An Archaeal Chitinase With a Secondary Capacity for Catalyzing Cellulose and Its Biotechnological Applications in Shell and Straw Degradation

Numerous thermostable enzymes have been reported from the hyperthermophilic archaeon Thermococcus kodakarensis KOD1, which made it an attractive resource for gene cloning. This research reported a glycosyl hydrolase (Tk-ChiA) form T. Kodakarensis with dual hydrolytic activity due to the presence of three binding domains with affinity toward chitin and cellulose. The Tk-ChiA gene was cloned and expressed on Pichia pastoris GS115. The molecular weight of the purified Tk-ChiA is about 130.0 kDa. By using chitosan, CMC-Na and other polysaccharides as substrates, we confirmed that Tk-ChiA with dual hydrolysis activity preferably hydrolyzes both chitosan and CMC-Na. Purified Tk-ChiA showed maximal activity for hydrolyzing CMC-Na at temperature 65°C and pH 7.0. It showed thermal stability on incubation for 4 h at temperatures ranging from 70 to 80°C and remained more than 40% of its maximum activity after pre-incubation at 100°C for 4 h. Particularly, Tk-ChiA is capable of degrading shrimp shell and rice straw through scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) analysis. The main factors affecting shell and straw degradation were determined to be reaction time and temperature; and both factors were optimized by central composite design (CCD) of response surface methodology (RSM) to enhance the efficiency of degradation. Our findings suggest that Tk-ChiA with dual thermostable hydrolytic activities maybe a promising hydrolase for shell and straw waste treatment, conversion, and utilization.