Mechanism for the stabilization by L-valine of L-leucine fermentation using an unstable mutant of Corynebacterium glutamicum.

The L-leucine production by an L-leucine producing mutant, H-1204, of Corynebacterium glutamicum was unstable because the strains (M- and V-types) exhibiting reduced L-leucine productivity appeared during cultivation. Stabilization of the L-leucine production was attempted on the basis of the properties of various strains: L-type, an original L-leucine producer (valine leaky strain); M-type, a prototrophic strain; and V-type, a leucine auxotrophic strain. The addition of L-valihe to the medium was found to be most effective. L-Valine had a double effect in that it not only stimulated the growth of the L-type but also inhibited the growth of the V-type as an antagonist as to its leucine uptake. It was also revealed that C. glutamicum has two different transport systems for branched chain amino acids and dipeptides, respectively.