Chapter 21 



THE EFFECT OF THE MEDIUM ON APPARENT VITAMIN-SYNTHESIZING 



DEFICIENCIES 



The importance of vitamin deficiencies in the diagnosis of gen- 

 etically different yeasts led us (Lindegren & Raut) to study a varie- 

 ty of synthetic media in an attempt to find the one most suitable for 

 our purposes. Beadle and Tatum's work on biochemical mutants 

 of Neurospora has resulted in wide acceptance of the view that it 

 is relatively easy to distinguish strains genetically capable from 

 those genetically incapable of vitamin synthesis. They discovered 

 many mutants apparently incapable of performing specific syn- 

 theses. Skoog and Lindegren (Chapter 16) showed that the ability 

 or inability of one culture to ferment glucose depended on the sub- 

 strate. Lindegren and Raut (1947) showed that different synthetic 

 media so affect the growth of organisms that conclusive demon- 

 stration of specific deficiency requires a much more critical study 

 of the environment than has hitherto been achieved. The fact that 

 one culture may grow and another may fail to grow in a medium 

 deficient of a specific vitamin in a synthetic medium has proved 

 very useful for genetical diagnosis but it does not necessarily 

 give reliable information concerning the synthetic ability of 

 the organism under other conditions. Without critical testing it is 

 difficult to say whether a given deficiency is absolute. Lindegren and 

 and Raut found that the standard test of ability to grow in the pres- 

 ence and inability to grow in the absence of a given vitamin in syn- 

 thetic medium is inadequate and that the criterion of equal incre- 

 ments of growth for equal additions of the vitamin may give an 

 ambiguous answer. 



A COMPARISON OF TWO SYNTHETIC MEDIA 



Table 21-1 shows the formulas of the synthetic media used by 

 Burkholder (1943), Hutner (unpublished), Wickerham (1946), and 

 Beadle and Tatum (1945). Many experiments have shown that Hut- 

 ner' s medium is a very different substrate for yeast growth than 

 Burkholder' s. This was clearly revealed by growing cultures No. 

 3 and No. 10 (Table 20-2) on two batches of each medium, one to 

 which no pantothenate was added and the other containing 507 of 

 pantothenate per liter (fig. 21-1). Culture No. 3 does not begin to 

 grow in Burkholder' s medium without added pantothenate until after 

 200 hours, but growth is completed in Burkholder' s medium con- 



21-1 



