240 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



veloped. Under certain conditions microorganisms may 

 attack nitrates, removing oxygen and changing them to 

 nitrites. Nitrites may also be attacked or reduced and 

 free nitrogen given off. These processes are usually termed 

 denitrification. Certain microorganisms are likewise capable 

 of taking up atmospheric nitrogen and converting it to 

 their own use, or in some cases turning it over to higher 

 plants, particularly the legumes. This process is termed 

 nitrogen fixation. For convenience in discussion it is 



Plant R*;n>(j^^ Pirrny j El \j >rnt./.c»< RpTonization 



ft, '^r ''" %\ iQitiiTioQrids \Ommonii'ica.lim' 



CIniinoQcidsi__.__ 'fe. %\ / 

 mplanis t^ ' -V ^wtXTnmonia. 



Nilratas**^^' ■^•Tslitrites 



Fig. 55. — Outline op nitrogen cycle. Heavy lines indicate changes 

 produced by bacteria. 



desirable to take up these various subdivisions or sections 

 of the nitrogen cycle one after the other. 



Proteolysis, Ammonification or Deaminization. — The 

 most complex of the nitrogen compounds are the proteins. 

 They have already been defined as complex organic com- 

 pounds made up of carbon, hydrogen, oxygen and nitrogen, 

 sometimes including also phosphorus, iron or sulphur, and 

 which yield, upon hydrolysis, a large portion of alpha- 

 amino acid (KCHNHjCOOH) . It has also been shown that 

 it is possible for the chemist to join chains of amino acid 

 radicles indefinitely, the cement which joins them together 

 being the abstraction of water. When proteins are decom- 

 posed as the result of the action of digestive enzymes or the 



