The occurrence of killer character in yeasts of various genera

Species of 7 of the 28 yeast genera in the National Collection of Yeast Cultures exhibited killing activity againstSaccharomyces cerevisiae. The highest incidence of killer yeasts was found in the genusHansenula (12 of the 29 strains examined).Saccharomyces, the best represented genus in the Collection, showed a low incidence of killer activity and many of the killer strains are hybrids with a commonS. cerevisiae parent. The activities of culture filtrates of the 59 killer yeast isolated responded differently to pH and four types of response were recognised.