Chafter VIl 



ANTAGONISTIC PROPERTIES OF ACTINOMY- 

 CETES AND PRODUCTION OF ANTIBIOTICS 



Antagonistic Effects of Actinomycetes:— Actinomycetes comprise 

 a large number of organisms which have the capacity of inhibiting the 

 growth of and even destroying other microorganisms, namely, bacteria, 

 fungi, and other actinomycetes. Several detailed reviews of this phe- 

 nomenon have been published during the last decade (448, 449, 451, 

 453). 



Any student of soil microorganisms who uses the plate method for 

 counting purposes has obser\^ed that some of the colonies of actino- 

 mycetes on the plate are surrounded bv clear zones free from the growth 

 of bacteria and fungi (483). In 1917, Greig-Smith (157) obser\'ed, 

 for example, that when a soil is plated out on a nutritive agar the growth 

 of certain spreading colonies of B. mycoides and B. vnlgatiis may be in- 

 hibited by other colonies on the plate. These will be surrounded by 

 a clear zone 2 to 10 mm. wide where the spreader does not penetrate. 

 Examination of the colonies that produce this toxic effect showed them 

 to consist of actinomycetes. Further study of the various tvpes of colo- 

 nies brought out the fact that the nonchromogenic strains produced the 

 most toxic effect. He postulated, therefore, that the ability of actino- 

 mycetes to antagonize bacteria and fungi may suggest their possible im- 

 portance in the soil as a factor which limits microbial development and 

 thus affects soil fertility processes. 



Although the soil may thus be considered to be a source of antago- 

 nistic actinomycetes (488), the enrichment or soil with specific patho- 

 genic bacteria, such as M. hiherculosis does not necessarily lead to the 

 development of specific actinomycetes active upon such bacteria (480, 

 489). The reason for this is that the growth-inhibiting effect of actino- 

 mycetes upon bacteria and fungi is brought about largely through the 

 production of toxic agents, which are now known as "antibiotics." The 

 production of such substances can easily be demonstrated for some or- 

 ganisms by the agar-cross-streak method. In many cases, however, or- 

 ganisms that show inhibition of bacteria on the plate do not produce any 

 antibiotic substance when grown in liquid media. 



Gasperini (130) was the first to demonstrate the antagonistic action 

 of actinomycetes. He observed that these organisms develop on fungus 

 mycelium, upon which they live to a limited extent in the form of a 



