ISOLATION AND PROMINENT CHARACTERISTICS OF AN L-LYSINE HYPERPRODUCING STRAIN OF CORYNEBACTERIUM-GLUTAMICUM

A strain of Corynebacterium glutamicum was isolated that accumulated up to 44 g/l of L-lysine-HCl from 100 g/l of glucose x H2O in a simple mineral salts medium. This strain was obtained from the wild-type by two mutagenesis steps. In the first step the aminoethyl-cysteine-resistant strain MH20 was obtained and in the second step the Leu- derivative MH20-22B. Enzymatic analysis of the hyperproducer MH20-22B revealed that this strain has feedback-resistant aspartate kinase and is devoid of isopropylmalate dehydratase. In addition, this strain has an extraordinarily high-secretion rate of lysine (0.57 mmol/g dry weight and h), whereas strain, MH20 has a low secretion rate (0.19 mmol/g per hour), and both strains have comparable cytosolic lysine concentrations. This suggests that the secretory step is influenced in the hyperproducer. Applying gene-directed mutagenesis, the aspartate kinase gene of the isolated strain (coding for feedback-resistant enzyme) was replaced by the gene coding of feedback-sensitive wild-type enzyme. The resulting strain still secretes lysine, although in low amounts (less-than-or-equal-to 2 g/1). This is proof of the superior role of kinase regulation in metabolite flow and is indicative of unknown mutations, one of which is probably in the secretory system.