Marine endophytic fungi isolated from Red Sea organisms were screened for the production of dextranase enzyme. The most potent isolate was from the Red Sea sponge Callyspongia spp. and was selected for identification. The18S rRNA amplification for phylogenetic study revealed that the isolate was highly related to Aspergillus flocculosus strain NRRL 5224 by 99 %. Medium composition and culture conditions for dextranase production were optimized by response surface methodology. A significant influence of dextran, yeast extract, K2HPO4, NaNO3, NaCl, MgSO4.7H2O and culture requirements such as incubation time, inoculum size, medium volume and inoculum age on dextranase production was evaluated by Plackett-Burman design. The most significant factors were further optimized using Box-Behnken design. The model predicted a dextranase activity of 438.15 U/ml when dextran concentration, medium volume and incubation time were 2.1 g/l, 52.47/250 ml flask and 80.48 h, respectively. Verification of the model showed that dextranase production of 440 U/ml was observed under the optimal condition confirming the validity of the model.
Keywords: Dextranase; Fungi; Optimization; Response surface methodology.