Actinomycetes 



81 



thcin to com ort the t)iosin of the protein molecule into dark-colored 

 melanins. 



The numerous species differ primarily in the length of their vegeta- 

 ti\e mycelium, nature of their aerial mycelium, absence or presence 

 of spores, method of spore formation, shape and color of colony, 

 pigmentation of colony and formation of soluble pigment, oxygen 

 requirement, production of diastatic and proteolytic enzymes, and 



Fig. 37. Growth of two typical strains of Micromonospora. 



a number of other morphological and physiological characters. These 

 vary in quantity as well as in quality, not only under the influence 

 of environmental conditions but even on continued cultivation under 

 the same conditions. The characteristic pigments produced by many 

 species may be lost or changed in kind; the color of the aerial my- 

 celium may be modified, and even the very property of forming such 

 mycelium may be lost. 



The ability of actinomycetes to produce antibiotics has recently 

 attracted considerable attention. Nearly seventy-five compounds or 

 preparations have now been obtained. They vary greatly in chemical 

 composition, toxicity to animals and to plants, in vivo activity, and 

 chemotherapeutic potentialities. Some, like streptomycin, chloram- 

 phenicol, aureomycin, terramycin, and neomycin, have found ex- 



