Filamentous fungi as microbial cell factories for lignocellulosic biomass valorization: A comprehensive review

The transition toward a sustainable bioeconomy requires efficient conversion of lignocellulosic biomass (LCB), the most abundant renewable biological macromolecular resource on Earth, into fuels, chemicals, and other high-value products. However, the complex architecture of cellulose, hemicellulose, and lignin imparts significant recalcitrance, limiting biomass deconstruction and industrial utilization. Although recent reviews have examined fungal biorefineries, lignocellulolytic enzymes, or fungal strain engineering separately, an integrated synthesis linking lignocellulosic biomass characteristics, fungal deconstruction mechanisms, hydrolysate utilization, and cell-factory engineering remains limited. This review presents an integrated framework for lignocellulosic biomass valorization using filamentous fungi as microbial cell factories. We examine biomass composition, recalcitrance, and pretreatment strategies, followed by the fungal macromolecular machinery responsible for biomass deconstruction, including cellulases, hemicellulases, lignin-active oxidoreductases, and auxiliary activity enzymes. Particular emphasis is placed on the regulatory networks and engineering strategies that govern fungal performance, including transcription factor engineering, promoter engineering, metabolic rewiring, heterologous pathway engineering, RNA interference, and CRISPR-Cas-based genome editing. The review further discusses the conversion of lignocellulose-derived hydrolysates into biofuels, organic acids, industrial enzymes, and other high-value compounds, together with emerging advances in co-culture fermentation, downstream processing, and integrated biorefinery design. Collectively, this review highlights how the integration of fungal enzymatic systems, strain engineering, and process-level innovations can overcome biomass recalcitrance and improve lignocellulosic bioconversion efficiency. These insights provide a framework for developing robust fungal platforms for the sustainable production of high-value bioproducts from renewable biomass.