Isolation and partial characterization of antifungal protein from Bacillus polymyxa strain VLB16

An antifungal protein produced by Bacillus polymyxa strain VLB16 has been purified to homogeneity by ammonium sulfate precipitation and Sephadex-G-200 column chromatography. The purified protein inhibited the growth of Pyricularia grisea and Rhizoctonia solani, the causative agents of rice blast and sheath blight diseases, respectively. Microscopy studies revealed that the antifungal protein caused severe alterations in cell morphogenesis that gave rise to swollen and rounded hyphae. The protein was a monomer with molecular weight of 37 kDa in sodium dodecyl sulfate-poly acrylamide gel electrophoresis and gave a single symmetrical peak in gel permeation chromatography. The presence of predominant random coil structure and other conformations such as β-sheet and β-turn was noticed from Fourier transform infra red spectroscopy. The protein was heat stable and remained active after sterilization at 121 °C for 15 min. The antifungal protein was resistant to hydrolysis by pronase and also to many protein-denaturing detergents like sodium dodecyl sulfate (SDS), hexa decyl trimethyl ammonium bromide (HDTMA) and Tween-20. The extraordinary thermo-stability of the protein can be of good prospect to be used as a new tool for biocontrol.