2.3. Antifungal activity of extrace

2.3. Antifungal activity of extracellular fractions from cultures ofB. subtilis
To obtain extracellular filtrates with antifungal activity, 500 mL
of PDB were inoculated to obtain an absorbance of 0.2 at 600 nm
with an overnight culture of each strain in PDB, and then incubated
at 28 C and 180 rpm. Samples of 5 mL were taken at 12, 24 and
60 h, which corresponds to the logarithmic, stationary, and late
stationary phases of growth of each strain, and were centrifuged
at 8000 rpm. The supernatants (extracellular fraction) were sterilized
in an autoclave. Then 200 ll was added to small bottomless
tubes placed on the surface overlaid with S. reilianum, and inoculated
in YEPD plates as described above. The plates were incubated
at 28 C for 120 h and observed every 12 h. The filtrates with antifungal
activity were those that inhibited the development of the
fungus. In this case, inhibition halos were observed, which were
measured in mm. For the control, 200 ll of PDB medium ware
added.