21-4 THE YEAST CELL 



HYBRIDS BETWEEN YEASTS SUPPOSEDLY DIFFERENT 

 IN VITAMIN-SYNTHESIZING ABILITY 



The members of this pedigree were characterized (Lindegren 

 and Lindegren, 1945) as "vitamin-synthesizers" and "vitamin-non- 

 synthesizers'." The distinction between ability and inability to syn- 

 thesize was made by Burkholder's method with his medium. This 

 procedure defines readings taken at 72 hours as diagnostic. We 

 have since discovered that this method does not give conclusive 

 results, for if growth were allowed to continue, the supposedly non- 

 synthesizing yeasts will eventually begin to grow and will finally, 

 in most cases, attain a level equal to that of the so-called synthe- 

 sizers. However, at the end of 72 hours a 10 or 20-fold difference 

 in growth often exists as indicated by reading the turbidity with a 

 Klett Photoelectric Colorimeter. Haploids of S. carlsbergensis 

 were characterized as biotin+, pantothenate +, and pyridoxine -; 

 haploids of S. cerevisiae were characterized as biotin -, panto- 

 thenate -, and pyridoxine +, according to Burkholder's technique. 



Table 21-2 shows the Klett readings obtained after 72 hours 

 by Burkholder's technique of these different cultures. It appears 

 that culture No. 4 is a non-synthesizer of pantothenate, while No. 

 7 is a synthesizer. A hybrid between No. 4 and No. 7 (culture No. 

 10) appears capable of synthesizing pantothenate, but the four hap- 

 loid progeny, Nos. 20, 21, 22, 23 do not reveal regular segrega- 

 tion for this character. It was subsequently discovered that none 

 of these cultures was a nonsynthesizer and that the data appearing 

 in Table 21-2 do not give an adequate picture of the synthetic abili- 

 ty of the organisms. The inadequacy of this characterization will 

 be dealt with in detail below. 



VITAMIN-SYNTHESIZING ABILITY OF SUPPOSEDLY 

 DEFICIENT YEASTS IN A NATURAL MEDIUM 



Dr. F. W. Tanner, Jr. (unpublished) grew various members of 

 the pedigree shown in Table 20-2 (Chapter 20) in a natural medium 

 containing molasses and corn-steep liquor for 72 hours. When the 

 yeast and the medium were assayed it was found that under these 

 conditions all the cultures synthesized similar amounts of the dif- 

 ferent vitamins. Apparently the cultures were not clearly differ- 

 entiated by ability and inability to synthesize the vitamins, but were 

 all capable of synthesis under certain conditions. 



CONTINUOUS OBSERVATION OF GROWTH 



Our present technique, an example of which has been presented 

 in fig. 21-1, requires a much longer observation period. Many of 

 the same cultures were reinvestigated and were sometimes ob- 

 served for as long as a month, readings being made over the entire 



