328 VITAMIN REQUIREMENTS 



e.g., in Ascoidea rubescens (67), Dlastocladia pringsheimii (35), Cera- 

 tostomella microspora (216), and Trichophyton discoides strains (152, 

 222). 



Inhibitory effects of vitamins have been reported occasionally. Thi- 

 amine depresses the growth of Fusarium spp. (55, 285, 304) and Rhizo- 

 pns spp. (142, 210, 238); biotin may reduce growth or enzyme forma- 

 tion (11, 228, 253, 316). Large amounts of pyridoxine do not, how- 

 ever, appear to depress growth (67). The mechanism of inhibition is 

 not always known; thiamine inhibition has been attributed to ammonia 

 accumulation in Trichoderma viride (16) and to ethanol accumulation 

 in Rhizopus suinus (247). 



3. THE METABOLISM OF VITAMINS 



Apart from their catalytic role in metabolism, vitamins are them- 

 selves metabolites and are both synthesized and destroyed in the cell. 

 More or less comprehensive surveys of vitamin synthesis have been 

 reported for Penicillium spp. (37, 100, 178, 274), and a good deal of 

 information is available on vitamin synthesis by Aspergillus spp. (37, 

 60, 85, 127, 181, 233, 262) and Streptomyces spp. (47, 100, 103, 105, 106, 

 151). The vitamin content of microorganisms is reviewed comprehen- 

 sively by Van Lanen and Tanner (288). As mentioned earlier, we may 

 assume that a fungus which does not require one of the water-soluble 

 vitamins known to be required by other fungi is able to synthesize it. 



Vitamins synthesized by a fungus usually appear in the medium and 

 are detected there by bioassay; however, in Penicillium chrysogenum 

 the greater part of the thiamine, riboflavin, and nicotinic acid pro- 

 duced remains in the cell (100), and the same is true of thiamine in 

 some other fungi (133) and of riboflavin in Aspergillus niger (60). 



The destruction of vitamins by fungi has been less thoroughly stud- 

 ied. Phycomyces blakesleeanus and Sclerotium rolfsii destroy the thia- 

 zole moiety of thiamine (21, 120). A mutant of Neurospora crassa 

 destroys pyridoxine, and this destruction is inhibited competitively by 

 thiamine (96). 



4. FUNGI IN THE BIOASSAY OF VITAMINS 



Analysis for individual vitamins by a biological assay is often, for 

 one reason or another, superior to chemical analysis. This is especially 

 true if a biologically active vitamin exists in more than one chemical 

 form. Bioassays employing filamentous fungi have been devised for 



