New bacterial behavior observed

PNAS study documents puzzling movement of electricity-producing bacteria near energy sources

Bacteria dance the electric slide, officially named electrokinesis by the USC geobiologists who discovered the phenomenon.

Their study, published online today in PNAS Early Edition, describes what appears to be an entirely new bacterial behavior.

The metal-metabolizing Shewanella oneidensis microbe does not just cling to metal in its environment, as previously thought. Instead, it harvests electrochemical energy obtained upon contact with the metal and swims furiously for a few minutes before landing again.

Electrokinesis is more than a curiosity. Laboratory director and co-author Kenneth Nealson, the Wrigley Professor of Geobiology at USC and discoverer of Shewanella, hopes to boost the power of microbe-based fuel cells enough to produce usable energy.

The discovery of electrokinesis does not achieve that goal directly, but it should help researchers to better tune the complex living engines of microbial fuel cells.

"To optimize the bacteria is far more complicated than to optimize the fuel cell," Nealson said.

Electrokinesis was discovered in 2007 by Nealson's graduate student Howard Harris, an undergraduate at the time.

Nealson had given Harris what seemed an ideal assignment for a double major in cinema and biophysics.

"I had asked him if he would just take some movies of these bacteria doing what they do," Nealson said.

Filming through a microscope is hardly simple, but with the help of co-author and biophysics expert Moh El-Naggar, assistant professor of physics and astronomy at USC, Harris was able to make a computer analysis of a time-lapse sequence of bacteria near metal oxide particles.

"Every time the bacteria were around these particles … there was a great deal of swimming activity," Nealson recalled.

Harris then discovered that bacteria displayed the same behavior around the electrode of a battery. The swimming stopped when the electrode turned off, suggesting that the activity was electrical in origin. ...

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