88 PRINCIPLES OF SOIL MICROBIOLOGY 



The bacterium was found to be related 68 to the fluorescein group in the 

 Lehmann and Neumann system, especially to the Bad. denitrificans 

 (Stutzer and Burri) L and N. 



According to Klein and Limberger 69 the thionic acid bacteria are 

 capable of oxidizing all sources of sulfur found in the soil (elementary 

 sulfur, hydrogen sulfide, other sulfides, sulfites and hydrosulfites) to 

 sulfate and polythionate. The sulfur can also be utilized in the form 

 of organic sulfur (cystin, albumin, nuclein, meat extract) and is oxidized, 

 through the sulfur stage, to sulfate. The organism reduces KN0 3 

 to nitrite and to ammonia, in the oxidation of sulfur. The claim, how- 

 ever, that this organism can also oxidize NH 4 C1 to nitrite needs further 

 confirmation, especially since the cultivation of these organisms in 

 pure culture may not often be a very easy matter. 



In this group of thionic acid bacteria, we have another connecting 

 link, between autotrophic and heterotrophic nutrition in nature. 



Group V. Minute, colorless, aerobic, non-spore and non-thread 

 forming bacteria, acting primarily on elementary sulfur and oxidizing it 

 rapidly to sulfuric acid (No. 22, PI. IV). 



When sulfur is mixed with soil, it is oxidized slowly at first and then 

 as the soil becomes acid it oxidizes rapidly. If powdered rock phos- 

 phate is added to the mixture of soil and sulfur, the rock is transformed 

 into soluble phosphates by the acid formed from the sulfur. This 

 process has been utilized 70 in composting sulfur, rock phosphate and 

 soil in various proportions. A direct correlation was found between 

 the acid formed, as shown by the increase in the hydrogen-ion con- 

 centration, and the amount of phosphates going into solution. When 

 a fresh compost is inoculated with some material from an old compost, 

 the reaction goes on more rapidly, indicating the biological nature of 

 the process. 



By inoculating a medium free from any organic compounds and car- 

 bonates and containing sulfur as the only source of energy, in addition 

 to minerals and tri-calcium phosphate as a neutralizing agent, the 



68 Trautwein, K. Die Physiologie und Morphologie der fakultativ auto- 

 trophen Thionsaurebakterien unter heterotrophen Ernahrungsbedingungen. 

 Centrbl. Bakt. II, 61: 1-5. 1924. 



69 Klein, G., and Limberger, A. Zum Kreislauf des Schwefels im Boden. 

 Biochem. Ztschr. 143: 473^S3. 1923. 



70 Lipman, J. G., McLean, H. C., and Lint, H. C. Sulfur oxidation in soils 

 and its effect on the availability of mineral phosphates. Soil Sci. 2: 499-538. 

 1916. McLean, H. C. The oxidation of sulfur by microorganisms and its relation 

 to the availability of phosphates. Soil Sci. 5: 251-290. 1918. 



