Chitosan Nanoparticles as Interfacial Adjuvants to Enhance the Biodegradation of Polyethylene Terephthalate by Ideonella sakaiensis

Abstract The escalating global crisis of polyethylene terephthalate (PET) pollution necessitates the development of efficient biological recycling strategies. While the bacterium Ideonella sakaiensis can utilize PET as a sole carbon source, its practical application as a biocatalyst is hampered by poor interfacial adhesion to hydrophobic plastic surfaces and limited degradation efficiency under ambient conditions. In this study, we developed chitosan nanoparticles (CS-NPs) via ionic crosslinking to serve as a novel electrostatic bridging adjuvant. The synthesized CS-NPs exhibited a uniform particle size of 360.1 ± 10.8 nm and a high positive zeta potential of + 40.1 ± 2.2 mV. Supplementation with an optimal dosage of CS-NPs (3 mL per 30 mL medium) significantly promoted the adhesion of Ideonella sakaiensis to diverse PET substrates. Under optimized environmental conditions (28°C, pH 7.0), CS-NPs were introduced as adhesion adjuvants, achieving a 91.2% degradation efficiency of PET fluorescent microspheres over 14 days compared to 58.9% without CS-NPs. Furthermore, application of the CS-NPs adjuvant to macroscopic PET films resulted in dense surface colonization and severe structural disruption, characterized by deep physical pitting and cracking. High-performance liquid chromatography-mass spectrometry (LC-MS) confirmed the robust hydrolytic depolymerization of PET into its constituent monomers: terephthalic acid (TPA), mono(2-hydroxyethyl) terephthalate (MHET), and bis(2-hydroxyethyl) terephthalate (BHET). While challenges remain regarding degradation of CS-NPs environmental fate and microbial competition, this work provides the CS-NPs adjuvant as promising tools for the bioremediation of PET pollution.