Fungal biodiversity and oxidative enzymes: nature-based solutions for lignin degradation and circular economy applications

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Lignin is one of the most abundant yet recalcitrant biopolymers in nature, and its inefficient depolymerization remains a major bottleneck in lignocellulosic biomass valorization and sustainable biorefinery development. Although fungal oxidative enzymes have emerged as promising biocatalysts for lignin degradation, current knowledge remains fragmented across fungal diversity, catalytic mechanisms, enzyme engineering, and industrial translation. This review critically integrates recent advances in fungal ligninolytic systems, focusing on the structure, catalytic mechanisms, and synergistic interactions of major oxidative enzymes, including lignin peroxidase, manganese peroxidase, versatile peroxidase, laccase, and auxiliary oxidases such as aryl alcohol oxidase and glyoxal oxidase. Particular emphasis is placed on the comparative catalytic efficiency, operational limitations, and industrial feasibility of these enzymes in lignin depolymerization and biomass conversion. Recent developments in protein engineering, directed evolution, heterologous expression, immobilized enzyme systems, synthetic biology, and AI-assisted enzyme optimization are also discussed as emerging strategies to improve enzyme stability, substrate specificity, and process scalability. The review further highlights the role of fungal oxidative enzymes in bioremediation, lignocellulosic biorefineries, wastewater detoxification, biofuel production, and synthesis of value-added aromatic compounds. Importantly, it establishes a direct link between fungal ligninolytic systems and circular bioeconomy models through sustainable waste valorization and biomass-to-value conversion. Overall, this review provides an integrated perspective on the challenges, technological advancements, and future prospects of fungal oxidative enzymes for sustainable industrial biotechnology.