616 



THE, FIXATION OF NITROGEN BY AZ0T6BACTER 

 CHROOCOCCUM. 



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

 Society. 



During the process of isolating Rhizobium leguminosarum from 

 a nodule of the Blue Lupin, a slimy colony was picked from a 

 plate and grown upon nutritive media. The culture formed 

 slime very readily, and as it proved to be a mixture of bacteria, 

 the components were separated and examined in order to see to 

 which bacterium the slime-formation was due. The first micro- 

 organism obtained in pure culture was Azotobacter chroococcum, 

 and as at that time experiments were being made upon the 

 influence of increasing amounts of asparagin upon the production 

 of slime by Rhizobium, the pure and the mixed cultures of Azoto- 

 bacter- were also tested. 



The following are the yields that were obtained, in seven days, 

 upon plates of medium containing dextrose 2 %, sodium phos- 

 phate 0*2 %, and agar 2 %, with increasing quantities of aspara- 

 gin. The tigures represent grams of slime from 100 c.c of medium. 



Asparagin % 0"0 O'Ol 0"02 0-03 0'04 0"05 0"06 0-08 O'lO 0"12 

 Mixed culture. 10 11 15 16 15 20 22 16 17 17 

 Azotobacter.. 2 3 4 8 14 17 19 19 IS 17 



The quantity of slime formed by Azotobacter in the absence of 

 asparagin is much the same as is produced by races of Rhizobium, 

 producing a similar optimum amount, as may be seen upon com- 

 paring the yield with that of the Pea race on p. 281. The slime 

 obtained from the mixed culture is in sharp contrast, and suggests 



