New Killer Toxins of HalophilicHansenula anomala

Abstract

Two strains of killer yeasts, both identified as Hansenula anomala, were isolated from shoyu moromi. Both killer yeasts showed killer activity toward Zygosaccharomyces rouxii EA under high salt concentration conditions. The killer toxins produced by these strains were purified by ultrafiltration and ion-exchange chromatography followed by gel filtration. The molecular weights of the toxins were about 300 kd and both toxins were glycoproteins. The isoelectric point of the toxin, Kh-I, produced by one strain was pH 2.9 and that of the toxin, Kh-II, produced by the other strain was pH 3.6. The amino acid composition of Kh-I was different from that of Kh-II. Kh-II was more thermolabile than Kh-I. The killer activities of both toxins were not observed in the absence of NaCl in the medium but increased with increasing NaCl concentration. The killer spectra of Kh-I and Kh-II were different from those of the killer toxins known as K1-K11. The killer activities of these strains were not abolished by cycloheximide treatment and by cultivation at 37°C. No plasmid was detected in either killer yeast.