608 



THE FIXATION OF NITROGEN BY RHIZOB1UM 

 LEG U MINOS A R UM. 



By R. Greig-Smith, D Sc, Macleay Bacteriologist to the 



Society. 



In the course of the research upon the formation of slime by 

 Rhizobium leguminosarum, it was noted that some races formed 

 more slime than others upon media to which no asparagin or 

 other nitrogenous substance had been added, and, being curious 

 to know whether there could possibly be a fixation of nitrogen, I 

 examined two races which gave the most promise of a positive 

 result. At the time, an experiment connected with the fixation 

 of nitrogen by Azotobacter chruococcuvi was about to be made, 

 and an extension was added to include the Robinia and Lupin 

 "d" (acidophile) races of the nodule-former. The results are 

 given in the following table. 



The Formation of Slime and Fixation of Nitrogen by Eaces of Rhizobium 

 alone and in combination.* 





Infected twice. 



Infected once. 





Slime, 



grms. 



Nitrogen 

 gained, 

 mgrms. 



Slime, 



grms. 



Nitrogen 

 gained, 



mgrms. 



Eobinia alone 



,, with B. levant formans 

 B. radiobacter ... 

 Azotobacter 



Lupin "d " alone 



,, with B. levaniformans 

 B. radiobacter . . . 

 Azotobacter 



7 



10 

 11 



5 



1 



15 

 15 



7 





 1 

 

 5 

 4 

 4 

 4 

 5 



3 



7 

 5 

 3 

 4 

 14 

 10 

 8 



2 

 2 

 o 





 1 

 3 

 3 

 3 



* The medium contained dextrose 2 %, sodium phosphate - 2 %, and agar 

 2 %. No nitrogenous constituent was added. The method of procedure in 

 this and the following experiments consisted in pouring 20 c. c. portions into 

 the ordinary 9 cm. Petri-dishes and smearing the plates with cultures of the 

 bacteria. The first set were infected twice, the slime being scraped off at the 

 end of the seventh day; the plates were reinfected and incubated at 22° for 

 a further period of 23 days when the experiment was finished. The nitrogen 

 was estimated in the whole test, i.e., agar+ slime, by the Kjeldahl-Gunning 



