微生物合成2-苯乙醇研究进展*

2-苯乙醇(2-PE)是一种具有广阔应用前景的高级芳香醇。由于化学合成的复杂性和天然提取的高昂成本,近年来,利用微生物发酵合成2-PE受到广泛关注。许多微生物有天然合成2-PE的能力,但产量相对较低,并不适合大规模生产。在最近几年的研究中,利用代谢工程和合成生物学技术,通过上调限速酶基因表达水平,改善前体转运,提高 2-PE耐受性等多方面优化,2-PE的微生物产量有了大幅度的提高。综述微生物合成2-PE的相关研究进展,分析关键代谢调控的机制,并就目前存在的问题提出了改进建议。     

微生物耐受乙醇与丁醇机制及其在生物燃料生产与生物转化中的应用

生物法获取乙醇与丁醇过程中有机溶剂的毒性是生产菌重要环境胁迫因素之一,且当有机溶剂超过一定浓度时便会抑制微生物的生长,甚至引起微生物的死亡,因此提高工业微生物的有机溶剂耐受性对工业生产具有重要的意义。对微生物乙醇及丁醇耐受机制的研究可为选育具有较强溶剂耐受菌提供理论基础。本文系统介绍了微生物耐受乙醇与丁醇的机制,并对其在生物燃料生产及生物转化中面临的机遇与挑战等问题进行简要的评述。     

耐有机溶剂微生物的耐受机制、改造策略和应用北大核心

耐有机溶剂微生物在生物燃料生产、全细胞催化、酶制剂的开发和生物修复等领域具有非常重要的作用。该文简要介绍了耐有机溶剂微生物及其耐受机制,并从基因过表达、基因敲除和全局转录机制三个方面总结了增强微生物有机溶剂耐受性的方法。通过对耐有机溶剂微生物应用的局限性进行分析,认为未来研究中应注重将微生物耐受表型和具体利用相结合,达到有机溶剂耐受和实际产出的最佳平衡状态,为耐有机溶剂工程菌的改造和选育提供参考。     

耐有机溶剂微生物的耐受机制、改造策略和应用

耐有机溶剂微生物在生物燃料生产、全细胞催化、酶制剂的开发和生物修复等领域具有非常重要的作用。该文简要介绍了耐有机溶剂微生物及其耐受机制,并从基因过表达、基因敲除和全局转录机制三个方面总结了增强微生物有机溶剂耐受性的方法。通过对耐有机溶剂微生物应用的局限性进行分析,认为未来研究中应注重将微生物耐受表型和具体利用相结合,达到有机溶剂耐受和实际产出的最佳平衡状态,为耐有机溶剂工程菌的改造和选育提供参考。     

耐受性工程调控微生物细胞工厂胁迫抗性

微生物细胞工厂的生产效率是由菌株生长性能、产品合成能力和胁迫抗性共同决定的,其中增强微生物细胞工厂的胁迫抗性是关键.耐受性工程基于微生物细胞工厂抵御胁迫压力的应激反应机制,通过巩固壁膜屏障增强胁迫防御能力,加快应激反应提高损伤修复能力,创制耐受进化工具筛选鲁棒性增强的工业微生物.文中分析归纳了耐受性工程的调控策略,并展...     

嗜热厌氧菌乙醇耐受机制的研究进展

生物能源因其原料具有来源丰富、价格低廉和可再生的优点,作为可替代化石能源的潜在能源受到世界各国的高度重视。有些嗜热厌氧菌因为具有木质纤维素降解能力和高温发酵的成本优势,被视为生物质转化乙醇等能源物质的理想微生物而成为近年来研究的热点,但乙醇耐受性较低是限制嗜热厌氧菌在工业化生产中应用的主要因素之一。本文从以下三个方面介绍嗜热厌氧菌乙醇耐受机制的研究进展：（1）嗜热厌氧菌生产乙醇的代谢途径;（2）嗜热厌氧菌的乙醇耐受机制;（3）提高嗜热厌氧菌乙醇耐受性的方法。     

中链脂肪酸毒性机制及耐受性菌株构建研究进展

中链脂肪酸(medium-chain fatty acids, MCFAs)作为一种重要的平台化学品,被广泛应用到能源、食品和医药等行业。工业微生物发酵生产MCFAs是一条绿色环保的路线,但MCFAs会对微生物细胞膜造成损伤,并导致细胞pH、渗透压失衡及氧化应激,从而严重抑制细胞的生长速率和生产能力。因此,构建MCFAs耐受性工业微生物菌株,有助于进一步提高MCFAs的生产效率。以大肠杆菌和酿酒酵母等工业微生物为例,首先简介了MCFAs对微生物细胞的毒性机制。其次综述了运用膜改造、转运体筛选等理性代谢工程手段构建MCFAs耐受性菌株的相关研究进展,并概括了运用适应性进化、代谢通量分析等方法系统性挖掘MCFAs耐受靶点进而增强菌株耐受性的研究进展。最后对后续提高工业微生物MCFAs耐受性和生产能力的研究方向进行了展望。     

代谢工程改造解脂耶氏酵母合成羧酸的研究进展

解脂耶氏酵母是一种具有独特生理代谢特征的非常规酵母.它具有可以利用多种廉价碳源、低pH值耐受性好、分泌能力强等优点,因此非常适合用于各种工业产品的微生物发酵.目前,解脂耶氏酵母已被证实具有高效生产多种(同源或异源)有机羧酸的能力.本文对近年来利用代谢工程及合成生物学技术改造解脂耶氏酵母生产羧酸的实例进行了总结,并重点介...     

实验室适应性进化技术在光合蓝细菌底盘工程中的研究进展

蓝细菌是唯一可进行放氧光合作用的原核微生物,基于光合蓝细菌构建“自养型细胞工厂”具有广阔前景。但以蓝细菌作为底盘进行生物燃料及化学品的合成仍存在细胞耐受能力差、产量低等问题,导致实现工业化生产的经济可行性还比较低,亟需通过合成生物学等技术手段构建新的藻株。近年来,实验室适应性进化(adaptive laboratory evolution,ALE)已被用于底盘工程中,实现了优化生长速度、增加耐受性、加强底物利用和提高产品产量等目标。ALE在提高蓝细菌鲁棒性方面取得了一定进展,已获得了耐受高光、重金属离子、高盐和高浓度有机溶剂胁迫的进化藻株。但是,蓝细菌中的ALE策略效率相对较低,耐受各胁迫的分子机制并未阐释完全。本文综述了ALE相关技术策略及其在蓝细菌底盘工程中的应用,讨论了如何借鉴其他微生物中ALE手段,构建更大ALE突变文库、增加菌株的突变频率、缩短进化时间、探索多重胁迫耐受工程菌构建原则及研究策略等,高效解析进化菌株的突变体库,构建高产量、鲁棒性强的工程菌株等,以期未来促进蓝细菌底盘的改造及其工程菌的规模化应用。     

细菌的有机溶剂耐受机制

有机溶剂有严重破坏微生物正常生理功能的毒害作用,但是研究工作者发现有些细菌能够在较高有机溶剂浓度下依赖独特的耐受机制得以生存,这种机制的发现大大鼓舞了工业菌尤其是溶剂生产菌和毒性有机物降解菌的工业适应性改造研究。以下概述了有机溶剂对细胞毒性作用机制,并在根据参数logP衡量不同溶剂对细胞的毒性程度的基础上,重点总结了溶剂耐受菌耐受有机溶剂的机制,即膜上顺反异构、增加饱和脂肪酸的比率、改变极性头部、外膜的生理变化、细胞的形态变化、胞内溶剂的降解和泵出等,结合本课题组在筛选溶剂耐受菌株和提高现有菌株溶剂耐受性研究方面的经验,希望对重要工业微生物溶剂耐受相关的生理功能进行更深入地研究,提高微生物的工业适应性。     

酵母菌合成2-苯乙醇的研究进展

2-苯乙醇是一种具有令人愉悦的玫瑰风味的芳香醇,在食品、化妆品和药品等领域具有广泛的应用。本文对酵母菌合成2-苯乙醇的代谢途径及其调控过程、以及提高2-苯乙醇产量的国内外研究进展进行了综述,并对通过微生物转化法合成2-苯乙醇目前存在的不足及进一步研究方向进行了讨论。     

生物转化法合成2-苯乙醇的研究进展

2-苯乙醇(2-phenylethanol,2-PE)是具有玫瑰香味的芳香醇,在食品、化妆品以及药品领域有着广泛的应用。但是从植物花卉中提取的天然2-苯乙醇产量低,成本高。目前,用微生物转化生产"天然"2-苯乙醇越来越受到关注。本文对近年来国内外报道的提高微生物转化合成2-苯乙醇产量的研究,尤其是生产菌株选育和发酵工程优化的研究进行了综述,并提出今后研究的新思路,旨在为利用微生物发酵进行2-苯乙醇生产提供参考。     

Screening of Yeasts Isolated from Brazilian Environments for the 2-Phenylethanol (2-PE) Production

Phenylethanol alcohol, or 2-phenylethanol (2-PE) production by yeasts has been considered a promising alternative to its chemical synthesis. In order to evaluate the potential of yeast strains isolated from different Brazilian environments, we evaluated the 2-PE production of 267 strains. Among them, the Kluyveromyces marxianus CCT 7735 yeast stood out as being the best 2-PE producer. The K. marxianus CCT 7735 growth was impaired by 2-PE; nevertheless, this effect is less pronounced than the inhibition reported for certain Saccharomyces cerevisiae strains. The maximum 2-PE titer obtained under optimized conditions was 3.44 g/L, 28% higher than the titer achieved under unoptimized conditions. The optimized conditions were: 30ºC, and glucose and L-phe concentrations of 3.0 and 4.0 g/L, respectively. Moreover, the specific production rate of 2-PE increased twofold compared to the unoptimized conditions.     

Enhanced Biotransformation of 2-Phenylethanol with Ethanol Oxidation in a Solid–Liquid Two-Phase System by Active Dry Yeast

2-Phenylethanol (2-PE) can be produced from l-phenylalanine (l-Phe) with the oxidation degradation of ethanol by active dry yeast. In this study, the catalysis effect of ethanol on biotransforming l-Phe into 2-PE by yeast was evaluated and optimized. The results indicated that increasing ethanol concentration was beneficial for enhancing 2-PE concentration but lowered the 2-PE productivity. Initial ethanol concentration above 25 g/l could strongly inhibit the 2-PE production. To obtain 2-PE with desirable concentrations with an economical operation mode, three fed-batch biotransformation operation methods using ethanol or/and glucose were carried out in a solid–liquid two-phase system. When using ethanol alone with the initial concentration of 10 g/l, the total concentration and overall productivity of 2-PE were 7.6 g/l and 0.065 g l⁻¹ h⁻¹, respectively. Furthermore, an experiment with controlled glucose solely (higher than 2 g/l) was finished. In this case, phenylacetaldehyde (PA) was detected along with ethanol accumulation, suggesting that reaction of PA → 2-PE in Ehrlich pathway was inhibited. To further enhance 2-PE production by using glucose only, a novel operation strategy to simultaneously control rates of glucose glycolysis and ethanol oxidative degradation with the aid of ISPR techniques was developed. With this strategy, 2-PE concentration and yield based on glucose consumption reached a higher level of 14.8 g/l and 0.12 g-PE/g-glucose, respectively, and these are the highest values reported up to date with the fed-batch biotransformation operation mode.     

Can yeast systems biology contribute to the understanding of human disease?

Saccharomyces cerevisiae is a unicellular eukaryal microorganism that has traditionally been regarded either as a model system for investigating cellular physiology or as a cell factory for biotechnological use, for example for the production of fuels and commodity chemicals such as lactate or pharmaceuticals, including human insulin and HPV vaccines. Systems biology has recently gained momentum and has successfully been used for mapping complex regulatory networks and resolving the dynamics of signal transduction pathways. So far, yeast systems biology has mainly focused on the development of new methods and concepts. There are also some examples of the application of yeast systems biology for improving biotechnological processes. We discuss here how yeast systems biology could be used in elucidating fundamental cellular principles such as those relevant for the study of molecular mechanisms underlying complex human diseases, including the metabolic syndrome and ageing.     

2-phenylethanol (rose aroma) production potential of an isolated pichia kudriavzevii through solid-state fermentation

2-phenylethanol (2-PE) is a higher alcohol widely used in industry that can be obtained by solid-state fermentation (SSF) using low-cost raw materials. This report describes the 2-PE production potential of an indigenous Pichia kudriavzevii isolated from solid-state fermented sugarcane bagasse that possesses attractive characteristics for processing waste streams such as its low-pH tolerance, high growth rate and temperature resistance. Besides, 2-PE production was optimized in batch-SSF using sugarcane bagasse supplemented with l-phenylalanine as substrate. Full factorial design allowed identifying the pH adjustment, micronutrient addition, inoculum and co-substrate load effects, and response surface methodology served to identify the maximum production based on temperature, initial moisture content (MC₀) and specific airflow rate (S_AFR). While the pH adjustment and micronutrient addition did not affect the 2-PE production, temperature and MC₀ resulted critical for the process. After optimization, the maximum 2-PE content was 27.2 ± 0.2 mg per gram of dry substrate at 31 °C, 76 % MC₀ and 0.129 L h⁻¹ g⁻¹ S_AFR. This result was 23.8 % higher than the sub-optimal condition, and it is the highest 2-PE production via SSF reported so far. These results confirm the ability of P. kudriavzevii for producing 2-PE, and its potential for using waste streams as substrate.     

Biotechnological production of 2-phenylethanol

2-Phenylethanol (2-PE) is an important flavour and fragrance compound with a rose-like odour. Most of the world's annual production of several thousand tons is synthesised by chemical means but, due to increasing demand for natural flavours, alternative production methods are being sought. Harnessing the Ehrlich pathway of yeasts by bioconversion of L-phenylalanine to 2-PE could be an option, but in situ product removal is necessary due to product inhibition. This review describes the microbial production of 2-PE, and also summarizes the chemical syntheses and the market situation.