CHAPTER XIX 



Influence of Available Energy upon the Transformation of 

 Nitrogenous Compounds by Microorganisms 



Carbon and nitrogen transformation by microorganisms. All micro- 

 organisms require a certain amount of energy for the building up of 

 their protoplasm as well as a certain minimum of nitrogen, phosphorus 

 and other minerals. In the case of heterotrophic, non-nitrogen-fixing 

 microorganisms, the energy is obtained either from nitrogen-free or- 

 ganic compounds or from proteins and their derivatives. The nitrogen 

 is obtained from inorganic nitrogenous salts, such as ammonium com- 

 pounds and nitrates, or from complex organic compounds, such as 

 proteins and their derivatives. Phosphates and other minerals are 

 obtained from the inorganic or organic compounds present. 



When an organism has to derive both its carbon and nitrogen from 

 proteins, only a small part of the nitrogen is reassimilated, while a 

 larger part will remain as a waste product (ammonia). Several fac- 

 tors contribute to this phenomenon: 



1. Only 10 to 40 per cent of the carbon is reassimilated by the or- 

 ganism and synthesized into protoplasm; a larger part is given off as 

 C0 2 (in the process of energy utilization) or is left in the form of unde- 

 composed material or in the form of intermediary products. The 

 smaller the amount of carbon assimilated by the organism, the less is 

 the amount of protoplasm synthesized and, therefore, the less is the 

 amount of nitrogen assimilated and the more of it is left in the medium 

 as a waste product (largely NH 3 ). 



2. The microbial protoplasm may contain a lower per cent of nitrogen 

 than the original protein. This will tend further to diminish the 

 amount of reassimilated nitrogen. The excess nitrogen will be liberated 

 as ammonia or left in the form of various protein degradation products. 



In the presence of available carbohydrates, however, the micro- 

 organisms will assimilate the available ammonia nitrogen and convert 

 it into microbial protoplasm. The greater the quantity of carbohy- 

 drate present for a given amount of protein or its derivatives the more 

 of the nitrogen will be reassimilated by microorganisms and the less 

 of it will be left as ammonia. The larger the ratio of the protein-free 



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