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 AKRlysine producers were derived from Brevibacteriumflavum No. 1 5-8 with the CSLand PCRcharacters and isolated as mutants resistant to 5-(2-aminoethyl)-L-cysteine plus threonine on the mediumcontaining acetate plus pyruvate as carbon sources.These mutants produced more than 40g/1 of lysine as its HC1salt in the medium containing 10%glucose.In particular, strain No. 664-7 with normally active and completely feedback-resistant AKproduced 45 g/1 of lysine, whereas an AKRlysine 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
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Yokota et al. (1988) studied this question.