UNITY AND DIVERSITY IN THE METABOLISM OF MICRO-ORGANISMS 



the living cell, undergo transformations that lead to their partial 

 excretion in altered form. 



You are sufficiently familiar with the notion that this applies to the 

 higher organisms; the idea that it is equally true for the microbes 

 follows immediately from the consideration that in so many cases the 

 presence of microbes is forced upon us by the very fact that we observe 

 chemical changes. When milk turns sour, when sugar- or protein- 

 containing solutions start to ferment, it is first of all metabolic activ- 

 ities that draw our attention, and, after half a century of microbiol- 

 ogical research, will lead to the inference that microbes are present. 



As the title of to-day's lecture indicates, it is my intention to dis- 

 cuss the unity and diversity in microbial metabolism. But I shall take 

 the liberty of changing the sequence and first to dwell upon the diver- 

 sity. Later on I shall then try to indicate some aspects of the unity by 

 which this diversity is tied together. In doing so I shall also follow in 

 the main the historical development of microbiology. 



When, owing to Pasteur's pioneer investigations, the idea had be- 

 come established that fermentation, putrefaction, and mineralization 

 were none other than metabolic processes of microscopically small 

 organisms, microbiologists obviously considered it their first duty to 

 make a survey of the multitude of different causative agents. 



Chemically the diversity manifested itself in two ways. It was ob- 

 served on the one hand that one and the same medium might yield a 

 variety of metabolic products; on the other that different microbes 

 differ greatly in their requirements for particular chemical substances. 

 Let me first illustrate the former aspect with some examples. 



If I inoculate a series of flasks, each containing a sterile solution of 

 5 per cent glucose in yeast extract, with pure cultures of a film-forming 

 yeast (Mycoderma cerevisiae), and with some common moulds, such as 

 Aspergillus niger and Citromyces glaber, respectively, a chemical analysis 

 of the cultures at the end of their development will yield different 

 results. Confining the investigation to a determination of the fate of 

 the consumed sugar, it will be found that the film yeast has oxidized 

 it to carbon dioxide and water; hence the over-all metabolism resem- 

 bles that of animals. In contrast we shall find that Asp. niger and C. 

 glaber have produced sizable amounts of oxalic and citric acid, respec- 

 tively, in addition to carbon dioxide. Consequently this simple exper- 

 iment reveals metabolic differences although these are not as yet very 



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