Evaluation of antifungal activity of iturin producing Bacillus subtilis strains

Bacillus subtilis strains produce a wide variety of antimicrobial substances, such as iturin family lipopeptides, which are effective in biological control of many plant pathogens. The aim of present study was to investigation the antifungal activity of indigenous strains Bacillus subtilis against Fusarium moniliforme and Verticillium dahliae.
The forest soil samples were collected from seven different parks at Tehran. The isolates were screened by antifungal activity. Two best strains with greater inhibition zone were identified by PCR. Then, nutrient broth media were optimized to produce of large volumes of the antifungal metabolites from the selected native strains. Following 4 day incubation, the bacterial metabolites were purified, and the presence of iturin was confirmed by chromatography method.
Totally, 23 isolated strains were confirmed as B. subtilis. In subsequent experiments, two strains 36 and 78 showed the greatest activity against the Fusarium moniliforme and Verticillium dahliae respectively. 16srRNA sequence analyses for selected isolates confirmed 100% similarity to B. subtilis. The nutrient broth with glucose, yeast extract, neutral pH and 30 ⁰C incubation temperature were optimized for the best production condition. The HPLC results showed that both the ability of these strains to produce iturin A in a specific period was as the same as standard iturin.
These indigenous strains showed the ability to produce antifungal metabolites. Therefore, these strains can be used as good candidates for the biological control of plant pathogenic fungi and as an alternative for chemical fungicides.