Fungal endophytes and leaf litter fungi as sources of novel inhibitor-resistant cellulase for biofuel production: a basic study

Hydrothermal pretreatments are commonly employed prior to the biotechnological conversion of lignocellulosic biomass (LCB) into value-added products, such as fuels and chemicals. However, the by-products of this pretreatment, including furaldehydes, lignin-derived phenolics, and carboxylic acids, can inhibit the enzymes and microbes used in the biotechnological process. In this study, LCB degrading enzymes of endophytic and litter fungi were screened for their tolerance to potential pretreatment-derived inhibitors. Several fungi produced endo- and exoglucanases that remained functional in the presence of lignocellulose-derived phenolics. Some were also active in the presence of tannic acid. Additionally, thermostable endoglucanase activity was observed in some fungi. The ability of some of these fungi to utilize furaldehyde inhibitors as a sole carbon source was also noted. The culture supernatants of the fungal strains were tested in hydrolysis experiments using microcrystalline cellulose as a substrate, in the presence of lignocellulose phenolics and tannic acid. With some strains, higher sugar yields were obtained in the hydrolysis of cellulose when phenolics were added. Our results highlight the need for more intensive exploration of endophytic and plant litter fungi for novel inhibitor-resistant cellulases for biofuel production.