Optimization of a synthetic mixture composed of major Trichoderma reeseienzymes for the hydrolysis of steam-exploded wheat straw

Lopes, Billard Hélène, Faraj Abdelaziz, Menir Sandra, Heiss-Blanquet, Heiss-Blanquet Senta

Description

An efficient hydrolysis of lignocellulosic substrates to soluble sugars for biofuel production necessitates the interplay and synergistic interaction of multiple enzymes. An optimized enzyme mixture is crucial for reduced cost of the enzymatic hydrolysis step in a bioethanol production process and its composition will depend on the substrate and type of pretreatment used. In the present study, an experimental design was used to determine the optimal composition of a Trichoderma reesei enzyme mixture, comprising the main cellulase and hemicellulase activities, for the hydrolysis of steam-exploded wheat straw. Methods Six enzymes, CBH1 (Cel7a), CBH2 (Cel6a), EG1 (Cel7b), EG2 (Cel5a), as well as the xyloglucanase Cel74a and the xylanase XYN1 (Xyl11a) were purified from a T. reesei culture under lactose/xylose-induced conditions. Sugar release was followed in milliliter-scale hydrolysis assays for 48 hours and the influence of the mixture on initial conversion rates and final yields is assessed. Results The developed model could show that both responses were strongly correlated. Model predictions suggest that optimal hydrolysis yields can be obtained over a wide range of CBH1 to CBH2 ratios, but necessitates a high proportion of EG1 (13% to 25%) which cannot be replaced by EG2. Whereas 5% to 10% of the latter enzyme and a xylanase content above 6% are required for highest yields, these enzymes are predicted to be less important in the initial stage of hydrolysis. Conclusions The developed model could reliably predict hydrolysis yields of enzyme mixtures in the studied domain and highlighted the importance of the respective enzyme components in both the initial and the final hydrolysis phase of steam-exploded wheat straw.

Sujets

• Trichoderma reesei
• Xylanase
• Enzymatic hydrolysis
• Design of experiments

Informations

• Publié par: biomed
• Publié le: 01 janvier 2012
• Nombre de lectures: 9
• Langue: English

Extrait

Billardet al.Biotechnology for Biofuels2012,5:9 http://www.biotechnologyforbiofuels.com/content/5/1/9

R E S E A R C HOpen Access Optimization of a synthetic mixture composed of majorTrichoderma reeseienzymes for the hydrolysis of steamexploded wheat straw 1 21 11* Hélène Billard , Abdelaziz Faraj , Nicolas Lopes Ferreira , Sandra Menirand Senta HeissBlanquet

Abstract Background:An efficient hydrolysis of lignocellulosic substrates to soluble sugars for biofuel production necessitates the interplay and synergistic interaction of multiple enzymes. An optimized enzyme mixture is crucial for reduced cost of the enzymatic hydrolysis step in a bioethanol production process and its composition will depend on the substrate and type of pretreatment used. In the present study, an experimental design was used to determine the optimal composition of aTrichoderma reeseienzyme mixture, comprising the main cellulase and hemicellulase activities, for the hydrolysis of steamexploded wheat straw. Methods:Six enzymes, CBH1 (Cel7a), CBH2 (Cel6a), EG1 (Cel7b), EG2 (Cel5a), as well as the xyloglucanase Cel74a and the xylanase XYN1 (Xyl11a) were purified from aT. reeseiculture under lactose/xyloseinduced conditions. Sugar release was followed in milliliterscale hydrolysis assays for 48 hours and the influence of the mixture on initial conversion rates and final yields is assessed. Results:The developed model could show that both responses were strongly correlated. Model predictions suggest that optimal hydrolysis yields can be obtained over a wide range of CBH1 to CBH2 ratios, but necessitates a high proportion of EG1 (13% to 25%) which cannot be replaced by EG2. Whereas 5% to 10% of the latter enzyme and a xylanase content above 6% are required for highest yields, these enzymes are predicted to be less important in the initial stage of hydrolysis. Conclusions:The developed model could reliably predict hydrolysis yields of enzyme mixtures in the studied domain and highlighted the importance of the respective enzyme components in both the initial and the final hydrolysis phase of steamexploded wheat straw. Keywords:Trichoderma reesei, cellulases, xylanase, wheat straw, enzymatic hydrolysis, experimental design

Background The production of bioethanol from plant biomass is seen as a possible strategy to reduce greenhouse gas emissions and the current dependence of industrialized nations on declining fossil fuels. Renewable lignocellulo sic biomass is generally cheap and abundant and does not compete with food production as is the case for agricultural crops. Raw materials include wood residues, dedicated crops such as poplar or Miscanthus, agricul tural residues and waste paper. Wheat straw is one of

* Correspondence: [e-mail] 1 IFP Energies nouvelles, Biotechnology Department, 1 et 4 Avenue de Bois Préau, 92852 RueilMalmaison Cedex, France Full list of author information is available at the end of the article

the most abundant crop residues in middle European countries with a production of over 130 million tons [1] and represents a lowcost source of lignocellulosic biomass. In nature, plant cell wall carbohydrates are hydrolyzed to soluble sugars by (hemi)cellulolytic enzymes from both bacteria and fungi, the latter being very efficient degraders [2].Trichoderma reeseiis the major fungus used for industrial cellulase production. The secreted cellulases comprise two cellobiohydrolases and eight endoglucanases from six glycoside hydrolase families [3] which act in a synergistic manner to degrade the plant biomass, together with betaglucosidases and hemicellu lases. In total, theT. reeseigenome contains 200

© 2012 Billard et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.