Production of α-ketoisovalerate with whey powder by systemic metabolic engineering of Klebsiella oxytoca

Whey, which has high biochemical oxygen demand and chemical oxygen demand, is mass-produced as a major by-product of the dairying industry. Microbial fermentation using whey as the carbon source may convert this potential pollutant into value-added products. This study investigated the potential of using whey powder to produce α-ketoisovalerate, an important platform chemical. Klebsiella oxytoca VKO-9, an efficient L-valine producing strain belonging to Risk Group 1 organism, was selected for the production of α-ketoisovalerate. The leucine dehydrogenase and branched-chain α-keto acid dehydrogenase, which catalyzed the reductive amination and oxidative decarboxylation of α-ketoisovalerate, respectively, were inactivated to enhance the accumulation of α-ketoisovalerate. The production of α-ketoisovalerate was also improved through overexpressing α-acetolactate synthase responsible for pyruvate polymerization and mutant acetohydroxyacid isomeroreductase related to α-acetolactate reduction. The obtained strain K. oxytoca KIV-7 produced 37.3 g/L of α-ketoisovalerate from lactose, the major utilizable carbohydrate in whey. In addition, K. oxytoca KIV-7 also produced α-ketoisovalerate from whey powder with a concentration of 40.7 g/L and a yield of 0.418 g/g. The process introduced in this study enabled efficient α-ketoisovalerate production from low-cost substrate whey powder. Since the key genes for α-ketoisovalerate generation were integrated in genome of K. oxytoca KIV-7 and constitutively expressed, this strain is promising in stable α-ketoisovalerate fermentation and can be used as a chassis strain for α-ketoisovalerate derivatives production.