Efficient L-valine production using systematically metabolic engineered Klebsiella oxytoca

• DOI: 10.1016/j.biortech.2024.130403
• Publication Date: 2024-01-29T16:44:23Z
• Authors: Menghao Cao; Weikang Sun; Shuo Wang; Haiyan Di; Qihang Du; Xiaoxu Tan; Wensi Meng; Zhaoqi Kang; Yidong Liu; Ping Xu; Chuanjuan Lü; Cuiqing Ma; Chao Gao
• Keywords: Klebsiella oxytoca; Acetoin; 2,3-Butanediol; Metabolic Engineering; Efflux

L-Valine, a branched-chain amino acid with diversified applications, is biosynthesized with α-acetolactate as the key precursor. In this study, the metabolic flux in Klebsiella oxytoca PDL-K5, a Risk Group 1 organism producing 2,3-butanediol as the major fermentation product, was rearranged to L-valine production by introducing exogenous L-valine biosynthesis pathway and blocking endogenous 2,3-butanediol generation at the metabolic branch point α-acetolactate. After further enhancing L-valine efflux, strengthening pyruvate polymerization and selecting of key enzymes for L-valine synthesis, a plasmid-free K. oxytoca strain VKO-9 was obtained. Fed-batch fermentation with K. oxytoca VKO-9 in a 7.5 L fermenter generated 122 g/L L-valine with a yield of 0.587 g/g in 56 h. In addition, repeated fed-batch fermentation was conducted to prevent precipitation of L-valine due to oversaturation. The average concentration, yield, and productivity of produced L-valine in three cycles of repeated fed-batch fermentation were 81.3 g/L, 0.599 g/g, and 3.39 g/L/h, respectively.