174 I'HYSIOLOGY OF THE FUNGI 



vitamins, meet all the requirements for normal growth and development 

 of the fungus under study. The effect of one deficient fungus on another 

 is shown in Fig. 30. 



Methods of detecting vitamin deficiencies. Tests for vitamin deficiencies 

 of fungi are not difficult to perform, but they do require clean glassware 

 and careful preparation of media. It is convenient to conduct pre- 

 liminary experiments using only the four vitamins (thiamine, biotin, 

 inositol, pyridoxine) for which fungi are most frequently deficient. A 

 greater number of vitamins may be included in subsequent tests if a 

 fungus does not grow well on any of the media first used. Either agar 

 or liquid media may be used, and the visual measure of growth is satis- 

 factory for the screening tests. A simple and convenient method for 

 preliminary tests for deficiencies in filamentous fungi isolated from nature 

 is by the use of agar media in test tubes, as shown in Fig. 31. Slight 

 growth on agar media without added vitamins may be due to impurities 

 in the medium. A high percentage of the deficiencies will be detected 

 by this method, since deficiencies for only one or two vitamins are com- 

 mon among the filamentous fungi. After the deficiencies have been 

 identified by preliminary experiments, it is then highly desirable to grow 

 a fungus in liquid media, so that the mycelium may be harvested and 

 dry weights determined (see Suggested Laboratory Exercises for direc- 

 tions). The casein hydrolysate-glucose medium, given in Chap. 10, has 

 proved quite satisfactory for accurate vitamin studies. From the dry 

 weights of cultures determined at intervals throughout the growth period 

 of a fungus, growth curves may be plotted. Such curves are necessary 

 for accurate interpretations of the effects of vitamins in the medium. 



A somewhat different method is used by Burkholder (1943) for defi- 

 ciency studies of yeasts, where deficiencies for more than two vitamins 

 are common. This method is illustrated in Fig. 32. A deficiency is 

 detected by the inability to grow in a medium which is complete except 

 for one vitamin. Failure to grow in a medium indicates a deficiency for 

 the vitamin omitted. Liquid media in test tubes are used for yeasts, 

 so that growth may be measured by photoelectric colorimeter. 



Total and partial deficiencies. Phycomyces hlakesleeanus was widely 

 used in the early studies of thiamine. Schopfer established the deficiency 

 for thiamine and determined the requirements for this vitamin. Schopfer's 

 graph (Fig. 33) shows the growth curves of the fungus over a period when 

 different amounts of thiamine were added to the basal culture medium 

 (Schopfer, 1943). The fact that no growth occurred in the medium 

 lacking thiamine is not shown by the graph. An increase in both the 

 rate and the total amount of growth, as the amount of thiamine is 

 increased, is clearly shown between the fifth and seventh days. Thus 

 P. hlakeslseanus is unable to synthesize thiamine, which it must obtain 



