PEER-REVIEWED ARTICLE bioresources.com Al Abboud et al. (2022). “Halo-, thermostable chitinase,” BioResources 17(3), 4763-4780. 4763 Halostability and Thermostability of Chitinase Produced by Fungi Isolated from Salt Marsh Soil in Subtropical Region of Saudi Arabia Mohamed A. Al Abboud, a Aisha M. H. Al-Rajhi, b Abdel-Rahman M. Shater, a,c Mohamed M. Alawlaqi, a Abdullah Mashraqi, a Samy Selim, d, * Soad K. Al Jaouni, e and Tarek M. Abdel Ghany f, * 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. DOI: 10.15376/biores.17.3.4763-4780 Keywords: Halo-stability; Thermostability; Chitinase; Fungi; Bioapplications Contact information: a: Biology Department, Faculty of Science, Jazan University, Jazan 82817, Saudi Arabia; b: Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, P.O. Box 84428, Riyadh 11671, Saudi Arabia; c: Biology Department, Faculty of Science, Thamar (Dhamar) University, Dhamar, Yemen; d: Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, Jouf University, Sakaka 72388, Saudi Arabia; e: Department of Hematology/Oncology, Yousef Abdulatif Jameel Scientific Chair of Prophetic Medicine Application, Faculty of Medicine, King Abdulaziz University, Jeddah 21589, Saudi Arabia; f: Botany and Microbiology Department, Faculty of Science, Al- Azhar University, Nasr City, Cairo 11725, Egypt; *Corresponding authors: sabdulsalam@ju.edu.sa (S.S.); tabdelghany.201@azhar.edu.eg (T.M.A.); amoalrajhi@pnu.edu.sa(AMHA) INTRODUCTION In recent decades, extreme environments have gained great attention from researchers for numerous reasons. Natural inhabitants from such sources have been adapted to produce several industrial, medicinal, and agricultural valuable compounds, such as hydrolytic enzymes. According to Liu et al. (2019), salt-tolerant enzymes secreted by microorganisms, particularly halophilic/halotolerant, are highly effective compared to