BACTERIAL ANTAGONISM WITH SPECIAL REFERENCE TO THE EFFECT OF PSEUDOMONAS FLUORESCENS ON SPORE FORMING BACTERIA OF SOILS

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Abstract
Pseudomonas fluorescens produces a thermostable, filterable, dialyzable bacterio-toxin which is both inhibitory and bactericidal. The toxin is not specific in its action but is more active against certain species than others. Fungi are more resistant than bacteria. Spore-forming bacteria and micrococci are very sensitive, while colon bacteria are resistant. The substance is not isoinhibitory. Amount of toxin produced depends on composition of culture medium and availability of O. Maximum production occurs in cultures grown on the sloped surface of Uschin-sky''s agar. The toxin persists longer in agar than in broth cultures and resists desiccation for long periods of time. It is soluble in alcohol, and is adsorbed by substances in soil and by charcoal. The toxin is produced in sterilized, manured soils inoculated with Ps. fluorescens. Alcoholic extracts from such soils are inhibitory for the more sensitive species only. Soils which have supported a vigorous growth of Ps. fluorescens in flask cultures are suitable for the growth of Bacillus cereus after sterilization. Samples of soil from fields, gardens, pastures and meadows failed to yield toxins by the same methods of extraction employed for pure cultures. It appears that the toxin is of a different nature from that of the thermolabile substances reported by others from soils.