kluyver's contributions to microbiology and biochemistry 



other of these groups. The subdivision of the two orders into genera 

 was based primarily on physiological criteria, and the genera, in- 

 cluding many new ones, were therefore largely physiologically defined. 

 The new names proposed were designed to express directly the main 

 morphological and physiological attributes of their members. 



Although the approach had much to recommend it, the increased 

 use of physiological properties also led to developments that may be 

 deemed less satisfactory. The medically oriented bacteriologists now 

 felt justified, and I believe rightly so, in regarding pathogenicity as a 

 differential character on a par with certain biochemical ones. Eventu- 

 ally this led to the creation of special genera for disease-producing 

 bacteria, and these sometimes overlapped with genera of non-patho- 

 genic organisms. For the development of a consistent system of clas- 

 sification it therefore became necessary to assess the relative values of 

 several unrelated physiological properties, and, in the absence of 

 acknowledged standards, it usually proved impossible to achieve con- 

 cordance amongst specialists of different persuasion. Another unfor- 

 tunate result of the application of physiological properties for the crea- 

 tion of taxa of higher order was that the extremely limited compre- 

 hension of what constitutes the fundamental characteristics often led 

 to the use of what later could be regarded as very minor qualities. 



Now, as mentioned earlier, the discovery of Acetobacter suboxydans, 

 and the comparison of its properties with those of other acetic acid 

 bacteria, provided the opening wedge for Kluyver's entrance in the 

 field of bacterial taxonomy. The very appearance of cultures of this 

 organism on sugar-calcium carbonate-agar plates left no doubt that 

 it represented a hitherto unknown type, and the biochemical studies 

 had shown that it could be characterized by its low oxidative capac- 

 ity. Because the other representatives of the acetic acid bacteria also 

 seemed to exhibit differences in this respect, it had become possible 

 to arrange all of them in order of their oxidizing ability, and to assign 

 to those with clearly recognizable differences the status of a species or 

 species group. This approach could also be applied readily to some 

 strains of acetic acid bacteria that Visser 't Hooft had isolated from 

 ditch water, through elective cultures in an acidic mineral medium 

 with alcohol as organic substrate. These strains differed from all other 

 Acetobacter cultures in being catalase negative and able to oxidize 

 molecular hydrogen. At the time this latter feature suggested that they 



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