70 PHYSIOLOGY OF THE FUNGI 



(Sumner and Somers, 1947). It is equally likely that magnesium is 

 involved in aerobic oxidation of carbohydrate. Low concentrations of 

 magnesium in the medium led to increased synthesis of riboflavin by A. 

 niger (Lavollay and Laborey, 1938). 



One ion may affect the physiological action of another. This is called 

 ion antagonism. In nature and in the laboratory fungi come in contact 

 with compounds of both essential and nonessential elements. Many of 

 the nonessential elements are toxic, although toxicity is not limited to the 

 nonessential elements. Copper is an essential element, but it is toxic to 

 most fungi when the concentration exceeds certain limits (Chap. 12). 

 The toxic effect of an ion may be overcome by the presence of one or more 

 other ions in the medium. Gortner (1949) has reviewed this subject from 

 the standpoint of colloidal chemistry and suggests that the relative 

 concentrations of various metallic ions may regulate the process of 

 adsorption. 



As an example of ion antagonism Lohrmann (1940) described the toxic 

 action of mercuric chloride and boric acid on Aspergillus niger, A. flavus, 

 Mucor pusillus, Penicillium glaucum, Fusarium coeruleum, Cunning- 

 hamella elegans, Ahsidia cylindrospora, and Rhizopus nigricans. The 

 inhibition caused by either of these toxic compounds was overcome in 

 part by increasing the concentration of magnesium sulfate. Similarly, 

 the toxic effects of high concentrations of magnesium sulfate were over- 

 come by mercuric chloride. Either mercuric chloride or boric acid in 

 certain concentrations "stimulated" growth in the nutrient solution used. 

 This is not evidence that either boron or mercury is an essential element, 

 but it does show that the nutrient solution used was unbalanced. The 

 effect of sodium and calcium ions upon growth and respiration of A. niger 

 depended upon the ratio of these nonessential ions present in the medium. 

 A sodium-calcium ratio of 19 to 1 gave the highest rate of respiration, 

 while a ratio of 4 to 1 was most favorable for growth (Gustafson, 1919). 

 Aluminum inhibits the production of itaconic acid by A. terreus. This 

 inhibition is overcome by magnesium sulfate (Lockwood and Reeves, 

 1945). Nickerson (1946) found the inhibitory effects of zinc ion on the 

 rate of respiration of Epidermophyton floccosum to be reversed by calcium 

 or magnesium ions. 



The phenomenon of antagonism is not confined to ions. Organic 

 compounds present in media may modify the activity of ions, and organic 

 compounds may antagonize the physiological activity of other organic 

 compounds (Chap. 11). All these possibihties exist. Whether a given 

 ion or compound will be physiologically active depends upon the other 

 constituents of the medium and the metabolic compounds excreted by the 

 fungus under study. 



