“Insights in the electro-fermentation process with 13C-labelled experiments supported by NMR spectroscopy analysis”

The electro-fermentation (EF) process is an interesting and promising approach to control the spectrum of products deriving from microbial anaerobic fermentations, in terms of both composition and concentration. In EF a polarized electrode, functioning either as an anode [1] or a cathode [2], is used to modify the intracellular redox balance so as to redirect the carbon flux towards the desired end-products. To date, however, it is still not clear whether an electron transfer between microorganisms and the electrode is involved or if the process is simply triggered by a change in the oxidation-reduction potential of the reaction medium. Here, in order to gain a deeper understanding on the effect of the polarized electrode on the microbial metabolism, EF experiments have been performed by supplying 13C-labelled glucose, along with ethanol and acetate, to anaerobic mixed cultures inoculated at the cathode chamber of H-type reactors with the electrode potential controlled at -0.70 V (vs. SHE). The fermentation pattern has been tracked over time with the nuclear magnetic resonance (NMR) spectroscopy, that is the elective technique for 13C-labelled analysis. Parallel control tests (under identical conditions but in the absence of electrode polarization) have been carried out and compared to EF experiments.