Harnessing Clostridium ragsdalei for conversion of CO₂ into ethanol: Insights from batch and continuous fermentation

CO₂ conversion into biofuels is a promising approach to lower carbon emissions and enhance biorefinery revenue. This study investigated CO₂ conversion into ethanol using Clostridium ragsdalei P11 in a 3-L bioreactor, comparing batch and continuous operation modes. The specific activities of carbon monoxide dehydrogenase (CODH), hydrogenase (H₂ase), formate dehydrogenase (FDH) and alcohol dehydrogenase (ADH) in the acetyl-CoA pathway were also assessed. In batch mode, strain P11 produced 7 g/L ethanol, achieving gas conversion efficiencies of 40 % for CO₂ and 60 % for H₂. In continuous mode, ethanol production increased to 21 g/L. During the initial growth phase, CODH and H₂ase exhibited higher activity, while FDH and ADH showed a gradual increase, corresponding with ethanol production. Enzyme activities in continuous mode were 3.6-7 fold higher than in batch operation. These results demonstrate that strain P11 effectively converts CO₂ to ethanol, providing a solid foundation for further optimization of CO₂ fermentation.