SELECTED PAPERS 



However, apart from the disregarded observation made by Sohn- 

 gen already in 1905 that methane bacteria are able to convert a mix- 

 ture of carbon dioxide and hydrogen into methane, it lasted till 1936 

 before experimental proof for the utilization of carbon dioxide in 

 special cases of heterotrophic metabolism was given. In that year 

 Woods showed that Bacterium coli was able to produce formic acid out 

 of carbon dioxide and hydrogen, whilst Barker succeeded in bringing 

 convincing proof that also in the fermentation of organic compounds 

 by methane bacteria the methane always originated from a reduction 

 of carbon dioxide. Now these conversions of carbon dioxide into other 

 compounds with one C-atom were undoubtedly interesting but they 

 did not throw any light on the problem of the indispensability of car- 

 bon dioxide for cell synthesis and growth. For this reason it was of great 

 importance that Wood and Werkman, also in 1936, showed that in 

 the fermentation of glycerol the strictly heterotrophic propionic acid 

 bacteria take up carbon dioxide from the medium, and that for every 

 mole of carbon dioxide reduced approximately equivalent quantities 

 of succinic acid with its 4 carbon atoms are formed. This result may 

 be deemed to be of far-reaching significance, since it strongly suggests 

 that here synthesis of a C 4 -compound out of a C 3 -compound and car- 

 bon dioxide has taken place, which would imply the formation of a 

 new bond between carbon atoms. It is easily understood that this ex- 

 perimental result together with the increasing evidence for the indispen- 

 sability of carbon dioxide for heterotrophic organisms in general made 

 several investigators surmise that the uptake of carbon dioxide into or- 

 ganic compounds under formation of new carbon-carbon bonds would 

 be a reaction of more or less common occurrence in heterotrophic cells. 



In 1939, when lecturing on this subject in Helsinki, I have expressed 

 this view with the following words : 'At present a lecturer still must be 

 prepared to meet with energetic protests when he contends that the 

 cattle at pasture, or even his distinguished audience assimilates carbon 

 dioxide. Nevertheless, the temptation to such an assertion is already 

 there!' Now seven years later the statement in question is no longer 

 open to scepticism, and many of my auditors will think it to be quite 

 commonplace : the synthetic utilisation of carbon dioxide by hetero- 

 trophic cells has been indubitably proved for representatives of very 

 much diverging classes of organisms, such as bacteria, yeasts, fungi, 

 protozoa and higher animals. 



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