BIOLOGICAL-ACTIVITIES OF 2 FUNGISTATIC ANTIBIOTICS PRODUCED BY BACILLUS-CEREUS UW85

Cultures and culture filtrates of Bacillus cereus UW85 suppress dampin g-off of alfalfa caused by Phytophthora medicaginis. We studied the ro le in disease suppression of two antibiotics from culture filtrates of UW85 that reversibly inhibited growth of P. medicaginis. We purified the two antibiotics by cation-exchange chromatography and high-voltage paper electrophoresis and showed that one of them, designated zwitter micin A, was an aminopolyol of 396 Dg that was cationic at pH 7.0; the second, designated antibiotic B, appeared to be an aminoglycoside con taining a disaccharide. Both antibiotics prevented disease of alfalfa seedlings caused by P. medicaginis. Purified zwittermicin A reversibly reduced elongation of germ tubes derived from cysts of P. medicaginis , and antibiotic B caused swelling of the germ tubes. Mutants generate d with Tn917 or mitomycin C treatment were screened either for antibio tic accumulation in an agar plate diffusion assay or for the ability t o suppress damping-off disease of alfalfa. Of 2,682 mutants Screened f or antibiotic accumulation, 5 mutants were substantially reduced in an tibiotic accumulation and disease-suppressive activity. Of the 1,700 m utants screened for disease-suppressive activity, 3 mutants had reduce d activity and they accumulated less of both antibiotics than did the parent strain. The amount of antibiotic accumulated by the mutants was significantly correlated with the level of disease suppression. Addit ion of either zwittermicin A or antibiotic B to alfalfa plants inocula ted with a culture of a nonsuppressive mutant resulted in disease supp ression. These results demonstrate that B. cereus UW85 produces two fu ngistatic antibiotics that contribute to suppression of damping-off di sease of alfalfa.