They knew that the conductivity of synthetic conducting organic materials can be attributed to aromatic ringed structures which share electrons, suspended in a kind of a cloud that allows the overlapping electrons to easily flow. It seemed possible that amino acids, which have similar aromatic rings, might serve the same function in biological protein structures like pili. Lovley's team looked for likely aromatic amino acid targets and then substituted non-aromatic amino acids for the aromatic ones to see if this reduced the conductivity of the pili.
It worked. The re-engineered pili with non-aromatic compounds substituted for aromatic ones looked perfect and unchanged under a microscope, but now they no longer functioned as wires. "This new strain is really bad at what Geobacter does best," Lovley says. "Geobacter is known for its ability to grow on iron minerals and for generating electric current in microbial fuel cells, but without conductive pili those capabilities are greatly diminished."
"What we did is equivalent to pulling the copper out of an extension cord," he adds. "The cord looks the same, but it can't conduct electricity anymore."
The ability of protein filaments to conduct electrons in this way not only has ramifications for scientists' basic understanding of natural microbial processes but practical implications for environmental cleanup and the development of renewable energy sources as well, he adds. Lovley's UMass Amherst lab has already been working with federal agencies and industry to use Geobacter to clean up groundwater contaminated with radioactive metals or petroleum and to power electronic monitoring devices with current generated by Geobacter.
His group has also recently shown that Geobact
|Contact: Janet Lathrop|
University of Massachusetts at Amherst