10 



NATURE, FORMATIOX. AXl) ACTIVITIES 



dowed with .selective antibacterial action 

 through antimetabolic mechanism." I'me- 

 zawa (1956) suggested the inclusion among 

 antibiotics not only of substances of mi- 

 ci'ol)ial origin but also those produced l)y 

 higher forms of life; their action should not 

 be limited to only microbes, but should also 

 include tumors. The definition thus becomes: 

 "Antibiotics are chemical substances that 

 are produced by living organisms and that 

 have the capacity to inhibit the growth of 

 microorganisms or other living cells." 



Words are but a means of conveying ideas 

 from the mind of one person to another. The 

 chief requisite is that the meaning of the 

 word be clear to everyone. 



We feel that the word antibiotic should be 

 used in its original meaning. An antibiotic 

 is not, howe\'er, a uniciue type of substance; 

 it can l)e an antibiotic and something else 

 at the same time. For instance, chloram- 

 phenicol is an antibiotic and also a synthetic 

 chemotherapeutic agent, since it can be 

 synthesized chemically. Citrinin is an anti- 

 biotic from PeniciUinm citrUinm and also an 

 antibiotic-like substance produced by a 

 plant. 



The word antibiotic does not imply any 

 specific type of action of the substance so 

 long as the effect is produced by minute 

 concentrations. Certain antibiotics act in an 

 indirect fashion. For instance, penatin, pro- 

 duced by certain penicillia, is toxic to micro- 

 organisms because of its enzymatic liberation 

 of hydi-()gen peroxide. 



Antibiotic Production in Soil 



Although antagonism caused by the pro- 

 duction of antibiotics is easily demonstrated 

 under the artificial conditions of laboi'atory 

 culture, it is rather difhcult to demonstrate 

 that production of antibiotics by soil micro- 

 organisms in natural soil does occur. This is 

 complicated by the fact that most of the 

 antibiotics are readily destroyed by some 

 of the microorganisms present in the soil. 



One method used to study this phenome- 

 non consists in inoculating soil with known 

 antibiotic-producers and, after a period of 

 incubation, attempting to detect the particu- 

 lai- antibiotic. Four different types of experi- 

 ments have thus been performed. The antag- 

 onist is inoculated: (1) into sterile soil 

 supplemented with various nutrients, such 

 as sugars, proteins, and peptones; (2) into 

 sterile unsupplemented soil; (8) into un- 

 sterilized soil with supplemented materials; 

 and (4) into unsterilized unsupplemented 

 soil. 



Demonstration of the production of an 

 antibiotic in sterile soil supplemented with 

 organic nutrients is easy, since the environ- 

 ment is highly artificial and not very differ- 

 ent from that of pure culture studies in 

 laboratory media (Siminoff and Gottlieb, 

 1952). In sterile unsupplemented soils, few 

 antibiotics have ever been produced. 



In the presence of a normal soil microflora, 

 demonstration of the production of a given 

 antibiotic in soil becomes most difficult be- 

 cause members of the microflora compete for 

 food with the artificially added antagonist 

 and, moreover, if the antil)iotic is formed, it 

 is commonly microbiologicall.v degraded. 

 In\'estigators have surmounted these diffi- 

 culties by adding massive inocula of the 

 antagonist imder study to nutritionalh" 

 favored loci in the soil. The production of 

 known antil)iotics in normal soil, in loci rich 

 in organic matter, was demonstrated by in- 

 oculating organic materials such as straw 

 and seeds of higher plants with the known 

 antibiotic-producers and burying them in 

 soil. After a period of incul)ation, proper 

 extraction techniques revealed in certain 

 cases the production of the antibiotic under 

 investigation. This method was successful 

 mainly in the study of fungal antibiotics 

 (Jeffreys et at., 1953; Wright, 1956). 



From these experiments we can conclude 

 that the production of antibiotics, as we 

 visualize it in the laboratory, does not occur 



