Identification of a laccase from Ganoderma lucidum CBS 229.93 having potential for enhancing cellulase catalyzed lignocellulose degradation

• 44 white-rot lignocellulytic fungal strains are screened.
• Ganoderma lucidum can grow on alkali lignin and expresses high laccase activity.
• The G. lucidum laccase extract enhances cellulase-catalyzed lignocellulose degradation.

Based on a differential pre-screening of 44 white-rot fungi on a lignocellulose-supplemented minimal medium, four basidiomycetes were selected for further study: Ganoderma lucidum, Polyporus brumalis, Polyporus ciliatus and Trametes versicolor. Only G. lucidum was able to grow vividly on malt extract or minimal media supplemented with alkali lignin. When grown on malt extract or minimal medium supplemented with lignocellulose (sugar cane bagasse), the crude G. lucidum protein extract exhibited high laccase activity, ∼3 U/mL toward syringaldazine. This activity was 13–17 fold higher than the corresponding activities of the crude protein extracts of P. brumalis, P. ciliatus and T. versicolor. Native PAGE electrophoresis of the crude G. lucidum extract confirmed the presence of an active laccase. The G. lucidum laccase had a molecular weight of ∼62.5 kDa, and a Km value of 0.107 mM (determined on ABTS). A partial amino acid sequence analysis of four short de novo sequenced peptides, defined after trypsin digest analysis using MALDI-TOF MS/MS analysis, revealed 64–100% homology to sequences in related laccases in the UniProt database, but also indicated that certain sequence stretches had low homology. Addition of the laccase-rich G. lucidum broth to lignocellulosic biomass (pretreated sugar cane bagasse) together with a state-of-the-art cellulase enzyme preparation (Cellic™CTec1) produced significantly increased cellulolytic yields, which were also better than those obtained with a T. versicolor laccase addition, indicating that the laccase from G. lucidum has unique properties that may be momentous in lignocellulosic biomass conversion.