Abstract: In order to develop chitin and chitosan bioconversion of active oligosaccharides and achieve the application of chitinase in food preservation and biocontrol, chitinase (ChiA-Sa62) was isolated and purified from Streptomyces aureofaciens XZ-Sa62, and its bioconversion and antibacterial function were studied. ChiA-Sa62 was purified by Q-Sepharose Fast Flow, Sephadex G-100 chromatography, and reverse phase high performance liquid chromatography (RP-HPLC), with a purification factor of 41.3 and a specific activity of 1 119.8 U/mg. sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) showed that ChiA-Sa62 was a single subunit protein with a molecular weight of 62.55 kDa. ChiA-Sa62 exhibited maximum activity at 50 ℃ and pH 5, and exhibited good stability below 60 ℃ and within pH range of 3.0-9.0. Ca2+, Mn2+, Mg2+, and Co2+ could activate enzyme activity. ChiA-Sa62 had a specific endonucleating hydrolysis activity on chitin and chitosan with a degree of deacetylation of 75%. Thin layer chromatography (TLC) showed that the hydrolysis products were 2-5 N-acetylglucosamine (GlcNAc) units of chitosan oligosaccharides and 2-4 D-glucosamine (GlcN) units of chitosan oligosaccharides, respectively. The colloidal chitin was used as the substrate, with ChiA-Sa62 Km and Vmax values of 2.75 mg/mL and 64.52 U/mg, respectively. ChiA-Sa62 strongly inhibited the tested pathogenic fungi, and propidium iodide (PI) staining showed that ChiA-Sa62 disrupted the integrity of the cell membrane of Botrytis cinerea. The hydrolyzed chitosan oligosaccharide had antibacterial activity against pathogenic G- bacteria (Escherichia coli and Pseudomonas aeruginosa) and G+ bacteria (Staphylococcus aureus and Bacillus cereus). LIVE/DEAD staining showed that chitosan oligosaccharide could cause the death of S. aureus. ChiA-Sa62 chitin and chitosan have great potentials for application in biotransformation, food preservation, and biological control.

Key words: chitinase; Streptomyces aureofaciens; enzymatic characteristics; biotransformation; antifungal activity