Researchers at the University of Massachusetts Amherst have used forced evolution to get more power from bacterial fuel cells.
According to the University, a film of natural geobacter sulfurreducens strain DL-1 can produce 1.4A/m2 and 0.5 W/m2 in a fuel cell.
By culturing DL-1 in a graphite electrode at -400mV (against Ag/AgCl) for five months, selective pressure produced a strain that the University claims can produce densities of 7.6A/m2 and 3.9W/m2.
"In very short order we increased the power output by eight-fold, as a conservative estimate," said researcher Derek Lovley. "With this, we've broken through the plateau in power production that's been holding us back in recent years."
Geobacter has hair-like 'pili' 3 to 5nm in diameter and several microns long that can move electrons.
"Pili are the secret to this particular microbe's ability to produce electric current from organic waste and sediment," said the University. "Geobacter's pili seem critical for forming the bio-film which aids transfer of the electron products to iron in soil and sediment."
The evolves strain, dubbed KN400, has more pili than DL-1, and its films have a lower resistance: 15mΩ/m2 compared with 130 for DL-1.
Lovely was part of a team that discovered geobacter, which respires iron and other metals instead of oxygen, in sediment under the Potomac River in 1987.
Originally investigated as a way of cleaning up contamination, it's electro-activity was discovered in 2002.
The electrically conductive pili were discovered in 2005.
Taking a reading from fuel cells