A potent chitinolytic activity of Alternaria alternata isolated from Egyptian black sand.

Eight fungal species characterized by chitinolytic activity were isolated from Egyptian black sand collected from Rosetta coast. Genus Aspergillus and Alternaria alternata exhibited the highest density (> 40% of the total count, each) on the isolation plates containing different treatments of native shrimp shell chitin. Genus Aspergillus was represented by A. flavus, A. niger, A. foetidus and A. tungius, with the former species being the most dominant. The other species were Cladosporium herbarum, Fusarium equisitum (5.71% of the total count, each) and Dendryphiella vinosa (3.21% of the total count). The isolated species were screened for chitinase production on agar plates containing 0.2% colloidal chitin. The chitinolytic activity of each individual was not always correlated with its density on the isolation plates. Alternaria alternata was the most promising species for chitinase excretion. The use of colloidal chitin (1.5%) as a sole carbon source was superior for the enzyme production by A. alternata. Maximum enzyme yield was obtained after 7 days incubation at 30 degrees C with shaking (150 rev min(-1)), with an initial pH value of the growth medium at 5.0. Presence of NaNO3 (0.3%), the best nitrogen source, and CaCl2 (100 microg/ml) stimulated the induction of the enzyme. The crude A. alternata chitinase revealed a potential insecticidal effect on the larvae of fruitfly (82% mortality) and could degrade crude shrimp shell waste.