Cellular-electrical connections have the potential to join the specialties of the living world, such as the capabilities to harvest energy, sense environmental changes, and self-replicate, to those of the technological world. The bi-directional electronic communication enabled by such connections will open new possibilities in bioenergy, biosensing, and cellular reprogramming technologies. My research aims to create 'living' electrical connections by genetically re-programming microbes to construct well-defined electrical pathways and interfaces with an electrode.
As a first step, I have focused on constructing a pathway to transfer respiration-derived electrons, initially found in the cytoplasm, to external metals. Shewanella oneidensis MR-1, provides inspiration for this approach: it has the unusual capability to transport electrons from the cytoplasm to extracellular metals and minerals. This electron transfer is believed to occur via a trans-membrane electron transport chain (ETC). I am attempting to reconstitute this Shewanella-derived trans-membrane ETC in Escherichia coli composed of hemoproteins called c-type cytochromes.
To build this ETC in E. coli, I have transformed a series of plasmids encoding different c-type cytochrome genes from Shewanella into E. coli and have assayed the resulting strains for cytochrome expression and function. As part of this work, I developed a novel quantitative assay to measure the metal-reducing ability of these strains that is approximately 10 times more sensitive than previous assays. I simultaneously monitored both product formation and the cytochrome heme redox state, which allows a first-ever quantitative dissection of this process on the whole-cell level. These experiments are not only the first steps towards a rational engineering of hybrid living-non-living systems, but furthermore shed insight on what proteins are necessary and sufficient to complete the ETC in Shewanella.
My future work will focus on addressing kinetic bottlenecks in the system to increase metal reduction rates and creating a library of c-cytochromes to find an optimized set of proteins for solid metal reduction. These additional experiments will provide a greater understanding of the complex processes involved in microbial metal reduction.
Favorite Scientist: Ludwig Boltzmann