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Friday, 10 August 2018 16:16

Using Bacterial Structures as Nanowires with Gemma Reguera

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Gemma Reguera discusses her studies of Geobacter pili, which transfers electrons to iron oxide and other minerals, and can be used for new biotech applications.

Host: Julie Wolf Reguera

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Julie’s Biggest Takeaways:

Geobacter sulferreducans, a bacterium that “breathes” rust, is the lab representative of the genus Geobacter that dump electrons onto rust. These specialized microbes use minerals like manganese oxide and iron oxide (also known as rust) for respiration in both terrestrial and aquatic sediments. Although many species are strict anaerobes, a few species can grow under microaerophilic conditions, in which the bacteria will respire the oxygen to eliminate its toxic effects on the cell.

Iron oxide respiration relies on the Geobacter pili, a simple structure composed of a single peptide repeat. The pili concentrate on one side of the bacterial cell, where they connect the cell with the iron oxide to release the electrons that have been accumulating. The pili immediately depolymerize and retract, shedding the mineral before returning into the cell.

Mass-producing pilin subunits in E. coli took a bit of trouble shooting, but now Reguera and her colleagues can make them on a much larger scale, which bodes well for expanding tests into electronic applications.

Commercialization grants address the “valley of death,” the chasm between the technologies developed at the bench and the scale of production necessary for industrialization.


Geobacter can bind and reduce many minerals using their pili, including uranium and other toxic heavy metals like lead and cobalt. Using Geobacter pili in agricultural soils or aquaculture waters may help remove these contaminants and improve the health of these ecosystems.

Featured Quotes:

“I remember when I started as a microbiology student, I think I underappreciated the role that electrons and the movement of electrons play in microbiology.”

“There is absolutely not a single process in living organisms that is not energized by the movement of electrons.”

“The Earth didn’t have oxygen for the first 2 billion years, if not longer - and there was life! On Earth! Those early organisms were really great at finding minerals, metals, just about anything other than oxygen to dump their electrons, continue to grow, and to colonize the Earth.”

“When you start comparing the structure and the amino acid composition of this subunit to any other known bacterial pilins, you really see 2 remarkable changes: one of them is the pilin of Geobacter is very small. the second is that little stick has aromatic amino acids. When the sticks come together to make the filament, they cluster very close to each other and create like a staircase for the electrons to move fast. It’s like a magic combination in which you have the right structural reduction and the right amino acids to really fit like a puzzle to create paths for electrons.”

“What has always motivated me is learning something new.”

Links for This Episode:

History of Microbiology Tidbit

In this History of Microbiology tidbit, I look into the question of who made the first microbial fuel cell?

A quick wikipedia search told me that there were a few scientists working in this are in the early 1900s. In 1911, professor of botany MC Potter published “Electrical Effects accompanying the decomposition of Organic Compounds,” but the idea for the first fuel cell is credited to Barnet Cohen, in a presentation titled “The Bacterial Culture as an Electrical Half-Cell,” presented at the 32nd meeting of the society of bacteriologists, the forerunner to the American Society for Microbiology.

Cohen, a member and later a president of the SAB, looked at the reduction potential of different bacterial cultures - in other words, how many electrons could the culture accept. He wrote, “in general, it has been found that the potential of a vigorous culture in ordinary media will mount up to about 0.5 to 1 volt over the control. The bacterial culture during the process of energy conversion is in a sense, therefore, a primary electrical half-cell, and as such should conceivably be able to perform work.”

This half-cell concept is the forerunner to modern microbial fuel cells that often separate electrode ends with physical distance or a semipermeable membrane and that use electrochemically active bacteria like Geobacter or Shewanella species which can efficiently transfer electrons to electrodes without need for a chemical facilitator to assist this transfer.

Cohen himself worked in many areas of science, including human nutrition and physiology, but had a lifelong love of microbiology. In a memoir published in Bacteriological Reviews, his friend and frequent collaborator William Mansfield Clark wrote that Cohen was not only a former SAB president but had also been an archivist for the society (although formed in 1899, there was less as much history to archive during Cohen’s time), making his highlight here in the history of microbiology tidbit that much more apt.

Have you tried the mudwatt? Let me know if it’s worth purchasing by tweeting us at @ASMicrobiology.

Send your stories about our guests and/or your comments to jwolf@asmusa.org.

Last modified on Friday, 10 August 2018 16:32
Julie Wolf

Julie Wolf is the ASM Science Communications Specialist. She contributes to the ASM social media and blog network and hosts the Meet the Microbiologist podcast. She also runs workshops at ASM conferences to help scientists improve their own communication skills. Follow Julie on Twitter for more ASM and microbiology highlights at @JulieMarieWolf.

Julie earned her Ph.D. from the University of Minnesota, focusing on medical mycology and infectious disease. Outside of her work at ASM, she maintains a strong commitment to scientific education and teaches molecular biology at the community biolab, Genspace. She lives in beautiful New York City.

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