Professor Mansfeld in the Viterbi School's Mork Family Department of Materials Science and Chemical Engineering. In fact, a bacterium of the same genus as MR-1, called S. algae, has previously been shown to prevent pitting of aluminum and some steel. MR-1, on the other hand, is able to actually incorporate metal into its metabolism. It inhales certain metal oxides and compounds in one form, and exhales them in another, according to the study. MR-1 was previously used to precipitate uranium out of contaminated water. "It can grow almost anywhere and does not cause disease in humans or animals," states Ms. Kus.

When tested in experiments, various metals incubated in growth mediums containing MR-1 exhibited high alternating current (AC) impedance.

Because electrical effects play a role in many forms of corrosion, higher AC impedance is associated with increased corrosion resistance. For all the materials, impedance increased with exposure to MR-1, and the longer the metals were exposed, the more resistant they became. Control metals showed obvious visual pitting and corrosion, but the metals incubated with MR-1 were reported to be "unscathed." The pattern of impedance varied from metal to metal. The copper MR-1 samples, for example, showed a profile similar to that demonstrated by copper covered with a protective polymer plastic film.

The next step, according to Ms. Kus, is to determine where and how the presence of bacteria is altering the corrosion equation. To do this, the group will be making molecular scale analysis of bacteria/metal interfaces and will look to determine the exact properties of MR-1 biofilm, as well as why the pattern of interaction differs from metal to metal.

These findings could prove very important for the paint and coatings industry.

The research will be presented at the 210th Meeting of the Electrochemical Society in Cancun, Mexico, October 29-November 3, 2006.