220 



THE ACTINOMYCETES, Vol. I 



ble ill water, l)ut not in organic solvents. It 

 was stable in an acid reaction, but was 

 rapidly destroyed in an alkaline reaction and 

 at 100°C. 



The onl}^ report of a substance active 

 upon actinomycetes and not upon true 

 bacteria or fungi was made by Szabo and 

 Marten (1955), who isolated from a culture 

 of an actinomycete an "anti-actinomycete 

 factor" that was highly active against ac- 

 tinomycetes, without any activity upon 

 gram-positi\'e and gram-negative bacteria. 



Effect of Actinomycetes upon Sapro- 

 phytic Soil Bacteria 



The effect of actinomycetes upon the 

 growth of soil saprophytes and upon plant 

 pathogens has also received considerable 

 attention. Nikolaieva first observed, in 1914, 

 that actinomycetes may exert a repressive 

 effect upon the growth of Azotohader. Nickell 

 and Burkholder (1947) studied the inhibition 

 of growth of Az. vinelandii by \'arious ac- 

 tinomycetes isolated from soil. When cul- 

 tures of actinomycetes were mixed with soil 

 samples and plated out, the nitrogen-fixing 

 bacteria were either greatly reduced in num- 

 ber or completely eliminated. It was sug- 

 gested that this serves to illustrate the 

 importance of microbial antagonism in eco- 

 logical investigations. 



Another antagonistic effect of actinomy- 

 cetes upon nitrogen-fixing bacteria may 

 prove to be of even greater economic im- 

 portance. Konishi and Fukuchi have shown 

 that certain actinomycetes are able to in- 

 hibit the growth of root-nodule bacteria; 

 some of the (!ultures, like »S'. flavus, were par- 

 ticularly effective. 



Babak (1958) tested the sensitivity of (iO 

 Azotobacter cultures to various species of 

 Streptomijces and to various antibiotics, 

 such as penicillin, streptomycin, gramicidin, 

 and chlortetracycline. They were all found 

 to be susceptible to the antibiotics. Their 

 sensitivity to the S. roelicolor grou]) was 



dissimilar; some strains pnn-ed inhibited and 

 others indifferent . 



When the antimicrobial properties of ac- 

 tinomycetes became well recognized, it was 

 only natural that attempts should be made 

 to encourage the development of these or- 

 ganisms in the soil, in order to depress the 

 growth of various organisms capable of 

 causing plant diseases. 



Activity of Actinomycetes upon Plant 

 Pathogenic Fungi 



An extensive literature has accumulated 

 upon the antagonistic effects of actinomy- 

 cetes upon fungi, especially upon plant 

 pathogens. References to such effects are 

 reported earlier in this chapter. Winter pre- 

 sented (1949) further evidence concerning 

 the ability of various actinomycetes to at- 

 tack Ophiobolus graminus, an important 

 parasite that attacks wheat. Sanford and 

 Cormack tested the effect of eight cultures 

 of actinomycetes upon the disease-producing 

 fungus Helminthosporium sativum. In com- 

 parison with a disease rating of 66 per cent 

 for the untreated pathogen, four actino- 

 mycetes depressed the \'irulence of the 

 pathogen to 33, 22, 22, and 1 per cent, re- 

 spectively; two had no marked effect; and 

 the other two appeared to increase the viru- 

 lence by 12 and 16 per cent, respectively'. 



Perrault demonstrated that the growth of 

 CoUetotrichum sepedonicum in agar media 

 was impeded by several microorganisms iso- 

 lated from potato tubers affected with ring 

 rot. Four of these organisms were actino- 

 mycetes and were able to produce antibiotic 

 substances that diffused readily through the 

 medium and prevented all growth of the 

 pathogen. One culture produced a lysis of the 

 plant pathogen. 



McGahen treated soils in the sugar-cane 

 belt of Louisiana with bagasse compost, with 

 cowpea and soybean trash, and with blood- 

 meal, tankage, bonemeal, and ammonium 

 sulfate. The actinomycete^ populations were 



