Metabolic engineering of a novel Klebsiella oxytoca strain for enhanced 2,3-butanediol production

• 2,3-Butanediol is a valuable platform chemical for synthetic rubbers production.
• A 2,3-BD hyper-producing and nonpathogenic Klebsiella oxytoca strain was isolated.
• The ldhA gene deletion successfully reduced lactic acid formation but enhanced 2,3-BD production.
• The ldhA-deficient K. oxytoca strain produced 115 g/L of 2,3-BD in a fed-batch fermentation.

Fermentative 2,3-butanediol (2,3-BD) production has been receiving increasing interest for its potential as a platform chemical intended for the production of synthetic rubbers, plastics, and solvents. In this study, Klebsiella oxytoca GSC 12206, a 2,3-BD native hyper-producing and nonpathogenic bacterium, was isolated from a cattle farm. Since this isolate produced a significant amount of lactic acid along with 2,3-BD, its mutant deficient in lactic acid formation was constructed by disrupting the ldhA gene which encodes lactate dehydrogenase. The ldhA gene was deleted precisely by using the pKGS plasmid. When compared to the wild-type strain, the mutant deleted with the ldhA gene in glucose fermentation resulted in an increase of 54%, 13%, 60%, and 78% of 2,3-BD titer, productivity, yield, and selectivity, respectively. A fed-batch fermentation by this mutant with intermittent glucose feeding produced 115 g/L of 2,3-BD with an yield and productivity of 0.41 g 2,3-BD per g glucose and 2.27 g/L h, respectively, indicating the usefulness for the industrial production of 2,3-BD.