PROSPECTS FOR A NATURAL SYSTEM OF CLASSIFICATION OF BACTERIA 



different that it will be distasteful to the majority of bacteriologists to 

 incorporate these organisms into one and the same genus. 



One is thus led to the conclusion that among the physiological char- 

 acteristics there are some which should be used in separating larger 

 groups and the question is which ones may be deemed to be essential 

 in this respect. Now it is clear that differences in nutritional require- 

 ments are conditioned by differences in the metabolic activities of the 

 organisms. Thus the problem resolves itself in grading the metabolic 

 properties according to their intrinsic value. A lack of insight in the 

 fundamentals of metabolism has thus far been the great stumbling- 

 block for a rational application of physiological characteristics in tax- 

 onomy and it also explains the horror with which many systematicians 

 have witnessed their ever increasing use. 



In surveying the metabolism of the various bacteria one is struck by 

 its great diversity which contrasts sharply with the relatively great uni- 

 formity characteristic for the metabolism of higher plants and animals. 

 An analysis of this situation bears out that, whereas the anabolic proc- 

 esses are essentially similar in both cases the fundamental differences 

 are to be found in katabolism. It is especially the many different ways 

 in which bacteria succeed in meeting their energetic requirements 

 which draw the attention. Besides the respiration process, as it is also 

 found in higher organisms, we encounter numerous instances in 

 which this process is substituted for by conversions in which free oxy- 

 gen does not take any part. Moreover, all these processes are char- 

 acterized as well by the diversity of their substrates as by the different 

 ways in which these substrates are converted into the final products of 

 katabolism. 



The fundamental nature of the energy providing processes justifies 

 the view that they should be rated first amongst the physiological 

 characters suitable for classification, the more so since these properties 

 are typically reflected in the cultural behaviour of the organisms. 



If, in consequence of this, one is led to the creation of systematic 

 groups on the basis of katabolic properties is not the principle of 

 phylogeny as a taxonomic basis endangered? This needs not be the 

 case provided this principle is duly subordinated to the requirements 

 ensuing from a primarily morphological classification. For it does not 

 seem excluded at all that in a single morphological group a physiolo- 

 gical evolution is responsible for the differences in katabolism observed, 



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