Optimization of the biological component of a bioelectrochemical cell

The efficiency of electron transduction by Shewanella oneidensis MR-1 was investigated both in batch culture and in a dual-chambered electrochemical cell. Aerobically grown bacteria were inoculated into an insoluble FeOOH suspension in an anaerobic environment. As the bacteria reduced Fe(III) to Fe(II) there was a visible color change from red to bluish black; this simple color change assay proved to be a robust method for determining the electrochemical activity of S. oneidensis MR-1. In an effort to improve electricity production by S. oneidensis MR-1, the performance of the electrochemical cell with lactate as a fuel was first optimized with respect to both poised potential and fuel concentration. Ultimately, electricity production proved to be proportional to both the poised potential and to fuel concentration. In particular, higher poised potentials increased charge production. Finally, we attempted to optimize the bacteria themselves for the efficient transduction of reduced carbon sources into electricity. The batch culture underwent a series of serial dilutions; after the 4th dilution the microbe population exhibited a 30% increase in charge production. We are further exploring whether this increase was due to metabolic adaptations or to genetic mutations, and examining additional ways to evolve electrogenic organisms.