生物学结构角度解析预处理破除木质纤维原料抗生物降解屏障和改善纤维素酶解的机理研究

Due to the limited availability of fossil carbon, as well as environmental concerns, comprehensive utilization of lignocellulosics for fuel and chemical production has currently raised much interest. A key step for bioconversion of lignocellulosic materials to fuels and chemicals is that the cellulose and hemicelluloses are first hydrolyzed by enzymes to fermentable sugars. However, biomass recalcitrance of lignocellulosic materials, which is caused by a variety of factors such as the inaccessibility of the cellulose due to its close association with the hemicelluloses and lignin, crystallinity, ultrastructure of cell wall, distribution of lignin and hemicellulose, different cell types, structure and types of lignin, etc., makes it difficult to hydrolyze enzymatically. Therefore, lignocellulosic materials must first be pretreated to break the biomass recalcitrance and improve enzymatic hydrolysis of cellulose. Different pretreatment process and optimization of process conditions have been investigated and published in many literatures. Up to now, however, the researches about pretreatment mechanisms mainly focused on effect of pretreatment on contents and properties of chemical components, changes of the specific surface area and porosity of cellulosic substrates, and effect of lignin changes on enzymes, etc. Less research has been conducted on the changes of biological structure of raw materials during different pretreatment and the relationship between the changes of biological structures and improvement of enzymatic digestibility of cellulose, and on the effect on action of cellulase enzymes components. In the project, biological structures of some lignocellulosics which includes hardwood, softwood and nonwood material, for example, anatomical structure and ultrastructure of cell wall, different types of tissue cells, distribute of different chemical components in the cell walls, and arrangement of cellulose microfibrils in cell wall,etc.,and its changes rules during pretreatment are studied. The relationship between the changes of the biological structures during pretreatment and improvement of enzymatic digestibility of cellulose will be interpreted. Effect of different cellulase enzyme components on degradation of microfibrils in pretreated/untreated lignocellulosics and its synergetic effectiveness will also be investigated. Based on the researches, we want to understand that pretreatment is how to break the biomass recalcitrance and improve the enzymatic digestibility of cellulose from a angle of biological structures changes. It was valuable for finding effective pretreatment methods to break biomass recalcitrance, reconstructing biological structure of cell wall to improve its enzymatic digestibility.

将资源丰富且可再生的木质纤维素通过生物转化生产液体燃料和大宗化学品，是当前研究热点。由于纤维原料具有天然的"生物质抗降解屏障"，直接对其进行生物转化的效率低下。预处理是改善纤维素酶解效率的最重要步骤，但目前对相关机制的研究主要集中在预处理对原料主要化学组分含量和性质、物料比表面积和孔隙率、木素结构变化等的影响方面，缺乏预处理对原料生物学结构的改变及它们与纤维素酶解之间的关系等规律的认识。针对上述问题，项目拟通过研究不同方法预处理过程中，原料在解剖结构和细胞壁超结构、细胞类型和形态、不同化学组分在细胞壁不同微区的分布、微纤维排列方式等方面的变化及规律，分析它们与纤维素酶水解之间的关系；研究纤维素酶不同组分在降解微纤丝过程中的作用及协同作用；在此基础上解析预处理破除生物质抗降解屏障和改善纤维素酶解性的机理。这对进一步完善预处理机制，采用遗传手段改造细胞壁结构以提高降解效率等具有重要意义

当前，人类社会发展面临着石油、煤炭等化石资源日益匮乏，以及环境污染严重等问题的严峻挑战。将资源丰富且可再生的木质纤维素通过生物转化生产液体燃料和大宗化学品，可望起到部分替代石油等化石资源的作用，从而促进人类社会的可持续发展，该领域也是当前国内外研究的热点。但由于纤维原料本身具有的复杂组织结构和组成，使其具有天然的“生物质抗降解屏障”，致使直接对其进行生物降解和转化的效率极其低下。已知预处理是提高原料纤维素酶解效率的最重要步骤，但目前对预处理改善纤维素酶解性能的内在机制的认识仍尚未完全清晰，已有研究主要集中在预处理对原料主要化学组分含量和性质、物料比表面积和孔隙率等的影响方面，缺乏对不同预处理过程中原料生物学结构的变化及它们与纤维素酶解效率之间的关系等规律的认识，阻碍了人们进一步研发和建立高效的预处理和纤维素酶解技术。针对上述问题，项目研究了不同方法预处理过程中，原料的生物学结构包括解剖学结构和细胞壁超结构、组织细胞类型、纤维细胞形态学特征、不同化学组分及其理化性质和在细胞壁中的分布等方面的变化规律，分析归纳了预处理造成的上述变化与原料纤维素酶解性能改善之间的可能的关系；在此基础上解析了预处理破除生物质抗降解屏障和改善纤维素酶解性的内在机制。进而结合基因工程手段对原料水解用纤维素酶的酶系进行了改良，实现了预处理后纤维原料的高效酶解。研究对进一步完善预处理机制和建立高效预处理方案，采用遗传手段改造细胞壁结构、研发高效纤维素酶制剂等，以提高纤维素降解效率和促进纤维原料的生物转化具有重要意义。