Enhanced Carbon Recovery and Butyrate Production in\nCocultivation of Clostridium tyrobutyricum and C. ljungdahlii

During\nthe decarboxylation of pyruvate to acetyl-CoA, recovering\nthe carbon and electrons lost as CO<sub>2</sub> and H<sub>2</sub> is\ncrucial for enhancing the carbon utilization from the sugar substrate\nin an inefficient microbial fermentation. In this study, cofermentation\nof Clostridium tyrobutyricum (Cty)\nand Clostridium ljungdahlii (Clj) was\nperformed to enhance carbon recovery and value-added chemical production.\nThe CO<sub>2</sub> and H<sub>2</sub> released by Cty during glucose\nmetabolism were converted to acetic acid and ethanol by Clj via the\nWood-Ljungdahl pathway. The acetic acid produced by Clj promoted butyrate\nproduction by Cty, while Clj also converted the butyrate to butanol.\nIn this way, the cofermentation system effectively recycled off gas,\nenhanced butyrate yield, and produced non-native metabolite butanol.\nBy optimizing the cofermentation conditions, the cofermentation yield\nof butyric acid and butanol was 0.726 and 0.012 mol/mol-Glc, respectively,\nachieving a carbon recovery of 63.1%, as compared to butyrate yield\nof 0.644 mol/mol-Glc and carbon recovery of 53.2% for monoculture\nof Cty. The addition of H<sub>2</sub> further increased these yields\nto 0.783 and 0.016 mol/mol of Glc, respectively, with a carbon yield\nof 67.4%, surpassing the heterotrophic limit. This study demonstrated\nthat Cty-Clj cocultivation effectively improves carbon recovery, offering\na promising approach for cost-efficient and carbon-conserving processes.