Halostability and thermostability of chitinase produced by fungi isolated from salt marsh soil in subtropical region of Saudi Arabia

Strategies based on halo- and thermostable enzymes are promising and attractive for biotechnological applications. Three fungal isolates, namely Aspergillus flavus, Cladosporium cladosporioides, and Alternaria alternata, and were subjected to chitinase production using a medium with different concentrations of NaCl up to 10%. C. cladosporioides was found to be the main chitinase producer at high concentration of NaCl; therefore, its identification was confirmed using 18S rDNA. The highest chitinase production (88.67 U/mL) was obtained by C. cladosporioides, followed by A. flavus (76.17 U/mL), and A. alternata (70.67 U/mL) at 5% NaCl, while their production without NaCl was 35.07 U/mL, 22.83 U/mL, and 21.33 U/mL, respectively. Thermal stability of chitinase was recorded at 50 °C at 20 min. Chitinase halostability at 20 min indicated that 10% NaCl was the optimum level, with activity 88.3 U/mL. Safranin dye decolorization by C. cladosporioides was enhanced to 88.25% via the addition of 5% NaCl to growth medium containing chitin. The inhibitory activity of chitinase was detected against C. lunata and F. oxysporium with or without NaCl. Culex pipiens larvae were more affected by C. cladosporioides chitinase produced at 5% than 10% NaCl. Energy scores of the molecular docking investigations confirmed the insecticidal activity of chitinase against C. pipiens larvae.