150 AGEICULTUEAL AND INDUSTEIAL BACTEEIOLOGY 



forms among the bacteria, yeasts, and molds, can utilize 

 nitrogen in the form of ammonia or of nitrates. Most of 

 the bacteria producing fermentation, decay, and putre- 

 faction belong here. 



Paratrophic Bacteria. — These bacteria require particular 

 compounds of carbon and usually of nitrogen for their 

 development. Most of them are parasitic, living upon 

 the tissues of plants and animals. When grown in the 

 laboratory care must be used that the right amino acids, 

 vitamines, and carbon compounds are supplied. This 

 group is important because of the disease-producing 

 organisms which belong to it. 



Methods of Securing Energy by Oxidation. — It has 

 already been emphasized that microorganisms secure 

 growth energy by oxidation. This may occur as a result 

 of direct oxidation of carbon or other compounds or ele- 

 ments by atmospheric oxygen, the oxidation of one com- 

 pound and simultaneous reduction of another, and by 

 intramolecular oxidation. 



Many of the aerobic bacteria secure their growth energy 

 by direct oxidation of inorganic or organic elements 

 and compounds with atmospheric oxygen. As an example 

 of this type of transformation may be cited the oxidation 

 of ethyl alcohol into acetic acid by the vinegar bacteria 

 of the genus Acetobacter. The change may be illustrated 

 by the equation : 



C.H^OH + O2 = CH3COOH + H^O 

 Alcohol Acetic acid 



The same bacteria are also capable of oxidizing acetic 

 acid to carbon dioxide and water. This may be illustrated 

 by the following equation: 



CH3COOH + 20, = 2CO2 + 2H2O 

 In these two steps the alcohol has been completely oxi- 

 dized and the maximum possible amount of energy is 

 secured from the alcohol. 



