生物质能团队在揭示优质水稻秸秆绿色高效转化纤维乙醇和纳米材料机制方面取得多项进展

作者：彭昊 余华

近日，生物质与生物能源团队于国际绿色化学领域权威期刊Green Chemistry在线发表了题为Distinct cellulose nanofibrils generated for improved Pickering emulsions and lignocellulose-degradation enzymes secretion coupled with high bioethanol production in natural rice mutant的研究论文，于国际高分子化学领域权威期刊Carbohydrate Polymers刊发了题为Insights into pectin dominated enhancements for elimination of toxic Cd and dye coupled with ethanol production in desirable lignocelluloses的研究论文。这两项研究利用优质水稻天然突变体，发现纤维素纳米结构缺陷增强功能材料特性的微观机理，解析果胶糖醛酸去除重金属和有机染料的作用机制，并构建秸秆纤维乙醇联产高值生物材料技术体系，从而开辟基于遗传背景的农业废弃物绿色高效利用的新路径。

农作物秸秆蕴含丰富的生物质资源，降解转化为“零碳”生物能源和高值生物制品，可助力我国“双碳”目标实现，促进农业可持续发展和现代农业产业链延长。然而，植物细胞壁天然抗降解屏障制约了生物质的全面综合利用，遗传改良细胞壁结构，可从源头解决农作物秸秆高值利用效率低、成本高、易二次污染的瓶颈问题。纤维素纳米纤维（CNF）因其纳米尺寸和界面效应，具有比表面积大、稳定性强、分散性好和反应活性高等优势，但其制备工艺能耗高或存在化学污染，限制了CNF的大规模应用。本研究发现，与普通水稻相比，天然水稻细胞壁突变体（Osfc16）秸秆的直接酶解效率显著提高37%，纤维乙醇产率显著提高19%，具有抗降解屏障降低的优良特性。同时，在更少循环次数的高压均质工艺下，酶解残渣中产生的CNF，其液滴粒径更小、界面活性更高，改善了皮克林乳化剂的乳液性能和储存稳定性。此外，还发现低剂量的CNF可以作为里氏木霉分泌纤维素酶复合物的有效诱导剂，诱导酶的蛋白质产量提高99%，内切葡聚糖酶和木聚糖酶活性分别提高27%和51%。该研究揭示了由低抗性木质纤维素产生新型CNF的多重作用，为充分利用生物质生产具有成本效益的生物乙醇和高价值的生物产品提供了一种绿色新型技术（Green Chemistry, 2022, DOI:10.1039/D1GC04447H）。

图1 水稻天然突变体纤维素纳米纤维作为皮克林乳化稳定剂与产酶诱导剂联产纤维乙醇模型图

果胶是一类富含半乳糖醛酸的细胞壁多糖，具有丰富的活性基团，对重金属和化学染料具有潜在的吸附性能。本研究发现，重金属镉（Cd）胁迫激活细胞壁网络动态调节，促进果胶在细胞壁中的沉积，而天然水稻细胞壁突变体（Osfc16）表现出更强的去甲酯化半乳糖醛酸积累能力和微量Cd富集能力。同时，重金属使细胞壁产生结构缺陷，进一步降低了细胞壁的抗降解性，显著增强生物质酶解糖化效率和生物乙醇产率，并且生物质的预处理工艺能够同步提取回收90%的Cd。利用果胶的特性，从富含果胶的柑橘皮中提取糖醛酸，与乙醇发酵残渣进行化学交联，生成一种同时吸附Cd和亚甲基蓝（MB）的增强型生物吸附剂。该研究阐明了果胶在Cd和MB吸附以及生物质酶促糖化中的多重作用机制，为农田重金属和化工染料的减污修复，植物修复收获物的无害化处理，农业废弃物的增值利用和重金属的回收处置，提供了新思路（Carbohydrate Polymers, 2022, 286:119298）。

图2 果胶在Cd和MB吸附以及生物质酶促糖化中的多重作用模型图

生物质能团队王艳婷高级工程师为两篇文章的通讯作者，博士生彭昊和赵雯悦硕士为Green Chemistry的共同第一作者，博士生余华为Carbohydrate Polymers第一作者，团队彭良才教授、夏涛副教授、食科院刘石林教授、理学院王运教授、湖北文理学院余海忠教授等参与研究。

王艳婷，华中农业大学高级工程师，主要从事植物细胞壁遗传改良与生物质降解转化相关工作，现主持国家自然科学基金（No. 32101701）和中央高校创新基金（No. 2662020ZKPY013）等项目。近年来，以第一或通讯作者在植物细胞壁基本特征结构模型（中国科学▪生命科学，2014）；果胶糖醛酸调控水稻秸秆高效降解机制（Bioresource Technology, 2015）；遗传改良植物细胞壁增强能源作物生物质产量与生物能源产率（Biotechnology Advances, 2016）；原位观测细胞壁多糖酶促水解动态（Carbohydrate Polymers, 2018）；能源植物纤维素纳米纤维制备食品级皮克林乳液稳定剂（Food Hydrocolloids, 2019）；量子点荧光免疫标记预处理下不同细胞壁聚合物的同步解聚（Talanta, 2020）；经济作物木质纤维素高效酶促糖化机制（Molecules, 2021）；能源作物细胞壁遗传改良、微生物基因工程改造和生物质绿色加工的多学科交叉融合研究（Renewable and Sustainable Energy Reviews, 2021）等方面取得了系统性进展，并受邀在国内外知名综述期刊发表多篇研究型综述。共发表SCI论文50余篇，总引用次数超过1600次，H指数22。

Green Chemistry摘要：

Although lignocellulose represents enormous and sustainable biomass resource convertible for biofuels and bioproducts, the green-like and cost-effective technology is increasingly considered to generate value-added bioproducts along with biofuel production. Herein, this study took advantage of the natural rice mutant (Osfc16) that is of recalcitrance-reduced lignocellulose, and performed a direct enzymatic hydrolysis of rice straw to achieve significantly raised bioethanol yield by 19% at p < 0.01, compared with wild type. Meanwhile, this work generated optimal cellulose nanofibrils (CNFs) from the remaining enzymatic residues under much less cycles of high-pressure homogenization. Notably, due to their characteristic surfaces, the CNFs at low dosage could not only act as the effective inducer for T. reesei secretion of cellulases complexes with significantly raised protein yields by 99% and enzymes (endoglucanases and xylanases) activities by 27% and 51% by using full rice straw as carbon source, but also play a more efficient stabilizer role for improving almost all major parameters of Pickering emulsions including emulsion index, droplet size, interfacial tension, zeta potential, water holding capacity and storage condition, compared to other chemical inducers and stabilizers (CNFs, proteins, starch) that have been applied in previous studies. Hence, this study has proposed a mechanism model to elucidate why the desirable rice mutant enables to generate the distinct CNFs that are favor for Pickering emulsions stabilization and mixed-cellulases induction coupled with relatively low-cost bioethanol production, providing multiple non-chemical processes as novel green-like technology for complete biomass utilization towards low-cost bioethanol production and high-value bioproducts.

原文链接：

https://pubs.rsc.org/en/content/articlepdf/2022/GC/D1GC04447H

Carbohydrate Polymers摘要：

Pectin is a minor wall polysaccharide with potential applications for bioproducts. Despite the application of specific plants and biomass-based sorbents for environmental remediation, little has been reported about characteristic roles of pectin. Using the natural rice mutant (Osfc16) treated with Cd, this study explored that pectin could predominately enhance Cd accumulation with lignocellulose, mainly due to remarkably raised uronic acids deposition. The Cd-treatment further reduced lignocellulose recalcitrance for significantly enhanced biomass saccharification and bioethanol production along with almost complete Cd release. Using all remaining fermentation rice residues that are of typical ribbon-structure and large surface, this study generated novel biosorbents by optimal chemical oxidation with the pectin extraction from citrus peels, and examined consistently raised Cd and methylene blue (MB) adsorption capacities. Therefore, this work has proposed a mechanism model about multiple pectin enrichment roles for Cd and MB removals in agricultural and industry locations with full lignocellulose utilization towards bioethanol production.

原文链接：

https://www.sciencedirect.com/science/article/pii/S0144861722002028