Temperature gradient-based high-cell density fed-batch fermentation for the production of pyruvate oxidase by recombinant E. coli

Pyruvate oxidase (PyOD) is a very powerful enzyme for clinical diagnostic applications and environmental monitoring. Influences of temperature on cell growth, plasmid stability, and PyOD expression during the PyOD fermentation process by recombinant Escherichia coli were investigated. Based on the influences of temperature on the physiological metabolism, a novel high-cell density fed-batch cultivation with gradient temperature decrease strategy for effective PyOD production was achieved, under which the biomass (OD₆₀₀) of recombinant E. coli could reach to 71 and the highest PyOD activity in broth could reach to 3,307 U/L in 26?hr fermentation.     

Expression of various genes to enhance ubiquinone metabolic pathway in Agrobacterium tumefaciens

Ubiquinone (UQ), a lipid-soluble component, acts as a mobile component of the respiratory chain by playing an essential role in the electron transport system in many organisms, and has been widely used in pharmaceuticals due to its antioxidant property. The biosynthesis of UQ involves 10 sequential reactions brought about by various enzymes. In this study, dps gene, which encodes decaprenyl diphosphate synthase, involved in ubiquinone biosynthesis from Agrobacterium tumefaciens, and coq2 gene of Saccharomyces cerevisiae, ppt1 gene of Schizosaccahromyces pombe and ubiA gene of Escherichia coli, all of them encoding 4-hydroxybenzoate:polyprenyl diphosphate (4-HB:PPP) transferase, were reconfigured into an operon under the control of a single promoter to yield various plasmids including pBIV-dps, pBIV-dpsq, pBIV-dpsp and pBIV-dpsca. The recombinant A. tumefaciens containing dps-ubiC-ubiA gene showed the highest level ubiquinone production than that of the other recombinants and the nonrecombinant bacterium. In an aerobic fed-batch fermentation, A. tumefaciens containing the pBIV-dpsca plasmid produced 25.2 mg of ubiquinone-10 per liter which was 1.68 times higher than that of nonrecombinant type. While in microaerobic fed-batch fermentation, recombinant cell pBIV-dpsca produced 30.8 mg L⁻¹ of ubiquinone-10. Compared to the original A. tumefaciens, the ubiquinone-10 yield and productivities of the recombinant bacterium pBIV-dpsca increased 88.9% and 77.7%, respectively, under microaerobic fed-batch conditions.     

Large-scale production of endotoxin-free plasmids for transient expression in mammalian cell culture

Transient expression of recombinant proteins in mammalian cell culture in a 100-L scale requires a large quantity of plasmid that is very labour intensive to achieve with shake flask cultures and commercially available plasmid purification kits. In this paper we describe a process for plasmid production in 100-mg scale. The fermentation is carried out in a 4-L fed-batch culture with a minimal medium. The detection of the end of batch and triggering the exponential (0.1 h(-1)) feed profile was unattended and controlled by Multi-fermenter Control System. A restricted specific growth rate in fed-batch culture increased the specific plasmid yield compared to batch cultures with minimal and rich media. This together with high biomass concentration (68-107 g L(-1) wet weight) achieves high volumetric yields of plasmid (95-277 mg L(-1) depending on the construct). The purification process consisted of alkaline lysis, lysate clarification and ultrafiltration, two-phase extraction with Triton X-114 for endotoxin removal, anion-exchange chromatography as a polishing step, ultrafiltration and sterile filtration. Both fermentation and purification processes were used without optimisation for production of four plasmids yielding from 39 to 163 mg of plasmids with endotoxin content of 2.5 EU mg(-1) or less.     

人源性抗HBsAg Fab抗体的发酵生产研究

为了适应工业生产的需要,利用fed—batch方法,重组人源性抗HBsAg Fab抗体酵母工程菌在30L发酵罐中进行了高密度发酵,发酵最适温度30℃,pH值范围5．0～5．3,溶氧范围20％～30％。发酵液OD600值达到300时开始诱导,甲醇最佳诱导浓度为10mL／L。重组人源性抗HBsAg Fab抗体经离子交换层析纯化,纯化产品经SDS-PAGE、Western blot进行分析和ELISA方法进行活性测定。结果显示,重组Fab抗体在Fed-batch发酵系统中可高效表达,经过192h的发酵生产,重组人源性抗HBsAg Fab抗体的表达量可达412mg／L。发酵上清经过离子交换层析纯化,获得纯度为95％的重组Fab抗体,该Fab抗体经ELISA分析具有较高的HBsAg抗原亲和力和特异性。结果证实可以通过高密度发酵毕赤酵母工程菌来高效生产重组人源性抗HBsAg Fab抗体,为后续的工业化生产应用奠定了基础。     

pcD-awte候选疟疾DNA疫苗制备及其质量相关性分析

本实验室构建的疟疾DNA疫苗经动物试验表明具有很好的免疫原性,为申请临床试验,进行了制备工艺的研究。本研究将含pcD-awte质粒的大肠杆菌DH5α在发酵罐中发酵培养,碱裂解法粗提质粒,再依次通过Sepharose 6FF分子筛层析、Plasmidselect 亲硫吸附层析和Source 30Q离子交换层析精制获得质粒纯品,并对纯品进行质量分析。结果每升培养液可获得质粒纯品43.9mg,质量符合Ferreira等推荐的药用标准。     

Spectral analysis of the effect of inflow noise on a fed-batch fermentation for recombinant β-galactosidase

The fermentative production of β-galactosidase from Escherichia coli CSH50 containing the plasmid pOU140 is mechanistically complex and difficult to model in a nonideal bioreactor. A spectral analysis has been done for a fed-batch fermentation with Gaussian disturbances in the feed stream. Inflow noise converts a smooth operation into aperiodic motion, as observed in some chemical reactions also. The disturbances also cause significant differences in the frequency responses of intra-cellular (plasmid DNA and β-galactosidase) and extra-cellular (concentration and mass fraction of recombinant cells) variables, whose implications are discussed.     

Efficient strategies to enhance plasmid stability for fermentation of recombinant Escherichia coli harboring tyrosine phenol lyase

Objective

To solve the bottleneck of plasmid instability during microbial fermentation of l-DOPA with recombinant Escherichia coli expressing heterologous tyrosine phenol lyase.

Results

The tyrosine phenol lyase from Fusobacterium nucleatum was constitutively expressed in E. coli and a fed-batch fermentation process with temperature down-shift cultivation was performed. Efficient strategies including replacing the original ampicillin resistance gene, as well as inserting cer site that is active for resolving plasmid multimers were applied. As a result, the plasmid stability was increased. The co-use of cer site on plasmid and kanamycin in culture medium resulted in proportion of plasmid containing cells maintained at 100% after fermentation for 35 h. The specific activity of tyrosine phenol lyase reached 1493 U/g dcw, while the volumetric activity increased from 2943 to 14,408 U/L for l-DOPA biosynthesis.

Conclusions

The established strategies for plasmid stability is not only promoted the applicability of the recombinant cells for l-DOPA production, but also provides important guidance for industrial fermentation with improved microbial productivity.

     

Expression of various genes to enhance ubiquinone metabolic pathway in Agrobacterium tumefaciens

Ubiquinone (UQ), a lipid-soluble component, acts as a mobile component of the respiratory chain by playing an essential role in the electron transport system in many organisms, and has been widely used in pharmaceuticals due to its antioxidant property. The biosynthesis of UQ involves 10 sequential reactions brought about by various enzymes. In this study, dps gene, which encodes decaprenyl diphosphate synthase, involved in ubiquinone biosynthesis from Agrobacterium tumefaciens, and coq2 gene of Saccharomyces cerevisiae, ppt1 gene of Schizosaccahromyces pombe and ubiA gene of Escherichia coli, all of them encoding 4-hydroxybenzoate:polyprenyl diphosphate (4-HB:PPP) transferase, were reconfigured into an operon under the control of a single promoter to yield various plasmids including pBIV-dps, pBIV-dpsq, pBIV-dpsp and pBIV-dpsca. The recombinant A. tumefaciens containing dps-ubiC-ubiA gene showed the highest level ubiquinone production than that of the other recombinants and the nonrecombinant bacterium. In an aerobic fed-batch fermentation, A. tumefaciens containing the pBIV-dpsca plasmid produced 25.2 mg of ubiquinone-10 per liter which was 1.68 times higher than that of nonrecombinant type. While in microaerobic fed-batch fermentation, recombinant cell pBIV-dpsca produced 30.8 mg L⁻¹ of ubiquinone-10. Compared to the original A. tumefaciens, the ubiquinone-10 yield and productivities of the recombinant bacterium pBIV-dpsca increased 88.9% and 77.7%, respectively, under microaerobic fed-batch conditions.     

High-density Escherichia coli cultivation process for hyperexpression of recombinant porcine growth hormone.

Fermentation studies were performed on an Escherichia coli culture that carries a recombinant plasmid composed of an ampicillin-resistant gene, a temperature-regulated pL promoter, and a porcine pituitary cDNA sequence coding for growth hormone. The objective was to achieve high cell density while maintaining the specific expression level of recombinant porcine growth hormone (r-pGH) observed in shake flasks. At a specific expression level of 20% of total cell protein, the cell density of a glucose-limited fed-batch process reached 38 units of OD600 in 14 h, compared to flask cultivation, which resulted in only 1.4 units of OD600 in the same period. The observed critical fermentation conditions for maximal expression included (1) limiting glucose concentration below 1 g l-1 throughout the fed-batch growth and induction phases, (2) keeping postinduction temperature at 42 degrees C for 5-7 h, and (3) maintaining a postinduction growth rate around 0.17-0.21 h-1.     

High-cell-density fermentation of recombinant Saccharomyces cerevisiae using glycerol

To obtain a high cell density of recombinant Saccharomyces cerevisiae (INVSc 1 strain bearing a 2 microm plasmid, pYES2 containing a GAL1 promoter for expression of the beta-galactosidase gene), the yeast was grown with glycerol as the substrate by fed-batch fermentation. The feeding strategy was based on an on-line response of the medium pH to the consumption of glycerol. The approach was to feed excess carbon into the medium to create a benign environment for rapid biomass buildup. During cell growth in the presence of glycerol, the release of protons in the medium caused a decrease in pH and the consumption rate of ammonium phosphate served as an on-line indicator for the metabolic rate of the organism. The extent of glycerol feeding in a fed-batch mode with pH control at 5.0 +/- 0.1 was ascertained from the automatic addition of ammonium phosphate to the medium. The glycerol feeding to ammonium phosphate addition ratio was found to be 2.5-3.0. On the basis of the experiments, a maximum dry cell biomass of 140 g per liter and a productivity of 5.5 g DCW/L/h were achieved. The high cell density of S. cerevisiae obtained with good plasmid stability suggested a simple and efficient fermentation protocol for recombinant protein production.     

Effect of cycle time on fungal morphology, broth rheology, and recombinant enzyme productivity during pulsed addition of limiting carbon source

For many years, high broth viscosity has remained a key challenge in large-scale filamentous fungal fermentations. In previous studies, we showed that broth viscosity could be reduced by pulsed addition of limiting carbon during fed-batch fermentation. The objective in this study was to determine how changing the frequency of pulsed substrate addition affects fungal morphology, broth rheology, and recombinant enzyme productivity. To accomplish this, a series of duplicate fed-batch fermentations were performed in 20-L fermentors with a recombinant glucoamylase producing strain of Aspergillus oryzae. The total cycle time for substrate pulsing was varied over a wide range (30-2,700 s), with substrate added only during the first 30% of each cycle. As a control, a fermentation was conducted with continuous substrate feeding, and in all fermentations the same total amount of substrate was added. Results show that the total biomass concentration remained relatively unaltered, while a substantial decrease in the mean projected area of fungal elements (i.e., average size) was observed with increasing cycle time. This led to reduced broth viscosity and increased oxygen uptake rate. However, high values of cycle time (i.e., 900-2,700 s) showed a significant increase in fungal conidia formation and significantly reduced recombinant enzyme productivity, suggesting that the fungi channeled substrate to storage compounds rather than to recombinant protein. In addition to explaining the effect of cycle time on fermentation performance, these results may aid in explaining the discrepancies observed on scale-up to larger fermentors.     

Enhanced production of D-(-)-3-hydroxybutyric acid by recombinant Escherichia coli

Wild-type bacteria including Escherichia coli normally do not produce extracellular D-(-)-3-hydroxybutyric acid (3HB). To produce extracellular chiral 3HB, a new pathway for synthesis of 3HB was constructed by simultaneous expression of genes of beta-ketothiolase (phbA), acetoacetyl-CoA reductase (phbB), phosphor-transbutyrylase (ptb) and butyrate kinase (buk) in E. coli strain DH5alpha. E. coli DH5alpha containing any one of the four plasmids pBHR69, pUCAB, p68CM or pKKAB that harbor the phbA and phbB genes produced small amounts of 3HB, ranging from 75 to 400 mg l(-1), while E. coli DH5alpha harboring p68CMPTK containing genes of phbA, phbB, ptb and buk increased the 3HB concentration to 1.4 g l(-1) in shake flasks supplemented with LB broth and 20 g l(-1) glucose. 3HB production was further improved to over 2 g l(-1) in shake flasks when E. coli DH5alpha hosted two plasmids simultaneously that separately contained phbA and phbB in one plasmid while ptb and buk in the other. A batch fermentation run in a 5-l fermenter produced approximately 5 g l(-1) 3HB after 24 h. A fed-batch process increased 3HB production to 12 g l(-1) after 48 h of fermentation.     

Fed-batch xylitol production with two recombinant Saccharomyces cerevisiae strains expressing XYL1 at different levels, using glucose as a cosubstrate: a comparison of production parameters and strain stability

Xylitol production with two recombinant Sacharomyces cerevisiae strains expressing the XYL1 gene, coding for xylose reductase (XR), at different levels, the 'low XR strain' at 0.51 U/mg and the 'high XR strain' at 10.8 U/mg, was compared in batch and fed-batch culture. Xylose was not consumed in the presence of high glucose concentrations, because both sugars are transported by the glucose transport system, which has a higher affinity for glucose than for xylose. When glucose was fed gradually to the culture, high concentrations were avoided, and xylose was converted to xylitol with a specific productivity of 0.10 g g(-1) h(-1) attained with the low XR strain and 0.19 g g(-1) h(-1) with the high XR strain, indicating that factors other than the XR-activity control the rate of xylose conversion.The overproduction of XR put a substantial protein burden on the high XR strain, contributing to a 50% decrease in specific growth rate and reduced biomass yield compared with the low XR strain. Despite the use of selective medium, the stability of the high XR strain was poor in long fed-batch and chemostat cultures, whereas the low XR strain was stable. The high XR strain lost its XR activity almost completely in some fed-batch cultures and in chemostat culture. In chemostat cultivation, part of the population lost the plasmid harboring the XR gene. This was due to the fact that leucine was released into the broth from plasmid containing cells, which enabled some cells to grow without the plasmid containing the LEU2 auxotrophic complementation selection marker. Furthermore, isolation and analysis of plasmids from a population that had lost its XR activity, showed that in addition to the original plasmid, a rearranged form of the plasmid, retaining the selection marker but not the expression of active XR, was present. However, these observations could only partly explain the decrease in XR activity. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 391-399, 1997.     

Microbial growth kinetics of fed-batch fermentations

Summary Fed-batch fermenters are generally operated with the addition of small doses of nutrients, therefore the volume of the fermentation broth increases with time. Batch fermenters generally contain and almost constant volume of broth and a logistic equation has been commonly employed to simulate microbial growth in them. Mass balances were determined with fed-batch fermentation to obtain expressions which account for the effect of volume increase and the subsequent dilution of the biomass. A growth rate expression was obtained for fed-batch fermentations. The new expression was very similar to the logistic equation. Therefore an anology between the values of the parameters of the new model and of the logistic equation was sought. The new model was also employed to simulate six sets of data from the literature and satisfactory results were obtained.     

温度对大肠杆菌L-色氨酸发酵过程的影响

目的：研究变温控制对大肠杆菌TRTH L-色氨酸补料分批发酵过程中生物量、色氨酸产量、比生长速率及质粒稳定性的影响。方法：利用5L自控发酵罐对L-色氨酸补料分批发酵过程进行温度控制,对不同温度下相关参数进行分析比较,确定优化的温度控制方案。结果：以30-36％顺序升温的工艺进行发酵得到理想结果,与单一温度控制策略相比,L-色氨酸产量提高了15．4％;色氨酸的比合成速率提高了21．6％;质粒稳定性增加,未出现质粒丢失现象,质粒拷贝数保持在恒定水平。结论：温度对大肠杆菌L-色氨酸发酵有重要影响。     

Growth monitoring and control through computer-aided on-line mass balancing in a fed-batch penicillin fermentation

A computer-aided methodology is developed for on-line monitoring and control of cell growth in fed-batch penicillin fermentation using a semidefined medium containing low corn steep liquor concentration (5.7 g/L). Cell growth is monitored and controlled with the use of experimental correlation and carbon-balancing equatiions on a real-time basis throughout the fermentation. Through a combination of feed-forward and feedback control of sugar addition, residual glucose concentration in the broth was maintained below 1 g/L and cell-growth rate was kept at constant at preset vaiues. The accuracy and reproducibility of this technique are demonstrated. The use of real-time control of cell growth is expected to aid future investigations of this antibiotic fermentation.     

Comparison of three different promoter systems for secretory alpha-amylase production in fed-batch cultures of recombinant Saccharomyces cerevisiae

Cloned gene expression in recombinant Saccharomyces cerevisiae 20B-12 containing three different plasmids was compared in batch and fed-batch cultures. The plasmids pNA3, pNA7, and pNA9 contain the alpha-amylase gene under the control of SUC2, PGK, and GAL7 Promoters, respectively. The synthesis of alpha-amylase was therefore induced by low glucose concentration for the SUC2 and PGK promoters, and by galactose for GAL7 promoter. The specific cell growth rates were similar among cells harboring the three different plasmids; they decreased from 0.35 to 0.38 h(-1) during the cell growth phase to 0.03 to 0.06h(-1) during the production phase. The secretory alpha-amylase activity of cells harboring plasmid pNA7 was 129 U/mL in fed-batch culture, which was 1.4 and 2 times as high as the activities of cells harboring plasmids pNA3 and pNA9, respectively. The secretion ratios (amount of extracellular alpha-amylase activity/amounts of total alpha-amylase activity) of cells harboring plasmids pNA3, pNA7, and pNA9 were 91.4%, 94.5%, and 95.3%, respectively. (c) 1993 Wiley & Sons, Inc.     

Plasmid vector for cloning in Streptococcus pneumoniae and strategies for enrichment for recombinant plasmids

A new plasmid, pLS101, was constructed for use as a vector for cloning in Streptococcus pneumoniae. This plasmid carries two selectable genes, tet and malM, each of which contains two or more restriction sites for cloning. Insertional inactivation of the malM gene allowed direct selection of TcRMal- clones containing recombinant plasmids. Other means of enriching a recipient population for cells containing recombinant plasmids were examined. The effect of removing vector terminal phosphate in attempts to clone heterogeneous DNA fragments, such as those from chromosomal DNA, was to abolish recombinant plasmid establishment altogether, presumably because donor DNA processing during entry into the cell prevented establishment of the hemiligated molecule. However, with homogeneous DNA fragments, such as those from plasmid or viral DNA, vector phosphate removal allowed enrichment for recombinant plasmids. In the cloning of heterogeneous DNA that was homologous to the recipient chromosome (i.e. chromosomal DNA from S. pneumoniae), recovery of recombinant plasmids could be enriched tenfold (relative to the regenerated vector) by the process of chromosomal facilitation of plasmid establishment. This involved an additional passage of the mixed plasmids in which interaction with the chromosome of plasmids containing chromosomal DNA inserts (i.e. recombinant plasmids) increased their frequency of establishment relative to the vector plasmid. An overall strategy for cloning in S. pneumoniae, depending on the nature of the fragment to be cloned, is proposed.