The regulation pattern of L-lysine biosynthesis has been investigated in protrophic revertant derived from an initially homoserine-auxotrophic strain of Coiynebacterium glutamicum and, additionally, in antimetabolite-resitant mutants. The influence of regulatory important amino acids of the aspartate family on growth and L-lysine biosynthesis and especially on the activity of aspartate kinase was studied. Furthermore the activity of homoserine dehydrogenase in dependence on the growth phase was estimated.
From a total number of ninety nine L-lysine forming, homoserine-prototrophic, and S-(2-aminoethyl)-L-cysteine-resistant (AEC) strains the best lysine producers were selected by an emerse cultivation assay as a preselection. Strain No. 132 forming 10 g .1-' lysine was selected for the derivation of a-amino+?hydroxyvaleric acid (AHV)-and lysine-resistant strains. From 121 double resistant mutants (hse'-", AEC, AHV') sixty two strains (= 51.2%) were isolated producing lysine. The best producer, strain 132-IV-37, reached 19.8 g . I-' after 8 optimization steps of the growth medium in comparison to 9.2 g . 1-' as the initial value. This higher potential for lysine synthesis in the mutant 132-IV-37 could be attributed to changed regulation of the homoserine dehydrogenase and aspartate kinase.
As was shown by the action of threonine or threonine i -lysine on the activity of aspartate kinase, a general desensibilization of this key enzyme exists in the mutant strain 132-IV-37, but not in the AEC-resistant parent strain. In addition to isoleucine none of several amino acids tested showed any significant influence on the aspartate kinase. This agrees with the increased lysine formation by this strain in comparison to the parent strain 132.