Enhanced laccase production by Paramyrothecium roridum under solid-state fermentation: Application in neutral-pH delignification and valorization of acorn shells.

This study focused on isolating and characterizing a soil-borne laccase-producing fungus, Paramyrothecium roridum, and optimizing the enzyme production under submerged (SmF) and solid-state fermentation (SSF). SSF achieved a 2-fold increase in laccase production compared to SmF, yielding an activity of 50.64 U g under optimized conditions (17.43 % w/w glucose, 19.30 % w/w yeast extract, 0.29 % w/w xylidine, and 0.31 % w/w ZnSO). Laccase was purified using a new synthetic affinity matrix, DHBA@NH@SiO@FeAlO, yielding a 4.9-fold purification. The maximum activity of purified laccase was achieved at pH 5 and 45 °C, while the enzyme was relatively stable (more than 50 %) over a wide pH range of 4-11. The purified laccase (0.3 U mL) in combination with a 6 mM 1-hydroxybenzotriazole (HBT) effectively depolymerized lignin in acorn shells (60 mg mL) at 50 °C and pH 7, achieving a delignification efficiency of 60.8 %. Gas chromatography-mass spectrometry analysis of the byproducts revealed some valuable substances, such as catechol (31.2 %), benzoic acid (14.3 %), and salicylic acid (13 %), providing insights into the bio-delignification pathway. This study illustrated the promising potential of the fungal laccase and enzymatic delignification for the environmentally friendly depolymerization of lignocellulosic biomass under neutral conditions.