13C-labelled glucose reveals shifts in fermentation pathway during cathodic electro-fermentation with mixed microbial culture

Cathodic Electro-Fermentation (CEF) is an innovative approach to manage the spectrum of products deriving from anaerobic fermentation. Herein, mixed microbial culture fermentation using a ternary mixture containing labelled C-13 glucose and non-labelled acetate and ethanol was studied to identify the role of polarization on the metabolic pathways of glucose fermentation. CEF at an applied potential of -700 mV (vs. SHE, Standard Hydrogen Electrode) enhanced the production yield of acetate, propionate, and butyrate (0.90 +/- 0.10, 0.22 +/- 0.03, and 0.34 +/- 0.05 mol/mol; respectively) compared to control tests performed at open circuit potential (OCP) (0.54 +/- 0.09, 0.15 +/- 0.04, and 0.20 +/- 0.001 mol/mol, respectively). Results indicate that CEF affected the C-13 labelled fermented product levels and their fractional( 13)C enrichments, allowing to establish metabolic pathway models. This work demonstrates that, under cathodic polarization, the abundance of both fully C-13 labelled propionate and butyrate isotopomers increased compared to control tests. The effect of CEF is mainly due to intermediates initially produced from the glucose metabolic transformation in the presence of non-labelled acetate and ethanol as external substrates. These findings represent a significant advancement in current knowledge of CEF, which offers a promising tool to control mixed cultures bioprocesses.