بررسي فعاليت و تركيبات باكتريBacillus subtilis عليه برخي از قارچ‎هاي بيماري‎زاي گياهي

An investigation on activity and compounds of Bacillus subtilis against some pathogenic plant fungi

Antifungal peptides of Iturin group are the most important antifungal compounds which are produced by most species of the Bacillus, especially Bacillus subtilis. They can potentially inhibit the growth of different pathogenic plant fungi. In this investigation, a few isolates of Bacillus subtilis bacterium were cultured in nutrient broth medium on 30 °C and 100 rpm for 24 hours. Their antifungal activity against Fusarium solani (ATCC 1460) and Pythium ultimum (ATCC 20692) fungi was evaluated via Agar wells method. Growth and the production of these antifungal metabolites of the screened bacterium in same medium for the factors like carbon source (Glucose, Arabinose, Lactose and Saccharose) nitrogen source (Yeast extract, Peptone, Ammonium nitrate and Potassium nitrate), pH and temperature were optimized. The metabolites were extracted and also evaluated in comparison with Iturin and Surfactin through the High Performance Liquid Chromatography (HPLC). The results indicated that the fungi growth was inhibited. The antifungal activity of the bacterium could inhibit the growth of Pythium ultimum (ATCC 20692) 8% more than Fusarium solani (ATCC 1460). Antifungal peptides of Iturin group, such as Iturin and Surfactin, were produced in nutrient broth medium with glucose and yeast extract at neutral pH and 30 °C. Chromatograms of HPLC were revealed the active compounds by identical peaks with the similar retention time as antibiotic compounds belonging to the Iturin group. Antifungal activity and synergistic effects of Iturin, Surfactin and antifungal metabolites of Bacillus subtilis were evaluated via Agar wells method. The average index of growth suppression of Pythium ultimum via Agar wells method in presence of 50 JLII of a suspension of Bacillus subtilis, itʹs metabolites, Iturin (lmg/ml), Surfactin (lmg/ml) and the complex of Iturin and Surfactin were 25, 20, 13, 13 and 16 mm respectively and mixture of the last three treatments led to 29 mm. This bacterium and/or its components probably can be suitable candidate for biological control of some plant pathogenic fungi