Effects of reduced citrate synthase activity and feedback-resistant phosphoenolpyruvate carboxylase on lysine productivities of Brevibacterium flavum mutants.
In order to re-examine the effects of reduced citrate synthase activity (designated as CSL) and feedback-resistant phosphoenolpyruvate carboxylase (PCR) on the lysine productivities of mutants with feedback-resistant aspartokinase (AK) (AKR), six AKR lysine producers were derived from Brevibacterium flavum No. 15-8 with the CSL and PCR characters and isolated as mutants resistant to S-(2-aminoethyl)-L-cysteine plus threonine on the medium containing acetate plus pyruvate as carbon sources. These mutants produced more than 40 g/1 of lysine as its HC1 salt in the medium containing 10% glucose. In particular, strain No. 664-7 with normally active and completely feedback-resistant AK produced 45 g/1 of lysine, whereas an AKR lysine producer, FA1-30, derived directly from wild strain No. 2247 produced only 20 g/1 at maximum. A homoserine dehydrogenase-defective (HD-) mutant, H-3-4, with the CSL and PCR characters also showed higher lysine productivity, 41 g/1, than an HD- mutant, H1013, which was derived directly from the wild strain and produced 35 g/1 of lysine. From the above results, it was concluded that the CSL and PCR characters were effective for enhancement of the lysine productivities of both AKR and HD- type producers.