Purification, Characteristics and Identification of Chitinases Synthesized by the Bacterium Serratia plymuthica MP44 Antagonistic Against Phytopathogenic Fungi

摘要

Once isolated from the rhizosphere, the chitinolytic bacterium Serratia plymuthica MP44 showed strong antagonistic action against such phytopathogenic fungal species as: Rhizoctonia solani, Cladosporium sp., Alternaria alternata and, to a lesser degree, to the species from the genera Fusarium and Chaetomium. In contrast, no antagonism between the bacteria and Aspergillus niger was observed. S. plymuthica MP44 demonstrated the highest chitinolytic activity on the fifth day of the cultivation on a medium with 1% colloidal chitin. The analysis of zymograms indicated that the studied bacterial strain synthesized 2 chitinolytic enzymes. After purification of culture supernatant of S. plymuthica MP44 with ammonium sulphate precipitation and hydrophobic chromatography on Phenyl-Sepharose CL-4B, 2 active fractions were obtained: fraction I (FI) containing exochitinase activity and fraction II (FII) containing endochitinase activity. The optimum pH and temperature for the purified enzyme were 6.3 and 45 degrees C and 5.4 and 50 degrees C for FI and FII, respectively. High thermal stability was revealed for enzyme from FII after 3 h of incubation at 50 degrees C. The purified chitinases displayed low fungistatic activity when compared to the activity of the bacteria per se.