Waksman — 50 — Actinomycetes 



designated as a "colony." This is not a true colony in a bacterial sense, 

 since it is not an accumulation of a number of cells originating from a 

 single cell or from several similar cells. It is rather a mass of branching 

 filaments which originated from a spore or from a bit of vegetative my- 

 celium. 



The actinomyces colony is made up often of two types of mycelium, 

 consisting primarily of vegetative or substrate growth and of secondary 

 aerial or sporogenous growth. These two types of mycelium often show 

 fundamental differences in appearance, composition, and biological ac- 

 tivities. The vegetative mycelium grows into the medium, whereas 

 the aerial mycelium grows on the surface; the well-developed sporulat- 

 ing hyphae and the reproductive spores are produced in the aerial 

 mycelium. Some actinomycetes form only the vegetative mycelium, 

 whereas others produce both types. 



Vegetative mycelium.— The vegetative growth of the actinomycetes, 

 or the stroma, is usually shiny, gel-like, or lichnoid in appearance and 

 varies in size, shape, and thickness. The color of the growth may be 

 whitish or cream colored, as well as yellow, red, pink, orange, green, or 

 brown. In addition to the insoluble pigments, certain water-soluble 

 pigments are produced. Some of the pigments, notably the brown and 

 the darker or chromogenic pigments are formed upon complex organic 

 media and are a result of the action of certain enzymes of the tyrosinase 

 type, which are able to oxidize some of the organic constituents of the 

 medium to give the particular pigments. The red, yellow, and blue pig- 

 ments are synthetic in nature. 



When actinomycetes spores are inoculated into a fresh medium, 

 they germinate rapidly, usually within 2 to 6 hours, and give rise to one 

 or more germ tubes, as shown in Fig. 13. These grow into long hyphae 

 or threads which gradually develop into a complex mycelium. The 

 length and diameter of the hyphae differ considerably for the various 

 organisms. Some are straight and long, reaching 600iJ. or more; others 

 are only 50 to lOOix in length, and are much branched and curved. The 

 vegetative mycelium varies in diameter from 0.2 to O.SpL. Occasion- 

 ally, involution forms are produced which have even a greater diam- 

 eter. The structure of the h)rphae also varies with the composition of 

 the medium, the conditions of growth, especially temperature, and the 

 presence of stimulating or injurious substances. On the basis of the 

 length of the hyphae, Lieske (186) divided the actinomycetes into 

 long-hyphal and short-hyphal forms. It is doubtful, however, whether 

 such a sharp line of demarkation can be drawn for all organisms within 

 this group and for all media upon which they are usuallv grown. 



In older cultures, the vegetative mycelium becomes brittle and 

 readily breaks into fragments of uneven length. The mycelial frag- 

 ments are very small, usually l[x or less in length. Together with the 

 cellular contents they form a granular mass which deposits on the bot- 

 tom of liquid cultures. Some cultures undergo rapid lysis, especially 



