La. Silosuh et al., BIOLOGICAL-ACTIVITIES OF 2 FUNGISTATIC ANTIBIOTICS PRODUCED BY BACILLUS-CEREUS UW85, Applied and environmental microbiology, 60(6), 1994, pp. 2023-2030
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.