Pretreatment with laccase and a phenolic mediator degrades lignin and enhances saccharification of Eucalyptus feedstock

Biotechnology for Biofuels

Ana Gutiérrez¹  Angel T Martínez²  José C del Río¹  Jorge Rencoret¹  Alejandro Rico¹ 

[1]Instituto de Recursos Naturales y Agrobiología de Sevilla, CSIC, Reina Mercedes, 10, E-41012 Seville, Spain

[2]Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, E-28040 Madrid, Spain

关键词: Saccharification;    Pretreatment;    Lignocellulose;    Lignin;    Laccase;    Enzymatic delignification;    Eucalyptus globulus;    Bioethanol;    Analytical pyrolysis;    2D NMR;   

Others  :  794084
DOI  :  10.1186/1754-6834-7-6

 received in 2013-09-20, accepted in 2013-11-06,  发布年份 2014

【 摘 要 】

Background

Biofuel production from lignocellulosic material is hampered by biomass recalcitrance towards enzymatic hydrolysis due to the compact architecture of the plant cell wall and the presence of lignin. The purpose of this work is to study the ability of an industrially available laccase-mediator system to modify and remove lignin during pretreatment of wood (Eucalyptus globulus) feedstock, thus improving saccharification, and to analyze the chemical modifications produced in the whole material and especially in the recalcitrant lignin moiety.

Results

Up to 50% lignin removal from ground eucalypt wood was attained by pretreatment with recombinant Myceliophthora thermophila laccase and methyl syringate as mediator, followed by alkaline peroxide extraction in a multistage sequence. The lignin removal directly correlated with increases (approximately 40%) in glucose and xylose yields after enzymatic hydrolysis. The pretreatment using laccase alone (without mediator) removed up to 20% of lignin from eucalypt wood. Pyrolysis-gas chromatography/mass spectrometry of the pretreated wood revealed modifications of the lignin polymer, as shown by lignin markers with shortened side chains and increased syringyl-to-guaiacyl ratio. Additional information on the chemical modifications produced was obtained by two-dimensional nuclear magnetic resonance of the whole wood swollen in dimethylsulfoxide-d₆. The spectra obtained revealed the removal of guaiacyl and syringyl lignin units, although with a preferential removal of the former, and the lower number of aliphatic side-chains per phenylpropane unit (involved in main β-O-4ʹ and β-βʹ inter-unit linkages), in agreement with the pyrolysis-gas chromatography/mass spectrometry results, without a substantial change in the wood polysaccharide signals. However, the most noticeable modification observed in the spectra was the formation of C_α-oxidized syringyl lignin units during the enzymatic treatment. Further insight into the modifications of lignin structure, affecting other inter-unit linkages and oxidized structures, was attained by nuclear magnetic resonance of the lignins isolated from the eucalypt feedstock after the enzymatic pretreatments.

Conclusions

This work shows the potential of an oxidative enzymatic pretreatment to delignify and improve cellulase saccharification of a hardwood feedstock (eucalypt wood) when applied directly on the ground lignocellulosic material, and reveals the main chemical changes in the pretreated material, and its recalcitrant lignin moiety, behind the above results.

【 授权许可】

   
2014 Rico et al.; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

Figure 2.

Figure 3.

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