Determination of optimal biomass pretreatment strategies for biofuel production: investigation of relationships between surface-exposed polysaccharides and their enzymatic conversion using carbohydrate-binding modules

Vinay Khatri,Simon Barnabé,Fatma Meddeb-Mouelhi,Marc Beauregard,Kokou Adjallé

doi:10.1186/s13068-018-1145-5

Vinay Khatri, Simon Barnabé + Show 3 more

Open Access

https://doi.org/10.1186/s13068-018-1145-5

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Abstract

BackgroundPretreatment of lignocellulosic biomass (LCB) is a key step for its efficient bioconversion into ethanol. Determining the best pretreatment and its parameters requires monitoring its impacts on the biomass material. Here, we used fluorescent protein-tagged carbohydrate-binding modules method (FTCM)-depletion assay to study the relationship between surface-exposed polysaccharides and enzymatic hydrolysis of LCB.ResultsOur results indicated that alkali extrusion pretreatment led to the highest hydrolysis rates for alfalfa stover, cattail stems and flax shives, despite its lower lignin removal efficiency compared to alkali pretreatment. Corn crop residues were more sensitive to alkali pretreatments, leading to higher hydrolysis rates. A clear relationship was consistently observed between total surface-exposed cellulose detected by the FTCM-depletion assay and biomass enzymatic hydrolysis. Comparison of bioconversion yield and total composition analysis (by NREL/TP-510-42618) of LCB prior to or after pretreatments did not show any close relationship. Lignin removal efficiency and total cellulose content (by NREL/TP-510-42618) led to an unreliable prediction of enzymatic polysaccharide hydrolysis.ConclusionsFluorescent protein-tagged carbohydrate-binding modules method (FTCM)-depletion assay provided direct evidence that cellulose exposure is the key determinant of hydrolysis yield. The clear and robust relationships that were observed between the cellulose accessibility by FTCM probes and enzymatic hydrolysis rates change could be evolved into a powerful prediction tool that might help develop optimal biomass pretreatment strategies for biofuel production.

Highlights

Pretreatment of lignocellulosic biomass (LCB) is a key step for its efficient bioconversion into ethanol
We developed four fluorescent protein-tagged fusion proteins for fluorescent protein-tagged carbohydrate-binding modules method (FTCM): Probe GC3a, specific to crystalline cellulose; Probe CC17, specific to non-crystalline cellulose; Probe OC15, specific to xylan; and Probe CBM15 (OC15) and eCFP-CBM27 (CC27), specific to mannan
These LCBs were derived from alfalfa (Medicago sativa) stover provided by TH-Alfalfa Inc. (Quebec, Canada), corn (Zea mays) crop residues provided by Ferme Olivier and Sébastien Lépine of Agrosphère Co. (Quebec, Canada), cattail (Typha) stems provided by International Institute for Sustainable Development (IISD) (Manitoba, Canada) and flax (Linum) shives provided by SWM International (Manitoba, Canada). Accellerase® DUET (Dupont Industrial Biosciences, USA) was used in this study to hydrolyze LCB

Summary

Introduction

Pretreatment of lignocellulosic biomass (LCB) is a key step for its efficient bioconversion into ethanol. For the production of biofuels from LCB, such as bioethanol, the principal goal is the complete hydrolysis of the polysaccharide components (mainly cellulose) in the raw material into monomers for subsequent fermentation [3]. It is difficult to break down the rigidity of plant biomass due to its complex structure, which consists of cellulose fibrils wrapped in a network of lignin and hemicelluloses [3, 4]. This network, collectively referred to as the lignin–carbohydrate complex, is highly recalcitrant and difficult to deconstruct [3, 4]. Several steps including pretreatments are needed to improve access to polysaccharides, mainly cellulose, before it can be used in value-added applications [5]

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