SPECIES CONCEPT !\ RELATION TO UTIN< >MYOETES 



r 'ganismSj like the actinomycetes, thai 



occur abundantly in nature; some of the 

 newly isolated cultures may differ greatly 

 from the fixed types. The difficulty of estab- 

 lishing and recognizing •"species" under these 

 conditions may become particularly perplex- 

 ing. Raper (1954) was fully justified in say- 

 ing, *Tt is almost axiomatic thai the ease 

 with which a species of microorganism can be 

 recognized tends to vary inversely with the 

 number of isolates available for observation 

 and examination." 



The concept of "species" first used during 

 the seventeenth century gradually came to 

 denote the fundamental units of a biological 

 classification. These units came to be re- 

 garded as fixed or static entities, created by 

 nature, which can be grouped into higher 

 categories, namely, genera, orders, and 

 classes. A> the evolutionary theory was grad- 

 ually accepted, especially with the develop- 

 ment of modern genetics and cytology, the 

 concept of "species" began to undergo a 

 change. 



Ilucker and Pederson (1931) emphasized 

 that the difficulty of dividing lower forms 

 into well-defined species has led many to 

 question whether these are natural groups 

 and whether they can be considered to be 

 similar to "species" among higher forms of 

 life. The problem always arises: How much 

 difference must exist between two cultures 

 of bacteria before we are justified in regard- 

 ing them as distinct species? 



Krassilnikov (1938) was very emphatic in 

 stating that many investigators, without 

 considering the rules of nomenclature pro- 

 posed at international congresses, either de- 

 Scribe the same forms under different names 

 or combine various organisms into the same 

 species. He said: "Even the concept of 

 'species' is considered differently by various 

 workers depending on their individual point 

 of view, frequently considering a minor lack 

 of correlation of a certain character as suffi- 

 cient justification for creating a new species." 



.lust as in the case of many groups of true 

 bacteria, one of the causes of the chaotic 

 state of nomenclature of the actinomycetes 

 is the lack of type cultures. It has actually 

 been suggested (Skerman, L949) that even 

 the available cultures be completely rede- 

 scribed, priorities being based on existing 

 names, and those names and descriptions for 

 which no type cultures are available be dis- 

 carded. 



In comparing the species concept among 

 microbes with that of higher plants and 

 animals, Cowan (1956) suggested that con- 

 sideration be given to the following aspects: 

 (a) whereas larger plants and animals have 

 geographical distribution areas, few microbe- 

 have such particular areas; (b) morphology 

 is essential for the separation of species 

 among algae, fungi, and protozoa, but it 

 barely distinguishes higher ranks among bac- 

 teria; (c) cytology is useful at the generic 

 level, but "at the species level the bacteriol- 

 ogist relies more on physiological than on 

 morphological differences"; (d) interfertility 

 is hardly to be considered as a species char- 

 acter, since bacteria and actinomycetes re- 

 produce asexually; (e) the introduction of 

 certain characters in microbiology not uti- 

 lized by botanists and zoologists adds satis- 

 factory classification criteria; these include 

 "nutritional requirements, metabolic and 

 catabolic products, antigenic structure and 

 pathogenicity." 



In discussing bacterial classification, 

 Sneath (1957) came to the following con- 

 clusions: (a i an ideal classification is one 

 which has the greatest content of informa- 

 tion; (b) over-all similarity is the basic con- 

 cept of such ;in ideal classification, and i- 

 measured in terms of the number of similar 

 feature- possessed by two organism-: c 

 every feature should have equal weight; (d) 

 the division into taxonomic group- i- made 

 upon correlated feat ures. 



To avoid the growing confusion from con- 

 flicting ideas, (iihnour ( l'.lAS) suggested sep- 



