基于一体化生物加工过程的木质纤维素合成生物丁醇的研究进展

一体化生物加工过程 (Consolidated bioprocessing,CBP) 是在一个生物反应器中完成水解酶生产、酶解、微生物发酵等多步生物过程的工艺。因其过程步骤简单、成本低,被认为是生产二代生物燃料最具发展前景的工艺。然而,由于木质纤维素降解与丁醇合成路径的复杂性,鲜有天然微生物可以直接利用木质纤维素合成丁醇。随着合成生物学技术的发展,在纤维素降解梭菌中引入丁醇合成途径,可以使单菌利用木质纤维素直接合成丁醇。但是该策略存在菌株代谢负荷重、丁醇产量低等问题。而混菌策略可以通过不同菌株的劳动分工,使单菌代谢负担得到缓解,因此进一步提高了丁醇合成效率。文中从单菌策略和混菌策略分析了近年来一体化生物加工过程利用木质纤维素合成丁醇的相关研究进展,为生物丁醇以及其他生物燃料的一体化生物加工过程研究提供借鉴。     

酿酒酵母纤维素乙醇统合加工(CBP)的策略及研究进展

木质纤维素乙醇的统合生物加工过程(Consolidated bioprocessing,CBP)是将纤维素酶和半纤维素酶生产、纤维素水解和乙醇发酵过程组合或部分组合,通过一种微生物完成。统合生物加工过程有利于降低生物转化过程的成本,越来越受到研究者的普遍关注。酿酒酵母Saccharomyces cerevisiae是传统的乙醇发酵菌株。介绍了影响外源基因在酿酒酵母中表达水平的因素,纤维素酶和半纤维素酶在酿酒酵母中表达研究进展及利用酿酒酵母统合加工纤维素乙醇的策略。     

酿酒酵母人造纤维小体的研究进展简

纤维素乙醇的统合生物加工过程（consolidated bioprocessing,CBP）是将（半）纤维素酶生产、纤维素水解和乙醇发酵过程组合,通过一种微生物完成的生物加工过程。 CBP有利于降低生物转化过程的成本,受到研究者的普遍关注。酿酒酵母（ Saccharomyces cerevisiae）作为传统的乙醇生产菌株,是极具潜力的CBP底盘细胞。纤维小体是某些厌氧微生物细胞表面由纤维素酶系与支架蛋白组成的大分子复合物,它能高效降解木质纤维,在酿酒酵母表面展示纤维小体已成为构建CBP细胞的研究热点。笔者综述了人造纤维小体在酿酒酵母细胞表面展示组装的研究进展,重点阐述了纤维小体各元件的设计和改造,并针对酿酒酵母分泌途径的改造,提出提高人造纤维小体分泌组装的可能性策略。     

酿酒酵母人造纤维小体的研究进展

纤维素乙醇的统合生物加工过程(consolidated bioprocessing,CBP)是将(半)纤维素酶生产、纤维素水解和乙醇发酵过程组合,通过一种微生物完成的生物加工过程。CBP有利于降低生物转化过程的成本,受到研究者的普遍关注。酿酒酵母(Saccharomyces cerevisiae)作为传统的乙醇生产菌株,是极具潜力的CBP底盘细胞。纤维小体是某些厌氧微生物细胞表面由纤维素酶系与支架蛋白组成的大分子复合物,它能高效降解木质纤维,在酿酒酵母表面展示纤维小体已成为构建CBP细胞的研究热点。笔者综述了人造纤维小体在酿酒酵母细胞表面展示组装的研究进展,重点阐述了纤维小体各元件的设计和改造,并针对酿酒酵母分泌途径的改造,提出提高人造纤维小体分泌组装的可能性策略。     

纤维素乙醇统合加工过程中的酵母多酶共展示体系研究进展

利用统合生物加工过程(Consolidated bioprocessing,CBP)生产纤维素乙醇是目前国内外的研究热点。CBP需要一种“集成化”微生物,既能生产水解木质纤维素的多种酶类又能利用水解木质纤维素产生的糖类发酵产乙醇。以酿酒酵母表面展示技术为依托,建立CBP菌株多酶共展示体系的研究主要分为以下两个方向：一是直接将纤维素酶展示在细胞表面,即非复合型纤维素酶体系;另一种是通过表面展示纤维小体(Cellulosome)将纤维素酶间接地锚定在细胞表面,即复合型纤维素酶体系,本文主要从以上两个方向阐述了近几年对于纤维素乙醇生物统合加工过程的研究进展。因纤维小体对纤维素的降解能力比非复合型纤维素酶体系更强,所以其在酿酒酵母细胞表面的组装研究受到越来越多的关注,为了更深入透彻地了解纤维小体的酵母展示技术,文中对纤维小体的结构与功能及其在纤维素乙醇发酵中的应用研究进行重点论述,并对该领域的发展方向进行展望。     

统合生物工艺与纤维素分解性高温菌乙醇转化的研究进展

生物乙醇是可再生的绿色能源,作为可以完全或部分替代化石能源的新型能源,近年来受到了世界各国的关注.木质纤维素作为生物乙醇的生产原料具有巨大的市场潜力,而统合生物工艺(CBP)能有效降低木质纤维素乙醇的生产成本,为纤维素乙醇的工业化生产提供了新的工艺思路.主要介绍利用高温纤维素分解菌的统合生物工艺策略以及国内外对高温纤维素分解茵代谢工程研究的最新进展.     

极端嗜热厌氧菌Caldicellulosiruptor木质纤维素降解研究

随着能源危机的加剧,木质纤维素作为生产生物能源的重要原料得到人们的广泛关注。目前,极端嗜热厌氧菌Caldicellulosiruptor属已发现8个种,具有高效的木质纤维素降解能力,甚至可以作用于未经预处理的木质纤维素。自从20世纪80年代以来,人们在Caldicellulosiruptor属的菌株生理生化性质、木质纤维素降解机制及转化能力、基因组、转录组及蛋白质组、遗传转化体系等方面,都取得了一系列研究成果。笔者对嗜热厌氧菌Caldicellulosiruptor属木质纤维素降解的研究现状及前景进行综述及展望。     

极端嗜热厌氧菌 Caldicellulosiruptor 木质纤维素降解研究简

随着能源危机的加剧,木质纤维素作为生产生物能源的重要原料得到人们的广泛关注。目前,极端嗜热厌氧菌Caldicellulosiruptor属已发现8个种,具有高效的木质纤维素降解能力,甚至可以作用于未经预处理的木质纤维素。自从20世纪80年代以来,人们在Caldicellulosiruptor属的菌株生理生化性质、木质纤维素降解机制及转化能力、基因组、转录组及蛋白质组、遗传转化体系等方面,都取得了一系列研究成果。笔者对嗜热厌氧菌Caldicellulosiruptor属木质纤维素降解的研究现状及前景进行综述及展望。     

一种木质纤维素类生物质水解重整制备生物汽油的方法

本发明公开了一种以木质纤维素类生物质为原料水解重整制备生物汽油的方法。该方法将木质纤维素类生物质的水解原料液直接进入水相催化重整系统,     

大肠杆菌对木质纤维素水解液抑制物的胁迫耐受性

木质纤维素类生物质是前景广阔的化石原料替代品，其生物炼制可生产生物能源、生物基化学品和生物材料等多种产品，可降低碳排放，有助于实现“双碳”目标，因此受到越来越多的关注。然而，木质纤维素生物炼制需要经过预处理、微生物发酵和产物纯化等多个步骤，其中，预处理过程产生的多种化合物抑制微生物的细胞生长和发酵性能，是制约生物转化效率的瓶颈之一。大肠杆菌是木质纤维素生物炼制常用的宿主，被广泛应用于多种化合物的生产，研究其对木质纤维素水解液中抑制物的耐受性，对于提高木质纤维素生物炼制效率具有重要意义。本文首先介绍了木质纤维素的主要成分和基本结构，对木质纤维素的预处理方法以及预处理后水解液中的主要抑制物种类进行了简单阐述；随后，总结了木质纤维素水解液中几类主要抑制物呋喃类、羧酸类和酚类对大肠杆菌细胞的毒性，以及大肠杆菌对上述抑制物的胁迫响应机制和基于机制的菌株改造靶点；最后，综述了提高大肠杆菌对上述抑制物的胁迫耐受性的菌株改造策略，包括随机突变、实验室适应性进化和组学辅助的理性设计等，为利用代谢工程构建用于木质纤维素生物炼制的高效大肠杆菌菌株提供参考。     

Endowing non-cellulolytic microorganisms with cellulolytic activity aiming for consolidated bioprocessing

With the exhaustion of fossil fuels and with the environmental issues they pose, utilization of abundant lignocellulosic biomass as a feedstock for biofuels and bio-based chemicals has recently become an attractive option. Lignocellulosic biomass is primarily composed of cellulose, hemicellulose, and lignin and has a very rigid and complex structure. It is accordingly much more expensive to process than starchy grains because of the need for extensive pretreatment and relatively large amounts of cellulases for efficient hydrolysis. Efficient and cost-effective methods for the production of biofuels and chemicals from lignocellulose are required. A consolidated bioprocess (CBP), which integrates all biological steps consisting of enzyme production, saccharification, and fermentation, is considered a promising strategy for reducing production costs.     

Consolidated bioprocessing and simultaneous saccharification and fermentation of lignocellulose to ethanol with thermotolerant yeast strains

Consolidated bioprocessing (CBP), which integrates enzyme production, saccharification and fermentation into a single process, is a promising strategy for effective ethanol production from lignocellulosic materials because of the resulting reduction in utilities, the substrate and other raw materials and simplification of operation. CBP requires a highly engineered microbial strain capable of hydrolyzing biomass with enzymes produced on its own and producing high-titer ethanol. Recently, heterologous production of cellulolytic enzymes has been pursued with yeast hosts, which has realized direct conversion of cellulose to ethanol. Specifically, the development of cell surface engineering, which provides a display of cellulolytic enzymes on the yeast cell surface, facilitates effective biomass hydrolysis concomitantly with ethanol production. On the other hand, the difference in optimum temperature between saccharification and fermentation is a drawback of efficient ethanol production in the simultaneous saccharification and fermentation (SSF). The application of thermotolerant yeast strains engineered to the SSF process would overcome the drawback by performing hydrolysis and fermentation at elevated temperature. In this review, we focus on the recent advances in the application of thermotolerant yeast to CBP and SSF of lignocellulosic material to ethanol. The development of thermotolerant and ethanologenic yeast strains with the ability to hydrolyze lignocellulosic materials is emphasized for high-temperature CBP.     

Biocatalysis in ionic liquids for lignin valorization: Opportunities and recent developments

Lignin holds tremendous potential as a renewable feedstock for upgrading to a number of high-value chemicals and products that are derived from the petroleum industry at present. Since lignin makes up a significant fraction of lignocellulosic biomass, co-utilization of lignin in addition to cellulose and hemicelluloses is vital to the economic viability of cellulosic biorefineries. The recalcitrant nature of lignin, originated from the molecule's compositional and structural heterogeneity, however, poses great challenges toward effective and selective lignin depolymerization and valorization. Ionic liquid (IL) is a powerful solvent that has demonstrated high efficiency in fractionating lignocellulosic biomass into sugar streams and a lignin stream of reduced molecular weight. Compared to thermochemical methods, biological lignin deconstruction takes place at mild temperature and pressure while product selectivity can be potentially improved via the specificity of biocatalysts (lignin degrading enzymes, LDEs). This review focuses on a lignin valorization strategy by harnessing the biomass fractionating capabilities of ILs and the substrate and product selectivity of LDEs. Recent advances in elucidating enzyme-IL interactions as well as strategies for improving enzyme activity in IL are discussed, with specific emphases on biocompatible ILs, thermostable and IL-tolerant enzymes, enzyme immobilization, and surface charge engineering. Also reviewed is the protein engineering toolsets (directed evolution and rational design) to improve the biocatalysts' activity, stability and product selectivity in IL systems. The alliance between IL and LDEs offers a great opportunity for developing a biocatalytic route for lignin valorization.     

Engineering microbes for direct fermentation of cellulose to bioethanol

Consolidated bioprocessing (CBP) by micro-organisms is desired for efficient conversion of lignocellulosic biomass to bioethanol fuels. Potential candidates have been discovered, including cellulolytic bacteria and filamentous fungi. Genetic and metabolic manipulation of these organisms further promotes their fermentation capacities and the ethanol tolerance. In addition, Saccharomyces cerevisiae and several other yeasts were genetically modified to express recombinant cellulases in media or display them on the cell surface for CBP of cellulose. To compensate the insufficient capacity of a single strain, various microbial consortia have also been developed. In this article, we reviewed the recent advances in CBP microbes and focused on the efforts in strain improvement employing genetic engineering.     

Consolidated bioprocessing of cellulosic biomass: an update

Biologically mediated processes seem promising for energy conversion, in particular for the conversion of lignocellulosic biomass into fuels. Although processes featuring a step dedicated to the production of cellulase enzymes have been the focus of most research efforts to date, consolidated bioprocessing (CBP)--featuring cellulase production, cellulose hydrolysis and fermentation in one step--is an alternative approach with outstanding potential. Progress in developing CBP-enabling microorganisms is being made through two strategies: engineering naturally occurring cellulolytic microorganisms to improve product-related properties, such as yield and titer, and engineering non-cellulolytic organisms that exhibit high product yields and titers to express a heterologous cellulase system enabling cellulose utilization. Recent studies of the fundamental principles of microbial cellulose utilization support the feasibility of CBP.     

Biohydrogen production from lignocellulosic feedstock

Due to the recent energy crisis and rising concern over climate change, the development of clean alternative energy sources is of significant interest. Biohydrogen produced from cellulosic feedstock, such as second generation feedstock (lignocellulosic biomass) and third generation feedstock (carbohydrate-rich microalgae), is a promising candidate as a clean, CO₂-neutral, non-polluting and high efficiency energy carrier to meet the future needs. This article reviews state-of-the-art technology on lignocellulosic biohydrogen production in terms of feedstock pretreatment, saccharification strategy, and fermentation technology. Future developments of integrated biohydrogen processes leading to efficient waste reduction, low CO₂ emission and high overall hydrogen yield is discussed.     

Advancements and future directions in enzyme technology for biomass conversion

Enzymatic hydrolysis of pre-treated lignocellulosic biomass is an ideal alternative to acid hydrolysis for bio-ethanol production, limited primarily by pre-treatment requirements and economic considerations arising from enzyme production costs and specific activities. The quest for cheaper and better enzymes has prompted years of bio-prospecting, strain optimization through genetic engineering, enzyme characterization for simple and complex lignocellulosic feedstock, and the development of pre-treatment strategies to mitigate inhibitory effects. The recent shift to systematic characterizations of de novo mixtures of purified proteins is a promising indicator of maturation within this field of study, facilitating progression towards feedstock assay-based rapid enzyme mixture optimization. It is imperative that international standards be developed to enable meaningful comparisons between these studies and the construction of a database of enzymatic activities and kinetics, aspects of which are explored here-in. Complementary efforts to improve the economic viability of enzymatic hydrolysis through process integration and reactor design are also considered, where membrane-confinement shows significant promise despite the associated technological challenges. Significant advancements in enzyme technology towards the economic conversion of lignocellulosic biomass should be expected within the next few years as systematic research in enzyme activities conforms to that of traditional reaction engineering.     

Feedstock design for quality biomaterials

Feedstock design is crucial for lignocellulosic biomass use. Current strategies for feedstock design cannot be readily applied to improve the quality of biomass-based materials, limiting the sustainability and economics of lignocellulosic biorefineries. Recent studies have advanced the understanding of biomass structure–property relationships and discovered several characteristics, such as molecular weight, uniformity, linkage profile, and functional groups, that are critical for manufacturing diverse quality biomaterials. These discoveries call for fundamentally different strategies for feedstock development. Such strategies need to rediscover the roles of monolignol biosynthesis enzymes and leverage lignin polymerization enzymes to achieve precise control of lignin molecular structure. These innovations could transform biomass into feedstock for high-quality biomaterials, addressing essential environmental challenges and empowering the bioeconomy.     

C_4 Plants as Biofuel Feedstocks: Optimising Biomass Production and Feedstock Quality from a Lignocellulosic Perspective

The main feedstocks for bioethanol are sugarcane (Saccharum officinarum) and maize (Zea mays),both of which are C4 grasses,highly efficient at converting solar energy into chemical energy,and both are food crops.As the systems for lignocellulosic bioethanol production become more efficient and cost effective,plant biomass from any source may be used as a feedstock for bioethanol production.Thus,a move away from using food plants to make fuel is possible,and sources of biomass such as wood from forestry and ...