Improvement of L-valine production at high temperature in Brevibacterium flavum by overexpressing ilvEBNrC genes

Abstract

Brevibacterium flavum ATCC14067 was engineered for L-valine production by overexpression of different ilv genes; the ilvEBNrC genes from B. flavum NV128 provided the best candidate for L-valine production. In traditional fermentation, L-valine production reached 30.08 ± 0.92 g/L at 31°C in 72 h with a low conversion efficiency of 0.129 g/g. To further improve the L-valine production and conversion efficiency based on the optimum temperatures of L-valine biosynthesis enzymes (above 35°C) and the thermotolerance of B. flavum, the fermentation temperature was increased to 34, 37, and 40°C. As a result, higher metabolic rate and L-valine biosynthesis enzymes activity were obtained at high temperature, and the maximum L-valine production, conversion efficiency, and specific L-valine production rate reached 38.08 ± 1.32 g/L, 0.241 g/g, and 0.133 g g-1 h-1, respectively, at 37°C in 48 h fermentation. The strategy for enhancing L-valine production by overexpression of key enzymes in thermotolerant strains may provide an alternative approach to enhance branched-chain amino acids production with other strains. © Society for Industrial Microbiology 2011.