1 laiislorniatioii oi Sullur 



2.33 



in size. Others are large and filamentous. Some are obligate auto- 

 trophic, that is, they depend on the energy liberated in the oxidation 

 of sulfur, and others are facultative autotrophic, or are also able to 

 derive their energy from organic compounds. 



The most numerous of these bacteria in the soil population are tlu> 

 autotrophic organisms. They function in a manner somewhat similar 

 to green plants, though the latter use the energy of sunlight (photo- 

 SNuthesis), whereas the autotrophic bacteria are able to utilize the 

 chemical energy liberated in the oxidation process ( chemosynthesis ) . 

 Both the bacteria and the green plants use the carbon dioxide of 

 the atmosphere as sources of carbon for cell synthesis. 



The following chemical reactions are involved in the oxidation of 

 sulfur and its compounds by bacteria: 



-2H2S + (), 

 So + 3O2 + ^^H.O 



-iHoO + S2 



^2H2S04 



Xa2S04 + H2SO4 



2Na2S203 + O2 = 2Na2S04 + S2 



The rate of oxidation of the sulfur and its simple compounds to 

 sulfuric acid and to sulfates is influenced not only by the nature of 

 the organism but also by the environmental conditions (Table 53). 



Table 5.3. Oxiuatidn of Klementaky Sulfur to Sulfuric Acid by 

 Thiobacilhis fhloo.ridans (from Waksman and Starkev) 



Of particular importance is the reaction of the soil or substrate, salt 

 concentration, and presence of organic materials. 



Each of the above reactions can be brought about by different 

 types of bacteria. The first reaction, which results in the precipita- 

 tion of sulfur, takes place largely in water basins and in peat bogs 



