ESSENTIAL METALLIC ELEMENTS 



69 



effects of magnesium than any other fungus. Within certain limits of 

 concentration, the amount of growth of A. niger is proportional to the 

 concentration of magnesium in the medium. This has been demon- 

 strated by Steinberg (1946), Lavollay and Laborey (1938), and others. 

 The application of this principle to the microbiological assay of magne- 

 sium is discussed in Chap. 10. Penicillium glaucum, Botrytis cinerea, and 

 Alternaria tenuis failed to grow in the absence of magnesium (Rabinovitz- 

 Sereni, 1933). Excess magnesium was not harmful to these three fungi 

 until the concentration of magnesium sulfate in the medium reached about 

 40 per cent. These three species were able to grow in the presence of 

 traces of magnesium but sporulated only when the concentration of mag- 

 nesium was increased. Respiration also increased as the magnesium con- 

 tent of the medium increased. Failure to sporulate unless sufficient 

 magnesium is available is probably to be expected with many fungi. 



Table 9. The Effect of 50 Milligrams of Sodium on the Amount of Mycelium 



Produced by Aspergillus niger in an Optimal Medium Containing Twice 



THE Normal Amounts of INIicro Elements when the Concentration 



OF Potassium Was Varied 

 (Steinberg, Avi. Jour. Botany 33, 1946.) 



Most of the magnesium in the mycelium of Aspergillus niger can be 

 extracted by means of dilute acids (Ripple and Behr, 1930), which indi- 

 cates that this element does not form stable organic compounds. A rela- 

 tion between the optimum concentrations of magnesium and phosphorus 

 for A. niger was discovered by Laborey et at. (1941). Some 36 phosphate 

 ions are required for every ion of magnesium. Many enzyme sj^stems are 

 activated by magnesium ion, and in view of the role of phosphate in 

 enzymatic transformations it is not surprising that there should be a close 

 relation between magnesium and phosphate concentrations. Magnesium 

 is involved in many of the enzymatic reactions involved in fermentation 



