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 25§C in YEPD medium. The maximum activity was achieved between pH 4.1 and 4.5 and between 22 and 25§C and maximum stability in the pH range 3.8 to 4.5 at -10§C. The killer toxin was inactivated by heating at 40§C 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.

Killer toxin of Saccharomyces cerevisae Y500-4L active against fleischmann and Itaiquara commercial brands of yeast

The strain Saccharomyces cerevisae Y500-4L, previously selected from the must of alcohol producing plants and showing high fermentative and killer capacities, was characterized according to the interactions between the yeasts and examined for curing and detection of dsRNA plasmids, which code for the killer character. The killer yeast S. cerevisae Y500-4L showed considerable killer activity against the Fleischmann and Itaiquara commercial brands of yeast and also against the standard killer yeast K2 (S. diastaticus NCYC 713), K4 (Candida glabrata NCYC 388) and K11(Torulopsis glabrata ATCC 15126). However S. cerevisae Y500-4L showed sensitivity to the killer toxin produced by the standard killer yeasts K8 (Hansenula anomala NCYC 435), K9(Hansenula mrakii NCYC500), K10(Kluyveromyces drosophilarum NCYC575) and K11(Torulopsis glabrata ATCC 15126). No M-dsRNA plasmid was detected in the S. cerevisae Y500-4L strain and these results suggest that the genetic basis for toxin production is encoded by chromosoma DNA. The strain S.cerevisae Y500-4L was more resistant to the loss of the phenotype killer with cycloheximide and incubation at elevated temperatures (40§C) than the standard killer yeast S. cerevisae K1.