Physico-chemical oxidative cleavage strategy facilitates the degradation of recalcitrant crystalline cellulose by cellulases hydrolysis

Huan Zhou,Yun Liu,Liuyang Wang

doi:10.1186/s13068-018-1016-0

Huan Zhou, Yun Liu + Show 1 more

Open Access

https://doi.org/10.1186/s13068-018-1016-0

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Abstract

BackgroundEfficient enzymatic conversion of recalcitrant crystalline cellulose is critical for enabling cost-effective industrial conversion of cellulosic biomass to biofuels and chemicals. Fully understanding enzyme digestion mechanism is paving a new way to design efficient process for biomass conversion. Accordingly, a continuing drive is inspiring to discover new routes to promote crystalline cellulose disruption.ResultsHerein, a physico-chemical oxidative cleavage strategy of irradiation oxidation/post-reduction (IOPR) was employed to treat crystalline cellulose I to cleave glycosidic bonds association with some new oxidized and reduced chain ends, thus boosting downstream degradation by cellulases from Trichoderma reesei. The hydrolysis performance of treated crystalline cellulose was conducted with either T. reesei Cel7A (TrCel7A) alone, or a cellulase enzyme mixture (90% Celluclast 1.5 L, 10% β-glucosidase). 81.6 and/or 97% of conversion efficiency have been reached for 24-h and 48-h cellulase hydrolysis, respectively. The high efficient conversion of crystalline cellulose after IOPR is mainly attributed to generating some new chain ends, which are identified by MAIDI-TOF–MS and HPLC. Furthermore, the nanoscale architectures of crystalline cellulose before and after IOPR are systematically investigated by XRD, EPR, ATR- FTIR, GPC, and XPS techniques. Together with TEM images, the results reveal a fascinating digestion mechanism of “peel-off” and “cavity-formation” paradigms toward degrading crystalline cellulose by cellulase mixtures after IOPR treatment.ConclusionsThis encouraging results show that the proposed IOPR approach will become a potential competitive alternative to current biomass pretreatment. It opens a new avenue toward the implementation of pretreatment and the design of enzyme cocktails in lignocellulosic biorefinery.

Highlights

Efficient enzymatic conversion of recalcitrant crystalline cellulose is critical for enabling cost-effective industrial conversion of cellulosic biomass to biofuels and chemicals
Irradiation and irradiation oxidation/post-reduction (IOPR) process boost the enzymatic degradation of recalcitrant crystalline cellulose Avicel cellulose was subjected to gamma-ray irradiation followed by reduction with sodium borohydride to enhance enzymatic degradability
The untreated (C-I), irradiated (IC-I), and irradiated and borohydride-treated (IpRC-I) cellulose materials (0.5% w/v) were incubated at pH 5.0 and 50 °C, with either T. reesei Cel7A (TrCel7A) alone, or a cellulase enzyme mixture (90% Celluclast 1.5 L, 10% beta-glucosidase), and the amount of glucose and cellobiose released over time was monitored by High‐performance liquid chromatograph (HPLC)

Summary

Introduction

Efficient enzymatic conversion of recalcitrant crystalline cellulose is critical for enabling cost-effective industrial conversion of cellulosic biomass to biofuels and chemicals. [4,5,6,7] These above techniques have demonstrated two major effects, one is to increase the enzymes accessibility to binding cellulose surface; the other is to decrease the free energy of enzymes for processive decrystallization through reducing cellulose crystallinity [8, 9]. It was demonstrated that LPMOs introduce oxidized chain breaks in the polysaccharide chains, and decrease the free energy for decrystallization [15, 16]. These unexpected findings provide new perspectives to design more efficient biorefinery process in future

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