18 



THE ACTIXOMYCETES, Vol. I 



Figure 11. Colonie.s of bacteria antl fiiiigi. This 

 early photograph clearly illu.strate.s typical zone.s 

 of inhibition bj' some organisms (Reproduced 

 from: Lohnis, F. and Fred, E. B. Textbook of agri- 

 cultural bacteriology. McGraw-Hill Book Co., New- 

 York, 1923, p. 28). 



servations; (b) plate culture studies; (c) se- 

 lective culture procedures. Each of these 

 methods has certain advantages and disad- 

 vantages, and each contributes toward the 

 elucidation of the nature and abundance of 

 actinomycetes in a natural environment. 



Need for Special Media and Standard 

 Conditions of Growth 



The problem of pure culture studies of 

 actinomycetes attracted attention in the 

 early days (ByAvid, 1889). Great progress 

 has been made since then. At present the 

 culture media used for the growth of actino- 

 mycetes can be di\'ided into three distinct 

 categories : 



1. Media used primarily for characteriza- 

 tion and identification purposes; standard 

 media, comprising both synthetic and or- 

 ganic, are most essential. Synthetic, chiefl}^ 

 inorganic, media have found extensive ap- 

 plication in the study of the morphology, 

 physiology, and cultural characterization of 

 these organisms. Oi-ganic media are used for 

 obtaining supplementary evidence of a cul- 

 tural nature, especially for strains that do 

 not grow at all or grow only very W6\'ikly on 

 the common inorganic media. 



2. Media used primarily for obtaining 

 maximum growth, especially for the maxi- 

 mum production of certain chemical sub- 

 stances, such as antibiotics, vitamins, or 



enzymes. These are usually complex in com- 

 position, utilizing plant and animal materi- 

 als directly or after preliminary enzymatic 

 or acid digestion. 



8. Media used for maintaining cultures of 

 actinomycetes in such a manner as to reduce, 

 to a minimum, degeneration and ^'ariation 

 of the culture. Suitable media, comprising 

 both artificial and natural, such as sterile 

 soil, and suitable conditions of growth thus 

 make possible the preservation of type cul- 

 tures for comparative purposes. 



Kiister and Grein (1955) made a compar- 

 ative study of media for the preparation of 

 actinomycete cultures for morphological and 

 physiological studies. They found, for exam- 

 ple, that oatmeal agar and potato agar pro- 

 duce exactly the same types of spores, as 

 detected by the electron microscope. Both 

 substrate and aerial mycelium were quite 

 alike on the two media, except for minor 

 differences in the length and degree of cur- 

 vature of the aerial hyphae. Although the 

 previous cultivation of the organisms fre- 

 quently affects greatly the physiological 

 constancy of the strains, it did not appear 

 to be the case with the above two complex 

 media. 



The great majority of actinomycetes are 

 aerobic; very few are anaerobic; many are 

 microaerophilic. To supply proper aeration, 

 the organisms are grown on the surface of 

 solid media, or in shallow liquid layers, or in 

 a thoroughly aerated submerged condition. 



For anaerobic growth, special procedures 

 are required. Temperatures of 25-30° C are 

 usually used for incubation of the great 

 majority of steptomyces, nocardias, and 

 micromonosporas. Pathogenic organisms re- 

 (luire 37° C, and thermophiles usually re- 

 (luire 50-60° C. 



Morphological and Physiological Prop- 

 erties 



Among the stable morphological proper- 

 ties of actinomycetes essential for piu'poses 



