ISOLATION OF AN L-METHIONINE-ENRICHED MUTANT OF KLUYVEROMYCES-LACTIS GROWN ON WHEY PERMEATE

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, proto troph) which accumulated 6-9 mg/g dry cells of total L -methionine was selected as the parental strain for the breeding Of L-methionine-enri ched mutants. Since the strain was unusually resistant to DL-ethionine , 0.1% of the DL-ethionine-sensitive mutant m-8 was induced by UV irra diation from the parental strain. The L-methionine-enriched mutant M-8 1 was selected among the ethyl methanesulfonate-treated mutants resist ant to 2% DL-ethionine from strain m-8. Strain M-81 accumulated 14.2 m g/g dry cells of total L-methionine. After repeated subculture in the liquid culture, the L-methionine-accumulating ability of the mutant be came stable.