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

摘要

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 similar to 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 beta-xylosidase derived from Trichoderma harzianum as the most promising in terms of tolerating 1-ethyl-3-methylimidazoliumdimethyl phosphate (EMIM-DMP), an IL. When tested with p-nitrophenyl-beta-D-xyloside, this extracellular xylosidase retained similar to 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 similar to 85% of the initial activity in 1.2 mol u L-1 EMIM-DMP after incubation for 9 h and similar to 80% after incubation for 48 h. Despite previous findings associating thermostability and IL tolerance, our findings related to the mesophilic T. harzianum beta-xylosidase(s) emphasize the need to include the marine habitat in the bioprospecting dragnet for identification of new IL-tolerant LCBdegrading enzymes.