Enhanced Carbon Recovery and Butyrate Production in Cocultivation of <i>Clostridium tyrobutyricum</i> and <i>C. ljungdahlii</i>

During the decarboxylation of pyruvate to acetyl-CoA, recovering the carbon and electrons lost as CO2 and H2 is crucial for enhancing the carbon utilization from the sugar substrate in an inefficient microbial fermentation. In this study, cofermentation of Clostridium tyrobutyricum (Cty) and Clostridium ljungdahlii (Clj) was performed to enhance carbon recovery and value-added chemical production. The CO2 and H2 released by Cty during glucose metabolism were converted to acetic acid and ethanol by Clj via the Wood-Ljungdahl pathway. The acetic acid produced by Clj promoted butyrate production by Cty, while Clj also converted the butyrate to butanol. In this way, the cofermentation system effectively recycled off gas, enhanced butyrate yield, and produced non-native metabolite butanol. By optimizing the cofermentation conditions, the cofermentation yield of butyric acid and butanol was 0.726 and 0.012 mol/mol-Glc, respectively, achieving a carbon recovery of 63.1%, as compared to butyrate yield of 0.644 mol/mol-Glc and carbon recovery of 53.2% for monoculture of Cty. The addition of H2 further increased these yields to 0.783 and 0.016 mol/mol of Glc, respectively, with a carbon yield of 67.4%, surpassing the heterotrophic limit. This study demonstrated that Cty-Clj cocultivation effectively improves carbon recovery, offering a promising approach for cost-efficient and carbon-conserving processes.