574 PRINCIPLES OF SOIL MICROBIOLOGY 



nitrite could be found in the cells of Azotobacter. 57 Loew and Azo 5S 

 considered the reaction of nitrogen-fixation by Azotobacter to take place 

 as follows: 



N 2 + 2 H 2 = NH 4 N0 2 



The ammonium nitrite is reduced to ammonia which will interact with 

 the decomposition products of carbohydrates to give amino acids. 59 



CH 3 • CO • COOH + NH 3 = CH 3 ■ CHN • COOH + H 2 

 pyruvic acid 



CH 3 • CHN • COOH -f H 2 = CH, • CHNH 2 • COOH 



alanine 



CHO • COOH + NH 3 = H • CNH • COOH + H 2 

 glyoxylic acid 



HCNH • COOH + H 2 = CH 2 • NH 2 • COOH 



glycocoll 



By the process of condensation, the amino acids are built up into proteins. 

 Beijerinck and van Delden 60 originally thought that the nitrogen is first 

 fixed in the form of an inorganic soluble compound which goes into 

 solution. No soluble inorganic nitrogen compounds could be demon- 

 strated in pure cultures, but in crude cultures the proteins may again be 

 hydrolyzed into soluble forms of nitrogen. It was suggested, 61 therefore, 

 that the nitrogen is attached to the nitrogen-free organic compounds 

 which are then changed to proteins. Soluble organic nitrogen com- 

 pounds were found, 62 however, not only in the filtrate of a phospho- 

 tungstic acid precipitate of a dead Azotobacter culture, but also after 

 the culture was filtered through a Chamberland filter. It was sug- 

 gested 63 that Azotobacter forms, in its early stage of development, a 

 complex consisting of sugar and nitrate which is similar to the sugar- 

 phosphoric acid complex which takes an active part in alcoholic fermea- 



57 Kellerman, F., and Smith, N. P. The absence of nitrate formation in 

 cultures of Azotobacter. Centrbl. Bakt. II, 40: 479. 1914. 



68 Loew and Aso. On changes of availability of nitrogen in soils. II. Bull. 

 Coll. Agr., Tokyo, 7: No. 5 (Centrbl. Bakt. II, 22: 452. 1909). 



69 Lipman, 1904-5 (p. 112). 



60 Beijerinck and van Delden, 1902 (p. 105). 



61 Gerlach and Vogel, 1903 (p. 379). 

 6 - Lipman, 1903 (p. 115). 



63 Bonazzi, 1921 (p. 567). 



