[Metabolic engineering of Escherichia coli for efficient production of L-valine]

L-valine is an important branched-chain amino acid widely used in the food, pharmaceutical, and feed industries. Microbial fermentation has become the primary production method for L-valine. However, current industrial production still faces issues such as inefficient carbon flux utilization, imbalance in cofactor supply and demand, and suboptimal fermentation processes, which limit the efficient synthesis of L-valine. To further enhance the production performance of L-valine, In this study, metabolic engineering was conducted for a previously constructed Escherichia coli strain with a high yield of L-valine to optimize carbon flux distribution and balance cofactor consumption. Dual-phase oxygen-controlled fermentation was carried out to enhance L-valine production. Firstly, to address the pyruvate loss, we knocked out multiple competing pathway genes (ldhA, poxB, pflB, frdA, and pta), which resulted in a 48% increase in flask yield of the constructed strain VL-04. Next, we optimized the cofactor supply and demand balance by replacing ilvE with bcd (NADH-preferential) from Bacillus subtilis to construct the strain VL-06, which achieved a flask yield of 22.80 g/L, a further improvement of 25.8%. Subsequently, the fermentation conditions of VL-06 were optimized in a 5 L bioreactor with dual-phase oxygen-controlled fermentation. After optimization, the L-valine production reached 86.44 g/L in 26 h, with a glucose-to-acid conversion rate of 44.08% and a production intensity of 3.32 g/(L·h). This study not only shortens the time for L-valine production but also improves the economic efficiency, providing insights for similar fermentation processes employing dual-phase oxygen control.