Identification of a new thermostable chitinase from Hydrogenophilus hirschii strain KB-DZ44

This paper reports the identification of an extracellular acido-thermostable endo-chitinase (called ChiA-Hh59) from thermophilic Hydrogenophilus hirschii strain KB-DZ44. The ChiA-Hh59 was purified and characterized. The maximum chitinase activity recorded after 36-h of incubation at 60°C was 3000 U/ml. Pure enzyme was obtained after heat and acidic treatment, precipitation by ammonium sulphate and acetone, respectively, followed by sequential column chromatographies on Sephacryl S-200 and Mono Q-Sepharose. Based on MALDI–TOF/MS analysis, the purified enzyme is a monomer with a molecular mass of 59103.12-Da. The 22 residue NH₂-terminal sequence of the enzyme showed high homology with family-18 bacterial chitinases. The optimum pH and temperature values for chitinase activity were pH 5.0 and 85°C, respectively. The pure enzyme was completely inhibited by p-chloromercuribenzoic acid (p-CMB) and N-ethylmaleimide (NEM). The obtained results suggest that ChiA-Hh59 might be an endo-chitinase. The studied chitinase exhibited high activity towards colloidal chitin, chitin azure, glycol chitin, while it did not hydrolyse chitibiose and amylose. Its catalytic efficiency was higher than those of chitodextrinase and ChiA-65. Additionally, TLC analysis from chitin-oligosaccharides showed that ChiA-Hh59 acted as an endo-splitting enzyme. In conclusion, this chitinase may have great potential for the enzymatic degradation of chitin.