Microbiologists led by Derek Lovley at the University of Massachusetts Amherst, who is internationally known for having discovered electrically conducting microfilaments or “nanowires” in the bacterium Geobacter, announce in a new paper this month that they have discovered the unexpected structures in many other species, greatly broadening the research field on electrically conducting filaments. Details appear online in the International Society of Microbial Ecology Journal.
Lovley, who published his first paper describing Geobacter 30 years ago, explains, “Geobacter have evolved these special filaments with a very short basic subunit called a pilin that assemble to form long chains that resemble a twisted rope. Most bacteria have a basic subunit that is two to three times longer. Having electrically conducting pili or e-pili is a recent evolutionary event in Geobacter, so the working hypothesis was that this ability would only be found in its close relatives.”
He adds, “It was surprising to us, and I think many people will be surprised to learn, that the concept that microbes need the short pilin subunit to produce e-pili is wrong. We have found that some much larger pilins can also yield e-pili and that the ability to express e-pili has arisen independently multiple times in the evolution of diverse microbial groups.” He and co-authors add that “e-pili can have an important role in the biogeochemical cycling of carbon and metals and have potential applications as ‘green’ electronic materials.”
Lovley says, “This is a great development, because now the field will widen. Microbiologists now know that they can work with other microbes to investigate electrically conductive filaments. We’ve found a broad range of microbes that have this. One interesting thing we already can report is that some of the new bacteria we’ve identified have filaments up to 10 nanometers in diameter. Geobacter’s filament are very thin, just three nanometers in diameter. For building electronic devices like nanowire sensors, it is a lot easier to manipulate fatter wires.
I am excited to find out if these new electrically conductive protein nanowires from other bacteria might function even better than the Geobacter wires for applications such as biomedical sensors.