Electrochemically Driven Fermentation of Organic Substrates with Undefined Mixed Microbial Cultures

Growing scientific interest in mixed microbial culture-based anaerobic biotechnologies for the production of value-added chemicals and fuels from waste organic residues requires a parallel focus on the development and implementation of strategies to control products distribution. This study examined the feasibility of an electro-fermentation approach, based on the introduction of a polarized (-700 mV vs. the standard hydrogen electrode) graphite electrode in the fermentation medium, to steer products distribution during the conversion of organic substrates (glucose, ethanol, and acetate supplied as single compounds or in mixtures) by undefined mixed microbial cultures. As a main result, in batch experiments the polarized electrode triggered a nearly 20-fold increase (relative to open circuit controls) in the yield of i-butyrate production (0.43±0.01 vs. 0.02±0.02 mol/ mol glucose) during the anaerobic fermentation of the ternary mixture of substrates, without adversely affecting the rate of substrate bioconversion. The observed change in the fermentative metabolism was most likely triggered by the (potentiostatic) regulation of the oxidation-reduction potential of the reaction medium rather than by the electrode serving as an electron donor.