Efficient Bioconversion of Chitinous Waste to N-Acetylchitobiose and N-Acetylglucosamine Using a Novel Salt-Tolerant Chitinase from Bacillus clausii

Chitin, a highly insoluble and poorly degradable polymer derived from seafood industry waste, can be converted into value-added products including N-acetylchitobiose ((GlcNAc)2) and N-acetylglucosamine (GlcNAc) by chitinase, which can overcome the disadvantages of chemical degradation. Here, we identified a novel salt-tolerant chitinase (CHI) involved in chitin degradation from Bacillus clausii TCCC 11004. Recombinant CHI (rCHI) displayed a great tolerance against high concentrations of NaCl, maintaining 376% of its initial activity in a solution containing 0.6 M NaCl, which was about NaCl concentration in seawater. Chitin binding domain (ChBD) engineering demonstrated that rCHI's ChBD was beneficial for its NaCl resistance property. As a multifunctional chitinase, rCHI exhibited dual exochitinase activity and N-acetylglucosaminidase activity, but no hydrolytic activity toward (GlcNAc)2 when using colloidal chitin as a substrate, which made it different from the typical reported chitinases. As a result, (GlcNAc)2 and GlcNAc achieved the maximum yield ((GlcNAc)2: 25.73 mg/mL and GlcNAc: 3.25 mg/mL) by hydrolyzing colloidal chitin from crab shells using rCHI alone. This study reported a valuable chitinase with the above dual activities and provided an eco-friendly and sustainable approach for cost-effective bioconversion of chitin-containing biowastes to bioactive (GlcNAc)2 and GlcNAc.