Disruption of the Butyrate Kinase (buk) Gene Is Vital for the High Butyric Acid Selectivity in Clostridium Acetobutylicum

Butyric acid is a valuable industrial chemical which utilized in food, pharmaceutical, animal feed supplement, and chemical industries. Several Clostridium strains, including Clostridium butyricum, Clostridium thermobutyricum, Clostridium tyrobutyricum, Clostridium beijerinckii and Clostridium acetobutylicum, can naturally produce butyric acid. Generally butyric acid producing Clostridium strains are co-produce acetic acid with butyric acid and increasing the butyric acid selectivity is important to economical butyric acid production. However, complex metabolic pathways and physiologies of clostridia induce the difficulties of economical butyric acid production. In this work, the second butyrate kinase of C. acetobutylicum encoded by bukII gene was employed instead of butyrate kinase I encoded by buk gene for the high butyric acid selectivity in C. acetobutylicum. Moreover, further metabolic engineering was used for the enhancement of the NADH-driving force. The metabolically engineered C. acetobutylicum strain produced 32.5 g/L of butyric acid with a butyric-to-acetic acid ratio (BA/AA ratio) of 31.3 g/g from 83.3 g/L of glucose in batch fermentation at pH 6.0. These results suggested that the buk gene knockout was vital for the high butyric acid selectivity in C. acetobutylicum. [This work was supported by the Technology Development Program to Solve Climate Changes on Systems Metabolic Engineering for Biorefineries from the Ministry of Science, ICT and Future Planning (MSIP) through the National Research Foundation (NRF) of Korea (NRF-2012M1A2A2026556 and NRF-2012M1A2A2026557)]