18-3 THE YEAST CELL 



trolling the fermentation of galactose, maltose, and melibiose 

 occurred. 



VITAMIN DEFIQENCIES 



In addition to the ability to ferment different sugars, yeasts 

 are differentiated by their ability or inability to grow in defined 

 media lacking specific vitamins, amino acids, or other growth sub- 

 stances. Most of these nutritional characters are relative. A 

 haplophase culture which we designate as capable of growth in the 

 absence of pantothenate will produce full growth in the deficient 

 medium in about 36 hours, while the so-called non-synthesizer 

 may require 5 or 6 days to attain full growth. 



The mating of No. 588 by No. 15 produced a pedigree in which 

 some asci showed regular segregation of genes affecting the abili- 

 ty to grow in media lacking specific Vitamins. S. cerevisiae is 

 capable of rapid growth in a defined medium lacking pyridoxine, 

 while S. carlsbergensis is not. S. carlsbergensis can grow in the 

 absence of biotin, although S. cerevisiae cannot S. microellip- 

 soideus also requires biotin. S. microellipsoideus cannot grow in 

 the absence of inositol, which is not required by either S. carls- 

 bergensis or S. cerevisiae. The pedigree including the segregants 

 from the CIA by No. 35 hybrid did not regularly show 2:2 segre- 

 gations of factors controlling vitamin synthesis. However, the back- 

 cross of No. 588 x No. 15 produced some asci in which 2:2 segre- 

 gations of the ability and inability to grow in pantothenate deficient 

 medium occurred. The mating No. 1426 x No. 1428 produced a hy- 

 brid in which the genes controlling mating type, fermentation of 

 galactose and maltose, and the ability to grow in defined medium 

 lacking of the following nutrilites: pantothenate, paraminobenzoic 

 acid, thiamin, and pyridoxine were all segregated 2:2 in nearly 

 every ascus. Two to two segregation of genes affecting the syn- 

 thesis of biotin did not occur in the particular pedigree although 

 the stock was descended from clones differentiated in regard to 

 biotin. 



Haplophase No. 2236 was derived from S. cerevisiae (Mrak 93)l 

 A hybrid of No. 2236 x No. 2090 eventually produced No. 2660. 

 Haplophase No. 4 was treated by Dr. E. L. Tatum and Mr. S. E. 

 Reaume with nitrogen mustard gas and a mutant incapable of grow- 

 ing in the absence of methionine was obtained by them. This was 

 mated to No. 2660 and introduced methionine dependence into the 

 stock. A second mustard mutant of No. 4, adenine dependence was 

 produced by them and we introduced it into the stock by mating it 



