Daniel Bond (left) and Jeffrey Gralnick (right)
“I work with bacteria that eat electricity and make electricity,” says Jeffrey Gralnick, a Distinguished McKnight University Professor in the Department of Plant and Microbial Biology. The idea may sound like science fiction, but the underlying chemistry is ancient, dating back to a time before oxygen filled the Earth’s atmosphere. Other life forms, including humans, also generate tiny electrical currents during respiration. The difference is that we transfer electrons to oxygen inside our cells, while the electricity-generating bacteria Gralnick studies push their leftover electrons outside the cell, often onto solid metal surfaces such as iron and manganese.
This remarkable process has practical implications. In the lab, Gralnick and his longtime collaborator, Professor Daniel Bond, grow the microbes on graphite electrodes that stand in for the natural minerals. The setup lets the team control and observe how the microbes respire. It also channels the electrons into a measurable electric current, effectively turning the microbial community into a living battery.
This ability to convert microbial respiration into electric current underpins the sustained support Gralnick and Bond have received from the U.S. Department of Defense’s Office of Naval Research and the Army Research Office. Both organizations support projects that probe the fundamental biology and genetics of these microbes, with potential applications such as microbial fuel cells that power sensors on the ocean floor. The research could also enable biosensors that interface directly with computers or microbial systems that produce valuable fuels through electrosynthesis, among other possibilities.
"The great part about collaborating with Jeff is we tend to look at a problem from very different angles,” Bond says. “Over the last 20 years, we’ve been able to combine new genetic approaches from his group with electrochemistry instruments built in my lab. This lets our students focus on how electrons move at the molecular level, or pull back to the level of organisms working together in a real application.”
Gralnick and Bond are currently collaborating on an Army-funded project that explores how two key microbial groups — Shewanella, which Gralnick’s lab specializes in, and Geobacter, Bond’s specialty — form cooperative communities on electrodes. The researchers are finding that the two species exchange food and waste products in ways that help them build stable communities and generate stronger electrical currents. “The system works more robustly when both species are together,” Gralnick says. “Shewanella in particular runs way faster when Geobacter is there, as opposed to when it’s just there on its own.”
Gralnick is also delving into the genetic programming that enables microbes to release electrons. To do this, his team is helping to develop and refine a next-generation gene-editing method called retron-mediated recombineering, which complements better-known techniques like CRISPR-Cas9. Whereas CRISPR lets researchers cut and replace specific sections of DNA, retrons serve as in-house copy machines, steadily generating short DNA fragments that cells can use to rewrite their own genes. “It allows us to not just make one mutation but to make a population of strains with many different mutations,” Gralnick explains.
This genetic engineering research, supported in part by the Office of Naval Research, could help pinpoint which genes are essential for extracellular electron transfer and ultimately allow scientists to design microbes that produce electricity even more efficiently. Although retron-mediated recombineering was first developed with E. coli, Gralnick’s lab is working with collaborators to extend and adapt the method to other microbial species, broadening its potential as a versatile genetic tool.
The focus on understanding how these microbes function at the most basic level places Gralnick’s work at the center of a dynamic, interdisciplinary scientific community. Within the International Society for Microbial Electrochemical Technologies, which Gralnick recently served as president, roughly half the members are microbiologists like himself and Bond, exploring these unusual organisms, while the other half are engineers developing devices powered by them.
“I'm mostly curious about the microbe,” he says. “Yet you never really know where the fundamental research is going to lead.” –Jonathan Damery