膜生物反应器 CCCF 过程中酵母细胞生长特性研究

渗透汽化膜生物反应器CCCF过程乙醇发酵中酵母细胞的生长表现出五个不同的阶段,即：快速生长期、乙醇抑制期、二次生长期、平衡期和衰亡期。采用摇瓶实验对发酵副产物（主要为有机酸和甘油）的抑制行为进行检测,结果表明随着副产物浓度的增加,抑制作用越来越强,细胞生长表现出较长的迟滞期和较低的细胞浓度。当副产物浓度达到膜生物反应器中发酵后期的浓度时,细胞的比生长速率和得率仅分别为0．061和0．024。     

重金属环境下酵母发酵性能研究

重金属离子对发酵生产乙醇的产率带来一定的影响,因此对重金属环境下酵母发酵性能研究显得尤为重要。本文利用5株重金属耐受性的酵母,通过不同酵母发酵性能分析、重金属迁移分析、酵母在甘蔗汁发酵中重金属吸收情况分析,探讨重金属迁移规律及酵母与重金属相互作用关系。最终得出实验结果：五株酵母细胞发酵行为,主要受Cd和Pb的影响。     

酿酒酵母乙醇耐受性的研究进展

酿酒酵母是重要的工业微生物之一,具有发酵速度快、乙醇产量高特性,主要应用于乙醇和酿酒行业。但在发酵过程中,随着乙醇积累会对酵母细胞产生毒害作用,从而抑制了菌体细胞生长和乙醇进一步形成。因此,对酿酒酵母乙醇耐受性机制研究具有重要的理论和实际意义,也为选育具有较强乙醇耐受性的酵母菌种提供了理论基础。本文综述了酿酒酵母乙醇耐受性研究进展,介绍了酿酒酵母乙醇发酵途径、乙醇耐受性机理,主要阐述了提高酵母乙醇耐受性方法。指出加强酵母乙醇耐受性机理研究,了解乙醇耐受性与其他胁迫耐受性联系,最终提高酵母菌乙醇转化效率是未来研究关键。     

镉、铅重金属环境下酵母发酵性能研究

重金属离子对发酵生产乙醇的产率带来一定的影响,对能适应重金属环境的酵母菌种及其发酵性能进行了研究。利用5株重金属耐受性的酵母,通过对不同酵母发酵性能、重金属迁移情况、酵母在甘蔗汁发酵中重金属吸收情况的分析,探讨重金属迁移规律及酵母与重金属相互作用关系。实验结果表示,工业菌种DBL91 (C2)因对Cd和Pb的吸收程度最大(分别为17.3%和81.96%),导致其乙醇的发酵性能最低,为4.11%。五株酵母细胞发酵行为,主要受Cd和Pb的影响。     

基于发酵吸附分离耦合制备生物乙醇的研究进展

原位产物分离技术可以解除发酵过程中产生的乙醇对酵母细胞生长的抑制作用。与传统蒸馏相比,原位产物分离可以极大地降低乙醇的分离能耗。分析和评述了乙醇发酵与吸附分离耦合工艺中涉及的吸附剂类型（如沸石、硅质岩、活性炭、树脂及生物质吸附剂等）,脱附方法（如常规热脱附、微波辐照脱附）和耦合模式（如原位耦合模式、异位耦合模式）。提出今后的研究重点在于开发出优良的吸附剂和选择合适的脱附方法。     

提高酵母乙酸胁迫耐性的方法概述

利用木质纤维素制备燃料乙醇新能源有利于人类社会的可持续发展,具有深远的社会效益和经济效益。预处理是利用木质纤维素类生物质的首要环节,在此过程中会产生一些抑制剂,其中乙酸是最主要的抑制剂之一,对酵母的生长和发酵产乙醇产生抑制作用。目前,可通过紫外诱变、驯化、代谢工程等菌种选育方法以及发酵过程中的控制等方式提高酵母在发酵过程中对乙酸的胁迫耐受性。     

氮源影响酵母耐受超高浓度乙醇发酵胁迫条件

为考察蛋白胨和酵母浸出膏对酵母耐受超高浓度乙醇发酵胁迫条件的影响,以300g/L起始浓度葡萄糖开展实验。结果表明,与对照组(3g/L蛋白胨+5g/L酵母浸出膏作为氮源)相比,单独提高发酵培养基蛋白胨至6g/L或酵母浸出膏至12g/L,均可明显促进菌体生长和葡萄糖利用,终点乙醇体积分数由对照组的13.1%分别提高至14.4%和14.7%。研究表明,在发酵过程中,生长于提高蛋白胨浓度或酵母浸出膏浓度培养基的菌体,其质膜ATP酶活力和胞内海藻糖积累量明显高于对照组,而且发酵参数(如菌体生长、葡萄糖利用和终点乙醇体积分数)的提高与酶活力和海藻糖含量的增加密切相关,提示质膜ATP酶和胞内海藻糖在酵母耐受超高浓度乙醇发酵胁迫条件中的作用。     

超高浓度乙醇发酵培养基优化与酵母生理变化

为促进超高浓度乙醇发酵(350 g/L起始葡萄糖),采用均匀设计法优化发酵培养基成分,结果为8.2 mmol/L Mg2+,1.0 mmol/L Ca2+,30.0 g/L蛋白胨和27.1 g/L酵母浸出膏。采用该优化培养基,实验测得发酵终点乙醇体积分数为18.3%,比未优化时提高约58%,同时,菌体生长和葡萄糖转化利用等其它参数也明显提高。实验进一步探索与发酵状况改善有关的酵母生理方面的变化。结果表明,在发酵过程中生长于优化培养基的菌体的质膜ATP酶活力和胞内海藻糖含量明显高于对照组,提示二者在促进发酵中的重要作用。这是超高浓度乙醇发酵培养基优化引起酵母质膜ATP酶活力和胞内海藻糖含量变化的首次报道。     

与膜耦合的细胞固定化串联发酵制乙醇的研究

利用植物纤维作为廉价的糖源生产燃料乙醇是解决世界能源危机的最有效途径.今研究采用海藻酸钙固定普通酿酒酵母细胞和嗜鞣管囊酵母细胞于两个串联的发酵罐内,连续发酵葡萄糖和木糖组成的糖液并与膜耦合来制取酒精.通过硅橡胶膜(PDMS)的渗透蒸发过程,将产品乙醇从发酵液中移出,减少了产物乙醇对发酵的抑制作用.实验结果表明,这套采用海藻酸钙固定酵母细胞进行连续发酵并与膜耦合的生物反应器系统,在稀释率为0.321 h-1下稳定运行,剩余葡萄糖和木糖浓度分别为0.134、4.921 g·L-1,乙醇得率为O.457 g(乙醇)·g-1(糖),是理论得率的92.64%.生产能力达到10.996 g·L-1·h-1.与其它发酵方式相比较,用海藻酸钙来固定细胞并与膜耦合的发酵过程可增大酵母细胞浓度,明显降低乙醇对酵母的抑制作用,并提高糖的转化率.     

纤维素乙醇生产重组酿酒酵母菌株的构建与优化研究进展

寻找化石能源的替代品以及开发和利用生物能源已引起国内外研究者的广泛关注。提高酿酒酵母利用来源广泛、贮存丰富的农林废弃物等木质纤维素原料生产燃料乙醇的效率是生物能源的重要研究内容,但是,重组酿酒酵母木糖发酵性能低是限制纤维素乙醇经济性的关键问题。本文总结了酿酒酵母中木糖代谢途径的构建和优化以及木糖转运对木糖利用的影响,分析了重组酵母利用纤维素水解液进行乙醇发酵的研究现状,并对进一步提高重组酿酒酵母纤维素乙醇生产效率的研究趋势进行了展望。目前国内外已经构建了可有效利用木糖产乙醇的重组酵母,但对其木糖代谢机制的研究还尚未深入,限制了重组菌株的定向改造。此外,目前缺少在纤维素生物质水解液发酵实际应用过程中对重组菌株的评价。因此,加强重组酵母菌株对木糖利用相关代谢调控机理的分析,注重多种抑制物对菌株发酵性能的影响,结合真实底物纤维素乙醇发酵过程进行重组菌株的构建和优化,从而进一步提高纤维素乙醇生产的经济性,是未来菌株构建的重要研究方向。     

Separation of tetra-, penta-, and hexaacyl triglycerides by high performance liquid chromatography

Synthetic triglycerides with more than three acyl groups were prepared by forming estolides from triglycerides containing one, two, or three monohydroxy fatty acyl moieties. These tetra-, penta-, and hexaacyl triglycerides were examined by high performance liquid chromatography (HPLC) and thin layer chromatography (TLC). HPLC separation by the number of acyl groups was obtained with both conventional phase and reverse phase columns. In all systems, triglycerides were eluted first, followed in sequence by tetra-, penta-, and hexaacyl triglycerides. Within each glyceride class, further separation occurred due to variations in chain length and degree of unsaturation among the component acids. TLC migration on silica gel was found to be a function of the number of acyl groups and the length of component acid chains. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Using viscosity‐time plots of Escherichia coli cells undergoing chemical lysis to measure the impact of physiological changes occurring during batch cell growth

BACKGROUND: Viscosity–time plots for plasmid‐bearing E. coli cells undergoing alkaline lysis are reported in this study. The plots demonstrate generic features that reflect the progress of fermentation and allow an assessment of the genomic DNA denaturation following cellular release into the alkaline solution. This rheological analysis could offer useful insights to the state of fermentation or the selection of operational specifications and predictions of the performance of subsequent downstream operations. RESULTS: Studies showed a distinct change in the rheological profile throughout the batch fermentation, with different viscosity versus time profiles for lag, exponential and stationary microbial growth phases. The DNA denaturation time was found to increase with fermentation time from about 120 s after 3 h of fermentation to about 180 s after 7 h of fermentation. CONCLUSION: The increase of denaturation time was mainly caused by a rise in the genomic content of cells during the exponential growth phase. The viscosity–time profiles were found to provide a good indication of the cellular contents, reflecting the physiological changes occurring during a batch fermentation process. Copyright © 2009 Society of Chemical Industry     

Mapping the structure-activity relationship of β-sitosteryl fatty acid esters in condensing phospholipid monolayers

The phase behavior of twelve synthesized β-sitosteryl fatty acid esters with acyl moieties with different chain lengths (C2:0-C18:0) and different degrees of unsaturation (C18:1-C18:3) were investigated in pure and mixed Langmuir monolayers with phospholipids. The surface-pressure isotherms showed that short chain β-sitosteryl fatty acid esters gave smaller mean molecular areas and had decreased monolayer stability and the long chain steryl esters did not produce collapsed plateaus. All the steryl esters displayed strong condensing effects, but there was a pronounced structural dependency: medium chain esters (C8 and C10) were less efficient than short and long chain esters. Atomic force microscopy imaging demonstrated that monolayers mixed with dipalmitoyl phosphatidylcholine (DPPC) displayed both DPPC-rich and steryl lipid-rich domains. However, the height and area differences between the two phases and the roughness and morphologic patterns were very dependent on the steryl lipid concentrations as well as the length, the degree of unsaturation and the molecular conformations of the acyl segments. These findings not only provide a better understanding of the interactions between phytosteryl hydrophobic derivatives and biomembranes, but also may be of general use for the design and engineering of phytosterol structural derivations for specific food and pharmaceutical applications.     

Fermentation patterns of gramicidin S formation by Bacillus brevis ATCC 9999 in high-yielding synthetic medium

Addition of the gramicidin S (GS)-constituent amino acids, other than the limiting precursor L -phenylalanine, to the high-yielding chemically defined F3/6 and G3/6 media, enhanced growth and volumetric GS-production by Bacillus brevis ATCC 9999 considerably, but did not yield a higher specific GS-production level. L -Leucine alone could duplicate this stimulatory effect in G3/6 medium. Replacing the fructose component of F3/6 medium by these four amino acids yielded a high specific GS-production level, but resulted in poor growth and low volumetric antibiotic production. Nutrient-utilisation patterns in F3/6 medium revealed that B. brevis initially grew at the expense of L -glutamine and L -arginine. After a diauxic lag period, D -fructose was consumed together with L -histidine. L -Proline was mainly used during the stationary phase. L -Methionine was broken down gradually throughout the whole fermentation cycle. L -Phenylalanine was metabolised only after GS formation started, and its disappearance was proportional to the amount of GS produced. Lowering the aeration rate caused an acidification of the medium, resulting in a slower and incomplete, although similar, nutrient-utilisation pattern. At a controlled pH of 7.3, under lowered aeration, utilisation patterns were again comparable with those of a fully aerated fermentation, but GS levels were enhanced considerably (0.220 mg of GS mg^?1 dry cell wt). Depending on environmental culture conditions, B. brevis also excreted different amino acids (L -lysine, L -alanine, L -valine, L -serine), which were in turn metabolised during late growth and differentiation stages. The onset of GS synthesis occurred on depletion of L -glutamine and L -arginine. Soluble GS synthetase 1 and 2 peaks coincided with ‘diauxic’ lag phases; this supported the idea that a high growth rate is incompatible with GS synthetase formation.     

Anaerobic digestion of seaweed for biogas: A kinetic evaluation

A kinetic study of biogas production in batch digesters by anaerobic digestion of seaweed, Sargassum tenerrimum, with a mixed bacterial culture consisting of methanogenic bacteria and an algin-degrading bacterial strain was carried out at different concentrations of dry total solids. Specific rate constants of biogas production during the lag, exponential and monomolecular (stationary) phases of bacterial growth were determined. About half the total volume of biogas was generated during the exponential phase irrespective of the concentration of seaweed in the digesters. The specific rates of substrate destruction and biogas generation in the stationary phase decreased with increasing substrate concentration. The yield of biogas per gram dry total solids of seaweed was about the same at all concentrations, but with a marked decline at 12% (w/v) total solids. The maximum destruction of volatile solids effected was about 63% over a period of 72 days.     

Chain length dependent thermodynamics of saturated symmetric-chain phosphatidylcholine bilayers

A molecular interpretation for the chain length dependent thermotropic behavior of saturated symmetric-chain phosphatidylcholine bilayers is proposed. It is suggested that the bilayer interface region and conformationally inequivalent terminal ends of the fatty acyl chains perturb the packing associations of the rest of the hydrocarbon chains in the gel phase of the bilayer. These perturbing effects, which are seen to increase with decreasing acyl chain length, have been quantitatively defined by a perturbation parameter, P. The thermodynamic parameters of the thermal phase transition of these phosphatidylcholines are found to be linearly correlated to P and these linear relationships can be used to predict the minimum number of carbon atoms in the acyl chain necessary in order for a bilayer phase transition to occur.     

Effect of extraction and enzymatic esterification of ethanol on glucose consumption by two Saccharomyces cerevisiae strains: a comparative study

Extractive alcoholic fermentations of high glucose concentrations (300 and 400 g dm^?3) using a flocculent (saké) and a non‐flocculent (DER24) Saccharomyces cerevisiae strain were compared. The introduction of a Rhizomucor miehei lipase, in the extractive fermentations of 300 g dm^?3 of glucose, increased the ethanol extraction due to its esterification with oleic acid, allowing complete glucose consumption at an organic solvent/fermentation medium phase ratio of 1. In these conditions, an increase of ethanol yield was observed. Total glucose consumption was also obtained in enzymatic extractive fermentations of 400 g dm^?3 of glucose, but only when oleic acid was added at the exponential growth phase. From the comparison of the extractive fermentation performances obtained using the two yeast strains it was observed that the flocculent strain led to a lower glucose metabolisation rate. This behaviour was related to the highest diffusional limitations that occur in the presence of flocs. The developed processes showed that the association of alcoholic fermentation with enzymatic extraction led to the reduction of inhibitory effects as well as to the simultaneous production of fatty esters which are compounds with several commercial applications. © 2001 Society of Chemical Industry     

Reactions of the diiron enzyme stearoyl-acyl carrier protein desaturase

Stearoyl-acyl carrier protein Delta(9) desaturase (Delta9D) produces oleic acid, a nutritionally valuable fatty acid containing a cis double bond between C-9 and C-10. This multiprotein diiron enzyme complex reacts with stearoyl-acyl carrier protein, reduced [2Fe-2S] ferredoxin, and O(2) to complete the highly regiospecific and stereoselective desaturation reaction. Interactions with the acyl chain provide stability to the enzyme-substrate complex, give an energetic contribution to catalytic selectivity, and help to order the electron transfer, O(2) binding, and C-H bond cleavage steps of catalysis. Reactions with natural acyl chains indicate the involvement of a highly reactive diiron intermediate capable of oxidizing secondary C-H bonds (bond dissociation energy approximately 95 kcal/mol), but also capable of diagnostic O-atom transfer reactions with the appropriate substrate analogues. For soluble Delta9D, the natural reaction may initiate at the C-10 position, in contrast to the well-established initial reactivity of the membrane enzyme homologue stearoyl-coenzyme A (CoA) Delta(9) desaturase at the C-9 position.     

赤藓糖醇发酵工艺优化

以解脂假丝酵母CGMCC2．2088为出发菌株,经过菌种选育得生产菌株为研究对象,对该菌株的发酵培养基和培养条件进行优化,其发酵最适温度为32％,对数生产期溶氧控制在30％,发酵期溶氧控制在20％,发酵结果糖醇含量达到181．6g／L。     

Decoding the Fatty Acid Profile of Bacillus licheniformis I89 and Its Adaptation to Different Growth Conditions to Investigate Possible Biotechnological Applications

Bacillus licheniformis I89 is a Gram-positive bacterium, a producer of the lantibiotic lichenicidin. No information is available on its fatty acid (FA) composition. Bacillus species are rich in branched FA (BrFA), claimed to be beneficial to human health and to treat diseases. Herein, the FA profile of B. licheniformis I89 was evaluated under different growth conditions: at two growth temperatures (37 and 50 °C) and at different growth phases (lag, exponential, and stationary), using gas chromatography–mass spectrometry. The FA profile revealed predominant BrFA of the iso-series and anteiso-series (i-15:0, ai-15:0, i-16:0, i-17:0, and ai-17:0) and low amounts of saturated FA (14:0, 16:0, and 18:0). Comparing the FA profiles at different temperatures, in the lag phase, at 50 °C, there was a decrease of ai-17:0 and a decrease of i-15:0 in the exponential phase, in comparison with 37 °C. In all growth phases, there was a decrease of ai-15:0 and an increase of i-17:0. From the lag to the stationary phase, at 50 °C, there was a decrease of ai-17:0 and i-16:0, whereas i-15:0 increased, while at 37 °C, there was an increase of i-15:0 and i-16:0, and a decrease in ai-15:0 and ai-17:0. B. licheniformis I89 can adapt its FA profile, at moderate temperatures, by changing the iso-FA and anteiso-FA composition and the iso/anteiso ratio. This nonpathogenic bacterium species can be used as a source of BrFA with putative beneficial health effects for gut protection and with reported antitumor properties, foreseeing its use for producing compounds with biotechnological applications.