CHAPTER XIII 

 NITROGEN METABOLISM 



THE cells of bacteria, yeasts and fungi may contain 

 as much as 87*5 per cent, of nitrogenous constituents, 

 although about 70 per cent, is a more usual value. 

 The greater proportion of these substances comprises the 

 proteins of the protoplasm and nuclear material of the 

 cells, but no less important in function, though smaller 

 in amount, are the enzymes, which are all nitrogenous. 

 In general the bacterial proteins are like those found in 

 other organisms, being built up of the same amino -acid 

 units, but individual differences occur from species to 

 species. Many of the serological distinctions between 

 bacteria of different species depend on differences between 

 the proteins contained in them. 



Obviously, in order that bacteria may grow and 

 reproduce, a supply of nitrogen, as well as of other con- 

 stituents, must be available from which the cells can 

 synthesise the proteins and enzymes and other nitro- 

 genous compounds to be incorporated in the newly formed 

 cells. We will first consider the forms in which nitrogen 

 is available to the organism, and then the mechanisms 

 by which it is converted into an integral part of the 

 structure of the cell. 



Nitrogen Requirements 



Elementary Nitrogen. — Free nitrogen can l)e utilised 

 by certain of tlie soil bacteria, notably Azotohacter and 

 Bhizobium which fix atmospheric nitrogen, probably 

 witli the intermediate formation of ammonia. There has 



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