548 PRINCIPLES OF SOIL MICROBIOLOGY 



According to MazeV 3 nitrate reduction is caused by the hydrogen 

 produced by anaerobic bacteria; however, not all hydrogen-forming 

 organisms are capable of reducing nitrate, as in the case of butyric acid 

 bacteria. Table 53 illustrates the role of nitrate in the decomposition of 

 carbohydrate (4 per cent sucrose) under anaerobic conditions and in a 

 nutrient bouillon; a much greater decomposition of the sugar and an 

 abundant formation of hydrogen in the absence of nitrate points to a 

 distinct difference in the mechanism of the decomposition of the 

 substrate. 



Reduction of nitrates to gaseous nitrogen and oxides of nitrogen. The 

 reduction of nitrates to atmospheric nitrogen always goes through 

 the nitrite stage. The following reaction was at first suggested 24 to 

 explain the complete reduction of the nitrate molecule : 



5 C 6 H 12 6 + 24 KN0 3 = 24 KHCO3 + 6 C0 2 + 18 H 2 + 12 N 2 



The carbohydrates or organic acids of the media are decomposed with 

 the formation of carbon dioxide and nascent hydrogen; 25 the nitrate is 

 then used by the organism as the hydrogen acceptor, which results in 

 the reduction of the nitrate. The theories concerning the nitrate reduc- 

 tion current about 1910 illustrate the reactions involved as follows: 



2 KNO3 + C = 2 KN0 2 + C0 2 



4 KN0 2 + 3C = 2N 2 + 2 K 2 COa + C0 2 



C designates the carbon source. In view of the fact that oxides of 

 nitrogen are always produced in the complete reduction of the nitrate 

 the above reactions had to be modified: 26 



2 KNO3 + C = 2 KN0 2 + C0 2 

 2 KN0 2 + C = N 2 + KjCOs 



2 N 2 + C = 2 N 2 + C0 2 



An abundant formation of N 2 takes place at a high nitrate concentra- 

 tion of the medium and at a high temperature. The above reactions 

 are altogether hypothetical and are not based upon sufficient experL 



23 Maz6, 1911 (p. 182). 



"Gayon and Dupetit, 1882 (p. 181); Dehe>ain, P. P., and Maquenne, L. 

 Compt. Rend. Acad. Sci., 95: 691. 1882. 



26 Stoklasa, J., and Vitek, E. Beitrage zur Erkenntnis des Einflusses 

 verschiedener Kohlenhydrate und organischer Sauren auf die Metamorphose des 

 Nitrats durch Bakterien. Centrbl. Bakt. II, 14: 102-118, 183-205. 1905. 



26 Beijerinck and Minkman, 1910 (p. 546). 



