Evaluation of various fungal pretreatment of switchgrass for enhanced saccharification and simultaneous enzyme production

In order to produce clean energy from renewable lignocellulosic biomass, the feedstock must be pretreated by means of one or combined cost-competitive methods to make the entire process economically feasible. Fungal cultivation may be one promising pretreatment approach, for which the effectiveness varies with different fungal strains in regard to biomass loss, sugar yield, enzyme loading, and co-product yield. Wild-type fungus might have a great potential in pretreating feedstock for both lowered enzyme loading and beneficial co-product enzyme production. In this study, 25 diverse fungal strains were screened for pretreatment of switchgrass biomass with regard to co-production of beneficial enzymes and the subsequent saccharification process, by examining switchgrass biomass loss, effectiveness of enzymatic hydrolysis, and ligninolytic activity. The most promising fungus was identified as an inedible mushroom, Agaricus molybdites (H4) with the highest saccharification efficiency and ligninolytic enzyme production. Additionally, eight accessory enzymes, e.g. pectinase, esterase, xylanase, β-glucosidase, chitinase, lipase, α-amylase, and laccase, were found to assist cellulase in enhancing saccharification of H4 pretreated switchgrass to varying degrees. Our experimental results suggest that pretreatment of switchgrass with an appropriate fungus, followed by exposure to cellulase and synergistic accessory enzymes can be an effective strategy for maximizing the process of saccharification.