Living cells gain energy for growth and survival by transferring electrons between the products of catabolism and a suitable electron acceptor. The most favorable terminal electron acceptor is oxygen, but in oxygen-poor environments most cells use other soluble factors to accept the electrons generated by metabolism. Bacteria in the genus Shewanella can actually use solid extracellular metals as substrates for respiration, and they have evolved a series of periplasmic and outer-membrane proteins to serve as a direct electrical junction with these metals. Several members of the shewanellae have clinical relevance as opportunistic pathogens, and the basis of their unique respiratory abilities thus warrants further investigation. Furthermore, the existence of a genetically-encoded pathway between manufactured circuits and the central metabolism of living cells opens new vistas in studying and engineering microorganisms. Recent results suggest that these conduits can also pass current in reverse, allowing extracellular electrons to enter the cell and drive synthetic processes. If combined with carbon fixation, applied current could make a versatile input for the production of high-value chemicals, including pharmaceuticals. This proposal outlines research to characterize and improve the capacity of Shewanella cells to accept electrical current, using electrically active bioreactors in combination with microscopy of cells expressing fluorescent protein sensors, transcriptome sequencing, and reverse genetics assays. Finally, a strain of E. coli expressing genes from Shewanella will be constructed in order to define an efficient genetic circuit conferring electron uptake.
The studies proposed in this document will contribute to our knowledge of microbial energetics of an opportunistic pathogen, and establish a chassis for efficient production of important biomedical products in the future.