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Abstract
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/l of lysine as its HCl salt in the medium containing 10% glucose. In particular, strain No. 664-7 with normally active and completely feedback-resistant AK produced 45 g/l of lysine, whereas an AKR lysine producer, FAl-30, derived directly from wild strain No. 2247 produced only 20 g/l at maximum.
A homoserine dehydrogenase-defective (HD−) mutant, H-3-4, with the CSL and PCR characters also showed higher lysine productivity, 41 g/l, than an HD− mutant, H1013, which was derived directly from the wild strain and produced 35 g/l 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.