408 PRINCIPLES OF SOIL MICROBIOLOGY 



Energy is liberated in the oxidation of the ethyl alcohol to acetaldehyde, 

 but only one-third of that energy is liberated in the oxidation-reduction 

 of the acetaldehyde. The nature of energy utilization by bacteria 

 capable of oxidizing hydrocarbons and amorphous carbon 46 still remains 

 to be studied. 



Heterotrophic utilization of energy by microorganisms. The great 

 majority of soil microorganisms, both in respect to numbers and species, 

 have to depend for their energy supply upon complex organic or car- 

 bonaceous substances. These may be simple or complex carbohy- 

 drates, fats, or proteins and their derivatives. The carbohydrates 

 contain about 40 to 45 per cent carbon, the proteins about 50, the 

 lignins about 60, and the fats about 75 per cent. In the combustion 

 of the carbon and the hydrogen, energy is liberated. 



The nutrient consumption by heterotrophic microorganisms follows 

 three courses; viz., energy, structural or reserve purposes and residual 

 substances. The energy goes to produce work against the exterior 

 and to elevate the chemical potential of the substances formed. 47 The 

 organism may derive its energy and material needed for the synthesis 

 of the protoplasm from the same nutrient or from two different nu- 

 trients. Fats form only a rather small part of the constituents of the 

 plant residues and manures added to the soil. Our chief attention 

 may, therefore, be devoted to the other two groups of substances. 

 Both carbohydrates and proteins may be utilized as sources of energy 

 by most of the aerobic and anaerobic heterotrophic microorganisms. 

 The decomposition products will differ. Under aerobic conditions a 

 carbohydrate is usually decomposed to C0 2 and H 2 or to various 

 organic acids, C0 2 and H 2 0. Under anaerobic conditions, it is de- 

 composed into H 2 or CH 4 , or both, and into different acids, C0 2 and 

 H 2 0. The amount of energy made available depends upon the nature of 

 the decomposition taking place. Under aerobic conditions the proteins 

 are decomposed to amino acids, NH 3 , C0 2 , and H 2 0; under anaerobic 

 conditions, to different products of putrefaction, such as various amines, 

 mercaptans, etc., NH 3 and C0 2 . 



46 Tausz, J., and Peter, M. Neue Methode der Kohlemvasserstoffanalysemit 

 Hilfe von Bakterien. Centrbl. Bakt. II, 49: 497-554. 1920. Any possible 

 action of bacteria upon amorphous carbon is still a matter of conjecture. See 

 Potter, M. C. Bacteria as agents in the oxidation of amorphous carbon. Proc. 

 Roy. Soc. B, 80: 239-259. 1908. 



47 Terroine, E. F., and Wurmser, R. L'energie de croissance. I. Le devel- 

 oppement de l'Aspergillus niger. Bull. Soc. Chim. Biol., 4: 519-567. 1922; 

 Wurmser, R. Ibid., 5: 506-528. 1923. 



