Unlocking raw-corncob consolidated bioprocessing for malic acid production by DyP-enabled lignin deconstruction in Myceliophthora thermophila

Abstract

l -Malic acid is an important C4 platform chemical, but its direct production from raw lignocellulosic biomass by consolidated bioprocessing (CBP) remains constrained by biomass recalcitrance. Here, we developed an integrated lignin-side and sugar-side engineering strategy in the thermophilic fungus Myceliophthora thermophila to improve malic acid production directly from raw corncob. Transcriptomic analysis and physiological characterization identified lignin-associated recalcitrance as a major barrier during CBP on raw corncob. Reinforcing lignin-side oxidative remodeling through overexpression of a dye-decolorizing peroxidase (DyP) improved malic acid production and biomass-deconstruction performance, while FTIR analysis of treated corncob residues supported its role in modifying lignin-associated structures. Carbohydrate conversion was further strengthened by improving cellulose deconstruction together with cellodextrin uptake and intracellular phosphorolytic processing. The final engineered strain produced 55.5 g/L malic acid in shake-flask culture using 75 g/L raw corncob as the sole carbon source. In a 5-L bioreactor, it achieved 157.6 g/L malic acid, corresponding to a productivity of 1.17 g/L/h and a yield of 0.55 g/g total raw corncob input. The recovered product reached 99% purity after downstream processing. By integrating raw-biomass deconstruction and intracellular carbon conversion within a single thermophilic fungal platform, this work demonstrates a more direct and lower-input route for valorization of agricultural residues into organic acids and provides a practical basis for greener lignocellulose biorefining.