Production of Escherichia coli as a source of nucleic acids

Present-day chemical and physical studies of the nucleic acid system of bacteria frequently call for quantities of cells which are beyond the capacity of traditional culture methods such as that of the shake flask. The case is therefore argued for an increased use of stirred deep cultures because a greater rate of output, at a higher cell concentration and with improved control of cultural conditions can be achieved. For the isolation of deoxyribonucleic acid and transfer ribonucleic acid, low growth-rate cells should be the most prolific source: whereas for ribosomes, ribosomal ribonucleic acid and messenger ribonucleic acid, high growth cells should give bigger yields. It is concluded that the information is somewhat obscure on what are the best growth conditions for the production of the related-enzymes. A batch method for producing low growth-rate cells of Escherichia coli, in lots of 1 kg dry wt., is then described, followed by a continuous method for producing high growth-rate cells, with an output of 3 kg of dry cells per day. Both cultures have been designed to give maximum yield of cells by promoting maximum assimilation of the carbon substrate. From the point of view of designing a culture, the section dealing with the continuous process discusses the rationale of medium formulation, the calculation of aeration requirements and briefly reviews earlier work on the kinetics of continuous culture.     

以预发酵淀粉废水为碳源生产微生物絮凝剂

以预处理后的淀粉废水为碳源,利用菌株NII 4培养生产絮凝剂,培养液对水样中的SS的去除率可达到85%或更高。培养液中还原糖的浓度波动能影响絮凝剂的产量,培养液中维持一定量的还原糖,有利于菌株NII 4不断地产生絮凝剂。收获絮凝剂最佳时段与加入的菌量、培养基中还原糖的量、培养条件等诸多因素有关,但收获絮凝剂应在NII 4活菌体快速增长和死亡的期间。     

Metabolic engineering of 2‐pentanone synthesis in Escherichia coli

Expanding the chemical diversity of microbial fermentation products enables green production of fuel, chemicals, and pharmaceuticals. In recent years, coenzyme A (CoA) dependent chain elongation, resembling the reversed β‐oxidation pathway, has attracted interest for its use in producing higher alcohols, fatty acids, and polyhydroxyalkanoate. To expand the chemical diversity of this pathway, we metabolically engineered Escherichia coli to produce 2‐pentanone, which is not a natural fermentation product of E. coli. We describe the first demonstration of 2‐pentanone synthesis in E. coli by coupling the CoA‐dependent chain elongation with the acetone production pathway. By bioprospecting for enzymes capable of efficient hydrolysis of 3‐keto‐hexanoyl‐CoA, production of 2‐pentanone increased 20 fold, reaching a titer of 240 mg/L. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3167–3175, 2013     

超临界制备生物柴油及副产甘油工艺研究

利用植物油和超临界甲醇制备生物柴油及副产甘油,增加了油相在其中的溶解度,提高了原料转化率和产品收率。实验考察了醇油摩尔比、压力、温度、时间等对生物柴油及副产物甘油产率的影响,结果表明:醇油摩尔比、压力、温度、时间等因素对生物柴油及甘油产率影响较为显著。通过正交实验设计得出的超临界甲醇制备生物柴油的工艺条件为醇油摩尔比30∶1,压力20 MPa,温度280℃,保温时间60 m in,生物柴油和甘油产率可分别达到89.14%和88.73%。     

Production of docosahexaenoic acid by Crypthecodinium cohnii grown in a pH-auxostat culture with acetic acid as principal carbon source

Crypthecodinium cohnii, a marine alga used for the commercial production of docosahexaenoic acid (DHA), was cultivated in medium containing sodium acetate as principal carbon source; the pH was maintained at a constant value by addition of acetic acid, which also provided an additional carbon source in a controlled manner. The accumulation of lipid by C. cohnii in this pH-auxostat culture was significantly greater than previously reported for batch cultures using glucose as principal carbon source. Of six strains tested in pH-auxostat cultures, C. cohnii ATCC 30772 was the best, with the cells reaching 20 to 30 g dry weight per liter after 98 to 144 h and containing in excess of 40% (w/w) total lipid, with DHA representing approximately half of the total fatty acids in the triacylglycerol fraction. A productivity of 36 mg DHAL⁻¹ h⁻¹ was achieved during cultivation for 98 h using a 5% (vol/vol) inoculum, and DHA production was in excess of 3 g per liter of culture. Most of the DHA was present in neutral lipids.     

Innovative preparation route for uranium carbide using citric acid as a carbon source

The preparation of uranium carbide (UC) by carbothermal reduction and its sintering into dense pellets by conventional means require high temperatures for long periods. We have developed a preparation route yielding fine UC powder with significantly increased sinterability. At first, a mixture of nanocrystalline UO₂ embedded in amorphous carbon (nano-UO₂/C) was obtained by thermal decomposition of a gel containing solubilised uranyl nitrate and citric acid. Later, the nano-UO₂/C powder was treated in a conventional furnace or in a modified spark plasma sintering facility at elevated temperatures (≥1200 °C) in order to obtain uranium carbide powder. The effects of initial composition, temperature, gas/vacuum atmosphere and the overall reaction kinetics are reported.     

Pinolenic acid as a new source of phyto‐polyunsaturated fatty acid

Pinolenic acid (PLA, all‐cis‐5,9,12‐18:3) is an interesting plant‐based polyunsaturated fatty acid of which little is known. The major source of PLA is pine nut oil. PLA has distinctive health benefits such as LDL/VLDL cholesterol lowering potential and displays an appetite suppressing effect. Enrichment of PLA can be carried out by physical procedures or by enzymatic reactions with lipases such as Candida antartica lipase B and Candida rugosa lipase.     

Production of glycerol carbonate using crude glycerol from biodiesel production with DBU as a catalyst

The biodiesel production technology catalyzed by 1,8-diazabicycloundec-7-ene (DBU) is developed in this work. Crude glycerol containing DBU and DBU/glycerol/CO₂ (DGC) ionic compounds reacts directly with dimethyl carbonate (DMC) to produce high value-added glycerol carbonate (GC) catalyzed by DBU and DGC. The catalytic performance of DBU and DGC, as well as the kinetics of the reaction catalyzed by DBU, were investigated. The results show that DGC has a weak catalytic effect on the transesterification of glycerol and DMC. When the temperature is higher than 60℃, DGC catalyzes the reaction jointly with DBU, which is produced from the decomposition of DGC. DBU has a good catalytic effect on the reaction between glycerol and DMC, with 90% conversion of glycerol and 84% selectivity to GC under the following conditions:DMC-to-glycerol molar ratio of 3:1, 4.0% DBU (based on glycerol mass), reaction time of 60 min, and reaction temperature of 40℃. The apparent kinetics results show that the activation energies are 30.95 kJ·mol^-1 and 55.16 kJ·mol^-1 for the forward and reverse GC generation reactions, respectively, and the activation energy of the decomposition reaction of GC to glycidol (GD) is 26.58 kJ·mol^-1.     

大肠杆菌Lin43利用甘油产丙酮醇-通过敲除gloB基因改善丙酮醛耐受性

采用重组大肠杆菌Lin 43利用甘油产丙酮醇。为了改善菌株对丙酮醛的耐受性,采取敲除glo B基因而不是gloA基因以阻断丙酮醛的脱毒途径。实验结果表明,菌株Lin43ΔgloB对丙酮醛的耐受性要明显优于Lin43ΔgloA。在含20 g·L-1的甘油磷酸盐缓冲液中,通过26 h静息细胞转化,菌株Lin43·gloB pCA24N-yqhE丙酮醇产量达到2.30 g·L-1,并能耐受3.5 mmol·L-1的丙酮醛。同时Lin43·gloB pCA24N-yqhE实现重复发酵,第二轮发酵的产量可达1.53 g·L-1,丙酮醇的得率与第一轮相同。     

Core‐shell latex synthesized by emulsion polymerization using an alkali‐soluble resin as sole surfactant

A series of alkali‐soluble resins were prepared from esterification reaction of styrene‐maleic anhydride copolymer (SMA) and four fatty alcohols having different alkyl chains. The critical aggregates concentration of the prepared hemiester was lower than SMA, indicating that modification of SMA resin with long alkyl chains could improve their emulsification efficiency. The detailed experiments of emulsion polymerization of methyl methacrylate and butyl acrylate using these hemiesters as sole surfactants showed that SMA‐C12‐75, SMA‐C14‐70, and SMA‐C16‐65 were good surfactants. In the end, we successfully prepared stable latexes using above three good surfactants with relatively low surfactant concentration and high solid content. Characterization of latexes by Zetasizer and transmission electron microscopy revealed that particles of these latexes have core‐shell nanostructure with average particle size below 60 nm. Compared with SMA, the improvement of emulsification efficiency of its hemiesters may come from the better hydrophilic‐lipophilic balance and steric stabilization after incorporation of long alkyl chain. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigation of enzymatic biodiesel production using ionic liquid as a co‐solvent

In this study, the lipase catalysed esterification reaction for biodiesel production was investigated in the presence of the ionic liquid [BMIM][PF₆]. Unlike regular organic solvents, many ionic liquids have no vapour pressure, and are therefore considered non‐volatile. When used in systems with enzyme catalysts, ionic liquids may enhance their activity, selectivity, and stability. The use of an enzyme (lipase) as a catalyst, and the ionic liquid as a solvent/immobilization agent also represents an environmentally friendly, “green” technology. Methyl acetate was used as the acyl acceptor as opposed to the more commonly used methanol due to the negative effects methanol and the glycerol by‐product has on lipase enzyme activity. The results of this research indicate that methyl oleate (i.e., biodiesel) was successfully produced, with an 80% overall biodiesel yield in the presence of ionic liquid, at a 1:1 ratio (v/v) to the amount of oil. This verified that the presence of an ionic liquid, at a specified amount, improved the activity of the lipase and the overall biodiesel yield. Results also indicate the addition of ionic liquid facilitated the separation of the methyl esters from the triacetylglycerol by‐product. The best conditions investigated was found to be: 14:1 molar ratio between oil and acyl acceptor; 20% (w immobilised lipase/w of oil; and a temperature in the range of 48–55°C. However, additional purification is required in order for the produced biodiesel to meet ASTM standards.