Chitosan nanoparticles as adjuvants to enhance the biodegradation of PET by Ideonella sakaiensis

The escalating global crisis of polyethylene terephthalate (PET) pollution necessitates the development of efficient biological recycling strategies. While the bacterium Ideonella sakaiensis 1.2597 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 I. sakaiensis to diverse PET substrates. Under optimized environmental conditions (28 °C, pH 7.0), CS-NPs were introduced as adhesion adjuvants, the fluorescence intensity of PET fluorescent microspheres decreased by 85.9% 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 a promising tool for the bioremediation of PET pollution. KEY POINTS: • The development of an interfacial adjuvant chitosan nanoparticles. • Addition of chitosan nanoparticles enhanced the degradation efficiency of PET. • Chitosan nanoparticles achieve accelerated degradation through electrostatic attraction.