TRANSFORMATION OF SULFUR 



609 



nitrifying bacteria. The influence of sulfates, elementary sulfur, and 

 reaction upon the oxidation of sulfur by Th. thiooxidans is shown in 

 figures 45 and 46. According to Guittonneau, 21 the oxidation of 

 elementary sulfur in the soil may be carried out by two different or- 

 ganisms, one of which oxidizes the sulfur (S) to hyposulfite (S 2 2 ) 

 and the other oxidizes the hyposulfite to sulfate (S0 3 ). An outside 

 source of energy, either in the form of organic acids, carbohydrates or 



Cm. o 10 20 30 40 tiO 



Sulfur per 100 cc. of medium 



Fig. 45. Influence of sulfur content of medium upon the oxidation velocity of 

 sulfur by Th. thiooxidans (from Waksman and Starkey). 



amino acids, is required. The rapidity of the process depends on the 

 nature of the carbon source and the active organisms. 



It has been suggested 22 that different sulfides are acted upon by 

 different groups of organisms. Among the iron sulfides, markazite 

 and ferrous sulfide are oxidized more readily than pyrite. 



21 Guittonneau, G. Sur la formation d'hyposulfites aux depens du soufre 

 par les microorganismes du sol. Compt. Rend. Acad. Sci., 180: 1142-1144. 1925; 

 181: 261-262. 1925; 182: 661-663. 1926. 



22 Gubin, B. M. On the oxidation of sulfur and sulfides by soil bacteria (Rus- 

 sian). Viestnik Bakt. Agron. Sta., 24: 52-74. 1926. 



