UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



The first ten represent oxidative dissimilation reactions of which 

 the upper three occur also in higher animals, the others being typical 

 dissimilatory processes of the earlier mentioned microbes. The dissim- 

 ilations listed under the heading 'fermentative' are examples of trans- 

 formations that satisfy the energetic requirements of organisms that live 

 temporarily or permanently in the absence of oxygen. 



These fermentative processes, understandably, are characterized by 

 a considerably smaller caloric effect, and the correctness of the ener- 

 getic approach to these transformations is reflected in the fact that per 

 unit weight of the causative organism comparatively much more food 

 is used, and much greater amounts of metabolic products are formed 

 during fermentative existence. Particularly clearly is this phenomenon 

 revealed by organisms which, depending on circumstances, derive 

 their energy either from an oxidative or from a fermentative dissim- 

 ilation. This is true, for example, for yeast; and Pasteur had already 

 established that the sugar consumption per unit weight is considerably 

 greater during anaerobic than during aerobic cultivation ; in the latter 

 case part of the sugar is also oxidized. 



Now it cannot be doubted that the energetic interpretation of metab- 

 olism can also be used for the clarification and systematization in 

 other directions. In the first place it forces the investigator to develop 

 a clearer picture than is customary of the metabolism of the organism 

 studied. To mention an example : it is usually stated without further 

 specification that the extensively investigated B. coli can grow in meat 

 extract broth both with and without sugar, and that it is a facultative 

 anaerobe, implying that it can develop both in the presence and in the 

 absence of oxygen. Many a microbiologist does not realize, however, 

 that the dissimilation of this bacterium consists in an oxidative degra- 

 dation of proteinaceous split products on the one hand, but in a fer- 

 mentative decomposition of carbohydrates or sugar alcohols on the 

 other, so that the presence of the last-mentioned substances is a pre- 

 requisite for anaerobic growth. This is in contrast to bacteria of the 

 Proteus-group which are usually similarly characterized in the litera- 

 ture, although they appear to possess the property of obtaining energy 

 from a fermentation of protein degradation products so that they can 

 lead an anaerobic existence even in the absence of carbohydrates. 

 While this example indicates that the vague designation of an organ- 

 ism as a facultative anaerobe should be replaced by a rational con- 



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