A simple technique for obtaining mating types in heterothallic diploid yeasts, with special reference to their uses in the genus Hansenula.

A procedure has been devised by which large numbers of ascospore isolates may be obtained from yeasts without the use of a micromanipulator and auxiliary costly laboratory equipment or a need for the exacting skills which such tools require. The procedure is being continually applied in this laboratory to the genus Hansenula. Some of the species of this genus produce many ascospores, but so few are viable that isolation of mating types by micromanipulator is often impractical. Hence for genetical studies different experimental procedures are required. In this genus the ascus ruptures when it is mature and the liberated ascospores often agglutinate in large masses. This habit of early escapement from the asci also tends to thwart the usual tetrad analysis that starts with isolation of the four ascospores by micromanipulation. It is intended that the new procedure for isolating mating types and simple ancillary techniques for genetical analyses will be modified to whatever extent is necessary so that they may be applied to a genus like Saccharomyces where viability of ascospores is usually high and the ascus usually remains intact until the ascospores germinate. Various uses of the new procedure will be presented with examples taken from results obtained for the most part with diploid species of Hansenula. The principal procedure for the isolation of cultures derived from single ascospores is based on the fact that ascospores can withstand slightly more heat than vegetative cells. For most species of Hansenula, 57 or 58 C is employed.