Biodegradation of polyurethane by marine-derived Cladosporium oxysporum SCSIO 81042 under seawater conditions and its enhancement by chitosan nanoparticles as adjuvant

The accumulation of microplastics in marine environments poses a significant ecological threat. This study reports the isolation and characterization of a marine-derived fungus, Cladosporium oxysporum SCSIO 81042, capable of degrading polyurethane (PU) under seawater conditions. Through tiered screening, the strain was selected based on its superior hydrolysis activity against Impranil® DLN and solid poly(1,4-butylene adipate)-based PU (PBA-PU). The strain demonstrated exceptional adaptability to seawater conditions, with optimal growth at 15-28 °C, ∼3% salinity, and pH 7.5-8.0. Under simulated seawater salinity, it degraded 94.5% of Impranil® DLN within four days while maintaining sustained activity over two successive cycles. In natural seawater, near-complete degradation of 0.1% Impranil® DLN was achieved within 7 days, and the degradation products showed negligible developmental toxicity to zebrafish. Notably, this efficiency successfully translated to a 10-L seawater mesocosm, where most Impranil® DLN was degraded within 7 days. The strain also caused structural damage to solid PBA-PU films and PU foam under simulated seawater salinity after 14 days, although no significant weight loss was observed. Metabolite analysis confirmed its ability to hydrolyze both ester and urethane bonds in PBA-PU. Furthermore, chitosan nanoparticle (CS-NP) was introduced as an adhesion adjuvant, enhancing degradation across all tested PU substrates, potentially through facilitated microbial adhesion and substrate contact. While challenges remain regarding degradation of complex PU foams, CS-NP environmental fate, and microbial competition, this work establishes C. oxysporum SCSIO 81042 and the CS-NP adjuvant strategy as promising tools for the bioremediation of marine PU pollution.