Analysing overexpression of L-valine biosynthesis genes in pyruvate-dehydrogenase-deficient Corynebacterium glutamicum.

L-valine biosynthesis was analysed by comparing different plasmids in pyruvate-dehydrogenase-deficient Corynebacterium glutamicum strains in order to achieve an optimal production strain. The plasmids contained different combinations of the genes ilvBNCDE encoding for the L-valine forming pathway. It was shown that overexpression of the ilvBN genes encoding acetolactate synthase is obligatory for efficient pyruvate conversion and to prevent L-alanine as a by-product. In contrast to earlier studies, overexpression of ilvE encoding transaminase B is favourable in pyruvate-dehydrogenase-negative strains. Its amplification enhanced L-valine formation and avoided extra- and intracellular accumulation of ketoisovalerate.