The antifungal activity of broth filtrate of Bacillus atrophaeus isolate #3
5 was studied on Ascosphaera apis (Ascosphaeraceae-Ascomycota), a pathogen
of honeybee larvae. Inhibition of hyphal growth was evident but varied with
batch of fermentation broth, dilution, and duration of treatment. Signific
ant growth inhibition and hyphal lysis were observed when the strength of t
he culture filtrate was at maximum. At the scanning electron microscope lev
el, the treatment induced morphological abnormalities including swelling, s
tunting, constriction, and rupture of hyphae. We also found aberrations in
the plasma membrane ranging from a serrated appearance in profile to total
degradation in lysed hyphae. In some hyphae, almost all membrane systems in
cluding mitochondria, endoplasmic reticulum, and Golgi bodies, had changed
drastically and in many cases formed membranous inclusions. Hyphae also con
tained electron-dense, bizarrely shaped structures that extended throughout
. In the most inhibitory treatment, the hyphal wall was uneven in thickness
, yet had N-acetyl-D-glucosamine label equal to that of the control, sugges
ting the irregular thickness of the wall was due to deposition of other pol
ysaccharides.