

Annals 



of the 



Missouri Botanical Garden 



Vol. 6 FEBRUARY, 1919 No. 1 



SOME CONDITIONS AFFECTING THE GROWTH AND 

 ACTIVITIES OF AZOTOBACTER CHROOCOCCUM 



E. R. ALLEN 



Visiting Investigator, Missouri Botanical Garden 

 Associate in Biochemistry. Washinaton University School of Medicine 





Introduction 



The problem of soil biology is concerned to a considerable 

 extent with studies of the activities of the oligocarbophilous 

 and of the oligonitrophilous bacteria. Representatives of 

 both the groups appear to be very widely distributed, and the 

 inference is that they are more or less active in all normal 

 arable soils. Of the former group the Nitrosomonas, Nitro- 

 sococcus, and the Nitrobacter of Winogradsky ("the nitrify- 

 ing bacteria") are the most widely known, while of the latter 

 group the Azotobacter and the Bacillus radicicola or legume 

 bacteria ("the nitrogen-fixing bacteria' ') are the most 

 familiar examples. All of these and related forms have 

 been the subjects of extended research, and consequently an 

 immense and growing literature exists on this general 



subject. 



Although the physiological powers and the presence in 

 ordinary soil of these organisms can be readily proven by suit- 

 able incubation experiments with soils or impure culture, at- 

 tempts to isolate and grow these organisms, especially the 

 Azotobacter and the nitrifiers, in synthetic media of entirely 

 known composition lead to very great difficulties. Pure cul- 

 tures are not readily isolated, and when obtained their growth 



media of entirely known composition is so slow that 



Ann. Mo. Bot. Gard., Vol. 6, 1919 



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