FOOD OF MICROORGANISMS I S3 



classed merely as one of the many food compounds. This is especially 

 significant since it will be shown later that free oxygen is not necessary 

 for microbial life, and that many organisms can exist without it. 



The oxidations are not always complete. The formation of nitrous 

 acid from ammonia, the oxidation of alcohol to acetic acid are such 

 examples. Some organisms are highly specialized in their food require- 

 ments, especially the mineral-attacking bacteria are usually limited 

 to one source of energy. The microorganisms oxidizing organic com- 

 pounds have, as a rule, the abiUty to decompose several coihpounds, 

 and some bacteria are common scavengers, able to feed on organic acids, 

 sugars, fats and proteins. 



Oxygen Relations 



It is characteristic of many microorganisms to provide for their 

 energy without using free oxygen. One such example has already been 

 given in urea fermentation. 



(NH2)2 COi! 4- 2H2O = (NHOaCOa 



Urea Ammonium carbonate 



Very common is the decomposition of sugars without oxygen. 

 The two most typical fermentations of this type are the alcoholic and 

 the lactic fermentations. 



CeHuOe = aCaHsOH + 2C02 + 22 Cal. 



Sugar Alcohol 



C6H12O6 = 2C^H60s -1- IS Cal. 



Sugar Lactic acid 



In fermentations of this type, the changes take place without an 

 oxygen gas partaking in the reactions. These fermentations seem to 

 be essentially reactions of the oxygen atoms within the sugar molecule. 

 One side of the molecule is reduced while the other side is oxidized. 

 In the sugar molecule, each carbon atom has one oxygen atom. In 

 the products of fermentation, carbon dioxide has two oxygen atoms to 

 one carbon atom, and in alcohol there is only one oxygen atom for two 

 carbon atoms. In the "lactic fermentation, the oxygen, which is dis- 

 tributed evenly in the sugar, is shifted to one side of the molecule in 

 lactic acid. 



