[Pathway analysis for production of L-leucine by Brevibacterium flavum TK0303].

Brevibacterium flavum is used for the production of a number of amino acids in the biotechnology industry. The yield of producing a metabolite is ultimately limited by the ability of the central metabolism and the desired biosynthesis pathway. Pathway analysis is a very useful tool for metabolic engineering, which can be applied to increase the yield of a metabolite or channeling a metabolite into desired pathways. It does not require any kinetic parameters and only uses the Stoichiometric equations. Pathway analysis for production of L-leucine by Brevibacterium flavum TK0303 at steady state was conducted in this paper. Theoretical yield and flux distribution for optimal pathway were determined. It is also concluded that pyruvate and acetyl-coenzyme A are the key nodes of the L-leucine biosynthesis pathway by analyzing the flux distributions of different modes. According to the pathway analysis, the production of L-leucine is expected to be raised by strengthening the flux of the key nodes (pyruvate and acetyl-coenzyme A) through changing the environmental factors. Because the flux of TCA cycle in Brevibacterium flavum TK0303 is weak, the production of L-leucine must be provided enough amido by adding glutamic acid to the fermentation medium. NH4Ac is both a carbon source and a nitrogen source, which could be helpful to the production of L-leucine. The effects of glutamic acid and NH4Ac on the production of L-leucine were further studied. The production of L-leucine increased 56% by adding glutamic acid. By improving the concentration of NH4Ac, the biosynthesis of L-leucine was greatly strengthened too. The results indicate that the flux of L-leucine can be largely increased by changing the chemical regulatory factors such as NH4Ac and glutamic acid and the modes established by pathway analysis prove to be efficient to describe the metabolic network of L-leucine production by Brevibacterium flavum TK0303.