Mining fungal genomic diversity for novel biomass deconstruction enzymes
Jonathan Walton, Zhuoliang Ye, Binglao (Crystal) Li, Yun Zheng*, Dina Jabbour, Reginald Storms*, and Melissa Borrusch, DOE Great Lakes Bioenergy Research Center and DOE Plant Research Lab, Michigan State University, E. Lansing MI 48824 USA, and *Department of Biology, Concordia University, Montreal, Canada
Enzymatic conversion of lignocellulosic materials to fermentable sugars is a limiting step in the production of biofuels. Approaches to produce better enzyme cocktails include identification of new accessory enzymes or better versions of existing enzymes. Extracts of the thermophilic fungus Sporotrichum thermophile gave synergistic release of glucose (Glc) and xylose (Xyl) from corn stover when combined with an 8-component synthetic cocktail of enzymes from Trichoderma reesei. The enhancing factor was identified as endo-β1,4- glucanase (StCel5A). This enzyme differs from the T. reesei Cel5A (TrCel5A) in having broader substrate range, which might account for its superiority. Another approach that takes advantage of fungal diversity is to seek enzymes that are lacking from T. reesei. For example, this fungus lacks secreted α-xylosidase, without which it cannot release free Glc and Xyl from xyloglucan, the major hemicellulose in many plants. An α-xylosidase from A. niger enhanced fermentable sugar yields by T. reesei cocktails from xyloglucan-containing cell wall preparations. In a third approach, we have identified cellulases from novel fungi that perform better at high pH (8-9) than those from T. reesei. Such enzymes could prove to be more compatible with alkaline pretreatments and allow more flexibility in an industrial setting.