VAN NIEL: SYSTEMATICS OF THE BACTERIA AND BLUEGREEN ALGAE 99 



The quotations from Babcock and Dobzliansky show that we cannot expect 

 that the same methods now so successfully used elsewhere will soon solve the 

 problem. But it is important to point out that much can be done, and that a 

 great deal of the present confusion in our thinking is the result of an utterly 

 inadequate appreciation of the truly "biological" possibilities that the bacteria 

 and bluegreen algae still offer. ]\Iost of the present difficulties have resulted from 

 studies with isolated, pure cultures, often grown under extremely artificial con- 

 ditions, having little if anything in common with those that have permitted the 

 persistence of various types of these microbes in nature. No one has realized 

 this fallacy better than Winogradsky who, about thirty years ago, started to inject 

 the notion that pure cultures may be necessary for an adequate study of certain 

 physiological problems, but that an understanding of the role of these organisms 

 in nature cannot be gained exclusively by this methodology (see Winogradsky, 

 1949). It is from investigations on their behavior in competition with others that 

 we may expect advances which will ultimately be of the greatest significance 

 for gaining a better perspective also concerning the systematics of the organisms. 

 It is quite possible that many of the artificially produced mutants of bacteria 

 can be maintained only under the abnormal conditions provided by the use of 

 pure cultures and culture media that bear no resemblance whatever to the envir- 

 onments in which the organisms are naturally found. For the development of 

 sound principles of bacterial classification it is of the utmost importance that 

 this criticism be heeded; it is a serious one, and suggests at the same time an 

 approach that is far better suited to the problem. 



Just as the modern taxonomists of the higher plants and animals have come 

 to insist on the need for far more than the detailed examination of a few museum 

 specimens and have stressed the importance of field studies on naturally occur- 

 ring populations, amplified by cytological and genetic investigations, bacteriolo- 

 gists must realize that bacterial systematics will not be greatly advanced so long 

 as it remains based largely on routine examination, by standard methods, of pure 

 cultures. In spite of the fact that those pure cultures are "living," they are in 

 some ways not much better than museum specimens; and their continued propa- 

 gation on the customary nutrient media all too often is apt to induce changes 

 in the organisms which make their recognition as offspring of the initial isolate 

 difficult, if not downright impossible. Numerous are the instances in which a 

 special feature that provided the first impetus to a detailed study of a bacterial 

 culture, be it a characteristic pigmentation, pathogenicity, or biochemical prop- 

 erty, such as the ability to live autotrophically as a hydrogen bacterium, or to 

 carry out a vigorous denitrification, was lost on continued cultivation, and the 

 evidence is strong indeed that the use of the routine meat extract-peptone-agar 

 media, on which,' to be sure, good growth of the pure culture could be secured, 

 must be held responsible for the changes in characteristics. 



It should be self-evident that these remarks are not intended to advocate that 

 pure cultures are useless for taxonomic purposes. AYere this implied, the devel- 

 opments would soon lead us back to the pre-Cohn era of experimentation, with 

 results so equivocal that their interpretation would become impossible. No; they 

 are meant to stress the necessity of learning more about the factors that operate 

 in maintaining the various types of bacteria and bluegreen algae in nature. In 

 the elective or enrichment cultures we possess a simple and powerful methodology 



