556 PRINCIPLES OF SOIL MICROBIOLOGY 



by microorganisms, the following may be mentioned in addition to 

 nitrates and nitrites: sulfates, 56 sulfur, sulfites, selenates, selenites, 

 tellurates and phosphates. H 2 S is formed not only from sulfates but 

 also from elementary sulfur, sulfites and polythionates. 57 The reduction 

 of selenium compounds, 58 including selenious acid 59 and various salts as 

 well as tellurium salts, to their elements has been demonstrated for a 

 number of bacteria 60 and fungi. The amount of reduction was found 61 

 to be proportional to the growth of the organisms. Selenic acid is re- 

 duced in two stages, first to selenious acid and then to free selenium. 62 

 The reduction of arsenic to arsine is carried out by Pen. brevicaule, 

 an organism found in the soil, 63 as well as by certain other organisms. 

 Various bacteria are also capable of reducing organic 64 and inorganic 

 phosphorus compounds. According to Rudakov, 65 mineral phosphates 

 are reduced, under anaerobic conditions, to phosphites (H 3 P0 3 ) and 

 hypophosphites (H 3 P0 2 ) as well as to phosphene. Pure cultures were 

 obtained of a bacterium capable of bringing about the reduction of the 

 phosphate. Different soils varied in their capacity of bringing about this 

 reduction. The addition of KN0 3 and MgS0 4 to the medium led to a 



66 Saltet, R. H. t)ber Reduktion von Sulfaten in Brackwasser durch Bakterien. 

 Centrbl. Bakt. II, 6: 648-695. 1900; van Delden, A. Beitrag zur Kenntnis des 

 Sulfatreduktion durch Bakterien. Centrbl. Bakt. II, 11: 81-94, 113-119. 1903; 

 Kochmann, R. Uber Schwefelwasserstoff-bildung aus Sulfaten durch Faeces. 

 Biochem. Ztschr., 112: 255. 1920. 



67 A detailed study of sulfate reduction in the soil is given elsewhere (p. 610). 

 58 First reported by Japha, A. Experimenta nomulla de vi selenii in organis- 



num animalem. Diss. Halle. 1842. 



69 Chabrie, C, and Lapicoque, L. Sur Taction physiologique de l'acide 

 selenieux. Compt. Rend. Acad. Sci., 110: 152. 1890. 



60 Scheurlen, E. Die Verwendung der selenigen und tellurigen Saure in der 

 Bakteriologie. Ztschr. Hyg., 33: 135-136. 1900. 



61 Klett, A. Zur Kenntnis der reduzierenden Eigenschaften der Bakterien. 

 Ztschr. Hyg., 33: 137. 1900. 



62 Levine, V. E. The reducing properties of microorganisms with special 

 reference to selenium compounds. Jour. Bact., 10: 217-264. 1925. 



63 Gosio, B. Azione di alcune muffe sui composti fissi d'arsenico. Riv. 

 d'igiene, 3: 201. 1892; Abel, R., and Buttenberg, J. Uber die Einwirkung von 

 Schimmelpilzen auf Arsen und seine Verbindungen. Ztschr. Hyg., 32: 449. 

 1899. 



61 Barrenscheen, H. K., and Beckh-Widmenstetter, H. A. t3"ber bakterielle 

 Reduktion organisch-gebundenen Phosphorsiiure. Biochem. Ztschr., 140: 279- 

 283. 1923. 



65 Rudakov, K. I. The biological reduction of mineral phosphates (Russian). 

 Viestnik Bact. Agron. Sta., 26: 171-188. 1926. 



