(II A I' r i: H 



Morphology, Cytology, and Life Cycles 



(ienoral Alorphological Properties of Ac- 

 tinoniyeeles 



As has hceu pointctl out, all tiic exicleiice 

 rt'ccntly sul)mitted conccrnin<!; the structure 

 and functions of actinomycctes definitely 

 establishes the fact that these organisms are 

 to be classified with the bacteria and not with 

 the fungi. Lehmann and Xeunuinn (189()) 

 were among the first to draw attention to 

 the close morphological relationship between 

 the diphtheria and the tubercle bacillus, on 

 the one hand, and the actinomycetes on the 

 other. Later (1920), they emphasized that 

 the distinction between mycobacteria and 

 actinomycetes is not very sharp, inasmuch 

 as some mycobacteria show only slight re- 

 sistance to decolorization by mineral acids, 

 and some of the actinomycetes possess 

 relati\'ely well-developed acid-fastness. As 

 pointed out previously, Cummins and Har- 

 ris suggested, on the basis of recent chemi- 

 cal evidence, that the order Actinomycetales 

 be abolished altogether and that the fami- 

 lies of the actinomycetes i)e included in the 

 Eubacteriales. 



Actinomycetes, like the true bacteria, are 

 procaryotes. Their growth (protothallus) is 

 made up of branching filaments, producing a 

 mycelium. This may be of two types, one 

 prostrate, forming a vegetative growth, 

 sometimes referred to as substrate myce- 

 lium; the other, erect or aerial mycelium. 

 The spore-bearing hyphae of the aerial my- 

 celium usually have a somewhat greater 

 diameter than the hyphae of the substrate^ 



mycelimn. These two types of mycelium, or 

 mycelial stages, are not only structurally 

 different but possess different growth re- 

 quirements. The secondary or aerial myce- 

 lium is considered by most investigators to 

 originate asexually from the primary or 

 substrate mycelium; some consider it as a 

 sexual stage. 



Actinomycetes produce two types of 

 spores: (a) true conidia, and (b) arthrospores 

 or chlamydospores. The earlier investigators, 

 notably Lachner-Sandoval, recognized "frag- 

 mentation" spores appearing as spherical to 

 cylindrical segments of old hyphae, pro- 

 duced by the contraction of the protoplasm; 

 and "segmentation" spores produced by the 

 septation of the tips of the aerial filaments, 

 usually formed in lateral branches of the 

 aerial hyphae but also extending to the main 

 filaments in substrate growths. According to 

 Xeukirch, the "segmentation" spores are 

 produced not by a process of septation of 

 the aerial mycelium, but by the successive 

 contractions of the protoplasm, until ap- 

 proximately isodiametric portions are sepa- 

 rated by regularly alternating empty spaces 

 (see also Domec) . 



On the basis of a study of a number of 

 saprophytic actinomycetes, belonging to 

 the genus now recognized as Streptomijces, 

 Drechsler summarized their morphological 

 characteristics as follows: 



1 . The vegetative growth consists of a myce- 

 lium composed of profusely branching hyphae, 

 the t(>rmiiial growing jjortions of which are densely 



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