308 INORGANIC NUTRITION AND METABOLISM 



(Chapter 10), the heme pigment of Neurospora crassa and Penicillium 

 notatum (103), and the pigment pulcherrimin of Torulopsis pulcher- 

 rirna (40, 107). Preparations of aspergillin, the spore pigment of the 

 black Aspergillus spp., contain 0.26 per cent iron (191). 



Aspergillus niger releases into the medium relatively large amounts 

 of a substance or substances, not citrate, which bind ferric iron (67); 

 the possible ecological value is obvious (158). 



A few of the metabolic effects of iron may be ascribed to direct use 

 of the element; increases in catalase (257) and in pulcherrimin (201) 

 are of this type. Other metabolic effects of iron concentration, e.g., 

 on organic acid formation (45, 57, 184, 185), on penicillin production 

 (108), on the balance of gentisyl alcohol and patulin (Chapter 6), and 

 on sporulation and spore color (118, 211), are known, but the opera- 

 tive mechanisms are obscure. Only one persistent pattern may be 

 discerned: the maximum formation of certain metabolites — strepto- 

 mycin (37), penicillin (100), and citrinin (9) — requires more iron than 

 is needed for maximum growth. The data on organic acid accumula- 

 tion as affected by iron are too much in conflict to allow any general- 

 ization (36, 57, 183); as discussed elsewhere (Chapter 6), it is most 

 probable that deficiencies or excesses of iron and other inorganic con- 

 stituents act positively on acid formation, when they do, by virtue of 

 interference with normal metabolism. 



6. ZINC 



The essentiality of zinc for growth in fungi has been confirmed 

 many times (35). Reported optima, determined, of course, under 

 different conditions, range from 0.001 to 0.5 ppm; probably 0.5-1.0 

 ppm is adequate in routine work (5, 36, 37, 76, 241). Higher con- 

 centrations of zinc may be toxic, especially at high pH (117, 174); the 

 toxicity is reversed by certain other divalent ions (130). Inhibition of 

 sporulation by zinc is reversed by iron (174, 200). High levels of zinc 

 induce genetically stable variation in Fusarium sp. (46) and Helmin- 

 thosporium sativum (145). Partial replacement of zinc by cadmium 

 (101) probably results from contamination of the cadmium with zinc 

 (227). 



The metabolic effects of zinc deficiency almost defy enumeration; 

 several reviews consider them in detail (35, 57, 58, 183). The major 

 types of metabolic effects are: 



1. Accumulation of organic acids at levels of zinc too low for normal 

 growth. Associated with this is a positive effect of the metal on the 



