Biodegradation of Low and High Molecular-Weight Polycyclic Aromatic Hydrocarbons by Lignolytic Enzyme Producing Trichoderma harzianum-OR485009

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are toxic, persistent organic pollutants with significant ecological and health risks due to their widespread distribution and resistance to natural degradation. This study evaluates the potential of Trichoderma harzianum-OR485009, isolated from petrochemical refinery effluent, to degrade representative PAHs (naphthalene, phenanthrene, and pyrene) individually and in combination, while also analyzing associated enzyme activity and degradation intermediates. Biodegradation experiments were conducted over a 25-day period using standard microbiological and analytical protocols. The fungal strain was exposed to 150 mg/L of each PAH, both singly and in mixture. Degradation efficiency was monitored using chromatographic analysis. Enzymatic assays were performed to evaluate the activity of lignolytic enzymes (laccase, manganese peroxidase, lignin peroxidase), and GC-MS was employed to identify intermediate degradation products. Trichoderma harzianum-OR485009 completely degraded naphthalene and phenanthrene (100%), and achieved 95.5% degradation of pyrene. Degradation efficiency declined with increasing PAH ring complexity. In mixed-PAH treatments, higher degradation rates were observed for low molecular weight compounds. Laccase activity was highest among the enzymes assayed and also decreased as the number of aromatic rings increased. GC-MS analysis revealed key degradation intermediates, including butenoic acid, oxalic acid, diisooctyl phthalate, and eicosane. The results confirm that T. harzianum-OR485009 is capable of efficiently degrading both individual and mixed PAHs, particularly low molecular weight compounds, through mechanisms involving lignolytic enzyme activity. The detection of specific metabolic intermediates indicates active enzymatic transformation pathways. This study proves the suitability of T. harzianum-OR485009 as a viable agent for mycoremediation of PAH-contaminated environments. Its efficiency, particularly in degrading persistent pollutants and producing environmentally benign metabolites, supports its inclusion in eco-friendly bioremediation strategies.