Improvement of L-Valine Production by Atmospheric and Room Temperature Plasma Mutagenesis and High-Throughput Screening in Corynebacterium glutamicum

As one of the branched-chain amino acids, L-valine is an essential nutrient for most mammalian species. In this study, the L-valine producer Corynebacterium glutamicum Delta ppc Delta aceE Delta alat Delta pqo was first constructed. Additionally, an improved biosensor based on the Lrp-type transcriptional regulator and temperature-sensitive replication was built. Then, the C. glutamicum strain was mutagenized by atmospheric and room temperature plasma. A sequential three-step procedure was carried out to screen L-valineproducing strains, including the fluorescence-activated cell sorting (FACS), 96-well plate screening, and flask fermentation. The final mutant HL2-7 obtained by screening produced 3.20 g/L of L-valine, which was 21.47% higher than the titer produced by the starting strain. This study demonstrates that the L-valine-producing mutants can be successfully isolated based on the Lrp sensor system in combination with FACS screening after random mutagenesis.