Rational modification of the carbon metabolism of Corynebacterium glutamicum to enhance L-leucine production.

L-Leucine is an essential amino acid that has wide and expanding applications in the industry. It is currently fast-growing market demand that provides a powerful impetus to further increase its bioconversion productivity and production stability. In this study, we rationally engineered the metabolic flux from pyruvate to L-leucine synthesis in Corynebacterium glutamicum to enhance both pyruvate availability and L-leucine synthesis. First, the pyc (encoding pyruvate carboxylase) and avtA (encoding alanine-valine aminotransferase) genes were deleted to weaken the metabolic flux of the tricarboxylic acid cycle and reduce the competitive consumption of pyruvate. Next, the transcriptional level of the alaT gene (encoding alanine aminotransferase) was down regulated by inserting a terminator to balance L-leucine production and cell growth. Subsequently, the genes involved in L-leucine biosynthesis were overexpressed by replacing the native promoters PleuA and PilvBNC of the leuA gene and ilvBNC operon, respectively, with the promoter Ptuf of eftu (encoding elongation factor Tu) and using a shuttle expression vector. The resulting strain WL-14 produced 28.47 ± 0.36 g/L L-leucine in shake flask fermentation.