Multi-analogue resistant mutants of Corynebacterium lilium were developed using UV and N-methyl-N,-nitro-nitrosoguanidine
(NTG) mutagenesis in order to overproduce methionine. Although the methionine yield at each stage of mutation by UV and NTG
mutagenesis were comparable, it was observed that the NTG mutants had higher cell growth and glucose utilization rates. From the parent NTG mutant C. lilium E 4 resistant to ethionine, the highest methionine producing strain C. lilium M-128 resistant to 3.5 mg m1 of ethionine, 3.0 mg m1 of norleucine, 3.8 mg m1 of methionine sulphoxide and 3.8 mg m1 of methionine methyl sulphoniumchloride was derived. When C. lilium M-128 was grown under optimised conditions, it produced 2.3 g1 of methionine
in a 15 l batch reactor. The maximum cell mass concentration obtained was 17 g1 dry cell weight resulting in a cell yield
coefficient of 0.34 g g1. The dissolved oxygen concentration was controlled at 40% saturation by cascade control of the airflow rate and agitation speed.