358 



ACTINOMYCETES 



ways so, however; both Waksman and Henrici have demonstrated 

 to one of us a single hypha bearing both dextro and sinistro coiled 

 chains of conidia. The spiral curvature begins to develop as the 

 spores are formed and increases during their development. When 

 the spores are mature, the filaments untwist and this mechanism may 

 serve to help discharge them into the air. 



The spore-bearing aerial hyphae are branched, and this branch- 

 ing may also be characteristic of the different species and serve as a 

 means of differentiation. Drechsler recognizes two main types: "(1) 



an erect dendroidic type in which 

 the sequence of development of 

 the sporogenous hyphae is suces- 

 sive; and (2) a prostrate, racemose 

 type in which the development is 

 more nearly simultaneous." In 

 addition, Waksman has described 

 a type in which the spore-bearing 

 branches are given off from the 

 main or axial filament in whorls. 

 It remains to be demonstrated, 

 however, that these characters of 

 the conidia and conidiophores are 

 sufficiently constant to serve as di- 

 agnostic characters. It has been 

 claimed ^ that the conidia are dip- 

 loid, union of nuclei taking place in the immature conidiophore and 

 reduction division in the germinating spore. This has not been con- 

 firmed. Consult Knaysi ^- for cytology of the actinomycetes. 



Physiology of the Actinomycetes. The colonies of the aerobic 

 actinomycetes must be familiar to all who have ever exposed agar 

 plates to the air, either intentionally or accidentally, for their spores 

 are ubiquitous. Small, round, flat, tenaciously adherent to the me- 

 dium, often highly pigmented, the surface often covered with a white 

 or greyish powdery film, the surrounding medium often dark brown 

 in color, and very frequently accompanied by a most penetrating 

 musty odor, colonies are easily recognized. 



Older colonies vary considerably in appearance. In general, two 

 main types may be recognized, corresponding to the forms that do 

 and do not readily undergo fragmentation of the mycelium. The 

 first type forms colonies which are very firm, almost cartilaginous in 

 consistency, and very adherent to the agar. They are usually slightly 

 conical in cross section, frequently have an elevated central papilla, 



Fig. 130. Conidia and conidiophores 

 of Streptomyces viridochromogenus. 



