Mecluuiisni of Nitrogen Fixation 



201 



Mechanism of Nitrogen • Fixation 



The amount of nitrogen fixed by various bacteria depends upon 

 the nature of the energy source, the presence of available nitrogen 

 and minerals, the soil reaction and other environmental conditions, 

 and the presence of various specific bacteria. Some species utilize 

 one source of energy more readily than another. Lipman recorded 



-6 



4 a> 



-3 



- 1 



3 

 CD 



Fig. 85. Comparison between nitrogen fixation and heat of combustion per gram 

 of organic acid, used as a source of energy (from Gainey). 



an increase in the amount of nitrogen fixed with an increase in 

 molecular weight of fatty acids, in the form of sodium salts, includ- 

 ing acetic, propionic, and butyric; the next number of the homologous 

 series (valerianic acid) presented a poor source of carbon; the sodium 

 salts of succinic and citric acids were not utilized at all. 



With glucose as a source of energy, Az. chroococcum was reported 

 to liberate 70 per cent of the carbon as CO2; 12 per cent was assimi- 

 lated in the bacterial cells, and 18 per cent was left among the vari- 

 ous decomposition products other than CO2. These were made up 

 of ethyl alcohol, aldehyde, and formic, acetic, lactic, tartaric, and 

 other acids. The bacterial cells contained 30 per cent protein, a 

 considerable amount of fat, and phosphatides. 



