THREE DECADES PROGRESS IN MICROBIOLOGY 



mediate in yeast and muscle metabolism, and which is one of the best- 

 known examples of a compound with an energy-rich phosphate bond. 



Here again we are confronted with a most remarkable unity in 

 metabolism of micro-organisms at first sight so widely separated. It is 

 clear that these important results mean a very real contribution to 

 the removal of the contrast between the autotrophic and the hetero- 

 trophic mode of life. 



It is impossible to discuss thirty years development of our know- 

 ledge of microbiological metabolism without giving some special atten- 

 tion to the change in our attitude towards the role of carbon dioxide 

 in this metabolism. We can state that until ten years ago the current 

 views were fully governed by the classical picture of the cycle of carbon 

 in nature. According to this picture carbon dioxide had to be con- 

 sidered as the endproduct of respiration in living animals and plants 

 and of their decay after death under the influence of bacteria and 

 fungi. The carbon dioxide once formed was unassailable by all heter- 

 otrophic organisms, and only entered into the second half of the cycle 

 owing to the special action of the green plants in which the radiant 

 energy of the sun managed to bring about the reduction ultimately 

 leading to the formation of the various organic constituents of the 

 plant. 



Now I shall not enter into details regarding the various observations 

 which are responsible for a considerable change of these views. To 

 begin with I briefly refer to the fact that the discovery of the chemo- 

 autotrophic bacteria already made exception to the rule that the con- 

 version of carbon dioxide to organic compounds could only proceed 

 with the aid of light energy. But besides this exception of a special 

 nature gradually several indications were obtained which seemed to 

 contradict the idea that in the colourless heterotrophic organisms car- 

 bon dioxide is only an indifferent endproduct of metabolism. A fast 

 increasing number of instances were recorded all pointing to the fact 

 that small amounts of carbon dioxide are indispensable to the initiation 

 of growth of a great variety of heterotrophic micro-organisms, and 

 that growth may be either completely suppressed or at any rate con- 

 siderably retarded by a more or less successful removal of carbon 

 dioxide from the culture. This seemed to indicate that the micro- 

 organisms in question in some way or other managed to utilize carbon 

 dioxide for the synthesis of essential cell constituents. 



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