Synergistic Effect Of Cellulase And Xylanase During Hydrolysis Of Natural Lignocellulosic Substrates

Lignocellulose is an important biomass for biofuels because of its abundance and renewability.As fossil resources become scarcer,lignocellulose materials are valuable candidates for the future sources of energy.One of the principal ways in saccharification of lignocellulose is chemical thermal cracking process which is also the main factor of restricting its large-scale application.Enzymatic saccharification of cellulose is a hotspot of research on cellulosic biofuels Synergistic combination of cellulase and xylanase has been proved to be an efficient method to improve the hydrolysis yield of the pretreated lignocelluloses.Many previous studies have been performed on the pretreated cellulosic substrates,while few on the natural lignocellulosic stubstrates.and these pretreatment methods were still focused on chemical heat treatment,acid and alkali treatment.During the enzymatic hydrolysis processing of unpretreated lignocellulose substrates,whether the synergistic effect of cellulase and xylanase could play an effective role and how to improve the multienzyme synergism effect would be of great significance to the development of cellulosic bioenergy.In this study,three unpretreated lignocellulosic substrates were studied,including corncob,corn stover,and rice straw.Cellulase,xylananse and the mixed cellulase and xylanase were added to each of the substrates.The hydrolysis efficiency was represented by the yield of reducing sugar and the substrate residues and the multienzyme synergism effect was represented by DS(degree of synergy)value.The results indicated that when the mixed cellulase and xylanase were applied to these three natural lignocellulosic materials at 37?,pH 5.0 for 12h,reducing sugar concentrations was calculated as 19.53,15.56,and 17.35 mg/ml,and the hydrolysis efficiency was 31.66%,17.92%and 24.69%,respectively.Besides,compared to addition of only cellulose,the hydrolysis yields caused by the mixed cellulase and xylanase were improved by 133%,164%,and 545%,respectively.The substrate morphology was also evaluated to further explore the synergistic mechanism of the mixed cellulase and xylanase.Our results indicated that swelling,perforation,and destruction of the fibrous network were accompanied with the addition of xylanase,suggesting that xylanase could increase the accessibility of cellulose by loosening its structure and increasing its porosity.Our study wanted to construct xylanase recombinant strains in Saccharomyces cerevisiae to explore the effect of whole-cell xylanase and cellulase in Saccharomyces cerevisiae on simultaneous sacchrification and fermentation of natural cellulose substrates.In this study,the recombinant vector of xylanase was constructed and the xylanase was expressed successfully in Saccharomyces cerevisiae,and the enzyme activity of crude enzyme in DNS method was about 67.65 U/mL to be used in subsequent research.Conclusions:1.Synergstic effect of cellulalse and xylanase was identified when the mixed enzymes were applied to the unpretreated lignocellulosic substrates.In the corncob,corn stover and rice straw,the the hydrolysis yields were improved by 133%,164%,and 545%,respectively.2.The xylanase hydolyzed the xylan that was cross-linked to cellulose,increasing the accessibility of cellulose to accelerate the hydrolysis of unpretreated lignocellulosic substrates.3.The xylanase was expressed successfully in Saccharomyces cerevisiae,and thus laid the foundation for saccharification and fermentation to produce ethanol in industrial production.