368 PRINCIPLES OF SOIL MICROBIOLOGY 



of the known soil bacteria are more or less selective in their action 

 (when grown, of course, upon artificial culture media) ; many soil fungi 

 and actinomyces and a number of bacteria can derive their carbon, both 

 for energy and structural purposes, from a great variety of substances. 

 Bad. pyocyaneum, for example, can obtain its carbon not only from 

 carbohydrates, but also from lactic and acetic acids, glycerol, ethyl 

 and methyl alcohols, and other substances. 1 Other bacteria like the 

 cellulose decomposing Spirochaeta cytophaga require only very specific 

 compounds, namely celluloses, as sources of energy. 



The autotrophic bacteria need no complex carbon compounds 

 as sources of energy or for structural purposes. They can derive 

 their carbon for the synthesis of their protoplasm from the carbon 

 dioxide of the atmosphere or in solution. The facultative auto- 

 trophic bacteria can obtain their carbon either from CO2 or from 

 organic compounds. There is some evidence, however, that growth 

 of heterotrophic organisms is also favorably affected by the presence 

 of C0 2 , as in the case of Bac. subtilis and Bad. vulgare, which could 

 not grow when both oxygen and carbon dioxide were removed. 2 The 

 presence of carbon dioxide is essential not only for the growth of aerobic 

 bacteria but also for the development of the anaerobic forms. 



In view of the fact that the microbial cells contain between 3 and 

 15 per cent of nitrogen, large quantities of this element have to be 

 assimilated, particularly by organisms producing an extensive growth. 

 Nitrogen is obtained from proteins and their degradation products or 

 simple inorganic nitrogenous compounds, including the ammonium 

 salts of organic and inorganic acids and nitrates. Some organisms, 

 especially the heterotrophic bacteria, prefer and many even require 

 complex proteins, albumoses or peptones as a source of nitrogen (and 

 energy), while other microorganisms, especially the fungi and auto- 

 trophic bacteria, will thrive just as well and sometimes even better 

 upon simple compounds of nitrogen. Bad. pyocyaneum can obtain its 

 nitrogen from amino compounds, amides, nitrates and nitrites, but 

 these substances must be changed, either by hydrolysis or by reduc- 

 tion, to ammonia before they are assimilated. The nitrogen-fixing 



1 Supniewski, J. Untersuchungen iiber den Stoffwechsel der Kohlenstoff- 

 verbindungen bei Bacillus pyocyaneus. Biochem. Ztschr., 154: 90-97, 98-103. 

 1924. 



2 Rockwell, G. E. The influence of C0 2 on the growth of bacteria. Jour. 

 Infec. Dis., 32: 98-104. 1923; 35: No. 6. 1924; 38: 92-100. 1926; Valley G., 

 and Rettger, L. F. Preliminary report on the influence of carbon dioxide on 

 bacterial growth. Abstr. Bact. (Proc), 9: 344-345. 1925. 



