Brass, mild steel (MS) and copper (Cu) samples

Exposed metal surfaces are highly vulnerable to corrosion, but paint or other protective coatings can interfere with some uses, as well as add significant costs. Now, a comprehensive series of experiments suggests a new form of protection: bacteria.

Scientists have long known that some bacteria can accelerate corrosion on metal surfaces, says Kus, who works in the Corrosion and Environmental Effects laboratory of Professor Florian Mansfeld of the Viterbi School’s Mork Family Department of Materials Science and Chemical Engineering. A bacterium of the same genus as MR-1, S. algae, has earlier been shown to prevent pitting of aluminum and some steel.

MR-1 is a remarkable organism that can incorporate metal into its metabolism, “inhaling certain metal oxides and compounds in one form, exhaling them in another,” according to Kus’s presentation. MR-1 has previously been used to precipitate uranium out of contaminated water. And “it can grow almost anywhere and does not cause disease in humans or animals,” Kus notes.

And it can protect metal.

The experiment was simple. Matched pairs of samples of four metals — aluminum 2024, zinc, mild steel, copper, and brass — were prepared. One sample 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, corrosion was monitored, both visually and by measuring electrochemical impedance (resistance to conducting alternating current.) Because electrical effects play a role in many forms of corrosion, higher AC impedance is associated with increased corrosion resistance.

The results were clearcut. For all the materials, impedance increased with exposure to bacteria, and the longer the metals were exposed, the more resistant they became. The increase was particularly marked in the aluminum samples. By the end of the week the control samples showed obvious visual pitting, while the ones with MR-1 colonies were unscathed.

MR1 may not be the product that replaces paint — and repainting — and repainting. But, this research may come up with a living ingredient, a component of MR1 that offers a one-time coating that lasts the lifetime of a metal structure.