Isolation of an l-methionine-enriched mutant of Kluyveromyces lactis grown on whey permeate

Abstract Nine strains of lactose-utilizing Kluyveromyces sp. were screened for the production of l -methionine-enriched cells in shake cultures using whey permeate as the fermentation medium. K. lactis IFO 1267 (a, prototroph) which accumulated 6·9 mg/g dry cells of total l -methionine was selected as the parental strain for the breeding of l -methionine-enriched mutants. Since the strain was unusually resistant to dl -ethionine, 0·1% of the dl -ethionine-sensitive mutant m-8 was induced by UV irradiation from the parental strain. The l -methionine-enriched mutant M-81 was selected among the ethyl methanesulfonate-treated mutants resistant to 2% dl -ethionine from strain m-8. Strain M-81 accumulated 14·2 mg/g dry cells of total l -methionine. After repeated subculture in the liquid culture, the l -methionine-accumulating ability of the mutant became stable.