UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



nitrogen of fallow soils was unquestionably the result of a biological 

 process, Winogradsky [1902] succeeded in isolating one of the caus- 

 ative agents, Clostridium pasteurianum, by means of the elective culture 

 method in 1893. It turned out to be an organism that can grow only 

 in the absence of air. The following remarkable experiment throws a 

 clear light on its extra-ordinary metabolism.* A solution containing 

 glucose and all other elements necessary for growth with the excep- 

 tion of nitrogen is inoculated with spores of this bacterium. The cul- 

 ture is placed in a container which is thereupon evacuated in order 

 to remove the toxic oxygen. Even after prolonged incubation one 

 does not observe any changes. At this point gaseous nitrogen, freed 

 from the last traces of oxygen and of nitrogenous compounds, is ad- 

 mitted. After 24 hours a vigorous fermentation ensues, and in a few 

 days the sugar has completely disappeared, the bacteria have grown 

 profusely, and nitrogen has been fixed. This demonstrates the remark- 

 able phenomenon of a living organism that is roused to life from a 

 latent state by the inert gaseous nitrogen! 



Closely related to this curious organism is the bacterium, Azoto- 

 bacter chroococcum, that was discovered a few years later by Beijerinck 

 and Van Delden. It, too, fixes nitrogen, and to an even greater extent. 

 But in contrast to C. pasteurianum it can do so only if an ample supply 

 of oxygen ensures a rapid oxidation of organic substrates.** 



Is it surprising that the activities of these organisms have elicited 

 the envy of men like Haber? 



Yet other specialists among bacteria demand our attention. How 

 curious a group of organisms are not the urea bacteria that more or 

 less intensively convert urea into ammonium carbonate ! Special men- 

 tion deserves Urobacillus pasteurii which under suitable conditions com- 



* In spite of the fact that the assimilation of gaseous nitrogen by CI. pasteurianum has 

 long been established beyond any doubt, it is, as far as I am aware, only recently 

 that the elegant demonstration has been devised (by H. J. L. Donker, Assistant at 

 the Laboratory of Microbiology of the Technological University) which illustrates 

 the sharp contrast between the harmful influence of oxygen and the salutary effect 

 of nitrogen gas. For the benefit of those who might wish to repeat this experiment, 

 it must be mentioned that the addition of a small amount of humate to the culture 

 medium is indispensable for its success. This does not affect the sense of the experi- 

 ment. 



** For additional details of the organisms studied by Beijerinck, reference may be 

 made to his 'Collected Works', published in 1922. 



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