Abstract
The persistent accumulation of polyurethane (PU) waste in landfills and natural ecosystems poses a severe environmental challenge, demanding sustainable bioremediation solutions. This study isolated, characterized, and evaluated indigenous fungi from five plastic-contaminated landfill sites in Faisalabad, Pakistan, for their polyurethane-degrading capabilities. A total of 87 morphologically distinct fungal isolates were obtained from 43 composite samples via enrichment culture on mineral salt medium with PU as the sole carbon source. Multi-stage screening primary (clear zone formation, degradation index ≥ 1.2) and secondary (weight loss ≥ 10% in liquid culture over 60 days) identified 12 potent degraders meeting stringent tertiary criteria (DI ≥ 1.5; weight loss ≥ 15%). Molecular identification via ITS region sequencing revealed diverse genera: Aspergillus (six species), Fusarium oxysporum, Penicillium chrysogenum, Alternaria alternata, A. tenuissima, Mucor circinelloides, and M. racemosus. A 120-day time-course study showed Aspergillus fumigatus KHF-05 achieved the highest weight loss (39.8%), followed by A. terreus KHF-12 (38.2%) and Fusarium oxysporum JRF-08 (34.5%). FTIR spectroscopy confirmed cleavage of ester carbonyl and urethane linkages; SEM documented extensive surface erosion, hyphal penetration, and biofilm formation. Peak extracellular enzyme activities were: esterase 1.42 U/mg, protease 0.82 U/mg, and urethanase 7.8 × 10⁻³ U/mg, with Pearson correlations to weight loss of r = 0.91, 0.67, and 0.88, respectively, confirming ester-bond hydrolysis as the primary mechanism.