Identification of a novel acido-thermostable chitinase from Bacillus altitudinis strain KA15

An extracellular acido-thermostable chitinase (called ChiA-Ba43) was hyper-produced and purified to homogeneity from a newly isolated Bacillus altitudinis strain KA15. This strain exhibited the highest chitinase activity (about 10,000 U/mL) after 46 h of incubation in an optimized meduim. Pure enzyme was obtained after ammonium sulphate precipitation (30-60%), followed by sequential column chromatographies on Sephacryl S-200 HR and Mono Q-Sepharose. The purified enzyme is a monomer with a molecular mass of 43,190.05 Da as determined by matrix assisted laser desorption ionization time-of-flight/mass spectrometry (MALDI-TOF/MS). The sequence of the 27 NH₂-terminal residues of ChiA-Ba43 showed high homology with other Bacillus species. Optimal activity was recorded at pH 4.0-5.5 and 85°C. The pure enzyme was inhibited by p-chloromercuribenzoic acid (p-CMB) and N-ethylmaleimide (NEM). Interstingly, ChiA-Ba43 showed higher activity towards colloidal chitin, chitin azure, glycol chitin, glycol chitosane, chitotriose, and chito-oligosaccharide, while it did not hydrolyse chitibiose and amylose. Moreover, ChiA-Ba43 acted as an endo-splitting enzyme as showed by thin-layer chromatography (TLC) from enzymatic catalyzed hydrolysis of chitin-oligosaccharides and colloidal chitin. More interstingly, ChiA-Ba43 showed a high level of catalytic efficiency compared to chitinases ChiA-Mt45, ChiA-Hh59, Chitodextrinase^®, N-acetyl-β-glucosaminidase^®, and ChiA-65. Thanks to its biochemical properties, ChiA-Ba43 may be used for the bioconversion of chitinous waste on an industrial scale.