Abstract:
During screening for antibiotic producing microorganisms from environmental soil samples, the supernatant of
a bacterial isolate was found to have antibacterial and antifungal activity on the standard indicator species. The
standard cylinder-plate method was used to determine the inhibitory effect of the crude supernatant of each
isolate on 6 bacterial and 3 fungal standard strains by measuring the diameter of inhibition zone. The highest
inhibition zone on Aspergillus niger belonged to culture broth of isolate FAS1 by 25 mm, and this isolate was
the most efficient microorganism to inhibit standard bacterial and fungal species. Based on morphological and
biochemical properties as well as 16S rDNA gene analysis, the selected isolate (isolate FAS1) belonged to
Bacillus genus. Investigation on the ability of different culture media for antibiotic production led to select
Luria-Bertani media for further studies. Treatment of the culture broth of the isolate FAS1 using typical protease
didn’t decrease the antimicrobial activity of the supernatant. After extracting of culture broth of the selected
isolate by ethyl acetate as an organic solvent, the inhibitory effect was mainly increased. More investigation was done by bioautography method where the ethyl acetate fraction of the broth culture was separated on TLC by chloroform:methanol, 60:40 as mobile phase and Rf were calculated for inhibition spots.
