Here is the excerpt (MFC = Microbial Fuel Cell = a kind of fuel cell to generate electricity):
"In order to produce electricity, it is imperative that MFC's bacteria conduct electrons to the cathode. The researchers at UMass Amherst realized that there has never been any natural selective pressure that would enhance electronic conduction in bacteria, so they used directed evolution to produce highly conducting bacteria.
G. sulfurreducens bacteria were cultured on a graphite electrode under a 400 mV applied bias. The goal was to force the bacteria to adapt to conditions inside the MFC with the hope that they would evolve greater functionality in the process. Several colonies were isolated after five months in the MFC environment and re-cultured under normal conditions. When placed in an MFC cell, the specially cultured bacteria grew much more rapidly—current saturated after 50 hours as opposed to 400 hours—and they provided twice the current density of normally cultured bacteria."