546 PRINCIPLES OF SOIL MICROBIOLOGY 



When the nitrate is reduced to atmospheric nitrogen, 



2 HN0 2 = N, + 1J O, + H 2 (+ 6.8 Cal.) (2) 



The second reaction gives, therefore, a net gain of 



1J X 112 + 6.8 - 174.8 Cal. 



In the reduction of nitrate to ammonia, the following reaction takes 

 place: 16 



HNO, + H 2 = NH, + 2 2 



The more complete the reduction of the nitrate, the more oxygen be- 

 comes available and, therefore, the greater is the amount of carbohy- 

 drate that can be oxidized and the greater is the gain in energy. 



In some cases two organisms may participate in the same process, as 

 in the decomposition of cellulose; one organism reduces the nitrate in 

 the absence of atmospheric oxygen, and the other decomposes the cellu- 

 lose. The second organism supplies energy to the first and utilizes 

 the oxygen liberated by the first. 16 Sulfur and thiosulfate may also 

 be used under anaerobic conditions as a source of energy, with nitrate 

 as a source of oxygen. This was first demonstrated by Beijerinck, 17 

 who assumed that two organisms are concerned in the process, one reduc- 

 ing the nitrate and the other oxidizing the sulfur chemosynthetically. 

 But he 18 later demonstrated that only one organism carries out the 

 complete reaction: 



6 KN0 3 + 5S + 2CaC0 3 = 3 K 2 S0 4 + 2 CaSO, + 2C0 2 + 3 N 2 



About 1 Calorie is produced per gram of nitrate reduced. When a mix- 

 ture of sulfur (10 per cent), calcium carbonate and KN0 3 solution (up 

 to 10 per cent) is inoculated with soil, spontaneous and intense gas 

 production takes place, accompanied by slime formation. The gas 

 consists of nitrogen and C0 2 . In the absence of organic matter and with 

 sulfur as the only source of energy, carbon dioxide of the atmosphere is 



15 Warburg, O., and Negelein, E. tlber die Reduktion der Salpetersaure in 

 griinen Zellen. Biochem. Ztschr., 110: 66-115. 1920. 



16 Groenewege, 1920 (p. 436). 



17 Beijerinck, 1904 (p. 84). 



18 Beijerinck, M. W., and Minkman, D. C. J. Bildung und Verbrauch von 

 Si ickstoffoxydul durch Bakterien. Centrbl. Bakt. II, 25: 30-63. 1910. 



