木质纤维素丁酸预处理及其高效合成丁醇的调控

Performance of butyric acid pretreatment of lignocellulose and its regulation for high-efficiently production of biobutanol

利用可再生的木质纤维素资源生产丁醇等液态燃料,可以实现农林废弃生物质的高值转化。以典型农林废弃物玉米秸秆为研究对象,选取丁醇生物合成前体物质丁酸作为预处理剂,拟建立生物质高效解聚/酶解及丁醇合成的优化工艺。结果表明:在180℃、50 g/L丁酸溶液中预处理0.5 h后,固体组分中的葡聚糖质量分数提高至47.25%,葡聚糖质量回收率达88.53%;在此预处理工艺下将固体组分进行酶解,当固液比和纤维素酶添加量分别为1∶5(g∶mL)和10 FPU/g底物时,酶解72 h的葡萄糖质量浓度达到70.8 g/L。这说明丁酸预处理可以有效破解玉米秸秆的复杂结构,进而提高纤维素酶的可及度。以丙酮丁醇梭菌(Clostridium acetobutylicum ATCC 824)为发酵菌株,探究了秸秆酶解得到的葡萄糖和预处理残余丁酸作为底物进行丁醇合成的性能。当利用秸秆酶解产生的葡萄糖作为补料碳源时,丁醇产量从4.89 g/L提高到9.34 g/L。将秸秆酶解液和残余丁酸作为共底物补料时,发酵结束时的丁醇产量和生产效率分别达到10.58 g/L和0.147 g/(L·h),比对照组提高了116%,这表明酶解葡萄糖和丁酸可以提高细胞中丁醇合成通路的代谢强度,实现了丁酸预处理条件下玉米秸秆高效合成燃料丁醇的目标。研究结果可为利用农林废弃物资源生产生物燃料提供理论和技术支撑。

Using renewable lignocellulosic resources to produce advanced liquid fuels(such as butanol)could achieve the goal for high-valued utilization of waste biomass from agricultural and forestry.However,it is difficult to directly utilize lignocellulosic biomass mainly due to its inherent complex structure and thus pretreatment is indispensable to improve enzymatic hydrolysis and fermentation performance.To achieve high-efficiently conversion of lignocellulosic biomass into biobutanol,as one of the typical agricultural residues,corn stover was studied in this study and butyric acid,the precursor of butanol biosynthesis,was selected as the pretreatment agent to develop an optimized strategy for efficient depolymerization/enzymatic hydrolysis and butanol production.Based on this,corn stover was firstly pretreated by butyric acid and the changing profiles of chemical compositions of pretreated corn stover were carefully analyzed.The results indicated that the glucan content in pretreated corn stover was improved up to 47.25%with a glucan recovery of 88.53%under the pretreatment conditions of 180℃,50 g/L butyric acid for 0.5 h.The obtained solid fraction of the corn stover after the optimal butyric acid pretreatment process was used for enzymatic hydrolysis by cellulase to produce fermentable sugars.When controlling the solid to liquid ratio at 1∶5(g∶mL)and adding cellulase with 10 FPU/g substrate,the final glucose concentration in biomass hydrolysate reached 70.8 g/L after the 72-h enzymatic hydrolysis.The results revealed that the butyric acid pretreatment process could efficiently destroy the complex structure of corn stover and the accessibility of cellulase was thus improved.Using Clostridium acetobutylicum ATCC 824 as the fermentable strain,the performance of butanol bioproduction from corn stover derived glucose and residual butyric acid after the pretreatment was further evaluated in this study.When using the produced glucose as feeding carbon source for C.acetobutylicum ATCC 824 metabolism,the butanol production was improved from 4.89 g/L to 9.34 g/L.Finally,the butanol titer and productivity reached 10.58 g/L and 0.147 g/(L·h),respectively,when feeding hydrolysate and residual butyric acid as co-substrates,which was enhanced by 116%compared with the control.It was indicated that the metabolic strength of butanol synthesis pathways in C.acetobutylicum ATCC 824 was enhanced when feeding hydrolysate and residual butyric acid as the co-substrates.The butanol fermentation performance obtained in this study achieved the goal for enhancing butanol biosynthesis by typical solventogenic clostridia from lignocellulosic biomass based on the butyric acid pretreatment.In summary,the results provided theoretical and technical support for the conversion of agricultural and forestry wastes into valuable biofuel products.