10-7 THE YEAST CELL 



2 Mating of haplophase with tested strains. 



3 Observation of positive matings and transfer to pre- 

 sporulation medium. 



5 Transfer to gypsum. 



6 Isolation of ascospores. 



HYBRIDIZATION PROCEDURES FOR THE 

 PRACTICAL YEAST WORKER 



In the genetical analysis of yeast, we rely exclusively on single 

 ascospore cultures isolated from the asci with the micromanipula- 

 tor. However, for the applied scientist in the industrial laboratory, 

 this refinement is not necessary. One can obtain an enormous vari- 

 ety of different segregants from a diploid culture by growing it on 

 presporulation medium and transferring it to gypsum until an abun- 

 dance of spores are obtained. The spores are more heat resistant 

 than the vegetative cells. If they are suspended in water and held 

 at 58°C. for from 2 to 4 minutes, most of the vegetative cells will 

 be killed and only the spores will survive. The suspension is cooled 

 quickly and plated on solid medium. The large variety of small, 

 rough colonies which appear are isolated and tested for their char- 

 acteristics. This should be an effective method for selecting new 

 varieties of beer or wine yeasts with different flavors or bouquets. 

 One could either start with a proven yeast of known commercial 

 value or could begin with any sporulating yeast. 



Interest is usually centered on the new hybrids, but the haploid 

 cells which are produced by breaking down a diploid also have dis- 

 tinct possibilities, and many of them may be found to be valuable in 

 industry. Generally speaking, wine and baking yeasts are diploid, 

 and beer yeasts are haploid. 



HYBRIDIZATION IN UNFAVORABLE MEDIA 



Hybrids capable of growing in an unfavorable medium such as 

 paper mill sulphite liquor could probably be obtained by mixing 

 masses of spores directly in the sulphite liquor itself and allowing 

 the copulation of those capable of survival to occur directly in this 

 unfavorable medium. Millions of copulations could occur, but only 

 the hybrids which are able to grow in sulphite liquor conditions 

 should survive. 



The possibility exists of improving the yield of alcohol from beet 

 molasses by hybridization. Much industrial alcohol is produced 

 from beet molasses which contains considerable amounts of raffin- 

 ose. S. cerevisiae is incapable of completely fermenting raffinose, 

 so all the potential alcohol is not realized. S. carlsbergensis, how- 

 ever, ferments melibiose and is distinguished from S. cerevisiae 

 by this characteristic. One could produce a raffinose -fermenter 



