Purification, characterization, and gene cloning of a chitinase from Stenotrophomonas maltophilia N4

The Stenotrophomonas maltophilia synthesises high‐activity chitinase in response to chitin or chitosan induction. The enzyme was purified 8.5 fold and subjected to characterisation. The optimum hydrolysis conditions for this enzyme when using colloidal chitin as substrate were pH 5.6 and temperature of 45 °C. The enzyme demonstrated high thermal stability at 45 °C within 2 h. The studied chitinase exhibited high activity towards colloidal chitin, glycol chitin and chitosan, while it did not hydrolyse glycosidic bonds in carboxymethylcellulose. The enzyme exhibited the highest activity, equalling 90 U/ml, towards Nitrophenyl β‐D‐N,N′,N″‐triacetylchitotriose and activity of 37 U/ml towards 4‐Nitrophenyl N,N′‐diacetyl‐β‐D‐chitobioside. The Km value in the presence of the two former substrates was:1.2 and 3.9 mM, respectively, which classifies the studied enzyme as an endochitinase. Cysteine and 2‐mercaptoethanol stimulated to a small degree the activity of the chitinase which may indicate the involvement of cysteine residues in the catalysis mechanism. The full length of the nucleotide sequence of this chitinase gene is 2106 bp, which amounts to 702 amino acids.