C h a p t e r I 



The Species Concept in Relation to 

 the Actinomycetes 



Systematic Position <>(' the Actinomy- 



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In the preface to this volume, the state- 

 ment was made thai "I am now certain of 

 one thing, namely, thai the place of the 

 actinomycetes is definitely among the bac- 

 teria and not among the fungi. Ample evi- 

 dence of this belief has been presented in 

 Volume I of this treatise." Nevertheless, 

 -nine reiteration is warranted at this point. 



The taxonomic position of the actino- 

 mycetes, notably their relationship to the 

 bacteria, on the one hand, and to the fungi, 

 on the other, has been one of the most de- 

 batable questions in microbiology. The size 

 (width of thallus) and staining properties of 

 the actinomycetes have usually placed t hem 

 with the bacteria. Their branching and man- 

 ner of sporulation have suggested their rela- 

 tionship to the fungi. Still other properties of 

 actinomycetes seemed to warrant their con- 

 sideration as a transition group between the 

 bacteria and the fungi. 



Recenl evidence seems to point definitely 

 to the fact that the actinomycetes are more 

 closely related to the bacteria : 



1. Some of the actinomycetes, such as 

 species of Actinomyces and Nocardia, are 

 closely related to true bacteria, notably spe- 

 cies of Lactobacillus and Coryni bactt num. 



2. Neither actinomycetes nor bacteria 

 have heei i shown to contain i rue nuclei; they 

 both contain only chromatin granules dis- 

 tributed through the hyphae or the cells. 



:!. The diameter of actinomycete my- 

 celium and spores is similar to that of bac- 

 teria. Actinomycetes also, a- a rule, hick 

 septa. 



}. Act inomycetes are subjeel to at tack by 

 phages just as bacteria are; filamentous 

 fungi are not . 



5. Actinomycetes are usually sensitive 

 (allowing for strain variability) to antibiotics 

 that are active upon bacteria; they are usu- 

 ally resistanl to those antibiotics, like the 

 polyenes, that are active upon fungi hut not 

 upon bacteria. 



(i. Chit in is absent from the cell substance 

 of actinomycetes as well as from bacterial 

 cells, but is present in fungus mycelium and 

 spores. In their lack of cellulose, actino- 

 mycetes are also similar to mosl bacteria and 

 unlike fungi. Avery and Blank (1954) con- 

 cluded that "from the chemical point of view 

 Actinomycetales have nothing in common 

 with the true fungi, but rather with the bac- 

 teria." Cummins and Harris (1958) went 

 even further by suggesting that the order 

 Actinomycetales be abolished altogether and 

 that the families of the actinomycetes be 



included in the Eubocti Hall S. 



7. hike bacteria, but unlike mosl fungi, 

 actinomycetes a- .-i rule are sensitive to 

 an acid react ion of I he medium. 



8. The close relationship of the actino- 

 mycetes to the bacteria is also evident from 

 the work of ( 'ouch L95 I . who found that 

 certain Micromonospora-like form- resemble 



