Effect of Pyruvate Kinase Deficiency on L-Lysine Productivities of Mutants with Feedback-resistant Aspartokinases

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The cultural conditions were investigated for a Brevibacteriumflavum mutant, No. 2-190, with a low level of citrate synthase (CS) and with feedback-resistant phosphoenoipyruvate (PEP) carboxylase and aspartokinase (AK). The productivity was increased from 28 to 38 g/l (as the HCl salt) with a medium containing 10% glucose. From this strain, pyruvate kinase (PK)-defective mutants were derived and selected as to the inability to grow on ribose. Among them, strain KL-18 showed higher lysine productivity than the parent under all cultural conditions tested, and produced 43 g/l of lysine, at maximum. A lysine-producing mutant, No. 536-4, with a feedback-resistant AK was derived from PK-defective strain KH-21 which had low CS activity and a feedback-resistant PEP carboxylase. The mutant was isolated by a new selection method, that is, on the basis of resistance to α-amino-β-hydroxyvaleric acid, a threonine analogue plus lysine. In this strain, HD had been altered so as to become feedback-resistant at the same time, resulting in the byproduction of threonine and isoleucine. The total amount of these aspartate family amino acids was higher on molar basis than that of lysine produced by strain No. 2-190.