ESSENTIAL METALLIC ELEMENTS 79 



decreased, A. niger became more sensitive to micro-element deficiencies 

 in the medium. The favorable effect of adding biotin to the medium 

 when only a few spores were used as inoculum suggests an intimate con- 

 nection between micro-element nutrition and the synthesis of this vita- 

 min. Whether the decreased yield due to small inoculum was due to 

 other deficiencies or to a decreased rate of growth is not entirely clear, as 

 all harvests were made after 4 days. 



Manganese (Mn++) has been shown to be the natural activator of 

 yeast arginase. Other enzymes are activated by this element (Sumner 

 and Somers, 1947). In view of the small amounts of manganese required 

 by fungi, it may be assumed that manganese functions as a constituent of 

 various enzymes. 



Molybdenum. The study of the role of this element emphasizes the 

 similarity in certain physiological processes throughout the plant king- 

 dom. The most striking feature of this essential element is its role in 

 nitrogen metabolism. The utilization of nitrate nitrogen by green plants 

 and fungi and the fixation of atmospheric nitrogen by bacteria {Azotohac- 

 terchroococcum, Clostridium pasteimanum) is dependent upon molybdenum 

 (Bortels, 1930, 1936). 



Our knowledge of the effect of molybdenum on fungi is largely confined 

 to Aspergillus niger. Steinberg (1936, 1937) found that more molybde- 

 num was required by A. niger for maximum growth in media containing 

 nitrate nitrogen than in media with ammonium nitrogen. Steinberg 

 expressed the opinion that molybdenum is essential for A . niger even when 

 ammonium nitrogen is available. Additional studies on A. niger and 

 other organisms (Mulder, 1948) indicated that an increased need for 

 molybdenum is associated with nitrate utilization. It may be assumed 

 that the enzymatic reduction of nitrate is carried out by enzymes which 

 require molybdenum as an activator. 



In view of the important role of molj^bdenum in the utilization of 

 nitrate nitrogen, care should be used in comparing the value of different 

 nitrates. Unless sufficient molybdenum is present, misinterpretations 

 may result. Steinberg (1937) found the amount of molybdenum present 

 as an impurity in various nitrates to vary. One sample of calcium nitrate 

 contained enough molybdenum to support maximum growth of A. niger. 

 Perhaps the report of Young and Bennett (1922) that many fungi made 

 better growth on calcium than on potassium nitrate may be partially 

 explained on the basis of the molybdenum content of these two salts. 

 This explanation, of course, must allow for the effect of calcium, which is 

 now known to be essential for certain fungi. 



Calcium. This element was one of the first to be recognized as essen- 

 tial for green plants and animals. In 1922, Young and Bennett reported 

 that Rhizocionia solani made no growth in the absence of this element 



