36 



THE ACTINOMYCETES, Vol. I 



with special antibiotic-producing properties. 

 Their excessive growth is no doubt due to 

 the introduction of a fresh supply of avail- 

 able nutrients in the form of bacterial cells. 



An examination of soils enriched with 

 streptomyces spores, using the Rossi-Cho- 

 lodny contact slide method, revealed that 

 those spores remained in the soil largely in 

 an ungerminated state. They grew only on 

 the rim of the soil adhering to the glass and 

 in the dead bodies of soil amoebae (Pfennig). 



Nature of the soil actinomycete population. 

 No attempt will be made to review here in 

 detail the numerous other investigations on 

 the abundance of actinomycetes in the soil, 

 as determined by the plate method. Suffice 

 to say that all these studies established the 

 fact that actinomycetes form an essential 

 constituent part of the soil microbiological 



200- 



< 

 O 



Od 

 LJ 

 Q. 



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z 

 o 



population. Although some assumptions 

 have been made that colony counts of bac- 

 teria, actinomycetes, and fungi represent the 

 numbers of spores in the soil and not of ac- 

 tive organisms, the evidence presented here 

 proves the contrary. By separating the no- 

 cardias (designated as proactinomycetes) 

 from the streptomyces (designated as actino- 

 mycetes). Topping failed completely to rec- 

 ognize the nature of these organisms, 

 namely, their vegetative versus sporulating 

 growth, and the possible confusion between 

 them; he did recognize, however, the nocar- 

 dias and nocardia-like organisms as members 

 of the native or ''autochthonous" microflora 

 of the soil. Further information on the occur- 

 rence of nocardias in the soil is found in the 

 work of Frey and Hagan (1931) and Gordon 

 and Hagan (1937). 



150 - 



100 - 



INCUBATION- DAYS 



Figure 19. Comi)aris()ii bctwccii donsity of vegetative inyeolium and ])late counts of actinomycetes 

 in soil. Continuous line: density of myceliiun; l)rok(>n line: platecounts (Reproduced from: Jensen, H. L. 

 I'roc. Linnean Soc. N. S. Wales 68: 69, 1943^. 



