Characterization of a chitinase with antifungal activity from a native Serratia marcescens B4A.

Chitinases have the ability of chitin digestion that constitutes a main compound of the cell wall in many of the phytopathogens such as fungi. In the following investigation, a novel chitinase with antifungal activity was characterized from a native Serratia marcescens B4A. Partially purified enzyme had an apparent molecular mass of 54 kDa. It indicated an optimum activity in pH 5 at 45°C. Enzyme was stable in 55°C for 20 min and at a pH range of 3-9 for 90 min at 25°C. When the temperature was raised to 60°C, it might affect the structure of enzymes lead to reduction of chitinase activity. Moreover, the Km and Vmax values for chitin were 8.3 mg/ml and 2.4 mmol/min, respectively. Additionally, the effect of some cations and chemical compounds were found to stimulate the chitinase activity. In addition, Iodoacetamide and Idoacetic acid did not inhibit enzyme activity, indicating that cysteine residues are not part of the catalytic site of chitinase. Finally, chitinase activity was further monitored by scanning electronic microscopy data in which progressive changes in chitin porosity appeared upon treatment with chitinase. This enzyme exhibited antifungal activity against Rhizoctonia solani, Bipolaris sp, Alternaria raphani, Alternaria brassicicola, revealing a potential application for the industry with potentially exploitable significance. Fungal chitin shows some special features, in particular with respect to chemical structure. Difference in chitinolytic ability must result from the subsite structure in the enzyme binding cleft. This implies that why the enzyme didn't have significant antifungal activity against other Fungi.