610 



PRINCIPLES OF SOIL MICROBIOLOGY 



Reduction of sulfur and its compounds. When sulfur is added to the 

 soil in an elementary form it is subject to reduction processes, especially 

 when it comes in contact with the living protoplasm of bacteria, 

 fungi, or yeasts; 23 thiosulfates, tetrathionates and pentathionates are 

 also subject to reduction processes, with the formation of H 2 S. Rey- 



Initial pH 



Fig. 46. Influence of hydrogen-ion concentration of medium upon sulfur oxida- 

 tion by Th. thiooxidans (from Waksman and Starkey). 



Pailhade 24 suggested that this process is enzymatic in nature. When 

 sulfates are added to the soil, they are either assimilated by the plants 



23 Rubner, M. liber den Modus der Schwefelwasserstoffbildung bei Bakterien. 

 Arch. Hyg., 16: 53-72. 1893. 



24 Rey-Pailhade, J. de. Etudes sur les propi6t6s chimiques de l'extrait al- 

 coolique de levure de biere; formation de l'acide carbonique et absorption d'oxy- 

 gene. Compt. Rend. Acad. Sci., 118: 201-203. 1894. 



