MICROORGANISMS CONCERNED IN THE OXIDATION 

 OF SULFUR IN THE SOIL 



I. INTRODUCTORY! 



SELMAN A. WAKSMAN 



Received for publication June 16, 1921 



Hydrogen sulfide and other sulfides in solution are slowly- 

 oxidized to sulfur, under natural conditions. The sulfur formed, 

 as well as elementary sulfur, particularly when present in a fine 

 state of subdivision and in the presence of certain catalytic 

 agents, undergoes further oxidation, the resulting product being 

 sulfuric acid. In the presence of specific bacteria, this phenom- 

 enon is much more rapid. These bacteria were first studied 

 extensivel}^ by Winogradsky and were designated by him as 

 sulfur bacteria; they possess a strong oxidizing power, in con- 

 tradistinction to the reducing bacteria, which form hydrogen- 

 sulfide from sulfur and its compounds. The sulfur bacteria, 

 originally studied by Winogradsky, contain sulfur granules within 

 their cells, as a result of the oxidation of the hydrogen sulfide. 

 Later investigators, in their studies of sulfur oxidation, also 

 included, under the term sulfur bacteria, organisms which are 

 able to oxidize hydrogen sulfide, sulfur, and thiosulfate, but 

 which do not, however, store any sulfur within their cells. 



The so-called sulfur bacteria are not related to one another 

 morphologically and belong to widely difTerent genera. By the 

 use of physiological and morphological differences, they can be 

 di\'ided into five groups: (1) colorless, thread forming bacteria, 

 accumulating sulfur within their cells. (2) Colorless, non- 

 thread-fonning bacteria, accumulating sulfur within their cells. 

 (3) Purple bacteria, oxidizing sulfur and accumulating it within 



'Paper No. 32 of the Technical Series, New Jersey Agricultural Experiment 

 Station, Department of Soil Chemistry and Bacteriology. 



231 



