UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



the metabolism of micro-organisms. Also in material respect there 

 exists a much greater unity than was assumed not so long ago. This 

 has been shown by recent studies; again, the circumstances do not 

 permit me to document this statement extensively. But it may be 

 pointed out that the investigations of Neuberg and collaborators have 

 made it very likely that acetaldehyde occurs as an intermediate pro- 

 duct in the fermentations provoked by yeast [cf. Fuchs 1922], coli 

 bacteria [Xeuberg and Nord 1919], butyric acid bacteria [Neuberg 

 and Arinstein 1921], and cellulose decomposers [Neuberg and Cohn 

 1923]. Furthermore, this intermediate product arises in butyric acid 

 fermentations both of substrates with 6 and with 3 carbon atoms per 

 molecule, which at least renders the formation of butyric acid with 

 its 4 carbon atoms from compounds of the C 3 type somewhat more 

 intelligible. The occurrence of pyruvic acid as an intermediate pro- 

 duct in diverse fermentations is equally suitable to demonstrate the 

 unity in material respect of at first sight very different processes. 



Even stronger does the material unity in metabolic reactions ap- 

 pear if now we consider the microbes that are characterized by a 

 typically oxidative dissimilation. It is evident from Table II that this 

 manner of fulfilling the energetic requirements, characteristic of all 

 higher plants and animals, is also encountered amongst rather diver- 

 gent groups of microbes. In contrast to the relatively extensive chem- 

 ical investigations of fermentative processes, these aerobic decompo- 

 sitions have not yet been much studied, however. The explanation 

 for this situation lies at hand; in general, aerobic organisms utilize 

 the energy of the proffered foodstuffs to the maximum extent, that is 

 to say that the oxidation is carried as far as possible, and the food is 

 oxidized to carbon dioxide and water, accompanied by ammonia in 

 the case of the oxidation of nitrogenous substrates. 



Nevertheless, exceptions to this rule have long been known. When 

 acetic acid bacteria had been discovered, it was immediately appar- 

 ent that they provided an instance of organisms characterized by an 

 incomplete oxidative metabolism. This manifested itself not merely in 

 the incomplete oxidation of alcohol to acetic acid, but also of glucose 

 to gluconic acid. Among other groups of aerobic organisms, too, some 

 specialists gradually appeared. Thus the mould, Aspergillus niger, ac- 

 quired some reputation as the causative agent of what has unfortun- 

 ately been called an oxalic acid fermentation; it was found that if 



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