Rothamsted Symposium on Trace Elements 



46 



ment of Aspergillus took place, thus showing, in agreement with 

 Steinberg, that molybdenum is an essential element for Aspergil- 

 lus niger when growing in a nutrient solution with nitrate nitro- 

 gen. Increasing amounts of molybdenum added to the nutrient 

 solution resulted in a progressive increase in weight of the mycelia 

 and in a more abundant spore formation (Table 6). The 

 growth-rate curve as well as the different sporulation were used for 

 the estimation of very small amounts of molybdenum in various 

 materials. 



When ammonium compounds were used as a nitrogen source 

 the response to molybdenum was much smaller. It was shown 

 that the difference in response to molybdenum between nitrate and 

 ammonium cultures was due to a much higher requirement of 



Table 6 : Ejfecf of increasing amounts of molybdenum on the yield 

 of Aspergillus niger in a medium with nitrate-N: — 



• Average of duplicate values. 



molybdenum when the fungus was grown in a solution with ni- 

 trate nitrogen (6). Probably molybdenum is required as a catalyst 

 in nitrate reduction. 



The importance of molybdenum in nitrate reduction was 

 shown in experiments with denitrifying bacteria and higher 

 plants. In the denitrification experiments four strains of bacteria 

 were used. Two of these strains did not show any growth in a 

 molybdenum-free solution; the other two brought about insignifi- 

 cant denitrification. With 5 [jig of Na2Mo04 added per bottle 

 all strains, however, showed intensive denitrification. Some of 

 the results are presented in Table 7. 



In experiments with tomato, barley and oat plants the impor- 

 tance of molybdenum for the normal growth of these plants was 



