Coupling the pretreatment and hydrolysis of lignocellulosic biomass by the expression of beta‐xylosidases

Abstract

Thermochemical pretreatment and enzymatic hydrolysis are the areas contributing most to the operational costs of second generation ethanol in lignocellulosic biorefineries. The improvement of lignocellulosic enzyme cocktails has been significant in the recent years. Although the needs for the reduction of the energy intensity and chemical consumption in the pretreatment step are well known, the reduction of the severity of the process strongly affects the enzymatic hydrolysis yield. To explore the formulation requirements of the well known cellulolytic cocktail from Myceliophthora thermophila on mild pretreated raw materials, this cocktail was tested on steam exploded corn stover without acid impregnation. The low hemicellulose yield and significant accumulation of xylobiose compared with the standard pretreated material obtained with dilute acid impregnation evidenced a clear limitation in the conversion of xylan to xylose. In order to complement the beta-xylosidase limitation, a selection of enzymes was expressed and tested in this fungus. A controlled expression of xylosidases from Aspergillus nidulans, Aspergillus fumigatus, and Fusarium oxysporum allowed recovering hemicellulose yields reached with standard acid treated material. The results underline the need of parallel development of the pretreatment process with the optimization of the formulation of the enzymatic cocktails.

Rio Tinto as a niche for acidophilus enzymes of industrial relevance

“…β‐glucosidases, β‐xylosidases, polysaccharide monooxygenases, xylanases, xyloglucanases, arabinofuranosidases, acetylxylan esterases, and α‐ and β‐galactosidases are the other hydrolytic enzymes found in the secretome. In M. thermophila , only four β‐xylosidases, belonging to the GH3 and GH43 families (Berka et al, 2011 ) were identified, and it has been suggested that the addition of hemicellulolytic enzymes to the commercial enzymatic cocktails could improve their performance; directly, by rending more xylose, and indirectly, by removing the hemicellulose coating increasing cellulose accessibility (García‐Aparicio et al, 2007 ; Martín Pérez et al, 2017 ; Yang & Wyman, 2004 ).…”

“…In the soluble fraction of PCS and PSCS, the content (in percentage) was 3.07 and 2.93 of glucose, 16.42 and 15.02 of xylose, 1.63 and 1.66 of arabinose, 0.11 and 0.25 of mannose, 1.19 and 0.61 of acetic acid, and 0.54 and 0.26 of furans, respectively (Rocha‐Martín et al, 2017 ). The total solids were adjusted to 20% (wt vol −1 ) and were hydrolysed with an enzymatic cocktail from M. thermophila C1 derived strain (7 mg of protein g −1 glucan for PCS hydrolysis and 9 mg g −1 glucan for PCSC hydrolysis) (Martín Pérez et al, 2017 ), supplied with purified β‐glucosidase from the same organism (1 mg of protein g −1 glucan) and, when indicated, with 1 mg of protein g −1 glucan of different Rio Tinto fungal secretomes. The final enzyme loading was 9 mg of total protein per g of glucan for PCS and 11 mg of total protein per g of glucan for PCSC.…”