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 (FeO) hybrid system, enhanced by exogenous carbon dioxide (CO), was proposed to improve carbon recovery and optimize metabolite production. The results demonstrated that exogenous CO improved metabolite selectivity towards acetate/butyrate, while also accelerating CO 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 FeO and exogenous CO acted synergistically, enhancing the activities of key enzymes involved in CO assimilation. Additionally, FeO facilitated intra- and extracellular electron transfer, further improving the fermentation process. This study offers new insights into the combined effects of exogenous CO and FeO on anaerobic fermentation, providing an efficient strategy for carbon recovery and selective acetate/butyrate production.