210 



THE ACTINOMYCETES, Vol. I 



tion of antibiotics does not appear to be 

 correlated, therefore, with the stimuhition 

 of reactions influencing the breakdown of 

 nutrients or certain other oxidation and fixa- 

 tion processes. 



Greig-Smith, in his studies on the occur- 

 rence of toxic substances in soil, gave a clear 

 description of the antagonistic effect of ac- 

 tinomycetes against bacteria and fungi; the 

 fact that actinomycetes grow only slowly in 

 normal soils suggested the possibility that 

 they comprise an important factor limiting 

 bacterial development. It may be of interest 

 to quote from his paper: 



"In making counts of soil-bacteria, it is not 

 uncommon to find colonies of Bac. mycoides or of 

 races of Bac. vuUjatus spreading over the surface of 

 the nutritive agar. Very often it will be noted that, 

 while the majority of the colonies are covered by 

 the spreading growths, there are a few that are 

 untouched. The mycoides-colony may approach to 

 within two, five, or ten millimetres, and then 

 spread out and surround the colony, leaving a ring 

 of clear agar medium. It is evident that there is 



some product secreted by these colonies which is 

 obnoxious to the spreading colony, whether it be 

 Bac. rnycuides, Bac. vulgaius, or to spreading 

 moulds such as Pemcillium or Aspergillus. An 

 examination of the colonies producing this toxic 

 effect showed that the majority consisted of Ac- 

 tinomj^ces or Streptothrix as they have been 

 called. Some of these darkened the medium and 

 were apparently j4c^ chromogenus . Certain of these 

 colonies were selected, and spotted upon fresh 

 plates, in the centre of which bacteria with spread- 

 ing colonies were planted. The white forms were 

 found to be very toxic, while the dark forms were 

 feebly toxic to the spreading Bac. vulgatus." 



Evidence concerning the antagonistic 

 potentialities of actinomycetes began to ac- 

 cumulate also as a result of a different ap- 

 proach. IMillard and Taylor succeeded in con- 

 trolling potato scab, caused by S. scabies, by 

 the use of green manures and grass cuttings. 

 When potatoes were grown in sterilized soil 

 infected with S. scabies, scab was reduced by 

 the simultaneous introduction into the soil 

 of S. praecox, a saprophytic organism. By 

 increasing the proportion of the saprophyte 



£. co/i 

 6. mycoides 

 S' subfilis 

 Staph, aureus 

 =■ Ps. aeruginosa 



TOTAL ACTIVE 



>20 



l|-20min 



ZONE OF INHIBITION AGAINST TEST 



lOmm 

 ORGANISMS 



Fi(;uRE 81. Disi ril)ut ion of antagonistic properties among freshly isolated actinomycetes (Rejjro- 

 ducc'dfrom: Rouatt,J. W., Leclievalier, M., andWaksman, S. A. Ant 11). Cliemoth. I : ISi), 1951). 



