UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



Perhaps it may appear to you that the interpretation has always lain 

 at hand that metabolic products such as citric, oxalic, and obviously 

 gluconic acids are normal metabolic products in the oxidation of 

 glucose. This notion had not been generally accepted, however. This 

 appears from the fact that Butkewitsch [1922, 1923] who, during the 

 past several years, has carried out extensive experimental investigations 

 on citric and oxalic acid formation by moulds, has independently 

 reached the same conclusion only quite recently. Experiments carried 

 out in the Delft laboratory during the last year on the metabolism of 

 various acetic acid bacteria have also led to the same concept of a 

 stepwise oxidative degradation. To begin with, De Leeuw probably 

 recovered the bacterium used by Boutroux, and long since lost ; it turned 

 out to be an acetic acid bacterium which we have called Acetobacter 

 suboxydans. This organism also shows a close relationship to Bertrand's 

 sorbose bacterium, although it clearly differs from the latter in some 

 respects. The investigations have shown that A. suboxydans can carry 

 out the same mild oxidations of different sugar alcohols as have al- 

 ready been mentioned in connexion with the sorbose bacterium. But 

 it also appeared that A. suboxydans possesses a still weaker oxidative 

 capacity than A. xylinum, as evidenced, for example, by the fact that 

 the former oxidizes calcium gluconate only to ketogluconate, while 

 the latter can also oxidize the gluconate to carbonate. Besides, A. sub- 

 oxydans, in contrast to A. xylinum, cannot be induced to oxidize sub- 

 stances like dihydroxyacetone and potassium ketogluconate. Thus the 

 latter bacterium appears capable of further oxidizing its characteristic 

 metabolic products under suitable conditions. And this shows up the 

 intermediate nature of these incomplete oxidations. 



Still more clearly does the correctness of these concepts follow from 

 the fact that we [Kluyver and De Leeuw 1924] have succeeded in 

 inducing acetic acid bacteria that under ordinary culture conditions 

 completely oxidize substrates like glycerol and mannitol to bring 

 about incomplete oxidations by the use of methods similar to those 

 employed by Molliard in his studies on Asp. niger. A few words may 

 here be devoted to a discussion of these methods through which 

 oxidations may be halted at various intermediate stages. Molliard 

 paid attention primarily to the quantitative regulation of the amounts 

 of N, P, and K in the culture medium. In connexion with earlier 

 observations of Beijerinck and Hoyer, we made use of the fact that the 



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