Heterologous expression of thermoregulated xylanases in switchgrass reduces the amount of exogenous enzyme required for saccharification

The expression of cell wall degrading enzymes in bioenergy crops has been proposed as a cost-effective method to produce fuel and chemicals. In this study, the thermoregulated intein-modified endo-β-1,4-xylanases GH10 and GH11 (iXyn GH10 and iXyn GH11) were expressed in switchgrass (Panicum virgatum). Two xylanase-expressing lines (Alamo background genetics) were compared to the wild type (Alamo genetics) to determine their composition, pretreatment, enzymatic hydrolysis, and ethanol fermentation. Three switchgrass samples with similar carbohydrate contents performed differently under four selected pretreatment conditions utilizing ammonia, oxalic acid/ferric chloride, sodium carbonate, or sodium hydroxide. Pretreated iXyn samples had higher glucan and lower xylan concentrations compared to the pretreated Alamo. An increased rate of glucose production and a higher glucan conversion ratio were observed in both iXyn lines. Pretreated iXyn samples required less exogenous enzyme to achieve similar levels of saccharification. Ethanol production increased from the glucan portion of the pretreated iXyn lines. However, the overall yield may vary depending upon the characteristics of the yeast and its conversion processes.