114 ACTINOMYCETES AS ANTAGONISTS 



ing those that were isolated at random from the soil and those taken 

 from a culture collection. 



Meredith (595) made a survey of the distribution of organisms an- 

 tagonistic to Fusarium oxys forum cubense in Jamaica soils j most of 

 these antagonists belong to the actinomycetes. The antagonists were not 

 evenly distributed in the various soil samples, 10 of the (iG samples giv- 

 ing 44 per cent of the antagonistic organisms. Those actinomycetes that 

 were antagonistic to Fusarium when grown in their own soil-solution 

 agar were not always antagonistic when tested in soil-solution agar pre- 

 pared from other soil. A culture of actinomyces isolated from a compost 

 produced lysis of the Fusarium,. When spores of both organisms were 

 mixed in an agar medium, the fungus developed normally for two days 

 but began to undergo lysis on the fifth day, large sections of the my- 

 celium disappearing. On the seventh day only chlamydospores were ob- 

 served. In 9 days the fungus completely disappeared, the actinomyces 

 making a normal growth. 



NATURE OF ANTIBIOTIC SUBSTANCES 



It has already been established that antagonistic actinomycetes read- 

 ily produce a variety of different types of antibiotic substances. Some of 

 these have been isolated and even crystallized and information has been 

 gained concerning their chemical nature. Others have been obtained in 

 the form of crude but highly active preparations. Still others are known 

 but they have not been isolated as yet and have, therefore, been rather 

 insufficiently studied. So far, six substances have been definitely recog- 

 nized j namely, actinomycetin, actinomycin, streptothricin, streptomy- 

 cin, proactinomycin, and micromonosporin. 



Among the various antagonistic actinomycetes, five species have 

 been studied in detail and, therefore, deserve particular attention, 

 namely, S. antibiotkus (945), Streftomyces lavendulae (973), Stref- 

 tomyces griseus (795), Nocardia gardneri (309), and 5. albus (970). 



S. antibiotkus produces two highly active antibiotic substances that 

 have been isolated and described as actinomycin A and B. The first of 

 these has been studied in greater detail. It was shown to be antagonistic 

 to all species of bacteria tested as well as to many fungi, as brought out 



