MICROORGANISIMS CONCERNED IN THE OXIDATION 

 OF SULFUR IN THE SOIL 



IV. A SOLID MEDIUM FOR THE ISOLATION AND CULTIVATION 

 OF THIOBACILLUS THIOOXIDANS' 



SELMAN A. WAKSMAN 



Received for publication April 4, 1922 



Thiobacillus thiooxidans is the organism chiefly responsible for 

 the oxidation of sulfur in the soil, particularly when elementary 

 sulfur has been added. This is true in ordinary .soils, with the 

 possible exception of the black alkaU soils, where other organisms 

 may also play an important part, as pointed out in the follow- 

 ing paper. Th. thiooxidans is usually not originally present 

 in the soil, but is introduced there artificially with the sulfur added. 

 Certain soils themselves may harbor organisms which are able 

 to oxidize small amounts of sulfur, to a much smaller extent how- 

 ever than Th. thiooxidans 



This organism has been isolated from soil-sulfur-rock phos- 

 phate composts (Lipman, Waksman and Joffe, 1921; Waksman 

 and Joffe, 1922) by the use of liquid media only. It can exist and 

 reproduce under very acid reactions, since it has its optimum 

 at a pH = 3.0 to 4.0, and can also grow at as low a pH as 1.0. 

 It derives its energy from the oxidation of inorganic, elementary 

 sulfur, and its carbon from the CO2 of the atmosphere, while its 

 nitrogen need is obtained from ammonium salts or nitrates and 

 its mineral need from traces of potassium, magnesium and iron 

 salts and phosphates. By the use of media containing such 

 substances, and by employing high dilutions the organism was iso- 

 lated in pure culture. The purity of the culture was established 

 by the following facts: the organism grew readily upon the inor- 

 ganic liquid media, giving always the same uniform turbidity; 



' Paper no. 84 of the Journal Series, New Jersey Agricultural Experiment 

 Station, Department of Soil Chemistry and Bacteriology. 



605 



