Properties of Revertants Appearing in L-Leucine Fermentation Culture Broth

Abstract

The L-leucine productivity of an L-leucine producing strain, H-1204, of Corynebacterium glutamicum substantially decreased during a large-scale culture or repetitive subculturing. This instability was found to be due to the appearance of revertants with lower or no L-leucine productivity. Strains in the culture broth could be roughly classified into three types on the basis of their phcnotypes: L-type, original L-leucine producing strain, Val^L Leu⁺ (valine leaky); M-type, Val⁺ Leu⁺ (prototroph); V-type, Val⁺ Leu^- (leucine auxotroph). The appearance of these revertants was determined to be caused by the distribution imbalance of α-ketoisovaleric acid, the common precursor for L-leucine and L-valine biosynthesis.