OXIDATION OF SULFUR IN THE SOIL 237 



a source of carbon. The organism, Thiobacillus thioparus, is a 

 short rod, 3 by 0.5^, not forming any spores, very motile and very 

 sensitive, so that on plates the organisms die off in a week. 



By using a medium consisting of canal water 100, powdered 

 sulfur 20, KNOs - 0.5, Na^COa - 0.02, CaCOj - 2.0, K2HPO4 

 — 0.02 parts, in a closed flask, incubated at 30°C., Beijerinck 

 obtained an oxidation of sulfur accompanied by a reduction of 

 the nitrate to atmospheric nitrogen. 



6KNO3 + 5S + 2 CaCO, = 2K0SO4 + 2 CaSOi + 2 COo + SNs 



+ 695.5 Cal. 



The sulfur is oxidized to sulfuric acid which acts upon the 

 CaCOj giving CaSO^ and CO2. By using a medium consisting 

 of tap water - 100, Na,So03. 5 H2O - 0.5, K.HPO4 - 0.01, 

 NaHCOa — 0.02, agar 2.0 parts, Beijerinck isolated, in pure cul- 

 ture, the organism, Thiobacillus denitrificans, which is a very mo- 

 tile, short rod, hardly distinguishable microscopically from Thio- 

 bacillus thioparus. Thiohacillus denitrificans was further studied 

 by Lieske (1912) and Gehring (1915) and was found to occur in 

 various soils. The organisms on the plate, lose their ability to 

 grow rapidly, long before they are dead. Beijerinck's work was 

 continued further by Jacobsen (1912, 1914), who found a crude 

 culture of Thiobacillus thioparus to be able to oxidize 58.8 mgm. 

 of sulfur to sulfuric acid, in five weeks, out of a total of 648 mgm. 

 added to the medium. Pure cultures oxidized, in eight weeks, 

 165 mgm. out of 648 mgm. of sulfur added. 



Gicklehorn (1920) has studied two organisms belonging to the 

 fourth group of sulfur-oxidizing bacteria, found in garden soil, 

 which are able to oxidize K2S with the liberation of free sulfur. 

 The organisms are 1 to 2 by 0.3 to 0.5^ and 2 to 4 by 0.5 to l^i in 

 size. However, he did not isolate his organisms in pure culture 

 and did not record any quantitative physiological data. 



Finally, we have a fifth group of sulfur bacteria, which are 

 studied in detail in the next paper. Two preliminary reports 

 on this organism by Waksman and Joffe (1921a, 1921b) and a 

 detailed study of the methods used in its isolation, by Lipman, 

 Waksman and Joffe (1921), were pubUshed elsewhere. 



