OCCURRENCE OF VITAMIN DEFICIENCIES 345 



growth factor for Arthrobacter terregens, although not identical with 

 either coprogen or ferrichrome, is evidently related to them; thus both 

 ferrichrome and coprogen are active for A. terregens (33, 148, 149) and 

 Pilobohis spp. (177a). 



Sterols are produced by many fungi (Chapter 6); so far only Laby- 

 rinthula vitellina — of uncertain taxonomic position but possibly a 

 myxomycete — has been shown to have a steroid requirement (293, 

 294). It has been claimed (4) that anaerobic growth of Saccharomyces 

 cerevisiae in a synthetic medium is dependent on ergosterol or other 

 sterols. 



Many still unknown factors have been postulated for particular 

 fungi. Mycorrhizal fungi are stimulated by materials from plant roots 

 and forest litter, and the effect cannot be traced to known vitamins or 

 amino acids (166, 167, 168). The myxomycetes apparently require for 

 their growth one or more bacterial proteins (112, 272), not vitamins as 

 we have here used the term. As mentioned earlier, growth-stimulating 

 effects of crude natural materials do not necessarily implicate a vita- 

 min. 



Other vitamins — ascorbic acid and vitamins A, D, and E — required 

 by animals do not appear to play any essential role in the fungi (28, 

 86); ascorbic acid may, however, affect growth through its effect on 

 the oxidation-reduction potential. 



17. THE OCCURRENCE OF VITAMIN 

 DEFICIENCIES IN THE FUNGI 



It will be clear from the preceding discussion of individual vitamins 

 that some deficiencies occur frequently, others more rarely. The vita- 

 min most often required by fungi from nature is thiamine; usually the 

 deficiency is for the pyrimidine moiety, and we have noted only a few 

 instances of a deficiency for thiazole (Table 1). Biotin is very often 

 required, and deficiencies in pyridoxine or its derivatives are fre- 

 quently encountered. Pantothenic acid and nicotinic acid require- 

 ments are rare in nature, and we have at present only single reports of 

 requirements for riboflavin and p-aminobenzoic acid among filamen- 

 tous fungi. 



This lop-sided distribution of vitamin requirements demands an 

 attempt at an explanation. Assuming that spontaneous mutations in 

 nature are like those induced by mutagens, forms deficient for ribo- 

 flavin of p-aminobenzoic acid must arise from time to time. Their 

 failure to survive — if it is real and not an artifact of screening methods 

 — may result from either or both of two conditions, viz.: 



