184 PHYSIOLOGY OF THE FUNGJ 



Neurospora crassa deficient for this vitamin was found to be influenced 

 by the pH of the medium (Wyss et al, 1944) (Fig. 41). 



The abiHty of a mutant of Neurospora sitophila to synthesize pyridoxine 

 was shown to be dependent not only on the pH of the medium but also 

 on the source of nitrogen (Stokes et al., 1943). When nitrate, amino, 

 amide, or certain other nitrogen compounds served as the nitrogen source, 

 no growth occurred without the addition of pyridoxine. However, in 

 the presence of ammonium salts, growth occurred at an initial pH range 

 of 5.6 to 7.3, without added pyridoxine. In this pH range, free ammonia 

 is formed. In the absence of free ammonia, the pyridoxine synthesized 

 is unavailable to this mutant (Strauss, 1951). 



According to Fromageot and Tschang (1938), the red yeast, Rhodotorula 

 sanniei, requires thiamine when the carbon source is glucose, but when 

 redistilled glycerol replaces glucose, thiamine is not needed. It is inter- 

 esting to speculate whether this fungus is better able to synthesize thia- 

 mine in a glycerol medium or whether much less thiamine is required to 

 metabolize glycerol than glucose. 



The concentration of the micro essential elements has also been shown 

 to influence the synthesis of vitamins by microorganisms (see Chap. 13 

 for specific information). 



INHIBITORY EFFECTS OF VITAMINS 



In certain cases vitamins may have an inhibitory effect on growth, 

 particularly when present in excessive dosages. The interrelated effects 

 of temperature and amount of inositol were described (Barnett and Lilly, 

 1948) for Sclerotinia camelliae. At a temperature below 26°C. the partial 

 deficiency was overcome by adding 5 mg. inositol to the medium. Above 

 26°C. the fungus was highly sensitive to small changes in temperature 

 and in amounts of inositol in the medium (Fig. 42). The same amount 

 of inositol which stimulated grow^th at or below 26°C. was strongly inhibi- 

 tory at 27°C. Increased amounts of inositol caused greater inhibition 

 of growth. Since the maximum temperature for growth is slightly above 

 27°C., it is believed that, as the temperature approaches this point, the 

 fungus becomes highly sensitive to the increased amounts of inositol in 

 the medium. 



Some vitamins are known to have a depressing effect on growth of 

 certain fungi not deficient for these particular vitamins. For example, 

 Fig. 36 shows that Lambertella pruni produces more dry weight in the 

 presence of both thiamine and biotin than when inositol and pyridoxine 

 are also added to the medium. Similarly, it is reported (Elliott, 1949) 

 that, for a self-sufficient isolate of Fusarium avenaceum, both the rate of 

 growth and maximum amount of mycelium were greater in vitamin-free 

 medium than when vitamins were added. The presence of thiamine also 



