280 Associative and Antagonistic Effects 



(a) the production of antibiotics is dependent upon the presence of 

 specific nutrients which usually are not found in normal soil; (b) 

 some antibiotics are readily destroyed by different soil-inhabiting 

 microorganisms; (c) the soil organisms exposed to the action of 

 antibiotics tend rapidly to develop resistance to them; (d) the sur- 

 vival or predominance of various microorganisms in the soil does not 

 appear to be correlated with the capacity of such organisms to 

 produce antibiotics. 



On the other hand, claims have been made which tend to suggest 

 that, under certain conditions at least, antibiotics may play a part 

 in soil processes. These are based on the following observations: 

 (a) the presence of small amounts of antibiotic substances in the 

 soil; (b) the formation of antibiotics by various pure cultures of 

 microorganisms in sterile soil; (c) the persistence of certain anti- 

 biotics added to the soil; (cZ) the capacity of various soil-inhabiting 

 organisms to inhibit the growth of plant pathogens; (e) the favor- 

 able eflFect upon the control of certain plant pathogens exerted by 

 stable manures, green manures, and other materials which favor the 

 development of antibiotic-producing organisms. Claims, not fully 

 confirmed, have been made that inoculation of soil with antagonistic 

 organisms will result in a depression in the development of the 

 pathogens. 



The presence in soil of substances toxic to plant growth has also 

 been definitely established. It is not known whether these are re- 

 lated to the antibiotics. It is known that some antibiotics, like actino- 

 mycin and glutinosin, have the capacity of causing certain plant 

 diseases, such as curly tips. There are not enough established facts, 

 however, to permit generalizations concerning the importance of 

 antibiotic substances, or of the organisms producing them, in the 

 control of soil fertility. 



Selected Bibliography 



1. Baron, A. L., Hamlhook of Antibiotics, Rdnliold Puljlishing Corp., New 

 York, 1950. 



2. Florey, H. W., Chain, E., Heatley, N. C, Jennings, M. A., Sanders, A. C, 

 Abraham, E. P., and Florey, M. E., Antibiotics, a Survey of Penicillin, 

 Streptomycin, and Other Antimicrobial Substances from Fungi, Actinomy- 

 cetes. Bacteria, and Plants, 2 vols., Oxford Uni\ersity Press, New York, 1949. 



