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Logo of biotbiofuelBioMed CentralBiomed Central Web Sitesearchsubmit a manuscriptregisterthis articleBiotechnology for Biofuels
 
Biotechnol Biofuels. 2012; 5: 9.
Published online Feb 28, 2012. doi:  10.1186/1754-6834-5-9
PMCID: PMC3310832
Optimization of a synthetic mixture composed of major Trichoderma reesei enzymes for the hydrolysis of steam-exploded wheat straw
Hélène Billard,1 Abdelaziz Faraj,2 Nicolas Lopes Ferreira,1 Sandra Menir,1 and Senta Heiss-Blanquetcorresponding author1
1IFP Energies nouvelles, Biotechnology Department, 1 et 4 Avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France
2IFP Energies nouvelles, Applied Mathematics Department, 1 et 4 Avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France
corresponding authorCorresponding author.
Hélène Billard: helene.billard/at/wanadoo.fr; Abdelaziz Faraj: abdelaziz.faraj/at/ifpen.fr; Nicolas Lopes Ferreira: nicolas.lopes-ferreira/at/ifpen.fr; Sandra Menir: sandra.menir/at/ifpen.fr; Senta Heiss-Blanquet: senta.blanquet/at/ifpen.fr
Received December 2, 2011; Accepted February 28, 2012.
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 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.
Keywords: Trichoderma reesei, cellulases, xylanase, wheat straw, enzymatic hydrolysis, experimental design
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