Contrasted enzymatic cocktails reveal the importance of cellulases and hemicellulases activity ratios for the hydrolysis of cellulose in presence of xylans.

Céline Cohen,Fadhel Ben Chaabane,Nathalie Aubry,Eve Dondelinger,Caroline Rémond,Jean Tayeb

doi:10.1186/s13568-016-0196-x

Abstract

Various enzymatic cocktails were produced from two Trichoderma reesei strains, a cellulase hyperproducer strain and a strain with β-glucosidase activity overexpression. By using various carbon sources (lactose, glucose, xylose, hemicellulosic hydrolysate) for strains growth, contrasted enzymatic activities were obtained. The enzymatic cocktails presented various levels of efficiency for the hydrolysis of cellulose Avicel into glucose, in presence of xylans, or not. These latter were also hydrolyzed with different extents according to cocktails. The most efficient cocktails (TR1 and TR3) on Avicel were richer in filter paper activity (FPU) and presented a low ratio FPU/β-glucosidase activity. Cocktails TR2 and TR5 which were produced on the higher amount of hemicellulosic hydrolysate, possess both high xylanase and β-xylosidase activities, and were the most efficient for xylans hydrolysis. When hydrolysis of Avicel was conducted in presence of xylans, a decrease of glucose release occurred for all cocktails compared to hydrolysis of Avicel alone. Mixing TR1 and TR5 cocktails with two different ratios of proteins (1/1 and 1/4) resulted in a gain of efficiency for glucose release during hydrolysis of Avicel in presence of xylans compared to TR5 alone. Our results demonstrate the importance of combining hemicellulase and cellulase activities to improve the yields of glucose release from Avicel in presence of xylans. In this context, strategies involving enzymes production with carbon sources comprising mixed C5 and C6 sugars or combining different cocktails produced on C5 or on C6 sugars are of interest for processes developed in the context of lignocellulosic biorefinery.

Highlights

A challenge for producing glucose from enzymatic hydrolysis of lignocellulosic biomass while limiting the process cost is to perform enzymatic hydrolysis at high solid concentration and to use low enzyme loadings
The experiments for TR2 and TR4 production were performed with the strain CL847 while the experiments concerning TR1, TR3 and TR5 were performed with the strain TR3002
Contrasted enzymatic activities ratios characterizing the obtained cocktails could be related to the strain and to the substrates used during the culture of T. reesei for enzymes production

Summary

Introduction

A challenge for producing glucose from enzymatic hydrolysis of lignocellulosic biomass while limiting the process cost is to perform enzymatic hydrolysis at high solid concentration and to use low enzyme loadings. Dondelinger et al AMB Expr (2016) 6:24 from steam-explosed corn stover, the supplementation by GH11 xylanases of commercial cellulase (Celluclast 1.5 L) allows reducing the cellulase loading by a factor 7 (Hu et al 2011) This was attributed to the removal of xylans and to the increase of cellulose accessibility by enhancing fiber porosity and swelling (Hu et al 2011). Another strategy is to develop enzymatic cocktails possessing both cellulases and hemicellulases activities by growing micro-organisms onto various simple or complex substrates. To the best of our knowledge, no study concerns the production of enzymes by T. reesei growing on hemicellulolytic hydrolysates

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