Applicability of a laccase from the eucalypt wood endophytic fungus Hormonema sp. CECT-13092 for advanced bioethanol production

This work studies, for the first time, the potential of a laccase from the endophyte fungus Hormonema sp. CECT-13092, compared to a laccase from the saprophyte fungus Trametes villosa, for delignification and detoxification of steam-exploded eucalypt to improve subsequent bioethanol production. Regarding laccase delignification, the use of Hormonema sp. and T. villosa laccases did not show evidence of delignification of steam-exploded material, and rather low glucose and xylose recoveries were obtained during saccharification assays of laccase-treated samples compared with their respective controls. With regard to laccase detoxification, the reduction of the total phenolic inhibitors content presents in steam-exploded material by both laccases (phenols removal of 47 % and 60 % by Hormonema sp. and T. villosa laccases, respectively), triggered the fermentation by Saccharomyces cerevisiae of laccase-treated samples when 0.2 g L^-1 of inoculum was used during a simultaneous saccharification and fermentation (SSF) process. Moreover, when the inoculum was increased from 0.2 to 1.0 g L^-1, both laccases shortened the yeast lag phase during the SSF process. Then, faster glucose consumption and ethanol production rates (ethanol productivity values of 0.25 and 0.28 g L^-1 h^-1 for T. villosa and Hormonema sp. laccases, respectively, compared to 0.02 g L^-1 h^-1 for control samples) were noticed. This fact proves the high potential of this new entophytic fungal laccase for bioethanol production enhancement, comparable to commercial laccases.