60 COMPOSITION OF BACTERIA 



Therefore, our knowledge of the composition of this organism is 

 probably more nearly complete than it is of many other species. 



Berthelot early recognized that the nitrogen fixed by the Azoto- 

 bacter is insoluble in water, thus indicating its protein nature. 

 Lipman found there was a small but appreciable quantity of nitro- 

 gen in both young and old cultures of A. mnelandii not precipi- 

 tated by lead acetate and a large proportion not precipitated by 

 phosphotungstic or tannic acid. Further work indicated that the 

 substance was either amino-acids or comparatively simple peptids. 

 He considered that one of the early substances synthesized by these 

 organisms was alanin. An analysis of the Azotobacter membrane 

 gave the following: 



Nitrogen as ammonia 0.98 per cent. 



Basic nitrogen 2.76 " 



Non-basic nitrogen 6.39 " 



Nitrogen in MgO precipitate 0.42 " 



Total nitrogen . . . 10.45 " 



This, he finds, corresponds remarkably closely to legumin. That 

 it is complex is indicated by the fact that it is not readily assimilated 

 by plants. 



Stoklasa found the Azotobacter cell to contain 10.2 per cent, of 

 total nitrogen and 8.6 per cent, of ash. The ash was from 58 to 

 62.35 per cent, phosphoric acid. The nitrogen and phosphorus 

 were mainly in the forms of nucleoproteins and lecithin. The 

 percentage of both nitrogen and phosphorus in the cell increases 

 with age. 



The most complete analysis of the Azotobacter cells, so far 

 reported shows them to contain, when grown on dextrin agar and 

 rapidly dried at 30 C., 12.92 per cent, of protein. The protein is 

 similar to other plant proteins. It contains 10 per cent, of ammonia 

 nitrogen, 26.5 per cent, of diamino-nitrogen, and 60 per cent, of 

 mono-amino-nitrogen. It contains the amino-acids normally found 

 in proteins but the quantity of lysin present is high, whereas the 

 histidin is present only in traces. 



An examination made by Nishimura of a pure culture of a water 

 bacillus gave the following as the composition of the dry matter in 

 the bacillus. 



Albumin 63.50 per cent. 



Carbohydrates 12.2 



Alcohol extract 3.2 



Ether extract 5.10 



Ash 11.20 



Lecithin 0.68 



Xanthin 0.17 



Guanin 0.14 



Adenin . 0.08 



