t46 NUTRITION AND METABOLISM 



A number of different types feeding exclusively on minerals has 

 been discovered during the last twenty years, and some of them are 

 of great economic importance. They resemble plants in as far as they 

 build their cells exclusively, from carbon' dioxide, nitrates and ash. 

 The food used for building material is quite different from the food 

 used for the provision of energy. 



Two typical examples are the nitrifying organisms in soil which 

 oxidize ammonia to nitrates. This process, according to Winogradski, 

 is divided distinctly into two phases: the Nitrosomonas oxidizes the 

 ammonia to nitrous acid, 



NHs + 30 = HNO2 + H2O + 78.8 Cal. 



and the Nitromonas oxidizes the nitrous acid to nitric acid, 



HNO2 + O =F HNO3 + 18.3 Cal. 



These oxidation processes yield a certain amount of energy which 

 enables the bacteria to build their cells from carbon dioxide, ammonia^ 

 and certain mineral salts. Without ammonia or without nitrous acid, 

 respectively, these bacteria cannot grow for lack of energy; they would 

 be like a plant without light. It is evident in'this case that the food for 

 energy is also used to some extent as food for growth. The nitrogen 

 necessary to the bacteria is supplied by the ammonia or the nitrous acid. 

 As an example distinguishing strictly between the food for growth 

 and the food for energy may be mentioned the hyposulphite bacterium 

 studied by Nathan'son. This organism oxidizes hyposulphites to sul- 

 phates and sulphur, largely following the formula 



Na2S203 + = NaaSOi + S + x Cal. 



Hyposulphite Sulphate Sulphur 



Besides, some more complex compounds, like sodium tetrathionate 

 (Na2S406), are formed. The bacterium builds its cells exclusively from 

 nitrates, carbon dioxide, and mineral salts; organic food is rejected. 

 The hyposulphite can hardly be used for the construction of the cell, 

 and must be considered entirely a food for energy. 



This distinction is not confined to mineral decomposition only. 

 The urea bacteria get their energy from the decomposition of urea into 

 ammonium carbonate which is hydrolysis. ' 



(NH2)2CO + 2H2O = (NH4)2C03 + 14.3 Cal. 



Urea Ammonium 



carbonate 



