Ionic liquid-tolerant cellulase system of Stachybotrys microspora exploited in the in situ saccharification of lignocellulosic biomass

Abstract

Ionic liquids (ILs) are used as green solvents for pretreatment of lignocellulosic biomass before enzymatic hydrolysis for bioenergy production. The enzymatic saccharification of regenerated biomass must be carried in a two steps process (IL treatment followed by enzymatic one) because the majority of cellulase are inactive in the presence of ILs. In this study, a highly tolerant IL-cellulase system from the halophilic cellulolytic fungus Stachybotrys microspora is developed. The cellulase activity was enhanced to 115.5% and 114.5% in the presence of 5% (v/v) of 1-Ethyl-3-methylimidazolium diethyl phosphate [EMIM][DEP] and 1-Allyl-3-methylimidazolium chloride [AMIM][Cl] and retained 84.4% and 76.7% of activity in presence of 30% (v/v) of each compound, respectively. The cellulase was most sensitive to 1-Ethyl-3-methylimidazolium methyl sulphate [EMIM] [MtSO4] loosing 72% and 25% of initial activity after incubation in 5% and 30% solution of IL, respectively. The effectiveness of ILs for wheat bran pretreatment process shows the sequence: [EMIM][DEP] > [AMIM][Cl] > [EMIM] [MtSO4]. The IL-activated wheat bran slurry was enzymatically hydrolyzed in the best solvent [EMIM][DEP] diluted to 5, 10, 15 and 20% (v/v), the highest yield of reducing sugars, 52.4%, was obtained with the 15% pretreated substrate. Results showed a very high digestibility of the slurry and confirmed a high glucose yield for the pretreatment methodology. Indeed, the in situ saccharification of IL-pretreated wheat bran was significantly improved compared to the untreated (2.6 fold). Thus, a successful system in a one-pot procedure was developed.