Discovered in the mud of the Potomac River, a microbe called Geobacter has been quietly showing off its unique electrical properties for a team of researchers at the University of Massachusetts for the past 20 years. The researchers, lead by microbiologist Derek Lovley, are developing ways to harness Geobacter for methane biogas production and environmental remediation, and just last week they announced a new discovery that could finally answer a “major objection” that other biologists have raised. Namely, how is it biologically possible for a microorganism to conduct electricity like a metal?
Geobacter’s Pili Advantage
The Lovley team originally started off by developing Geobacter as a bio-based “green remediation” tool that could efficiently clean up soil or groundwater contaminated by petrochemicals or even radioactive materials.
As the research progressed, the team branched out to explore Geobacter’s ability to generate electricity from the organic materials in wastewater. They successfully demonstrated that networks of long, hairlike “pili” are the mechanism that enables Geobacter to create a highly conductive biofilm.
The implications of the discovery are enormous. In addition to bioremediation and methane biogas production, Geobacter opens up the potential for producing custom-designed or “tunable” conductive materials that self-assemble through biological processes, fed by low-cost, low-impact fuels such as acetic acid. That’s a stark contrast to conventional mechanical fabrication.
The team also began developing more powerful strains of Geobacter, resulting in a current strong enough to be used as the basis for a microbial fuel cell (that, by the way, attracted the attention of the U.S. Navy, which has been funding the research along with the Department of Energy).
A Biological Explanation For Geobacter
In the latest development, the team has successfully demonstrated that amino acids are the biological platform for Geobacter’s unique electrical properties.
The discovery is significant because, though the team succeeded in identifying the physics behind Geobacter’s conductivity fairly early on, describing the biological mechanism was much more challenging. As Lovley explains:
“For biologists, Geobacter’s behavior represents a paradigm shift. It goes against all that we are taught about biological electron transfer, which usually involves electrons hopping from one molecule to another.”
As described by U Mass writer Janet Lothrop, the new research began to develop in 2011, when the team discovered, for the first time, that the conductivity of pili is based on the same kind of electron transportation found in the synthetic organic materials that are commonly used in electronics.
That conductivity is based on aromatic ringed structures (aromatic refers to the stabilization of certain molecular structures), and since Geobacter possesses similar structures in the form of aromatic amino acids, that is where the researchers focused their efforts.
Sure enough, when they subbed in non-aromatic amino acids that were otherwise identical to their aromatic counterparts, they came up with a new strain of Geobacter that looked the same but had pili that no longer behaved as conductive wires.
As Lovley puts it, “What we did is equivalent to pulling the copper out of an extension cord.”
More And Better Methane Biogas
Methane biogas recovery is already emerging as an attractive investment for dairy farms and other livestock operations, as well as wastewater treatment plants, landfills, food production facilities and even breweries.
The value of the biogas is only part of the payoff, since the process cuts down the amount of waste going to landfills, and it can also yield an inert, organic substance that can be used as a soil amendment.
On the other hand, despite the advantages of biogas recovery an up-front investment in the equipment is still a hurdle to be overcome. That’s where Geobacter could make a signicant difference, by leading to the development of more efficient, affordable and compact biogas recovery systems.