Characterization of the Saccharomyces cerevisae Y500-4L killer toxin

The strain Saccharomyces cerevisiae Y500-4L, selected from the must of alcohol producing plants, liberates a toxin which is lethal to the commercial yeast produced by Fleischmann Royal Nabisco and other strains of yeast. This toxin was characterized, and the maximum production was obtained after 24 hours of incubation at 25oC in YEPD medium. The maximum activity was achieved between pH 4.1 and 4.5 and between 22 and 25oC and maximum stability in the pH range 3.8 to 4.5 at -10oC. The killer toxin was inactivated by heating at 40oC for 1 hour at pH 4.1. After concentration by ultrafiltration of culture supernatants and purification by gel filtration chromatography, the molecular weight of the purified toxin was estimated by SDS-PAGE to be about 18-20 kDa.