Abstract
Ethionine-resistant mutants derived from Corynebacterium glutamicum KY 9276 (Thr-) were found to accumulate L-methionine in culture media. One of the mutants, ER-107-4, which produced 250μg/ml of L-methionine was subjected to further mutagenesis to obtain better L-methionine producers. L-Methionine production increased stepwise by successive endowing such markers as selenomethionine, 1, 2, 4-triazole, trifluoromethionine and methionine hydroxamate resistance. Thus, a mutant multi-resistant to ethionine, selenomethionine and methionine hydroxamate, ESLMR-724, produced 2mg/ml of L-methionine in a medium containing 10% glucose.
Increase of L-methionine production was accompanied by increased levels and reduced repressibility of methionine-forming enzymes. The levels of methionine enzymes in ESLMR-724 increased to 2.5_??_4.2 fold of those in KY 9276. In addition, homoserine-O-trans-acetylase and cystathionine γ-synthase which were strongly repressed by L-methionine in KY 9276 were stimulated by exogenous L-methionine in ESLMR-724. Implications of these results were discussed in relation to the productivity of L-methionine and the regulation of L-methionine biosynthesis.
