Characterization of β-mannanase extracted from a novel Streptomyces species Alg-S25 immobilized on chitosan nanoparticles

Abstract

The potential applications of β-mannanase in bioenergy, biorefinery, detergent, fodder, food processing, oil and gas, pharmaceutical, pulp and paper and textile industries, and the high cost of commercially available enzyme have attracted considerable research efforts to identify potent microbial strains for cost-effective production of this enzyme. The advantage of microbial biocatalyst is that the crude enzyme can be used directly in bioprocessing instead of the purified enzyme. In this study, β-mannanase was extracted from a novel Streptomyces sp. Alg-S25 (GenBank accession no. MK494177) and immobilized onto chitosan nanoparticles using glutaraldehyde as a crosslinker. The covalent binding of β-mannanase onto chitosan nanoparticles was confirmed by Fourier-transform infrared spectroscopy. The functionalized chitosan nanoparticles retained 83.6% ± 3.46% of β-mannanase activity. Free and immobilized β-mannanase of this novel Streptomyces sp. Alg-S25 displayed maximal activities at pH 7.5 and at temperature 50 °C and 55 °C, respectively. Immobilized β-mannanase exhibited higher values of activation energy (47.4 kJ/mol), enthalpy (44.9 kJ/mol) and entropy (–73.5 J/mol/K) of catalysis compared to the free enzyme. The substrate-specific kinetic analysis suggested that the immobilized β-mannanase had a strong affinity toward locust bean galactomannan by showing a low Km (4.94 mg/mL) and a high Vmax (93.5 U/mg-protein) values. Furthermore, the immobilized β-mannanase was not affected by 2% NaCl and retained 81.2% of the maximal activity after 10 cycles of successive reuse. These results indicate the potential of chitosan nanoparticle-immobilized β-mannanase for sustainable and cost-effective bioprocessing of mannan-containing agricultural, forest, seaweed and industrial wastes.

Keywords

• chitosan
• β-mannanase
• nanoparticles
• sargassum
• seaweed
• streptomyces