CHAPTER III 



Autotrophic Bacteria 



The nature of autotrophic bacteria. Autotrophic bacteria are organisms 

 which are capable of obtaining their carbon from C0 2 of the atmosphere 

 and their energy from the oxidation of inorganic substances, including 

 simple inorganic compounds (or the elementary form) of nitrogen, 

 sulfur, iron, hydrogen and carbon. Some of these transformations, 

 particularly those of the nitrogen and the sulfur compounds are of great 

 importance in the soil. 



Obligate autotrophic bacteria, or anorgoxydants, are characterized 1 

 by a series of physiological properties, which differentiate them sharply 

 from the rest of the bacteria. These properties are as follows: 



1. Their development in nature takes place only in strongly elective, 

 almost pure mineral media, which contain specific oxidizable inorganic 

 substances. 



2. Their existence is connected with the presence of these substances, 

 which undergo oxidation as a result of the life activities of the organisms. 



3. This oxidation process supplies their only source of energy. 



4. The organisms do not need any organic nutrients for structure or 

 for energy. 



5. They are almost incapable of decomposing organic matter and may 

 even be checked in their development by its presence. 



6. They use, as an exclusive source of carbon, carbon dioxide, which is 

 assimilated chemosynthetically. 



These original conceptions of Winogradsky may be modified at 

 present in two respects: 



1. The presence of organic matter may not prove injurious to the 

 activities of the autotrophic bacteria. As a matter of fact, the presence 

 of small quantities of certain organic substances may even be stimulating 

 to some. Further, the existence of these organisms in the soil, where 

 they carry on their life processes, takes place in the presence of soluble 

 organic substances. 



1 Winogradsky, S. Eisenbakterien als Anorgoxydanten. Centrbl. Bakt. II, 

 67: 1-21. 1922. 



61 



