Published on October 20th, 2014 | by Tina Casey1
Super Electric Mud-Loving Bacteria Really Is Electric
October 20th, 2014 by Tina Casey
They had us at microbial nanowires, but apparently some scientists have been skeptical of research showing that a mud-loving bacteria called Geobacter can produce electricity and conduct it through tiny wires, much in the same way that copper wire conducts electricity. If you can imagine low cost, tunable, biodegradable, self-assembling components for electronic devices, then you can imagine some of the practical implications of the discovery.
As for the skeptics, wait ’til they get a load of the findings from a new electrostatic force microscopy study of Geobacter.
A Brief History Of Geobacter
The Geobacter research team is based at the University of Massachusetts at Amherst, headed up by microbiologist Derek Lovley.
They first crossed our radar back in 2009 but the research dates back years before, when they discovered the mud-loving microbe feasting along the banks of the Potomac River.
At first attracted by the potential for Geobacter in soil remediation, the team initially focused on the microbe’s ability to “breath” iron and other metals instead of air. Additional research into this super-power showed that Geobacter can convert petroleum-based contaminants into carbon dioxide, and it can even address radioactive groundwater contamination.
By the early 2000’s, Lovley and the team were exploring Geobacter’s ability to generate electricity from organic matter, and conduct it. Here’s how we described it in 2009:
…By 2005 they had identified the mechanism: the “pili,” hairlike protuberances that festoon Geobacter like nanowires. They create a thin biofilm that conducts electrons from the organism to iron in the mud or wastewater.
Meanwhile, in 2010 we noted that the research had caught the attention of the US Navy for potential use in microbial fuel cells that run on seawater.
The Navy has also been funding the current project along with the Energy Department and the National Science Foundation, so go ahead and hug it in you taxpayers.
Getting back to our timeline, in 2013 we also took note of an additional role for Geobacter, to improve methane biogas production.
Geobacter Microbial Nanowires, Revealed
We’ve been following the Geobacter story for like five years now and we had no idea — no idea! — that a raft of doubters were out there.
Apparently there were, because here’s the lede from yesterday’s UMass announcement about the results of the new Geobacter study:
The claim by microbiologist Derek Lovley and colleagues at the University of Massachusetts Amherst that the microbe Geobacter produces tiny electrical wires, called microbial nanowires, has been mired in controversy for a decade…
We’re not saying the new study will convert all the doubters overnight, but it does appear to strengthen the case for Geobacter’s electric superpowers.
As described in the current issue of Nature Nanotechnology, the new study deployed electrostatic force microscopy to create a visual image of the electrical current. If you follow the link at Nature.com you’ll see that the results weren’t nearly as colorful as the image we’ve included here, which was provided by UMass, but it was enough to enable the researchers to claim that the Geobacter pili conduct a charge very similar to that of carbon nanotubes, and under similar conditions of temperature and pH.
That’s significant because although biological electron transport is a familiar phenomenon, until now it has been primarily known as a kind of “hopping” mechanism that involves a series of “biochemical stepping stones.”
The new research indicates that the electron transport is based on delocalized charges, meaning that the electrons are not associated with discrete molecules. Instead, when electrons are introduced at one point, the entire pili will appear to “light up” under electrostatic force microscopy as the charge propagates along its length. This type of activity is also known as metallic-like activity.
Electrostatic Force Microscopy (EFM)
EFM is typically used to study carbon nanotubes, so its application to Geobacter could also help convince some of the skeptics. Here’s a couple of key points about EFM from the Warsaw University of Technology:
[The] sensitivity is sufficient to detect a few tens of elementary charges stored in nanostructures, and, in specific cases, enables to observe single charge events at room temperature and atmospheric pressure.
[Lateral resolution is limited to] a few tens of nanometers in ambient air at most, which is, however, sufficient to address and map the electrostatic properties of single nanostructures or nanodevices such as carbon nanotubes or CNTFETs.
Another important aspect of the Geobacter study was the use of a control group. The research team subjected pili to EFM that were modified to remove key aromatic amino acids. Since these provide the platform for Geobacter’s metal-like conductivity, you would expect different results, and that’s what happened. With one of the critical factors removed, EFM did not demonstrate charge propagation.
We’re still a long way off from grow-your-own solar panels, but on the other hand if you take a look at developments involving another bacteria, E. coli, (bioluminescent sustainable ink, for example) you can see big potential in those little bugs.