Formation of intergeneric hybrids of yeast by protoplast fusion of Yarrowia and Kluyveromyces species.

Prototrophic hybrids have been obtained by the fusion of auxotrophic haploid strains of the two yeasts Yarrowia (Saccharomycopsis) lipolytica and Kluyveromyces lactis. The hybrid fusants had a colonial morphology intermediate between that of the two parent strains, were uninucleate, and contained an approximately diploid amount of DNA per cell. The growth rates of all the fusants on a minimal glucose medium were slower than those of the two parents. Two of the fusants studied could utilise a novel range of carbon sources.All of these data suggested that the hybrids contained a diploid nucleus formed by the fusion of the two haploid parental nuclei. However, analytical CsCl density gradient centrifugation demonstrated that the nuclear DNA of the fusants was derived almost entirely from the Y. lipolytica parent. Moreover, an examination of the protein constitution of the fusants by two-dimensional gel electrophoresis showed that their protein patterns were indistinguishable from that of Y. lipolytica. Two possible mechanisms for the formation of a diploid nucleus containing DNA derived almost entirely from one of the haploid parents are discussed.