304 



INORGANIC NUTRITION AND METABOLISM 



Element added, mg per liter 



Figure 2. The response of Cephalosporium salmosynnematum to potassium, mag- 

 nesium, phosphorus, and sulfur. Redrawn from Pisano et al. (187), by permission of 

 the Williams and Wilkins Company. 



3. SULFUR 



Media in common use incorporate excess sulfur as magnesium sul- 

 fate; at moderate carbohydrate concentrations the sulfur requirement 

 is about 0.0001-0.0006 M (13, 91, 228). 



Most fungi can supply all their needs for sulfur from inorganic sul- 

 fate, i.e., they reduce the sulfate and incorporate it into organic mole- 

 cules. The organic sulfur compounds known in fungi include amino 

 acids (cysteine, cystine, and methionine), vitamins (thiamine and 

 biotin), cyclic choline sulfate (Chapter 2), sulfur-containing anti- 

 biotics, e.g., penicillin and gliotoxin, and such miscellaneous com- 

 pounds as junipal (Chapter 6), thiourea (177), and methyl mercaptan 

 (Chapter 6). Sulfur incorporation into organic combinations is often 

 very large; whether or not sulfur is released on autolysis appears to be 

 determined by the species studied (84, 192, 197). 



The fungi which as isolated from nature are unable to utilize sul- 

 fate sulfur are all aquatic phycomycetes: most Saprolegniales and all 

 known members of the Blastocladiales (30, 31). Other phycomycetes — 

 Chytridiales, Leptomitales, Peronosporales, and the Zygomycetes — uti- 

 lize sulfate. Whether dependence on reduced sulfur is biochemically or 

 ecologically related to the lower oxygen requirement or to the fermen- 

 tative capacity of the Blastocladiales is still uncertain. Mutants re- 

 quiring reduced sulfur have been obtained from Neurospora crassa 



