BACTERIA FIXING ATMOSPHERIC NITROGEN 121 



gram of glucose consumed; the organism soon loses this property, but 

 it can regain it on passage through soil. 82 Planobacillus nitrofigens, 

 a large, rod-shaped, spore-forming bacterium, capable of fixing in three 

 weeks in a soil extract medium containing 2 per cent of mannite, 3.57 

 nigra, of nitrogen in 100 cc. of solution, was described. 83 A form 

 related to B. vulgar -e was found capable of fixing 1.8 to 4.7 mgm. of 

 nitrogen for one gram of sugar consumed. 84 A nitrogen-fixing organism 

 (Bac. azophile) was also isolated from manure. 85 Certain thermophilic 

 bacteria, growing in mixed culture at 61°C, are capable of fixing 

 appreciable quantities of nitrogen. 86 



Azotobacter may also live symbiotically with algae 87 and other 

 bacteria. 88 The quantities of nitrogen thus fixed may be considerable. 89 

 The symbiotic action between CI. pastorianum and Azotobacter, where- 

 by the second uses up the oxygen making conditions favorable for the 

 former, has been demonstrated. 90 The various acids produced by the 

 former are neutralized by the soil bases and can be utilized by the 

 Azotobacter as sources of energy; this symbiotic action leads to a 

 maximum economy in the utilization of energy. 



In respect to non-symbiotic nitrogen-fixation in the soil, Wino- 

 gradsky 91 distinguishes three catagories: 1. Very active soils are charac- 

 terized by an abundance of aerobic nitrogen-fixing bacteria and by the 

 ability to give readily spontaneous cultures of these bacteria when 

 enriched with an assimilable carbon source. 2. Soils only moderately 



62 Bredemann, G. Untersuchungen ilber die Variation und das Stickstoff- 

 bindungsvermogen des Bacillus asterosporus A. M. ausgefiihrt an 27 Stammen 

 verschiedener Herkunft. Centrbl. Bakt. II, 22: 44-89. 1908. 



83 Bondorff, K. A. Planobacillus nitrofigens n. sp. Den. Kgl. Veterinaer og 

 Landboholskr. Aarskr. 1918, 365-369. 



84 Truffaut, G., and Bezssonoff, N. Un nouveau bacille fixant d'azote. Compt. 

 Rend. Acad. Sci.175: 544. 1922. 



85 Fulmer, H. L., and Fred, E. B. Nitrogen-assimilating organisms in manure. 

 Jour. Bact. 3: 422-434. 1917. 



86 Pringsheim, H. Ueber die Assimilation des Luftstickstoffs durch thermo- 

 phile Bakterien. Centrbl. Bakt. II, 31: 23-27. 1911. 



87 Fischer, 1904 (p. 105); Heinze, B. Einige Beitrage zur mikrobiologischen 

 Bodenkunde. Centrbl. Bakt. II, 16: 640-653, 703-711. 1906. 



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



89 Hutchinson, C. M. Soil biology. Agr. Res. Inst. Pusa., Sci. Rpts. 1922-23, 

 43^9. 



90 Omeliansky, 1916 (p. 109). 



91 Winogradsky, S. Etudes sur Ies microbes fixateurs d'azote. Ann. Inst. 

 Past. 40: 455-520. 1926. 



