Roughly 30 years ago, microbiologists discovered a new group of bacteria that “breathe” iron in the same way we breathe oxygen: by the transfer of electrons. Baffled by the concept of “breathing” a solid substance, scientists further researched the respiratory mechanisms of these bacteria—aptly named metal-respiring bacteria. The scientific findings prompted two different years-long senior thesis projects under Associate Professor of Biology Mike McCormick.
The projects, now headed by Alexa Bosco ’22 and Avery Lum ’22, use oxygen-free lab environments and diverse bacterial samples, one of which came from the Hamilton golf course. They want to find out more about the respiratory mechanisms used when metal-respiring bacteria cannot directly contact the iron they need to breathe. These mechanisms, known as electron shuttles and nanowires, could offer insight into the ways microbial communities structure themselves and interact with each other.
“I think microbiology is really interesting because we can learn so much about these bacteria without even being able to see them with the naked eye,” Lum said. “It’s an awesome opportunity to find out what they’re doing and to quantify something so small.”
When metal-respiring bacteria lack direct contact with iron, they can still “breathe” using electron shuttles, soluble chemicals that carry electrons outside of the cell and to the iron, where they transfer the electrons. This process creates a kind of looped cycle between the iron and the bacteria. Bosco and McCormick mimic this cycle with a newly-operational, oxygen-free “loop flow system.”
Simply put, the system separates the bacteria from its metal electron acceptor, which forces capable bacteria to create electron shuttles. Those that cannot create electron shuttles will not survive. Through DNA analysis, McCormick and Bosco hope to use this system to find more species of electron-shuttle-producing bacteria and confirm their importance in shaping microbial communities.
“I think microbiology is really interesting because we can learn so much about these bacteria without even being able to see them with the naked eye.”
“Not a lot of people are doing this specific electron shuttle research,” Bosco said. “So I think what we do this semester can be applied to other projects and help those projects succeed. And that’s really exciting when you consider the long-term implications of this research.”
Bosco finds the future health and environmental implications particularly interesting, she said. Learning more about electron shuttles can lead to a better understanding of healthy human gut microbiomes (the bacteria in our guts), as more electron shuttles may correlate with a healthier gut. Electron shuttle research can also help microbial fuel cells (a potential renewable energy source) to optimize energy production, making them a more viable option.
Lum’s research on nanowires could also generate important findings for future renewable energy research. Like electron shuttles, the creation of nanowires is a respiratory response for when bacteria lose contact with their metal electron acceptor.
“Some of the bacteria have an ability to sprout these little filaments called nanowires,” McCormick said. “They stick out and reach around, trying to find something that they can breathe. If they find a solid, they connect to it so that they can breathe again.”
If a nanowire-producing bacterium cannot find a solid, it can connect to a neighboring, breathing bacterium for survival, McCormick said. This mechanism leads to the formation of networks, in which many bacteria are connected through nanowires. Lum, who is the sixth student to work on this project, analyzes these networks. The ultimate goal is to discover any inherent architectural traits in the nanowire networks that have a biological benefit and influence interactions between the bacteria involved. In the long-term, these findings could inform future research on increased renewable energy output.
“Research takes a lot of time, and it’s a lot of problem solving,” Bosco said. “Just today, I got some data that was not ideal. Sometimes, it can be really defeating when things aren’t going right. But I’m staying curious and staying optimistic, and those are things that I’ll take with me in any job I go into.”
