68 PHYSIOLOGY OF THE FUNGI 



THE ESSENTIAL MACRO ELEMENTS 



Potassium. This element is essential for all organisms, so far as is 

 known. There is an immense amount of information on the specific 

 effects of potassium on green plants and animals, l)ut such data are not 

 common for the fungi. The quantitative relation between the amount of 

 potassium in the medium and the weight of mycelium produced by 

 Aspergillus niger was studied by Steinberg (1946). This work was done 

 with extraordinary care using a highly purified optimal medium (except 

 potassium). The optimum amount of potassium w-as 150 mg. per liter. 

 The relative amounts of mycelium formed increased as the potassium 

 content of the medium decreased. The fungus produced almost three 

 times as much mycelium per milligram of potassium when 15 instead of 

 150 mg. per liter were used. Jarvis and Johnson (1950) have reported 

 that Penicillium chrysogenum Q176 requires 40 mg. of potassium and 8 

 mg. of magnesium per liter of medium for optimum growth. 



The physiological effects of potassium on fungi have been studied but 

 little. The enzymes in yeast maceration juice which ferment glucose are 

 activated by either potassium or ammonium ions (Muntz, 1947). Mol- 

 liard (1920) noted that a low potassium content of the medium resulted in 

 increased synthesis of oxalic acid by A. mger. The chemical composition 

 of A. niger mycelium varies, depending upon the amount of potassium in 

 the medium (Rippel and Behr, 1934). 



The problem of biological substitution arose early in the study of fungus 

 nutrition. Biological substitution means that one element can replace 

 another, in whole or in part. The possibility of biological substitution 

 was investigated by Steinberg (1946) using A. niger as the test fungus. 

 This investigation was made to determine whether the alkali metals 

 (lithium, sodium, rubidium, or cesium) could replace potassium, and 

 whether the alkaline-earth metals (calcium, beryllium, strontium, or 

 barium) could replace magnesium. Under these conditions sodium and 

 beryllium gave increased yield of mycelium in media containing sub- 

 optimal amounts of potassium and magnesium. These effects are 

 illustrated in Table 9. 



Some increases in weight of mycelium were noted under certain con- 

 ditions with some of the other metallic ions tested, but the effects of 

 these elements were ascribed to ion antagonism. 



Studies of biological substitution require great care and a detailed and 

 extensive knowledge of the composition of the media and of the behavior 

 of the fungus under the experimental conditions used. 



Magnesium. This element is one of the alkaline-earth group. It is 

 essential for green plants and animals as well as for fungi and bacteria. 

 Aspergillus niger has been more carefully investigated with respect to the 



