Isolation and Properties ofα-Ketobutyrate-resistant Lysine-producing Mutants fromBrevibacterium flavum

Abstract

The growth of Brevihacterium flavum F Al-30, a L-Iysine-producing mutant strain with an aspartokinase desensitized to feedback inhibition, was almost completely inhibited by a:-ketobutyrate (a:KB) at concentrations more than 4 mg/ml. Aspartic acid hydroxamate (Asphx) did not inhibit the growth at a concentration up to 6 mg/ml, but slightly stimulated the a:KB inhibition. Mutants resistant to a:KB in the presence and absence of Asphx (type-I and -II, respectively) were derived and further selceted by their lysine productivity. The best producers among the type-I and -II mutants produced 41.9 and 29.4 g/liter of L-Iysine·HCI, 1.9-and 1.4-fold that by the parent, respectively. The type-II mutant was confirmed to be resistant to a:KB alone, but was still sensitive to a:KB in the presence of Asphx, similar to the parent. The type-I mutants were resistant to a:KB in the presence and absence of Asphx. Pyruvate dehydrogenase (PD) activity or both PD and citrate synthase (C8) activities significantly decreased in the type-II or -I mutants, respectively. The apparent Km of PD with respect to pyruvate and that of C8 with respect to oxaloacetate