Chemical Engineering Seminar

Electron transfer is central to all life processes. To avoid damage, organisms have evolved strategies to eliminate the surplus of electrons created by their metabolic processes. Most of these strategies involve transferring electrons to soluble oxygen-like electron acceptors acting as electron sinks. However, microbes that live in areas with limited or no oxygen, such as those that reside in the deep ocean, in soil, or the human body, have evolved strategies to export electrons to extracellular acceptors such as minerals or other bacteria. Geobacter uses long, thin, conductive filaments called "nanowires" to export electrons1. Nanowires are fundamental to global environmental processes1, including methane degradation, a major greenhouse gas2.

Geobacter nanowires have intrigued the scientific community since they were first identified in 2002. Until recently, nanowires were considered Type IV pili (T4P) polymers of the PilA-N pilin subunit, partly because T4P is required for electron transfer. Type IV pili (T4P), polymers of the PilA-N pilin subunit, partly because T4P are required for electron transfer3. However, my lab showed that PilA-N pairs with a second protein, PilA-C, to form a T4P structurally inconsistent with electron transfer4. We further showed that Geobacter produces additional filaments comprising cytochrome subunits that could transfer electrons through a chain of heme groups2,5. We are now testing our hypotheses that (i) these cytochrome filaments are the electron-conducting nanowires and (ii) the role of T4P in electron transfer is akin to a piston to secrete cytochrome nanowires on the bacterial surface. Our team is now exploring nanowires' structure, assembly, and electron transfer mechanism and evaluating their role in bacterial respiration, communication, and pathogenesis. By combining experimental and computational studies, our team is addressing three key questions:

• How do microbes build & use nanowires2?
• How are electrons transferred from the bacterial cytoplasm to surface-displayed nanowires6?
• Can nanowire conductivity be tuned using light7, pressure8, temperature9, electromagnetic fields8, and non-natural ‘click' chemistry10 functionalities to control bacterial behavior?

References

1. Malvankar et al. Nature Nano., 2011
2. Gu et al. Malvankar Nature Micro., 2023
3. Yalcin & Malvankar Current Opinion, 2020
4. Gu et al. Malvankar Nature, 2021
5. Wang & Gu et al. Hochbaum, Egelman & Malvankar Cell, 2019
6. Portela & Shipps et al. Malvankar, Nature Comm. 2024
7. Neu & Shipps et al. Malvankar, Nature Comm. 2022
8. Yalcin & O'Brien et al. Malvankar, Nature Chem. Bio., 2019
9. Dahl et al. Malvankar, Science Adv., 2022
10. Shapiro et al. Malvankar & Isaacs, Nature Comm. 2022