380 ANNUAL REPORT OF THE Off. Doc. 



and protecting from the light, a giowtli began to develop ou the 

 surface of the medium composed of a peculiar large, round to oval 

 celled organism, not unlike yeast cells, to which he gives the name 

 Azotohacter Chroocnccum. This latter organism Beijerinck found 

 later on to bear a most important relation to nitrogen assimilation. 



A little later Gerlach and Vogel* succeeded in isolating from gar- 

 den soil the Azotobacter of Beijerinck. 



In the medium composed of dextrose 2 parts; patassium phosphate, 

 sodium chloride, calcium chloride each 0.5 parts; and ferrous sul- 

 phate 0.1 part, the J isolated and grew this organism in pure culture. 



Analyses of the culture at seeding, and after three weeks growth 

 showed a gain of 5.1 to 18.0 grams of nitrogen in 1,000 c. c. of culture. 

 According to these investigators Azotobacter Chroococcum appeared 

 to possess, when growing in pure culture in nitrogen free media, the 

 power of utilizing free atmospheric nitrogen. 



In a later communication, however, Beijerinck challenges this as- 

 sertion, claiming that the cultures of the former authors were not 

 pure cultures of Azotobacter, but mixed with other forms very dif- 

 ficult to separate. 



Furthermore, Beijerinck showed that Azotobacter alone, in pure 

 culture, was devoid of nitrogen assimilating power, and possessed it 

 only when growing in symbiosis with other forms. 



Beijerinck in his study of the Oligonitrophiles of the soil, or of 

 those organisms which grow in media containing mineral salts and 

 some carbohydrate such as dextrose or mannit. and therefore devoid 

 or containing but a trace of nitrogen, isolated three types of bac- 

 teria — (1) The Azotobacter, with which is associated (2) several 

 species of Granulobacter, and (3) Radiobacter. 



The Azotobacter is a strict aerobe and grows only on the surface 

 of the medium. It is what the author terms a macroaerophile. 



The Granulobacter are large spore bearing bacilli of the Clostri- 

 dium type, and when grown in saccharine media show the granulose 

 reaction. They, therefore, belong to the same type as Oloatridium 

 pasteuranum of Winogradsky. 



The Radiobacter, characterized by their polymorphic habit, and 

 commonly radiate arrangement of the cells, are, possibly, closely re- 

 lated or identical with B. radicicola of leguminous root tubercles. 



Both Granulobacter and Radiobacter while they do grow singly, 

 grow best in symbiosis with Azotobacter. 



Furthermore, both Granulobacter and Radiobacter singly possess 

 only feeble or negative nitrogen assimilating properties, but when 

 grown in symbiosis with Azotobacter there is a gain of nitrogen of 

 from four to seven milligrams per gram of sugar, in the medium, as- 

 similated. 



•Gerlach and Vogel. Centralblatt f. Bakterlologle, 2 t Abt. VIII. 1902. p. «74. 



