SELECTED PAPERS 



sideration of potential dissimilation processes in order to permit a 

 proper insight into the conditions needed for development, the follow- 

 ing example may further illustrate this. 



The organisms that can be assembled in the group of genuine lactic 

 acid bacteria are often designated as facultatively anaerobic. In a 

 sense this is permissible because the majority can indeed develop in 

 the presence as well as in the absence of air. It would, however, be a 

 glaring error if one were to infer from this fact that these organisms, 

 like the above-mentioned facultative anaerobes, can display both 

 an oxidative and a fermentative metabolism. On the contrary, even 

 in the presence of air the lactic acid bacteria do not utilize oxygen in 

 their metabolism. They are therefore purely fermentative organisms; 

 carbohydrates or sugar alcohols are essential for their growth; and 

 they differ from other strictly fermentative microbes only in the fact 

 that free oxygen does not completely inhibit their development. 



In this connexion it is not without significance to point out that 

 the absence of an oxidative metabolism among the lactic acid bacte- 

 ria is undoubtedly related to a property that Beijerinck in 1893 estab- 

 lished for all lactic acid bacteria, viz., the absence of the enzyme cat- 

 alase which decomposes hydrogen peroxide into water and oxygen, 

 and which had been found in all cells of higher plants and animals, 

 and until then also in all microbes that had been tested. Later Orla- 

 Jensen pointed out that the exclusively anaerobic butyric acid bacte- 

 ria also lack catalase, and we have established the same situation in 

 the case of anaerobic protein-decomposing bacteria. The widely ac- 

 cepted, though still hotly disputed [Dakin 1922] hypothesis that in 

 all aerobic organisms, the higher as well as the lower, catalase plays a 

 role in the transfer of oxygen to the oxidizable substrate is undoubted- 

 ly supported by these facts. Conversely it seems likely that a study of the 

 occurrence of catalase in a newly isolated microbe can be fruitfully 

 employed to determine the presence of an oxidative metabolism. 



The great significance of the establishment of the nature of a mi- 

 crobe's dissimilation processes, these primarily characterizing its me- 

 tabolism, also resides in the fact that the natural relationships of 

 micro-organisms are unquestionably expressed in their metabolism.* 



* But - as Orla-Jensen too points out correctly - it does not follow that identical 

 metabolic processes may not also be encountered among phylogenetically independ- 

 ent evolutionary lines. 



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