KLUYVER S CONTRIBUTIONS TO MICROBIOLOGY AND BIOCHEMISTRY 



which new students were initiated in the mysteries of microbiological 

 techniques. The morphological and physiological properties of the 

 isolated pure cultures were then further investigated, which generally 

 permitted their identification as members of the Acetobacter rancens 

 group in the sense of Beijerinck. But it so happened that in 1923 

 F. J. G. de Leeuw, after streaking such a beer culture on a malt ex- 

 tract-calcium carbonate-agar plate, obtained results strikingly different 

 from those commonly encountered. The developing colonies caused 

 an initial dissolution of the carbonate, due to acid production, that 

 was far more pronounced than what was generally observed with cul- 

 tures of A. rancens. Furthermore, the cleared areas gradually became 

 riddled with well-developed and large crystals, in such abundance 

 that it was relatively easy to obtain them in sufficient quantity for 

 chemical analysis. The crystals were found to be composed of a slight- 

 ly water-soluble calcium salt, readily soluble in dilute acid, from 

 which solutions the original calcium salt could be reprecipitated by 

 neutralization. This provided a simple and effective method for the 

 purification of the material. The pure substance reduced Fehling's 

 solution in the cold, and was eventually identified as the calcium salt 

 of 5-ketogluconic acid, a product of bacterial glucose oxidation that 

 had been discovered in 1887 by Boutroux. 



A detailed study of the physiological and biochemical properties 

 of the newly isolated bacterium [Kluyver and De Leeuw, 1924] re- 

 vealed it to be a typical vinegar bacterium. It was named A. suboxy- 

 dans to emphasize its pronounced tendency to perform only incom- 

 plete oxidations. Thus it was found to oxidize simple primary alcohols 

 to fatty acids, secondary alcohols to ketones, poly-alcohols to their 

 keto-derivatives, aldoses to aldonic acids, and, if the latter possessed 

 the requisite configuration, beyond this stage to the corresponding 

 keto-acids. Many of these properties are shared by A. xylinum, Bert- 

 rand's 'sorbose bacterium', but the latter, in contrast to A. suboxydans, 

 usually proceeds to oxidize the products of incomplete oxidation, after 

 these have started to accumulate, so that ultimately only carbon di- 

 oxide and water are produced. 



On account of its inability to effect a further oxidation of acetic 

 acid, ketoses, etc., A. suboxydans could thus be regarded as the ideal 

 acetic acid- and 'sorbose' bacterium. It has frequently proved its use- 

 fulness for the preparation of ketoses from the respective poly-alcohols, 



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