New insight into Clostridium butyricum-ferroferric oxide hybrid system in exogenous carbon dioxide-assisted anaerobic fermentation for acetate and butyrate production

Mixotrophic cultivation, utilizing both gas and organic substances, is commonly employed to minimize the carbon loss during anaerobic fermentation of bulk chemicals. Herein, a novel Clostridium butyricum-ferroferric oxide (Fe₃O₄) hybrid system, enhanced by exogenous carbon dioxide (CO₂), was proposed to improve carbon recovery and optimize metabolite production. The results demonstrated that exogenous CO₂ improved metabolite selectivity towards acetate/butyrate, while also accelerating CO₂ fixation. Compared to pure Clostridium butyricum, the hybrid system significantly increased carbon conversion to primary metabolites, boosting butyrate and acetate production by 18.7 % and 18.4 %, respectively. Enzyme activity assays revealed that Fe₃O₄ and exogenous CO₂ acted synergistically, enhancing the activities of key enzymes involved in CO₂ assimilation. Additionally, Fe₃O₄ facilitated intra- and extracellular electron transfer, further improving the fermentation process. This study offers new insights into the combined effects of exogenous CO₂ and Fe₃O₄ on anaerobic fermentation, providing an efficient strategy for carbon recovery and selective acetate/butyrate production.