088: Using Bacterial Structures as Nanowires with Gemma Reguera

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

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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:

• Gemma Reguera lab website
• Gemma Reguera interview on "People Behind the Science"
• HOM: Thirty-Second Annual Meeting of the Society of American Bacteriologists
  
• HOM: Barney Cohen: An Appreciation (Bacteriological Reviews memorial)