燃料乙醇的代谢工程研究进展

乙醇是来自可再生资源的最有发展前景的液态燃料,目前采用生物发酵法生产乙醇仍然是最重要的途径。利用代谢工程技术改造乙醇代谢网络、提高乙醇产量是生物工程科学家的研究重点。从扩展代谢途径和构建新的代谢途径等方面全面阐述了代谢工程技术在燃料乙醇生产中的应用。     

代谢工程

代谢工程,也称途径工程,是基因工程一个重要分支,一般是多基因的基因工程,与细胞的基因调控、代谢调控和生化工程密切相关。讨论了代谢工程的应用,包括通过改变代谢流和代谢途径提高产量,改善生产过程,构建新的代谢途径和产生新的代谢产物等。     

生物丁醇制造技术现状和展望

丁醇是大宗基础化工原料,并有望成为新一代生物燃料。利用可再生原料通过微生物发酵生产丁醇受到人们的很大关注。然而,与石油原料制造丁醇相比,目前生物丁醇的制造成本偏高。生物丁醇制造技术按重要性排序:在廉价原料替代、低丁醇浓度及存在丙酮、乙醇低值副产物3个方面有改进空间。上海生物丁醇协作组设定了由易到难的技术路线图:通过代谢工程提高丁醇比例;在丁醇高耐受菌株中导入和优化丁醇合成途径;去除葡萄糖阻遏效应使之可利用复杂原料。协作组相信,通过与国内外广泛的产学研合作,应可在不远的将来开发出有经济竞争力并可持续发展的生物丁醇生产工艺。     

非传统酵母代谢工程研究进展

近30年来解脂耶氏酵母、克鲁维酵母、毕赤酵母、假丝酵母、汉逊酵母等非传统酵母因其具有天然的生理代谢优势,如快速生长、多底物利用、胁迫耐受性等,在代谢工程领域得到了广泛关注,多种基因工程改造工具正逐渐被开发用于非传统酵母的特性拓展,使其成为合成重组蛋白、生物可再生化学物质的高效细胞工厂.文中总结了非传统酵母中基因编辑工具...     

甲醇酵母代谢工程研究进展

甲醇酵母由于独特优点被认为是绿色生物制造的潜在宿主.特别是其天然甲醇利用性能有望建立甲醇生物转化路线,拓展生物炼制底物,具有重要经济价值和环保意义.文中综述了代谢工程改造甲醇酵母合成蛋白质和化学品的最新研究进展,并比较了其与模式生物酿酒酵母作为细胞工厂的优缺点.随后,分析了甲醇酵母代谢工程改造面临的挑战,并展望了潜在解...     

丝状真菌代谢工程研究进展

丝状真菌(Filamentous fungi)作为重要的工业发酵微生物,在有机酸、蛋白质及次级代谢产物等关键生物基产品生产方面发挥着重要作用.自20世纪90年代代谢工程理念提出以来,尤其是代谢工程使能技术的创新及发展,极大地促进了丝状真菌细胞工厂的构建及其在工业发酵领域的应用.文中将系统介绍近年来丝状真菌代谢工程技术的...     

生物发酵产丁醇研究进展

丁醇作为新一代生物燃料,已成为世界研究的热点。利用可再生原料通过微生物发酵生产丁醇受到人们的普遍关注。目前通过发酵法产丁醇的成本较石化途径高。降低丁醇的生产成本,可以从以下几个方面入手:使用廉价的非粮食原料,开发新的高产低能耗发酵工艺,选育高产丁醇菌株。相信在不久的将来,研究者们将研发出高经济竞争力和可持续发展的丁醇生产工艺。     

丁醇基因在大肠杆菌中表达的现状与展望

随着化石能源过度开采带来的能源短缺与环境恶化,丁醇凭借着其优越的理化性质成为了最具潜力的绿色燃料之一。近几年微生物在生物能源生产研究中受到广泛关注,主要集中在梭菌丁醇合成途径的异源表达。目前利用大肠杆菌产丁醇的产量已经接近产丁醇的天然菌株的产量。然而,大肠杆菌产丁醇仍存在很多限制性因素。主要从乙酰辅酶A依赖途径评述大肠杆菌生产丁醇的限制因素,并讨论提高丁醇产量需要解决的问题。     

合成支架在代谢工程中的研究进展

代谢工程作为通过引入外源合成途径或改造优化代谢网络,进行高附加值的天然代谢产物生物合成的技术,已经得到广泛应用。但随着目标合成产物的结构日渐复杂,构建多基因的从头合成途径造成宿主生物代谢失衡与中间产物对宿主细胞产生毒害作用等一系列问题发生的可能性也随之增加。为解决这些问题合成支架策略应运而生,合成支架将途径酶共定位以提高局部酶和代谢物的浓度,来增强代谢通量并限制中间产物与宿主细胞环境间的相互作用,成为生物催化和合成生物学研究的热点之一。尽管由核酸、蛋白质构成的合成支架策略已经应用于多种代谢物的异源合成,并取得了不同程度的成功,但合成支架的精确组装仍然是一项艰巨的任务。文中详细介绍了合成支架技术的研究现状,详细阐述了合成支架技术的原理和实例,并初步探讨了其应用前景。     

原位分离耦合技术制备生物丁醇的研究进展

笔者对吸附法、液液萃取法、气提法、渗透汽化法等提取技术原位分离耦合丁醇进行了综述,并对其分离特性与效果进行了比较。针对目前原位分离耦合发酵制备生物丁醇的应用现状和面临的挑战,并结合本课题组已取得的成果,对原位分离耦合发酵制备生物丁醇的前景进行了展望。     

微生物木糖发酵产乙醇的代谢工程

利用木质纤维素发酵生产乙醇具有广泛的应用前景。而自然界中缺少有效转化木糖为乙醇的微生物是充分利用纤维素水解产物、提高乙醇产率、降低生产成本的关键因素。多年来研究者利用分子生物学技术对微生物菌株进行了代谢工程改造,使其能更有效地利用木糖生产乙醇。以下主要对运动发酵单胞菌、大肠杆菌和酵母等候选产乙醇微生物的木糖代谢工程研究进展进行了概述。     

酿酒酵母生产羧酸的代谢工程策略

羧酸广泛地应用于食品、医药和化工等行业,具有广阔的市场前景.作为真核模式微生物,酿酒酵母作为代谢工程平台用来生产有机酸具有明显优势.本文论述了酿酒酵母生产重要羧酸的策略:首先构建一条能够和糖酵解途径相连接的高效的重要羧酸积累途径,进而探讨如何将碳代谢流由乙醇转向目的产物,在此基础上研究有机酸的转运及涉及到的能量问题.最后,对当前研究存在的问题进行了分析,并对未来研究方向进行了展望.     

Metabolic engineering of l-leucine production in Escherichia coli and Corynebacterium glutamicum: a review

l-Leucine, as an essential branched-chain amino acid for humans and animals, has recently been attracting much attention because of its potential for a fast-growing market demand. The applicability ranges from flavor enhancers, animal feed additives and ingredients in cosmetic to specialty nutrients in pharmaceutical and medical fields. Microbial fermentation is the major method for producing l-leucine by using Escherichia coli and Corynebacterium glutamicum as host bacteria. This review gives an overview of the metabolic pathway of l-leucine (i.e. production, import and export systems) and highlights the main regulatory mechanisms of operons in E. coli and C. glutamicum l-leucine biosynthesis. We summarize here the current trends in metabolic engineering techniques and strategies for manipulating l-leucine producing strains. Finally, future perspectives to construct industrially advantageous strains are considered with respect to recent advances in biology.     

Metabolic engineering for the optimization of hydrogen production in Escherichia coli: A review

Hydrogen is a potential sustainable energy source and it could become an alternative to fossil fuel combustion, thus helping to reduce greenhouse gas emissions. The biological production of hydrogen, instead of its chemical synthesis, is a promising possibility since this process requires less energy and is more sustainable and eco-friendly. Several microorganisms have been used for this purpose, but Escherichia coli is one of the most widely used in this field. The literature in this area has increased exponentially in the last 10 years and several strategies have been reported in an effort to improve hydrogen production. In this work, the stay of the art of hydrogen biosynthesis by E. coli and metabolic engineering strategies to enhance hydrogen production are reviewed. This work includes a discussion about the hydrogenase complexes responsible for the hydrogen synthesis in this microorganism and the central carbon metabolism pathways connected to this process. The main metabolic engineering strategies applied are discussed, including heterologous gene expression, adaptive evolution and metabolic and protein engineering. On the other hand, culture conditions, including the use of carbon sources such as glycerol, glucose or organic wastes, have also been considered. Yields and productivities of the most relevant engineered strains reported using several carbon sources are also compared.     

Metabolic engineering for higher alcohol production

Engineering microbial hosts for the production of higher alcohols looks to combine the benefits of renewable biological production with the useful chemical properties of larger alcohols. In this review we outline the array of metabolic engineering strategies employed for the efficient diversion of carbon flux from native biosynthetic pathways to the overproduction of a target alcohol. Strategies for pathway design from amino acid biosynthesis through 2-keto acids, from isoprenoid biosynthesis through pyrophosphate intermediates, from fatty acid biosynthesis and degradation by tailoring chain length specificity, and the use and expansion of natural solvent production pathways will be covered.     

Metabolic engineering for production of functional polysaccharides

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Metabolic engineering of bacteria for ethanol production

Technologies are available which will allow the conversion of lignocellulose into fuel ethanol using genetically engineered bacteria. Assembling these into a cost-effective process remains a challenge. Our work has focused primarily on the genetic engineering of enteric bacteria using a portable ethanol production pathway. Genes encoding Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase have been integrated into the chromosome of Escherichia coli B to produce strain KO11 for the fermentation of hemicellulose-derived syrups. This organism can efficiently ferment all hexose and pentose sugars present in the polymers of hemicellulose. Klebsiella oxytoca M5A1 has been genetically engineered in a similar manner to produce strain P2 for ethanol production from cellulose. This organism has the native ability to ferment cellobiose and cellotriose, eliminating the need for one class of cellulase enzymes. The optimal pH for cellulose fermentation with this organism (pH 5.0-5.5) is near that of fungal cellulases. The general approach for the genetic engineering of new biocatalysts has been most successful with enteric bacteria thus far. However, this approach may also prove useful with Gram-positive bacteria which have other important traits for lignocellulose conversion. Many opportunities remain for further improvements in the biomass to ethanol processes. These include the development of enzyme-based systems which eliminate the need for dilute acid hydrolysis or other pretreatments, improvements in existing pretreatments for enzymatic hydrolysis, process improvements to increase the effective use of cellulase and hemicellulase enzymes, improvements in rates of ethanol production, decreased nutrient costs, increases in ethanol concentrations achieved in biomass beers, increased resistance of the biocatalysts to lignocellulosic-derived toxins, etc. To be useful, each of these improvements must result in a decrease in the cost for ethanol production. Copyright 1998 John Wiley & Sons, Inc.     

Metabolic engineering of beta-lactam production

Metabolic engineering has become a rational alternative to classical strain improvement in optimisation of beta-lactam production. In metabolic engineering directed genetic modification are introduced to improve the cellular properties of the production strains. This has resulted in substantial increases in the existing beta-lactam production processes. Furthermore, pathway extension, by heterologous expression of novel genes in well-characterised strains, has led to introduction of new fermentation processes that replace environmentally damaging chemical methods. This minireview discusses the recent developments in metabolic engineering and the applications of this approach for improving beta-lactam production.     

Metabolic engineering of Propionibacterium freudenreichii for n-propanol production

Propionibacteria are widely used in industry for manufacturing of Swiss cheese, vitamin B₁₂, and propionic acid. However, little is known about their genetics and only a few reports are available on the metabolic engineering of propionibacteria aiming at enhancing fermentative production of vitamin B₁₂ and propionic acid. n-Propanol is a common solvent, an intermediate in many industrial applications, and a promising biofuel. To date, no wild-type microorganism is known to produce n-propanol in sufficient quantities for industrial application purposes. In this study, a bifunctional aldehyde/alcohol dehydrogenase (adhE) was cloned from Escherichia coli and expressed in Propionibacterium freudenreichii. The mutants expressing the adhE gene converted propionyl- coenzyme A, which is the precursor for propionic acid biosynthesis, to n-propanol. The production of n-propanol was limited by NADH availability, which was improved significantly by using glycerol as the carbon source. Interestingly, the improved propanol production was accompanied by a significant increase in propionic acid productivity, indicating a positive effect of n-propanol biosynthesis on propionic acid fermentative production. To our best knowledge, this is the first report on producing n-propanol by metabolically engineered propionibacteria, which offers a novel route to produce n-propanol from renewable feedstock, and possibly a new way to boost propionic acid fermentation.