Biocontrol Efficiency of Bacillus subtilis SL-13 and Characterization of an Antifungal Chitinase

Abstract

The seed germination and tomato seedling tests showed that Bacillus subtilis SL-13 could promote the sprouting and seedling growth of tomato. The fresh and dry weight of tomato seedlings increased 42.86% and 18.75%, respectively. The control efficacies of the SL-13 to tomato Rhizoctonia rot were 20.65% and 35.23% in the greenhouse and field, respectively. The growth of the plant-pathogenic fungus Rhizoctonia solani was considerably inhibited in the presence of the strain SL-13 culture supernatant. The main antifungal protein was detected to be chitinase through vitro assay. The chitinase was purified with DEAE-Sepharose fast flow ion exchange column chromatography and Sephadex G-75 gel filtration for further characterization. The optimal pH and temperature for the chitinase activity were 7.0 and 50 (C, respectively. It was demonstrated that the enzyme was stable at pH 5-9 and 40-60 (C. 70% of the enzyme activity was retained when incubated at 121 (C and 0.11 MPa for 20 min, and the enzyme was not sensitive to protease K and ultraviolet radiation. Thus it is suitable for effective biological control in relatively unstable environment.