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Contact: Eric Mankin
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University of Southern California

Bacteria can protect metal

The MR-1 germ works as well as paint keeping copper shiny

Electron microscope picture of MR-1

Bacteria, also known as germs, have a bad reputation. They can spoil milk and can cause diseases.

But University of Southern California researcher Florian Mansfeld has found that one kind of bacteria has a remarkable and potentially very useful power: it can protect metal from corrosion.

Corrosion, which makes metals change color and weakens them, is a major problem in many jobs. Rust is what corrosion of the metals iron and steel is called. Unprotected steel can rust away into powder.

For centuries, people have used paint and other chemical coatings to prevent corrosion. Now, they may have found a brand new method.

Mansfeld is part of a USC team studying a creature called Shewanella oneidensis MR-1. In a set of experiments he found that when MR-1 is growing on metals, corrosion stops.

MR-1 is a remarkable organism that "can grow almost anywhere and does not cause disease in humans or animals," Mansfeld notes.

And it can protect metal.

His experiment was simple. He prepared matched pairs of samples of four metals -- aluminum, zinc, mild steel, copper, and brass. He then incubated one set of each pair was incubated in a growth medium containing MR-1; the other in a sterile bath of the same growth medium, containing neither MR-1 nor any other organism.

After a week, he monitored the corrosion, both by looking at it, and also by measuring how much it resisted carrying electrical current. Because electrical effects play a role in many forms of corrosion, higher electrical resistance is associated with increased corrosion resistance.

The results were clear-cut. For all the materials, resistance increased with exposure to bacteria, and the longer the metals were exposed, the more resistant they became. The pattern of impedance varied from metal to metal, but was unmistakable for all the metals. In fact, the copper showed a profile similar to copper coated with paint.

The next step, according to Mansfeld, is to figure out exactly what is going on and determine where and how the presence of bacteria is altering the corrosion equation. To do this, the group will be looking closely at what happens when the bacteria contacts the metal and forms a "biofilm."

While MR-1 itself may not be the metal protector of the future, it may well suggest an agent that can be, Mansfeld says. He will present his research at the 210th Meeting of the Electrochemical Society in Cancun, Mexico October 29-November 3, 2006