614 PRINCIPLES OF SOIL MICROBIOLOGY 



Another source of sulfur in an organic form is bile which contains 

 taurine. 



CH 2 • S0 2 OH 



CH, • NH, 



These substances are decomposed in the soil or in culture media by 

 microorganisms. The sulfur is liberated as H 2 S or in the form of 

 mercaptans, 35 depending on the organisms and environmental condi- 

 tions, especially oxygen supply. The production of mercaptan from 

 Z-cystine by Bad. vulgare is not affected by the presence of glucose, lac- 

 tose and glycerol. Bad. vulgare and B. coli are also capable of forming 

 H 2 S and ethyl sulfide from Z-cystine, independent of the presence of the 

 carbon sources just named. Mercaptans, either the ethyl or methyl 

 form (C 2 H 5 'HS or CH 3 -HS) often accompany H 2 S as a decomposition 

 product of proteins under anaerobic conditions. These are often 

 produced in mere traces. A definite parallelism has been found be- 

 tween the influence of carbohydrates on bacterial multiplication and 

 on the production of H 2 S from proteins. The rate of formation of 

 H 2 S even increases in the presence of glucose, although the formation 

 of amino-nitrogen remains stationary. 31 

 Taurine is very resistant to the action of microorganisms. 37 

 Influence of sulfur oxidation upon the transformation of minerals 

 in the soil. The acid produced from the oxidation of elementary sul- 

 fur by microorganisms can be utilized (1) as a solvent for such difficultly 

 soluble minerals, as phosphorus in rock phosphate, potassium in glau- 

 conite, or green-sand marl; (2) for the neutralization of excess base in 

 alkaline soils; (3) for the control of certain plant diseases. 



When a compost of soil, sulfur and insoluble calcium phosphate is 

 made, the sulfuric acid formed from the oxidation of the sulfur acts upon 

 the phosphate and makes it soluble. By comporting 100 grams of soil, 

 5 grams of flowers of sulfur and 15 grams ground rock phosphate, 

 85 per cent of the phosphate is made available after a period of 30 

 weeks. 38 A compost consisting of 100 parts of soil, 120 parts of 

 sulfur and 400 parts of rock phosphate is the most economical com- 



35 Petri and Maassen, 1893 (p. 611); Kondo, M. Uber die Bildung des Mer- 

 captans aus 1-Cystin durch Bakterien. Biochem. Ztschr., 136: 198-202. 1922. 



36 Heap, H., and Cadness, B. H. E. The influence of carbohydrates on H 2 S 

 production by Bacillus acrtrycke (Mutton). Jour. Hyg., 23: 77-93. 1924. 



37 Sasaki and Otsuka, 1912 (p. 613). 



38 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. 



