Screening of Three Chitinase-producing Strains, Optimization of Their Chitinase-producing Conditions and Application in the Hydrolysis of Shrimp Shells

Objective: This study aimed to screen and identify chitinase-producing strains and optimize the fermentation conditions of the target bacteria, which were eventually applied to the degradation fermentation of shrimp shells. Methods: The chitin degradation bacteria were screened on chitin hydrolysis zone taking marine mud from beach in Yancheng as samples, identified via bioinformatics technology, and analyzed in the form of phylogenetic tree. Fermentation conditions for the target strains were modified depending on the single-factor experiment. Results: Photobacterium sp. LYM-1, Vibrio sp. WM-1, and Shewanella sp. ZXY-1 were isolated and identified via 16S rDNA sequence analysis. The optimal fermentation conditions were determined as follows: For Photobacterium sp. LYM-1, chitin (10 g/L) as the carbon source, NH₄Cl (2.0 g/L) as the nitrogen source, the inoculated quantified of 3%, initial medium pH6.5, and 32 ℃ for 1 d, in which the highest chitinase activity in the supernatant reached 15.37±0.55 U/mL, achieving 4.37 times higher than that before optimization. For Vibrio sp. WM-1, chitin (10 g/L) as the carbon source, NH₄Cl (2.0 g/L) as the nitrogen source, the inoculated quantified of 3%, initial medium pH7.5, and 22 ℃ for 2 d, in which the highest chitinase activity reached 40.82±6.03 U/mL, achieving 1.60 times higher than that before optimization. For Shewanella sp. ZXY-1, chitin (10 g/L) as the carbon source, (NH₄)₂SO₄ (2.0 g/L) as the nitrogen source, the inoculated quantified of 3%, initial medium pH6.5, and 22 ℃ for 1 d, which contributed the highest chitinase activity to reaching 25.64±3.29 U/mL, achieving 2.47 times higher than that before optimization. All three strains in this study could realize chitinase production under optimized conditions using shrimp shell powder as the sole substrate. The chitinase activities of Photobacterium sp. LYM-1, Vibrio sp. WM-1, and Shewanella sp. ZXY-1 on shrimp shell powders were 10.25±0.95, 32.16±2.25 and 21.81±4.27 U/mL, respectively, which was lower than those on chitin powder. Conclusion: Three chitinase-producing strains were successfully screened from saline-alkali soil, of which the enzyme activity was elevated after optimization. All of them could produce chitinase with the shrimp shell utilized as the substrate, serving as potential strains for chitinase production from the fermentation of shrimp shell.