Biocatalytic traits of a new nanobiocatalyst prepared via immobilization of alginate lyase from a novel Streptomyces sp. LB55 onto silicon dioxide nanoparticles

Alginate lyase, which catalyzes the cleavage of alginate, has potential biocatalytic applications in agriculture, food, fodder, nutraceutical, pharmaceuticals, medical diagnostic and bioenergy industries. In this study, a novel alginate lyase-producing Streptomyces sp. LB55 (GenBank Accession No. MT176164) was isolated from Sargassum seaweed waste, and its extracted alginate lyase was immobilized onto glutaraldehyde cross-linked silicon dioxide nanoparticles. Fourier-transform infrared (FTIR) spectroscopic analysis suggests the binding of extracted alginate lyase with silicon dioxide nanoparticles via covalent bonds. FTIR analysis also revealed the retention of the secondary structure of immobilized alginate lyase by exhibiting amide I and amide II bands. The glutaraldehyde cross-linked silicon dioxide nanoparticles retained 71.9 ± 2.63% of alginate lyase activity. The optimal pH and temperature for maximal alginate lyase activity were recorded at pH 7.5 and temperatures of 40 and 45 °C, for free and immobilized forms, respectively. In comparison to free alginate lyase, the immobilized enzyme was thermodynamically efficient by displaying higher values of activation energy (52.3 kJ/mol), enthalpy (49.8 kJ/mol) and entropy (–69.7 J/mol/K) of catalysis. The immobilized alginate lyase had a strong affinity for alginate by exhibiting low Km (1.75 ± 0.12 mg/mL) and high Vmax (30.4 ± 2.66 U/mg-protein) values. The immobilized alginate lyase activity was unaffected at 2% NaCl concentration and could be successively reused six times without considerable loss of activity. The overall results demonstrate for the first time the potential of silicon dioxide nanoparticles as an effective matrix to immobilize alginate lyase for sustainable and cost-effective depolymerization of alginate.