联合生物加工产纤维素乙醇中真菌的开发与应用

联合生物加工（consolidated bioprocessing,CBP）是在单一或组合微生物作用下,将纤维素酶生产、纤维素水解糖化、戊糖和己糖发酵产醇整合于单一步骤的生物加工过程。本文从真菌在CBP产纤维素乙醇中的开发历程着眼,回顾了纤维素乙醇产业化的发展进程,介绍了CBP产纤维素乙醇的作用机理,系统总结了目前国内外文献中报道的CBP底盘真菌的主要种类及优缺点,并综述了CBP真菌的开发策略,包括工程化策略和共培养策略,着重阐述了工程化策略的技术路线和研究进展。指出综合运用先进生物技术和基于代谢分析数据的计算机模拟系统开发CBP目标微生物,设计新型高效的生物反应器以及将CBP技术与现有生物工业整合,是未来将CBP技术应用于纤维素乙醇产业的关键。     

纤维素乙醇产业现状及关键过程技术难点

目前生产燃料乙醇主要以糖质和淀粉质粮食为原料,随着清洁能源需求增加和粮食短缺问题日益突出,因此研究以木质纤维素为原料的第二代燃料乙醇势在必行。介绍了木质纤维素燃料乙醇国内外研究现状和产业化现状,从技术层面分析了纤维素乙醇研究及产业化过程中的主要技术难点,提出了目前研究认为可行的一些建议解决斱案。     

纤维素乙醇的研究进展

近年来以纤维素类生物质为原料制备乙醇的研究取得了许多进展,使纤维素乙醇的开发更具商业化前景.重点介绍了木质纤维素转化为乙醇的原料预处理方法、纤维素和半纤维素的酶法降解、有效可靠的发酵菌种的选育及木质纤维素乙醇制备工艺的开发.     

木质纤维素类生物质制备生物乙醇研究进展

以木质纤维素类生物质为原料制备第二代生物乙醇的研究取得了较大进展,重点阐述了生物乙醇制备过程中的关键问题,包括原料预处理、水解和发酵工艺、各种方法的优缺点比较等,并介绍了我国生物乙醇的发展现状。     

酵母细胞表面工程在生物乙醇生产中的应用

介绍了国内外利用酵母表面工程转化各种生物质原料生产生物乙醇的最新技术进展。该技术为在酵母表面基因水平固定淀粉酶、纤维素酶和木聚糖酶从而生产乙醇提供了新的策略。重点阐述了利用淀粉质和木质纤维素原料的重组酿酒酵母表达系统,并对其在生物乙醇生产中的应用潜力以及目前存在的问题做了初步总结。     

木质纤维素生产燃料乙醇的糖化发酵工艺研究进展

目前用于生产木质纤维素燃料乙醇的工艺主要有4种:分步糖化和发酵(SHF)、同时糖化和发酵(SSF)、同时糖化和共发酵(SSCF)以及联合生物加工(CBP).本文综述了以上4种工艺的优缺点及其研究现状,着重介绍了具有应用前景的SSCF和CBP,指出它们的研究重点都在于通过基因工程构建适合的高产菌株.同时,提出了木质纤维降...     

生物燃料的技术现状及研究趋势分析

生物液体燃料(燃料乙醇、生物柴油、生物丁醇等)是生物能源战略的重要组成部分,世界范围内产业化运作的液体生物燃料主要包括生物柴油和燃料乙醇。重点对生物柴油和纤维素乙醇这两种生物燃料的技术现状和技术研究趋势进行分析。工业生产生物柴油的主要方法是酯交换法,即利用动植物油脂和低碳醇在催化剂的作用下经酯交换反应生成脂肪酸酯。纤维素乙醇技术目前主要研究集中在开发可高效水解新型木质纤维素原料;开发新型温和预处理工艺;开发新型高效纤维素降解酶系;开发木质素高效利用产品;开发乙醇发酵基因工程菌株这五个方面。还对生物柴油和纤维素乙醇的研究趋势进行了方向性的分析。     

利用CBP发酵纤维素生产燃料乙醇的研究进展

介绍了联合生物加工(CBP)技术,并阐述通过该技术对发酵纤维素生产燃料乙醇的工艺进行技术改造,为利用纤维素低成本生产燃料乙醇提供了有效途径.     

木质纤维素类生物质制取燃料及化学品的研究进展

木质纤维素类生物质含有丰富的纤维素和半纤维素多糖,通过微生物发酵将它们转化为能源及高附加值的化学品,对于缓解全球能源危机带来的压力和解决环境污染问题具有重要意义。介绍了木质纤维素类生物质的结构特征;评述了预处理方法,包括稀酸、高温液态水蒸气爆破、CO2爆破、氨爆、碱法、有机溶剂法、生物处理法;重点介绍由生物质生产乙醇、丁醇及生物柴油的研究现状。指出开发高效环保的预处理方法、构建耐毒高产菌株和应用连续发酵或补料批式发酵方式等是加快木质纤维素类生物质发酵利用工业化进程的关键所在。     

木质纤维素燃料乙醇生物转化预处理技术

由丰富的木质纤维素资源制备乙醇有利于缓解能源紧缺、减少环境污染、实现可持续发展.然而某些物理、化学因素阻碍了木质纤维素中纤维素和半纤维素的转化和利用.预处理引起物理和/或化学上的变化,主要目的是改变或去除各种结构和(或)化学障碍,增加纤维素酶解率和转化效果,是一系列纤维素乙醇转化技术中的关键和核心.本文就纤维素乙醇生物...     

Engineering Saccharomyces cerevisiae for next generation ethanol production

Conversion of cellulose, hemicellulose or starch to ethanol via a biological route requires enzymatic conversion of these substrates to monosaccharides that can be assimilated by a fermenting organism. Consolidation of these events in a single processing step via a cellulolytic or amylolytic microorganism(s) is a promising approach to low‐cost production of fuels and chemicals. One strategy for developing a microorganism capable of such consolidated bioprocessing (CBP) involves engineering Saccharomyces cerevisiae to expresses a heterologous enzyme system enabling (hemi)cellulose or starch utilization. The fundamental principle behind consolidated bioprocessing as a microbial phenomenon has been established through the successful expression of the major (hemi)cellulolytic and amylolytic activities in S. cerevisiae. Various strains of S. cerevisiae were subsequently enabled to grow on cellobiose, amorphous and crystalline cellulose, xylan and various forms of starch through the combined expression of these activities. Furthermore, host cell engineering and adaptive evolution have yielded strains with higher levels of secreted enzymes and greater resistance to fermentation inhibitors. These breakthroughs bring the application of CBP at commercial scale ever closer. This mini‐review discusses the current status of different aspects related to the engineering of S. cerevisiae for next generation ethanol production. © 2013 Society of Chemical Industry     

Distributive and collaborative push-and-pull in an artificial microbial consortium for improved consolidated bioprocessing

The consolidated bioprocessing (CBP) of lignocellulose by the synthetic microbial consortium of Trichoderma reesei and Saccharomyces cerevisiae is a promising way of biomanufacturing d -glucaric acid. However, the hindrance factor to its industrial application is the low efficiency. Therefore, we engineered T. reesei and S. cerevisiae to improve the CBP for d -glucaric acid production. T. reesei was engineered to produce more cellulase and release more fermentable sugars from lignocellulose, that is, pushing more sugars to S. cerevisiae. S. cerevisiae was engineered to metabolize cellobiose and siphon more sugars into d -glucaric acid biosynthetic pathway, that is, pulling more sugars to S. cerevisiae. This is the strategy of distributive and collaborative push-and-pull we developed and proposed in this work, which was proven successful in improving efficiencies of the CBPs of steam-exploded corn stover (SECS) for d -glucaric acid production and distiller's grains for single cell protein (SCP) production. The titer, yield and productivity of d -glucaric acid produced from 50 g/L SECS by the microbial consortium of T. reesei C10 and S. cerevisiae LGA-1C3S2 were 6.42 g/L, 0.128 g/g SECS, and 0.917 g/L/d, respectively. The titer, yield, and productivity of SCP produced from 80 g/L distiller's grains were 50.5 g/L, 0.631 g/g distiller's grains, and 8.417 g/L/d, respectively. These were much higher than the initial microbial consortia of T. reesei Rut-C30 and S. cerevisiae LGA-1 or INVSc1. The results confirmed the applicability and generalizability of distributive and collaborative push-and-pull, which has profound meaning for science and engineering.     

Lignocellulosic and marine biomass as resource for production of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are considered as sustainable ‘green/bio plastics’ because they have potential to replace their depleting petroleum-based competitors in the recent future. To reach this goal, PHAs must be able to compete with the established petroleum-based plastics in both technical and economic aspects. The current PHA production is based on high-priced substrates of high nutritional value and simple carbon sources such as glucose, sucrose, starch, or vegetable oils. Non-food based carbon-rich complex polysaccharides of lignocellulosic and marine biomass can be used as alternative and suitable feedstock through consolidated bioprocessing (CBP). CBP is a promising strategy that involves the production of lytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products in a single process step. CBP offers very large cost reductions if microorganisms possessing the abilities are found or microbial processes are developed to utilize substrate and simultaneously produce products. This review focuses on possible available complex polysaccharides of lignocellulosic and marine biomass that can be used as resources to produce PHAs in biorefineries, including CBP.     

酶水解木质纤维材料制取可发酵糖研究进展

本文对木质纤维材料的化学组成、结构特点,纤维素酶和半纤维素酶及影响酶水解的关键因素,如产物抑制、酶学特性、木质素的存在、表面活性剂的使用、酶的回收等进行了综述,对高效酶水解制取发酵糖技术的研究进行了展望。     

木质纤维“一锅法”制备生物乙醇的研究进展

木质纤维是地球上最丰富的资源,既可以用于制备生物乙醇、生物氢气等生物能源,同时也可以制备各种化工原料及生物基材料,具有绿色、环保、可再生等特点。"一锅法"制备生物乙醇是将预处理、酶解糖化与发酵中的2个或3个连续过程放在同一反应器中进行,具有节约用水、避免物料损失以及在一定程度上提高乙醇产量等优点。通过对预处理与酶解糖化"一锅法",酶解糖化与发酵"一锅法",酶制备、酶解糖化与发酵"一锅法"和预处理、酶解糖化与发酵"一锅法"4类"一锅法"制备生物乙醇方法的介绍,分析了"一锅法"制备生物乙醇的优越性及存在的问题,为使用"一锅法"制备生物乙醇的相关研究提供一定的参考。     

木质纤维素转化为燃料乙醇的研究进展

以木质纤维素为原料生产燃料乙醇的生物转化方法包括预处理、酶水解和发酵过程,对这些过程中的技术进展以及解决现存问题的方法进行了评述。氨法爆破技术是较好的预处理方法,超声波、微波处理等新技术有助于改善酶水解。阐述了酶水解机理、纤维素酶的生产以及酶水解过程的优化方法。指出固定化酶糖化发酵技术在生物转化木质纤维原料技术中的前景广阔;选择合适的发酵方法,优化发酵过程,以及解决抑制问题对于提高乙醇产率尤为重要;利用基因重组技术构建旨在发酵混合糖的重组菌对于生产生物乙醇具有里程碑意义。     

Bioethanol production from optimized pretreatment of cassava stem

The current ethanol production processes using crops such as corn and sugar cane are well established. However, the utilization of cheaper biomasses such as lignocellulose could make bioethanol more competitive with fossil fuels, without the ethical concerns associated with the use of potential food resources. A cassava stem, a lignocellulosic biomass, was pretreated using dilute acid to produce bioethanol. The pretreatment conditions were evaluated using response surface methodology (RSM). As a result, the optimal conditions were 177 °C, 10 min and 0.14 M for the temperature, reaction time and acid concentration, respectively. The enzymatic digestibility of the pretreated cassava stem was examined at various enzyme loadings (10–40 FPU/g cellulose of cellulase and 30 CbU/g of β-glucosidase). With respect to economic feasibility, 20 FPU/g cellulose of cellulase and 30 CbU/g of β-glucosidase were selected for the test concentration and led to a saccharification yield of 70%. The fermentation of the hydrolyzed cassava stem using Saccharomyces cerevisiae resulted in an ethanol concentration of 7.55 g/L and a theoretical fermentation yield of 89.6%. This study made a significant contribution to the production of bioethanol from a cassava stem. Although the maximum ethanol concentration was low, an economically efficient overall process was carried out to convert a lignocellulosic biomass to bioethanol.     

Membrane process opportunities and challenges in the bioethanol industry

Increasing oil prices and growing environmental concerns in recent years have driven the development of renewable biofuels. Until now, most of the bioethanol production concepts are based on sugar and starch crops as feedstock, while research on second generation of bioethanol concepts is investigating the use of cellulosic biomass such as straw, wood, etc. as feedstock. The first part of the paper will review membrane opportunities in the present bioethanol production concepts, while the second part will provide an outlook on the future potentials of membrane technologies in the second generation concepts. For both production concepts, application opportunities for conventional membrane processes such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) as well as the emerging membrane processes pervaporation (PV) and vapour permeation (VP) will be presented. Overall, this paper demonstrates that membrane technology as a highly selective and energy-saving unit operation has a great potential in the bioethanol industry of today and in future. Hence, membrane technology will contribute to solving future energy and environmental problems.     

Waste paper sludge as a potential biomass for bio-ethanol production

This review describes the utilization of paper sludge (PS), which is waste from the pulp and paper industry. Its advantages make PS the cellulosic biomass with the most potential for bio-refinery research and applicable for industrial scale. Some of the grain based biofuels and chemicals have already been in commercial operation, including fuel ethanol or biochemical products. Unfortunately, research and application of PS are yet in their infancy and suffer from large scale because of low productivity. Reviewing the many researches that are working at the utilization of PS for bio-refineries could encourage the utilization of PS from laboratory research to be applied in industry. For this reason, PS usage as industrial raw material will be effective in solving the environmental problems caused by PS with clean technology. In addition, its conversion to bio-ethanol could offer an alternative solution to the energy crisis from fossil fuel. Two methods of PS utilization as raw material for bio-ethanol production are introduced. The simultaneous saccharification and fermentation (SSF) using cellulase produced by A. cellulolyticus and thermotolerant S. cerevisiae TJ14 gave ethanol yield 0.208 (g ethanol/g PS organic material) or 0.051 (g ethanol/g PS). One pot bioethanol production as a modified consolidated biomass processing (CBP) technology gave ethanol yield 0.19 (g ethanol/g Solka floc) and is considered to be the practical CBP technology for its minimizing process.