Design of Functionalized Silica Immobilization of PETase from Kibdelosporangium aridum: Comparison of Glyoxyl and Glutaraldehyde Strategies for PET Depolymerization

Abstract

Polyethylene terephthalate (PET) is a widely used thermoplastic that poses a major challenge to global resource sustainability because of its extensive consumption and contribution to plastic pollution. This study aimed to enhance the performance of PETase derived from Kibdelosporangium aridum (KaPETase) through immobilization onto aldehyde-functionalized silica supports with varying active groups: (i) 3-aminopropyl silica gel via glutaraldehyde (Si-NH2@KaPETase), (ii) (3-aminopropyl)triethoxysilane (3-APTES) functionalized silica via glutaraldehyde (Si-Glu@KaPETase), and (iii) glyoxyl silica (Si-Ald@KaPETase). The immobilized biocatalysts exhibited 4.6- to 5.1-fold greater thermal stability at 75 °C than that of the free enzyme. Catalytic efficiency was also significantly enhanced, increasing by 2.6- to 5.0-fold. Under optimized conditions, PET depolymerization assays demonstrated improved hydrolytic performance. HPLC analysis confirmed terephthalic acid (TPA) and mono(2-hydroxyethyl) terephthalate (MHET) as the primary degradation products. After 1 h of reaction, degradation product concentrations reached 43.4, 75.6, 93.4, and 61.2 mg mg–1 protein for free KaPETase, Si-NH2@KaPETase, Si-Glu@KaPETase, and Si-Ald@KaPETase, respectively. Surface-sensitive XPS measurements revealed more pronounced PET surface chemical modifications for PET surfaces incubated by aldehyde- and especially glutaraldehyde-functionalized KaPETase systems, indicating enhanced enzyme–surface interactions. Overall, immobilization on functionalized silica supports significantly improved catalytic activity, thermostability, and reusability. These findings demonstrate the strong potential of robust immobilized KaPETase systems for sustainable and industrially relevant PET biodegradation.