416 



PRINCIPLES OF SOIL MICROBIOLOGY 



allow the synthesis of 58 Cal. of fungus mycelium, 100 Cal. in the form 

 of protein will allow the synthesis of only 39 Cal. of fungus mycelium. 

 There is also a large loss of energy in the process of deaminization. 



Fungi generally waste (give out) about as much energy as they 

 assimilate in their bodies. Under unfavorable conditions, the amount 

 of energy assimilated by the body is much smaller in comparison with 

 that utilized. The coefficient of utilization was found to decrease with 

 age of culture, due to the fact that, after the nutrients have been used 

 up, the cells of the organism begin to undergo autolysis and its con- 

 stituents are used as sources of energy 



Terroine and Wurmser determined, for Asp. niger, "the utilization 

 quotient" of sugars by comparing the dry weight of the mycelium pro- 

 duced with the weight of the sugar consumed. It was found to be 



TABLE 27 

 Influence of energy source upon the growth of fungi 



SOURCE OF ENERGY 



Tartaric acid 

 Citric acid . . 



Glucose 



Glycerol 

 Peptone .... 

 Olive oil ... . 



43 to 44 per cent for glucose, levulose, saccharose, maltose, arabinose 

 xylose. The concentration of the nitrogenous substance, varying from 

 0.5 to 4 per cent, does not influence the quotient of utilization, which 

 was found to be lower with sodium and aluminum nitrate as a source 

 of nitrogen (0.34 to 0.35) than with ammonium sulfate or nitrate, 

 urea or guanidine (0.42). The addition of sulfuric acid to the sodium 

 nitrate medium resulted in an increase in the quotient. The utiliza- 

 tion of an energy source by A. niger was calculated as follows. 



The heat of combustion of mycelium was 4.8 Cal. per gram and that of glucose 

 3.76 Cal. The energy utilization is, therefore, (44 parts of mycelium X 4.8) 

 -J- (100 parts of sugar X 3.76) = 56 per cent. The combustion of glucose in the 

 culture medium was, however, not complete. A combustion of the medium, 

 made before and after the cultivation of A. niger, gave 6.46 and 0.51 respectively. 

 The difference of these figures, 5.95, represents the metabolizable energy U for 



