202 PHYSIOLOGY OF THE FUNGI 



In so far as we are aware, no filamentous fungus isolated from nature 

 has been shown to be deficient for p-aminobenzoic acid. Tatum and 

 Beadle (1942) described a mutant of Neurospora which was unable to 

 synthesize this vitamin. Wyss et at. (1944) found that the availability 

 of p-aminobenzoic acid to the deficient mutant of Neurospora crassa was 

 a function of the pH of the medium (see Fig. 41). 



Mode of action. The functions of p-aminobenzoic acid are unknown. 

 We may assume, on the basis of the behavior of other vitamins, that it 

 functions as a coenzyme, or as a part of a coenzyme. Recent work 

 indicates that p-aminobenzoic acid is a constituent part of folic acid. 



RIBOFLAVIN 

 The structure of riboflavin is given below: 



CH2OH 



I 

 HC— OH 



I 

 HC— OH 



I 

 HC— OH 



CH2 



I 



N N 



\c^ \c=o 



N C 



s 



Riboflavin 



Many bacteria, especially species of Lactobacillus are unable to synthe- 

 size riboflavin (Peterson and Peterson, 1945). So far as we are able to 

 determine, none of the fungi isolated from nature have been found to be 

 deficient for riboflavin. This vitamin is synthesized by the fungi. 

 Mitchell and Houlahan (1946) described a mutant of Neurospora which 

 required the addition of riboflavin to the medium for growth at tempera- 

 tures above 28°C. Between 15 and 25°C. the growth rate of the mutant 

 without added riboflavin was equal to that of the wild type. The rate 

 of growth decreased rapidly as the temperature increased from 25 to 



28°C. 



SUMMARY 



It is assumed that all living organisms require a number of vitamins, or 

 growth factors, for normal growth, reproduction, and other vital proc- 

 esses. However, organisms differ widely in their synthetic capacities 

 for the various vitamins. Some fungi are self-sufficient with respect to 

 vitamins, being able to synthesize their vitamins from pure chemicals 

 of a synthetic medium. Others lack the ability to synthesize sufficient 



