Clostridium ljungdahlii as a biocatalyst in microbial electrosynthesis – Effect of culture conditions on product formation

Microbial electrosynthesis enables the production of value-added chemicals from CO₂ and electrons provided by an electrode. Clostridium ljungdahlii is an electroactive acetogen that potentially could be used in microbial electrosynthesis systems. However, the optimal operational parameters for microbial electrosynthesis using C. ljungdahlii are not known. Here, we explored the effects of yeast extract, pH, and cathode potential. A low initial pH increased the rate of acetate production from CO₂ and H₂ in serum bottle cultures. When cultivated in bioelectrochemical systems, the optimal coulombic efficiency (i.e. close to 100 %) was observed at a cathode potential between −0.8 V and −1.0 V, while the highest productivity was reached at −1.0 V. Addition of yeast extract to the medium was needed to ensure reproducible results. Using cyclic voltammetry, we detected hydrogen-mediated extracellular electron transfer of C. ljungdahlii during growth on CO₂ in a bioelectrochemical system. These results show that operational parameters should be chosen carefully to maximise the efficiency of microbial electrosynthesis.