Wan-Taek Ju

Perspectives of Chitin Deacetylase Research

Chitin and chitosan are copolymers of N-acetyl-D-glucosamine (GlcNAc) and D-glucosamine (GlcN) units linked with β-(1-4) glycosidic bond, where the predominant units are GlcNAc for chitin or GlcN for chitosan in their polymeric chains (Fig. 1). While chitin remained an unused natural resource for a long term, interest in chitosan and chitooligosaccharides (COS) has increased in recent years due to their unique biodegradability, biorenewability, biocompatibility, physiological inertness, and hydrophilicity. Based on these properties, chitosan and COS have been widely and continuously applied in various fields, such as agriculture, cosmetics, water treatment, food industry, pharmaceuticals and biomedicine. Actually, most biological activities of chitosan are strongly dependent on its degree of polymerisation (DP) which defines the molecular mass of the polymers, degree of acetylation (DA) which defines its charge density and pattern of acetylation (PA) which defines the distribution of GlcNAc and GlcN moieties in the chitosan chain.

Occurrence of Bursaphelenchus mucronatus (Nematoda: Aphelenchoididae) and the microhabitat distribution of fungi in declining pine trees in a locale in Korea

A total of 33 pine trees with symptoms of decline were collected in Jeonnam Province, South Korea, and were examined for the presence of nematodes. About 20% of the trees sampled were positive with Bursaphelenchus species. All Bursaphelenchus species were found in recently dead or dying trees. Based on morphological observations, the nematode extracted from the declining pine trees was identified as B. mucronatus. The highly pathogenic pine wood nematode B. xylophilus was not found in any pine trees sampled. B. mucronatus was easily reared on fungus Botrytis cinerea. Twenty one fungal isolates were isolated from dead trees, fallen twigs, and healthy pine trees. The fungal isolates belonged to Trichoderma genus and were dominant in the wood of partially declining pines. The blue‐stain fungi transmitted by the Monochamus beetle were not detected. The B. mucronatus population decreased markedly on Auxarthron reticulatum DY‐2 isolated from soils. The number of nematodes also reduced on Verticillium saksenae A‐1, a nematophagous fungus, and Beauveria bassiana, an entomopathogenic fungus. This observation suggested the fungal production of nematicidal activity against B. mucronatus. When the fungal culture filtrates were also used for nematicidal activity on B. mucronatus, the culture filtrates of A‐1, DY‐2 and B. bassiana showed over 50% mortality within 48 h exposure. The fungi BC4, BC5 and BC6 isolated from declining pine trees inhibited the reproduction of B. mucronatus, and their culture filtrates also expressed nematicidal activity, indicating a possible interaction between the fungi in pine trees and nematodes at microhabitat level.

Purification and characterization of a β-N-acetylhexosaminidase from wheat bran and its applicability to biocontrol of Fusarium solani

N-acetyl-β-d-hexosaminidase was purified from wheat bran and characterized. The purified enzyme showed two protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with molecular mass of 75 and 78 kDa. The enzyme exhibited optimum pH and temperature at 5.0 and 50°C, respectively. The enzyme was active on the substrates of p-nitrophenyl-N-acetyl-β-d-glucosaminide (pNP-GlcNAc) and p-nitrophenyl-N-acetyl-β-d-galactosaminide (pNP-GalNAc), whereas inactive on pNP-β-d-glucopyranoside, pNP-β-d-galactopyranoside, swollen chitin, and colloidal chitin, suggesting high substrate specificity. The enzyme activity for pNP-GlcNAc was stable at pH 3–6 and under 50°C. The Km, Vmax and Kcat for pNP-GlcNAc were 0.014 mM, 0.05 μmol/min, and 3.01×106 min−1, respectively. The enzyme could be completely inhibited at 1–10 mM HgCl2 and AgNO3, suggesting that the intact thiol group is essential for activity. β-N-Acetylhexosaminidase from wheat bran could inhibit the conidial germination and digest the hyphae of Fusarium solani.

Purification and characterization of a 34-kDa chitobiosidase from Aeromonas sp. GJ-18

Chitobiosidase was purified and characterized from Aeromonas sp. GJ-18 by ammonium sulfate precipitation, anion-exchange chromatography, and gel filtration chromatography. The purified enzyme has a molecular weight of 34 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme showed an optimum pH and temperature of 6.0 and 30–50°C, respectively. The enzyme was stable at pH 5–8 and 50°C and was completely inhibited in the presence of 10 mM Zn2+ ions. The enzyme could efficiently hydrolyze colloidal chitin into N,N′- diacetylchitobiose as the major product, indicating that the purified enzyme is a chitobiosidase. When colloidal chitin was used as the substrate, the Km and Vmax of this enzyme were established as 3.45 mg/mL and 2.91 μmol/min, respectively.