Thirty-four bacterial isolates were isolated from soil samples collected from the North Western Coast and a water sample collected from brackish water at Siwa Oasis, Matrouh Governorate, Egypt. Only six isolates showed chitinase activity when screened on colloidal chitin agar medium. The highest chitinolytic activity was achieved by a bacterial isolate labeled as A.S. This isolate was identified as Aeromonas hydrophila based on analysis of 16S rRNA gene sequence and morphological, physiological, and biochemical characteristics. Optimization of the cultural conditions for maximum chitinase production by A. hydrophila revealed that the highest level of chitinase was recorded when the bacterium was grown in malt nitrogen-based medium containing 1% colloidal chitin at pH7 for 48 h incubation at 30°C. Crude chitinase from isolate A. hydrophila was evaluated against first instar larvae of the greater wax moth; Galleria mellonella L. (Lepidoptera: Pyralidae) at different concentrations of 0, 185, 205, 235, 265, 295 U/mg protein. It increased larval and pupal mortality rates in a concentration-dependent manner. The tested crude chitinase significantly induced a decrease in adults' emergence rate and their fecundity.

n a laboratory study, the impact of crude chitinase from Aeromonas hydrophila on the nutrient indices and on the major biochemical components of Galleria mellonella was studied. Fourth larval instar of Galleria mellonella was treated with 135.0 U/mg protein (LC50). Treatment with crude chitinase reduced the larval feeding efficiency, retarded larval growth and reduced larval weight, whereas approximate digestibility was increased. The total protein contents in the supernatant of the homogenate larvae post-treatment was decreased, as affected by crude chitinase (LC50) comparing with the check treatment. A significant reduction in the total lipid content was observed and it may due to its conversion to proteins in order to compensate the reduction in protein content or to produce supplementary energy. The total carbohydrate contents were significantly reduced to be ~111.17±4.24 µg/larva with respect to the control (147.21±1.77 µg/larva). Crude chitinase from Aeromonas hydrophila may serve as a powerful biocontrol tool against insects and provide a suitable substitute for synthetic pesticides.

No abstract

No abstract