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

[Display omitted] •C. butyricum-Fe3O4 hybrid system enhances carbon recovery in anaerobic fermentation.•Exogenous CO2 improves the metabolite selectivity for acetate and butyrate.•Fe3O4 and exogenous CO2 synergistically boost the key enzyme activities.•Fe3O4 accelerates intra- and extracellular electron transfer.•Hybrid system increases butyrate and acetate production by 18.7 % and 18.4 %. 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.