Galactose-limited fed-batch cultivation of Escherichia coli for the production of lacto-N-tetraose

Lacto-N-tetraose (Gal(β1-3)GlcNAc(β1-3)Gal(β1-4)Glc) is one of the most abundant oligosaccharide structures in human milk. We recently described the synthesis of lacto-N-tetraose by a whole-cell biotransformation with recombinant Escherichia coli cells. However, only about 5% of the lactose was converted into lacto-N-tetraose by this approach. The major product obtained was the intermediate lacto-N-triose II (GlcNAc(β1-3)Gal(β1-4)Glc).In order to improve the bioconversion of lactose to lacto-N-tetraose, we have investigated the influence of the carbon source on the formation of lacto-N-tetraose and on the intracellular availability of the glycosyltransferase substrates, UDP-N-acetylglucosamine and UDP-galactose. By growth of the recombinant E. coli cells on D-galactose, the yield of lacto-N-tetraose (810.8 mg L⁻¹ culture) was 3.6-times higher compared to cultivation on D-glucose.Using fed-batch cultivation with galactose as sole energy and carbon source, a large-scale synthesis of lacto-N-tetraose was demonstrated. During the 26 h feeding phase the growth rate (μ = 0.05) was maintained by an exponential galactose feed. In total, 16 g L⁻¹ lactose were fed and resulted in final yields of 12.72 ± 0.21 g L⁻¹ lacto-N-tetraose and 13.70 ± 0.10 g L⁻¹ lacto-N-triose II. In total, 173 g of lacto-N-tetraose were produced with a space-time yield of 0.37 g L⁻¹ h⁻¹.     

Use of fed-batch cultivation for achieving high cell densities for the pilot-scale production of a recombinant protein (phenylalanine dehydrogenase) in Escherichia coli

A fed-batch process for the high cell density cultivation of E. coli TG1 and the production of the recombinant protein phenylalanine dehydrogenase (PheDH) was developed. A model based on Monod kinetics with overflow metabolism and incorporating acetate utilization kinetics was used to generate simulations that describe cell growth, acetate production and reconsumption, and glucose consumption during fed-batch cultivation. Using these simulations a predetermined feeding profile was elaborated that would maintain carbon-limited growth at a growth rate below the critical growth rate for acetate formation (mu < mu(crit)). Two starvation periods are incorporated into the feed profile in order to induce acetate utilization. Cell concentrations of 53 g dry cell weight (DCW)/L were obtained with a final intracellular product concentration of recombinant protein corresponding to approximately 38% of the total cell protein. The yield of PheDH was 129 U/mL with a specific activity of 1.2 U/mg DCW and a maximum product formation rate of 0.41 U/mg DCW x h. The concentration of aectate was maintained below growth inhibitory levels until 3 h before the end of the fermentation when the concentration reached a maximum of 10.7 g/L due to IPTG induction of the recombinant protein.     

Comparison of polysialic acid production in Escherichia coli K1 during batch cultivation and fed-batch cultivation applying two different control strategies

The polysialic acid (PSA) production in Escherichia coli (E. coli) K1 was studied using three different cultivation strategies. A batch cultivation, a fed-batch cultivation at a constant specific growth rate of 0.25 h⁻¹ and a fed-batch cultivation at a constant glucose concentration of 50 mg l⁻¹ was performed. PSA formation kinetics under different cultivation strategies were analyzed based on the Monod growth model and the Luedeking-Piret equation. The results revealed that PSA formation in E. coli K1 was completely growth associated, the highest specific PSA formation rate (0.0489 g g⁻¹ h⁻¹) was obtained in the batch cultivation. However, comparing biomass and PSA yields on the glucose consumed, both fed-batch cultivations provided higher yields than that of the batch cultivation and acetate formation was prevented. Moreover, PSA yield on glucose was also correlated to the specific growth rate of the cells. The optimal specific growth rate for PSA production was 0.32 h⁻¹ obtained in the fed-batch cultivation at a constant glucose concentration of 50 mg l⁻¹, with highest conversion efficiency of 43 mg g⁻¹.     

A simple feedback control of Escherichia coli growth for recombinant aldolase production in fed-batch mode

Fed-batch production of recombinant fuculose-1-phosphate aldolase (FucA) by Escherichia coli XL1 Blue MRF′ (pTrcfuc) has been automated by using a simple feedback specific growth rate control strategy. Non-induced continuous cultures were conducted in order to characterize substrate consumption and carbon dioxide production yields and rates. In fed-batch cultures, substrate feeding rate was adjusted using on-line biomass estimation based on exhaust gas analysis and macroscopic mass balances. Overexpression of recombinant protein induced by isopropyl-β-d-thiogalactopyranoside (IPTG) under trc promoter did not affect significantly the control of specific growth rate during 7 h after induction. Growth and protein production curves were parallel until high level of protein expression started to inhibit cell growth. The proposed specific growth rate control strategy has been successfully applied to both non-induced and induced fed-batch cultures that do not exhibit severe growth rate depression.     

High-level production of human leptin by fed-batch cultivation of recombinant Escherichia coli and its purification.

Human leptin is a 16-kDa (146-amino-acid) protein that is secreted from adipocytes and influences body weight homeostasis. In order to obtain high-level production of leptin, the human obese gene coding for leptin was expressed in Escherichia coli BL21(DE3) under the strong inducible T7 promoter. The recombinant leptin was produced as inclusion bodies in E. coli, and the recombinant leptin content was as high as 54% of the total protein content. For production of recombinant human leptin in large amounts, pH-stat fed-batch cultures were grown. Expression of leptin was induced at three different cell optical densities at 600 nm (OD600), 30, 90, and 140. When cells were induced at an OD600 of 90, the amount of leptin produced was 9.7 g/liter (37% of the total protein). After simple purification steps consisting of inclusion body isolation, denaturation and refolding, and anion-exchange chromatography, 144.9 mg of leptin that was more than 90% pure was obtained from a 50-ml culture, and the recovery yield was 41.1%.     

重组类人胶原蛋白工程菌补料发酵过程建模

对产类人胶原蛋白的重组大肠杆菌Escherichia coli(E. Coli) 的批式和分批-补料培养动力学进行了研究。通过检测发酵过程的基质浓度、菌体量和产物浓度,建立了一组反映发酵的动力学模型,并考虑了非工程菌存在的影响,分析了细胞生长、底物消耗、基因工程产物生成的过程,结果显示该动力学模型可以很好的拟合发酵过程。     

Soft sensor control of metabolic fluxes in a recombinant Escherichia coli fed-batch cultivation producing green fluorescence protein

A soft sensor approach is described for controlling metabolic overflow from mixed-acid fermentation and glucose overflow metabolism in a fed-batch cultivation for production of recombinant green fluorescence protein (GFP) in Escherichia coli. The hardware part of the sensor consisted of a near-infrared in situ probe that monitored the E. coli biomass and an HPLC analyzer equipped with a filtration unit that measured the overflow metabolites. The computational part of the soft sensor used basic kinetic equations and summations for estimation of specific rates and total metabolite concentrations. Two control strategies for media feeding of the fed-batch cultivation were evaluated: (1) controlling the specific rates of overflow metabolism and mixed-acid fermentation metabolites at a fixed pre-set target values, and (2) controlling the concentration of the sum of these metabolites at a set level. The results indicate that the latter strategy was more efficient for maintaining a high titer and low variability of the produced recombinant GFP protein.     

Simplified feeding strategies for the fed-batch cultivation of Kluyveromyces lactis GG799 for enhanced recombinant xylanase production

A xylanase gene (xyn2) from Trichoderma reesei ATCC 58350 was previously cloned and expressed in Kluyveromyces lactis GG799. The production of the recombinant xylanase was conducted in a developed medium with an optimised batch and with fed-batches that were processed with glucose. The glucose served as a carbon source for cell growth and as an inducer for xylanase production. In a 1-L batch system, a glucose concentration of 20 g L^?1 and 80 % dissolved oxygen were found to provide the best conditions for the tested ranges. A xylanase activity of 75.53 U mL^?1 was obtained. However, in the batch mode, glucose depletions reduced the synthesis of recombinant xylanase by K. lactis GG799. To maximise the production of xylanase, further optimisation was performed using exponential feeding. We investigated the effects of various nitrogen sources combined with the carbon to nitrogen (C/N) molar ratio on the production of xylanase. Of the various nitrogen sources, yeast extract was found to be the most useful for recombinant xylanase production. The highest xylanase production (110.13 U mL^?1) was measured at a C/N ratio of 50.08. These conditions led to a 45.8 % increase in xylanase activity compared with the batch cultures. Interestingly, the further addition of 500 g L^?1 glucose led to a 6.2-fold increase (465.07 U mL^?1) in recombinant xylanase activity. These findings, together with those of the exponential feeding strategy, indicate that the composition of the C/N molar ratio has a substantial impact on recombinant protein production in K. lactis.     

Closed-loop control of fed-batch cultures of recombinant Escherichia coli using on-line HPLC

This article describes a fully automated system for the on-line monitoring and closed-loop control of a fed-batch fermentation of recombinant Escherichia coli, and presents two case studies of its used in limiting production of unwanted byproducts such as acetic in fed-batch fermentations. The system had two components. The first components, on-line monitoring, comprised an aseptic sampling device, a microcentrifuge, and HPLC System. These instruments removed a Sample from a fermentor, spun it at high speed to separate solid and liquid components, and then automatically injected the supernatant onto an HPLC column for analysis. The second component consisted of control algorithms programmed using the LabView visual programming environment in a control computer that was linked via a remote components were linked so that results from the on-line HPLC were captured and used by the control algorithm was designed to demonstrate coarse feedback control to confirm the operability of the controller. The second case study showed how the system could be used in a more sophisticated feedings strategy providing fine control and limiting acetate concentration to a low level throughout the fermentation. (c) 1994 John Wiley & Sons, Inc.     

High-level production of bacillus subtilis glycine oxidase by fed-batch cultivation of recombinant Escherichia coli Rosetta (DE3)

A fed-batch process for the high cell density cultivation of Escherichia coli Rosetta (DE3) and the production of the recombinant protein glycine oxidase (GOX) from Bacillus subtilis was developed. GOX is a deaminating enzyme that shares substrate specificity with d-amino acid oxidase and sarcosine oxidase and has great biotechnological potential. The B. subtilis gene coding for GOX was expressed in E. coli Rosetta under the strong inducible T7 promotor of the pET28a vector. Exponential feeding based on the specific growth rate and a starvation period for acetate utilization was used to control cell growth, acetate production, and reconsumption and glucose consumption during fed-batch cultivation. Expression of GOX was induced at three different cell densities (20, 40, and 60 g . L(-1)). When cells were induced at intermediate cell density, the amount of GOX produced was 20 U . g(-1) cell dry weight and 1154 U . L(-1) with a final intracellular protein concentration corresponding to approximately 37% of the total cell protein concentration. These values were higher than those previously published for GOX expression and also represent a drastic decrease of 26-fold in the cost of the culture medium.     

Simple control of fed-batch processes for recombinant protein production with E. coli

A very simple but effective process control technique is proposed that leads to a high batch-to-batch reproducibility with respect to biomass concentration as well as the specific biomass growth rate profiles in E. coli fermentations performed during recombinant protein production. It makes use of the well-established temperature controllers in currently used fermenters, but takes its information from the difference between the controlled culture temperature T (cult) and the temperature T (coolin) of the coolant fed to the fermenter's cooling jacket as adjusted by the fermenter temperature controller. For process control purposes this measured difference is corrected regarding stirrer influences and cumulated before it is used as a new process control variable. As a spin-off of this control, it becomes possible to estimate online the oxygen mass transfer rates and the corresponding k(L)a values during the real cultivation process.     

Enhancement of recombinant cholera toxin B subunit production in Escherichia coli by applying a fed-batch control strategy

Summary High production levels of recombinant cholera toxin B subunit in Escherichia coli were obtained with the design of an efficient fed-batch process and control strategy. The fed-batch results demonstrated a biomass production of 58 g/L (Cell Dry Weight) attaining production levels of heterologous protein of 4.7g/L in the intracellular fraction, 0.96 g/L exported into the periplasm and 0.27 g/L secreted into the culture supernatant.     

Constitutive production of human leptin by fed-batch culture of recombinant rpoS- Escherichia coli

High-level production of human leptin by fed-batch culture of recombinant Escherichia coli using constitutive promoter system was investigated. For the constitutive expression of the obese gene encoding human leptin, the strong constitutive HCE promoter cloned from the D-amino acid aminotransferase gene of Geobacillus toebii was used. To develop an optimal host-vector system, several different recombinant E. coli strains were compared for leptin production. In flask cultures, E. coli FMJ123, which is a rpoS mutant strain, showed the highest level of leptin production (41% of total proteins). By comparing the expression levels of leptin in several different rpoS- and rpoS+ strains, it could be concluded that rpoS mutation positively affected constitutive production of leptin. For the large-scale production of human leptin, fed-batch cultures of recombinant E. coli FMJ123 were carried out using three different feeding solutions--chemically defined, yeast extract-containing, and casamino acid-containing feeding solutions. Among these, the use of casamino acid-containing feeding solution allowed production of leptin up to 2.1 g/L, which was 2.1- and 1.8-fold higher than that obtained with chemically defined and yeast extract-contained feeding solutions, respectively. These results suggest that the HCE promoter can be used for the efficient production of leptin, and most likely other recombinant proteins, in a constitutive manner.     

High cell density cultivation of recombinant Escherichia coli for prodrug of recombinant human GLPs production

Glucagon-like peptide-1 (GLP-1)(2) has been attracting increasing interest on account of its prominent benefits in type 2 diabetes. However, its clinical applications are limited by the short half-life in vivo. To overcome this limitation, a new polymer of GLP-1 was developed by prodrug strategy. In this study a recombinant protein, rhGLPs, was successfully constructed, cloned into plasmid pET30a (+) and expressed in Escherichia coli ArcticExpress(DE3)RP in the form of inclusion body. The recombinant fusion protein productivity could be enhanced by high cell density culture of the recombinant strain. As a result, about 40g wet weight cells per liter were obtained. The protein was purified by size-exclusion chromatography on a Superdex 75 column and refolded using reverse dilution and dialysis methods. SDS-PAGE, HPLC and MALDI-TOF mass spectrometry were undertaken to determine the purity and molecular weight of rhGLPs. Bioactivity assay revealed that it had glucose-lowering and insulin-releasing action in vivo.     

Simple fed-batch technique for high cell density cultivation of Escherichia coli

A simple fed-batch process for high cell density cultivation of Escherichia coli TG1 was developed. A pre-determined feeding strategy was chosen to maintain carbon-limited growth using a defined medium. Feeding was carried out to increase the cell mass concentration exponentially in the bioreactor controlling biomass accumulation at growth rates which do not cause the formation of acetic acid (μ < μ_crit). Cell concentrations of 128 and 148 g per 1 dry cell weight (g 1⁻¹ DCW) were obtained using glucose or glycerol as carbon source, respectively.     

Optimization of a cultivation process for recombinant protein production by Escherichia coli.

A single-stage fed-batch bioprocess for the production of a recombinant protein beta-galactosidase, by E. coli has been developed. The XL1-blue strain of E. coli which harbors a multi-number foreign plasmid PT was cultured in a reformulated medium. Critical medium components were selected and their respective concentrations were optimized with the Orthogonal Table method. An exponential substrate feeding schedule was used to maintain optimum conditions. Inhibition of growth and protein expression caused by excessive concentrations of glucose and acetate was investigated and subsequently minimized with an incremental nutrient feeding schedule which limited the specific growth rate of a culture. The program necessary to facilitate the control of substrate addition is fully described. This program has been used with a 2.5 l bioreactor and a commercially available software package for optimization without on-line or off-line measurement of optical density (OD), CO2, glucose or acetate. The optimized fed-batch process limited the acetate concentration to less than 20 mM; maintained an exponential growth phase for 50 h; and produced a cell density of 51 g l-1 dry cell weight (DCW) or 154 OD600 with a beta-galactosidase activity of 990 U ml-1.     

High cell density cultivation of recombinant Escherichia coli for hirudin variant 1 production

A synthetic medium, TK-25, for high cell density cultivation (HCDC) of Escherichia coli K-12 was modified to support HCDC of strain JM109. By optimizing the culture conditions, the cell concentration of 65 g/l in 14 h was obtained in the optimized medium, namely TK-10, with glucose-fed batch cultivation. When these conditions were further applied for HCDC of E. coli JM109 harboring pUC-based recombinant plasmid which expresses a hirudin variant, HV-1-fused protein under the control of trp promoter, it grew to 24 g/l of dried cells expressed as an inclusion body as 15.9% of the total protein, corresponding to 1908 mg/l hirudin-fused protein.     

High level production of human proapo A-I by fed-batch culture of recombinant Escherichia coli

Three Escherichia coli strains, two recA⁻ strains (DH1 and YK537) and one recA⁺ strain (KS476) harboring human proapo A-I expression plasmid pUS(pAI), were cultivated in fed-batch mode using a synthetic medium and the amounts of human proapo A-I accumulation were compared under various cultivation conditions. In the expression plasmid, nine proapo A-I genes were tandemly ligated downstream of the tac promoter. Experimental results indicated that selection of the host strain and cultivation temperature was important. Among the three E. coli strains checked, strain DH1 yielded the most effective production of human proapo A-I at 30°C.