SPORE-FORMING BACTERIA 87 



of the plates inoculated with the antagonist. Inhibition of growth and 

 lysis were used as measures of antagonistic action. 



Hettche and Weber (408) isolated 41 strains of B. mesentericus 

 from 25 samples of soil. These were streaked on blood agar, and the 

 diphtheria organism was used for testing their effect. In 1 8 strains the 

 antagonistic action was detected in 24 hours j there was no parallelism 

 between inhibition and hemolysis. Of the 18 active strains, 1 1 lost the 

 property after two transfers and 2 were exceedingly active. 



Dubos (190) isolated from a soil enriched with various living bac- 

 teria a gram-negative, spore-bearing bacillus {B. brevis) that had a 

 marked lytic effect against gram-positive bacteria, including staphylo- 

 cocci and pneumococci. The antagonist was grown for 3 to 4 days in 

 shallow layers of peptone media at 37° C. The bacterial cells were re- 

 moved by centrifuging, and the filtrate was acidified, giving a precipi- 

 tate from which a highly active substance (tyrothricin) was isolated. 

 Dubos and Hotchkiss (205) soon demonstrated the presence in natural 

 substrates, such as soil, sewage, manure, and cheese, of various spore- 

 forming bacteria that have marked antagonistic properties against vari- 

 ous gram-positive and gram-negative bacteria. 



Hoogerheide (427) isolated from the soil an aerobic, spore-forming 

 bacterium that produced a highly active bactericidal substance j it also 

 prevented the formation of capsules by Friedlander's bacterium. This 

 substance appeared to be similar to gramicidin (885). 



It has thus been definitely established (857) that strains of spore- 

 forming bacteria possessing antagonistic properties are widely distrib- 

 uted in the soil and possess certain physiological characteristics that 

 differentiate them from the inactive strains. This is brought out in 

 Table 13. 



Spore-forming bacteria are also able to produce substances antagonis- 

 tic to fungi (231, 695, 734, 738). Cordon and Haenseler (149) iso- 

 lated an organism {B. simplex) that was antagonistic to Rhizoctonia 

 solani, an important plant pathogen. The antagonist produced a thermo- 

 stable substance that inhibited the growth and even caused the death of 

 the fungus. When the substance was added to the soil it controlled to 

 some extent seed decay and damping-off disease of cucumbers and peas. 

 Christensen and Davies (128) found that a strain of B. mesentericus 



