VITAMIN-SYNTHESIZING DEFICIENCIES 



21-7 



fig. 21-2 were obtained by taking readings at various times. At 

 50 hours there appears to be a straight line relation between the 

 amount of added vitamin and the amount of growth over a consid- 

 erable portion of the curve. 



THE EFFECT OF MULTIPLE DEFICIENCIES 

 OF THE B VITAMINS 



A haploid culture of S. cerevisiae which grew well on agar 

 containing Hutner's synthetic medium with the vitamins bio tin, 

 inositol, thiamin, and pantothenate, but which was unable to grow 

 on the same agar medium lacking all these vitamins, was tested 

 on agar containing various combinations of vitamins. Pour plates 

 following Lederberg and Tatum's (1946) technique were made. In 

 this technique a layer of sterile agar is poured in the bottom of 

 the petri dish. Then a layer of agar seeded with 500 ceUs is poured 

 on top, and a third layer of sterile agar on top of the second. This 

 technique prevents colonies at the top and bottom of the agar from 

 growing diffusely over and under the agar. A penicillin assay cup 

 placed in the center of each plate was filled with a solution con- 

 taining the combination of vitamins. 



Colonies were counted and a number of methods of scoring were 

 tested, but simple + and - scoring is probably the most informa- 

 tive. The following tabulation gives the results: 



The addition of inositol is apparently not very helpful in this 

 concentration (10,000 >^ per liter) when biotin, thiamin and pantothen- 

 ate were also present for there was more growth when it was ab- 

 sent than when it was present. Actually there were fewer colonies 

 when it was absent, but those which grew did much better. However, 

 the culture supplied pantothenate alone grew less well than that sup- 



