Bioremediation of methotrexate by Pleurotus ostreatus pellets: effects on morphology and biotransformation insights.

Methotrexate (MTX), a widely used antineoplastic drug, poses significant environmental risks due to its persistence and toxicity. This study evaluated the potential of Pleurotus ostreatus fungal pellets for MTX degradation and investigated the underlying removal mechanisms and morphological effects. Fungal pellets were produced under optimized conditions and exposed to MTX in minimal media. MTX removal kinetics were assessed using HPLC, and associated enzymatic activity was quantified. Pleurotus ostreatus achieved over 90% MTX removal within five days. The removal process was primarily enzymatic, as demonstrated by the ineffectiveness of heat-inactivated biomass and the lack of impact from cytochrome P450 inhibition. Elevated laccase activity coincided with MTX degradation, suggesting its key role in the biotransformation pathway. Mass spectrometry revealed 16 MTX metabolites, including 7-hydroxymethotrexate and 2-oxoglutaric acid, indicating progressive oxidation, ring cleavage, hydroxylation, and eventual integration into primary metabolism. Scanning electron microscopy showed significant structural degradation of fungal pellets during the process, highlighting stress-induced morphological changes. The findings establish the feasibility of employing P. ostreatus pellets as an environmentally compatible biotechnological tool for the degradation of cytotoxic compounds like MTX. To our knowledge, this is the first report of MTX biotransformation by fungal pellets of P. ostreatus, and it contributes valuable insights into fungal-based bioremediation strategies for pharmaceutical pollutants.