FIXATION OF ATMOSPHERIC NITROGEN 571 



bacter cells grown on solid media was given as 11.81 per cent and, when 

 grown in the same medium without agar, the cells contained 30.56 

 protein. 40 The difference in these results is due to the fact that a large 

 part of the membranous material and the slime surrounding the cells 

 consist of carbohydrates, free from proteins. 41 This material is filtered 

 out in the case of liquid media; this tends to increase greatly the 

 amount of protoplasm in the residual material. 



A different phosphorus content has also been recorded varying from 

 4.93 per cent P 2 5 33 to 2.51 per cent 39 of the dry material. Azotobacter 

 grown on agar media was found to contain 0.57 per cent phosphorus and 

 1.43 per cent potassium. 40 The following analysis of dry Azotobacter 

 cells has been reported: 42 moisture 6.63 per cent, ash 4.16 per cent, pro- 

 teins 12.93 per cent, nitrogen-free material 76.28 per cent. The nitro- 

 gen-free materials consist of polysaccharides which show 33 per cent 

 sugar, on hydrolysis with 1.25 per cent H 2 S0 4 and 10 per cent HC1. Bei- 

 jerinck and Van Delden believed this material to be of the nature of 

 pectin 43 ; others reported an abundance of pentosans. 44 The reserve 

 substances of the cell were found to consist of fats and volutin; the 

 slime, a complex carbohydrate, yielded a dextro-rotatory fermentable 

 sugar on inversion. 41 



On hydrolysis, Azotobacter showed the following constituents: 



■per cent 



Ammonia nitrogen 9.9 



Melanin nitrogen 3.7 



Total diamino nitrogen 26 .4 



Total monoamino nitrogen 60.0 



The diamino nitrogen consisted of 14.5 per cent lysine, 10.4 per cent argi- 

 nine, and 1.6 per cent histidine. The secretion of soluble nitrogen com- 

 pounds by the nitrogen-fixing organisms is of importance. Az. chroo- 



40 Hunter, O. W. Protein synthesis by Azotobacter. Jour. Agr. Res., 24: 

 263-274. 1923. 



41 Stapp, C. tlber die Reserveinhaltsstoffe und den Schleim von Azotobaktcr. 

 Centrbl. Bakt. II, 61: 276-292. 1924. 



42 Omelianski, V. L., and Sieber, H. O. Zur Frage der chemischen Zusam- 

 mensetzung der Bakterienkorper des Azotobacter chroococcum. Ztschr. physiol 

 Chem., 88: 445-459. 1913. 



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



44 Hoffmann, C. The protein and phosphorus content of Azotobacter cells. 

 Centrbl. Bakt. II, 36: 474-476. 1913. 



