570 PRINCIPLES OF SOIL MICROBIOLOGY 



Thus for every kilogram of nitrogen fixed, the soil loses about 100 kgm. 

 of energy material. If 1 kgm. of material is equivalent to 4000 Calories, 

 1 kgm. of nitrogen fixed requires an energy consumption of 464 kilowatt 

 hours, greatly in excess of that used in chemical processes (about 46 to 

 48 kilowatt hours). Such a large expenditure of energy is due to the 

 fact that not all the energy is used by the organism for nitrogen fixation, 

 but a part of the energy is utilized for life activities and for the synthesis 

 of proteins of a high molecular weight. At most only one-half of the 

 energy liberated by nitrogen-fixing bacteria is used for nitrogen fixation 

 and one-half for metabolic processes and cell activities. 35 We must also 

 consider the fact that not all the energy is made available to the nitro- 

 gen-fixing bacteria, since the nutrient is not completely broken down to 

 C0 2 and water, but a part is left in the form of intermediate compounds. 



The amount of available energy actually utilized by Azotobacter 

 for the fixation of atmospheric nitrogen was calculated 36 as one per cent, 

 assuming that all the sugar is used up and converted into C0 2 and water. 



Protein synthesis by Azotobacter. Azotobacter was reported 37 to 

 contain 10.45 per cent total nitrogen, of which 6.39 per cent was non-basic 

 N, 2.76 per cent basic N, and 0.98 per cent ammonia N. In young 

 cultures the nitrogen was believed to be present largely in a soluble 

 form which is not precipitated by phosphotungstic acid ; as the culture 

 grows older, the material becomes more insoluble. When cultivated in 

 liquid media Azotobacter was found 38 to contain 11.3 per cent nitrogen 

 and 8.6 per cent ash of which 58 to 62.35 per cent was phosphoric acid ; the 

 nitrogen and the phosphorus were present in the cells chiefly in the form 

 of nucleo-proteins and lecithin. Both the nitrogen and the phosphorus 

 content increase with the age of the cell. 



When the nitrogen-fixing organism is grown on solid media, such as 

 an agar surface, and all the growth collected and dried, a much smaller 

 relative amount of nitrogen is found, amounting to not more than 2 to 

 3 per cent of the dry weight of the cells. 39 The protein content of Azoto- 



36 Christiansen-Weniger, F. Der Energiebedarf der Stickstoffbindung durch 

 die Knollchenbakterien im Vergleich zu anderen Stickstoffbindungsmoglichkeiten 

 und erste Versuche zur Ermittlung desselben. Centrbl. Bakt. II, 58: 41-66. 

 1923. 



36 Linhart, G. A. The free energy of biological processes. Jour. Gen. Physiol., 

 2: 247-251. 1919. 



37 Lipman, 1904-1905 (p. 112). 

 38 Stoklasa, 1908 (p. 562). 



39 Hoffmann and Hammer, p. (563). 



