Characterization of an ionic liquid-tolerant β-xylosidase from a marine-derived fungal endophyte

Ionic liquids (ILs) are used in lignocellulosic biomass (LCB) pretreatment because of their ability to disrupt the extensive hydrogen-bonding network in cellulose and hemicellulose, and thereby decrease LCB recalcitrance to subsequent enzymatic degradation. However, this approach necessitates the development of cellulases and hemicellulases that can tolerate ∼20% (w/v) IL, an amount that either co-precipitates with the sugar polymers after the initial pretreatment or is typically used in single-pot biomass deconstructions. By investigating the secretomes from 4 marine-derived fungal endophytes, we identified a β-xylosidase derived from Trichoderma harzianum as the most promising in terms of tolerating 1-ethyl-3-methylimidazolium-dimethyl phosphate (EMIM-DMP), an IL. When tested with p-nitrophenyl-β-d-xyloside, this extracellular xylosidase retained ∼50% activity even in 1.2 mol·L^-1 (20% w/v) EMIM-DMP after incubation for 48 h. When tested on the natural substrate xylobiose, there was ∼85% of the initial activity in 1.2 mol·L^-1 EMIM-DMP after incubation for 9 h and ∼80% after incubation for 48 h. Despite previous findings associating thermostability and IL tolerance, our findings related to the mesophilic T. harzianum β-xylosidase(s) emphasize the need to include the marine habitat in the bioprospecting dragnet for identification of new IL-tolerant LCB-degrading enzymes.