Abtsract:
Nobel Laureate Albert Szent-Györgyi stated that “life is nothing but an electron looking for a place to rest,” highlighting the judicious use of energy as an essential ingredient for life. All organisms convert electron potential energy into cellular processes that sustain them. With rare exceptions, multicellular organisms, like humans, are aerobic – breathing oxygen: our cells rip high energy electrons out of chemical bonds in the organic food we eat, extract their energy, and dump the spent electrons onto molecular oxygen (respiration). Microbial life, on the other hand, has evolved to exploit nearly all sources of energy on Earth, including from inorganic solids. We are surrounded by microorganisms that “breath” and even “eat” rocks by passing electrons across their cell membranes. This metabolic trick, called extracellular electron transfer (EET), is centrally involved in microbial activity ranging from metal mining and fuel cells to infections and elemental geochemical cycles. This talk will discuss the nuts and bolts of how microbes accomplish EET, including the large protein assemblies that carry electrons into or away from the cell. But the protein construction of these structures exposes a gap in our understanding of how these processes work: decades of studies have established that there is nothing special about proteins as a medium for electron transfer. So what makes these EET proteins special, and why are they so good at conducting electrons that they can sustain microbial life? The lessons learned from the structure of these proteins can inform designs of synthetic material building blocks for bioenergy, biosensing, and environmental remediation technologies. They can also provide clues into how microbial life evolved in the oxygen-free atmosphere of early Earth, how these microbes continue to shape geochemical cycling and human microbiomes, and what life may look like elsewhere in our solar system.