Lignin degradation and detoxification of eucalyptus wastes by on-site manufacturing fungal enzymes to enhance second-generation ethanol yield

Abstract

Novel laccases have promising and valuable applications in biorefineries. This investigation documents, for the first time, the potential of depolymerising and repolymerising lignin by the secretome, rich in laccases, from a newly isolated white-rot basidiomycete Marasmiellus palmivorus VE111, for further saccharification and ethanolic fermentation steps. Proteomic analyses of the secretome of M. palmivorus show that laccases are the most predominant enzyme released by this fungus. The whole crude enzymatic broth is used for the delignification of lignin in Eucalyptus globulus wood, with the aim of enhancing the saccharification by cellulolytic and xylanolytic enzymes from Penicillium echinulatum S1M29. In addition, two different strategies, namely, laccase treatment before and after enzymatic hydrolysis, are employed to detoxify steam-exploded E. globulus wood. The objective is to increase the fermentative performance by removing substances formed during the feedstock pretreatment that can inhibit microbial fermentation. The E. globulus wood delignification results in a 31% decrease in the lignin content and a 10% increase in the glucose yield after hydrolysis. An important finding of the present work is the successful wood delignification in the absence of laccase mediators. This laccase-rich preparation also demonstrates its potential in removing the phenolic inhibitors present in steam-exploded E. globulus wood, increasing the ethanol yield by an additional 10%. Furthermore, it is important to highlight that these findings are achieved in the absence of commercial enzymes, making M. palmivorus laccases a potential candidate not only for the production of biofuels but also for the generation of lignin-derived aromatic compounds for different applications in the biotechnology industry.