Evaluating propionate production in Clostridium ljungdahlii inoculated bioelectrochemical system

Abstract

Bioproduction of chemical building block such as propionic acid (propionate) is of great interest in current time as it is a sustainable alternative to petrochemical synthesis. Clostridium ljungdahlii as an electroactive homoacetogen is able to ferment sugars or utilize CO2 to produce organic acids under bioelectrochemical system (BES). However, few reports evaluated the ability of bioelectrochemically assisted propionate production via C. ljungdahlii. In this study, BES equipped with three-dimensional nanostructure electrode and inoculated with C. ljungdahlii in cathode chamber was developed to evaluate propionate production. It found that applied negative potential on cathode was necessary to stimulate propionate production from fructose. Bioelectrochemical characterizations of bacteria attached electrode revealed that C. ljungdahlii was able to assimilate extracellular electron. Notably, optimization of negative potential on electrode remarkably increased NAD(P)H/NAD(P)+ ratio, ATP amounts, and propionate production. Furthermore, BES optimization results showed that propionate achieved 16.29 ± 0.16 mM maximum titer (43 % ratio of total organic acids) and 0.2 g/g mass yield (0.24 mol/mol carbon atom yield) from fructose. A theoretical value (1.6 mmol) of fixed CO2 was calculated from mass/electron balance analysis. This work not only evaluated the performance of bioelectrochemical technology but also provided a new choice for sustainable and efficient propionate production.