SELECTED PAPERS 



the organism is grown on sugar-rich media, considerable quantities 

 of oxalic acid were formed. A number of other moulds, closely related 

 to the well-known Penicillium glaucum, appeared to produce citric 

 acid under similar conditions; this has been considered a sufficient 

 reason for collecting these specialists in a separate genus, Citromyces. 

 Moreover, as early as 1886 the French chemist, Boutroux [1886], had 

 discovered a conversion of glucose, in the presence of calcium carbon- 

 ate, into calcium keto-gluconate under the influence of an aerobic 

 bacterium that was not described. And around 1900 appeared the 

 publications of Bertrand [1904] on the biochemistry of the so-called 

 sorbose bacterium [Acetobacter xylinum) which rightly caused a sensa- 

 tion also amongst organic chemists. Although from the start it was 

 obvious that this bacterium should be classed with the acetic acid 

 bacteria, its metabolism showed nonetheless important deviations 

 from that of the bacteria used in the manufacture of vinegar. This 

 appeared, for instance, from the fact that it produced large amounts 

 of sorbose when cultivated in the presence of sorbitol; mannitol 

 yielded fructose; and glycerol dihydroxyacetone. All of these represent 

 conversions that the ordinary acetic acid bacteria did not effect. 



Hence a number of specialists had gradually begun to stand out 

 amidst the at first sight metabolically quite uniform group of aerobic 

 microbes. And the discoverers of these organisms did not tire of sing- 

 ing their praise. 



Now it is certainly most interesting that recent investigations have 

 shown that the performances of all these apparently so diverse special- 

 ists may be correlated. Firstly, the experiments of Currie [191 7], and 

 particularly those of Molliard [1920, 1922], showed that by changing 

 the culture conditions it is possible at will to cause A. niger to convert 

 an important fraction of the sugar into gluconic, or citric, or oxalic 

 acid. Consequently one could make this organism, hitherto known 

 only as an oxalic acid specialist, produce substances that until that 

 time had been known only as specific products of acetic acid bacteria, 

 and of Citromyces species, respectively. This very fact made it quite 

 likely that the above-mentioned compounds are none other than inter- 

 mediate products of the oxidative degradation of glucose to carbon 

 dioxide and water. The difference between the specialists would then 

 merely consist in the fact that one organism would stop at an earlier 

 intermediate stage. 



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