Over-production of human interferon-γ by HCDC of recombinant Escherichia coli

Giving the cells what they need when they need it: Biosensor-based feeding control

"Giving the cells exactly what they need, when they need it" is the core idea behind the proposed bioprocess control strategy: operating bioprocess based on the physiological behavior of the microbial population rather than exclusive monitoring of environmental parameters. We are envisioning to achieve this through the use of genetically encoded biosensors combined with online flow cytometry (FCM) to obtain a time-dependent "physiological fingerprint" of the population. We developed a biosensor based on the glnA promoter (glnAp) and applied it for monitoring the nitrogen-related nutritional state of Escherichia coli. The functionality of the biosensor was demonstrated through multiple cultivation runs performed at various scales-from microplate to 20 L bioreactor. We also developed a fully automated bioreactor-FCM interface for on-line monitoring of the microbial population. Finally, we validated the proposed strategy by performing a fed-batch experiment where the biosensor signal is used as the actuator for a nitrogen feeding feedback control. This new generation of process control, -based on the specific needs of the cells, -opens the possibility of improving process development on a short timescale and therewith, the robustness and performance of fermentation processes.

Optimisation of recombinant TNFα production in Escherichia coli using GFP fusions and flow cytometry

Escherichia coli is commonly used industrially to manufacture recombinant proteins for biopharmaceutical applications, as well as in academic and industrial settings for R&D purposes. Optimisation of recombinant protein production remains problematic as many proteins are difficult to make, and process conditions must be optimised for each individual protein. An approach to accelerate process development is the use of a green fluorescent protein (GFP) fusions, which can be used to rapidly and simply measure the quantity and folding state of the protein of interest. In this study, we used GFP fusions to optimise production of recombinant human protein tumour necrosis factor (rhTNFα) using a T7 expression system. Flow cytometry was used to measure fluorescence and cell viability on a single cell level to determine culture heterogeneity. Fluorescence measurements were found to be comparable to data generated by subcellular fractionation and SDS-PAGE, a far more time-intensive technique. We compared production of rhTNFα-GFP with that of GFP alone to determine the impact of rhTNFα on expression levels. Optimised shakeflask conditions were then transferred to fed-batch high cell density bioreactor cultures. Finally, the expression of GFP from a paraBAD expression vector was compared to the T7 system. We highlight the utility of GFP fusions and flow cytometry for rapid process development.

High cell density culture of recombinant E. coli in the miniaturized bubble columns

Miniaturized bubble columns (MBCs) can provide mass transfer characteristics similar to stirred tank bioreactors. In this study, a new application was developed for MBCs to investigate the effect of feeding strategy and medium type on the fed-batch culture of recombinant E. coli. The results showed that the exponential feeding strategy and defined M9 medium were more suitable to achieve the high cell density culture (HCDC). The maximum obtained cell concentration in exponential feeding strategy in the defined medium without induction, was at OD₆₀₀ of 169, while glucose concentration was maintained under 2 g/L. To the best of our knowledge, this cell concentration cannot be achieved in lab or pilot scale bubble columns. At the end of the process, adverse effect of the metabolic burden due to induction and mass transfer limitations decreased the obtained final cell concentration to OD₆₀₀ of 116. Finally, a comparison of the results for fed-batch culture in the stirred tank bioreactor with those of the MBCs showed that their lower cell concentrations were due to the hydrodynamics limitations of MBCs. Yet, it was found that the MBCs are efficient tools in development of feeding strategies and evaluation of medium components for HCDC of recombinant E. coli.

Optimization of medium composition to increase the expression of recombinant human interferon-β using the Plackett-Burman and central composite design in E. coli SE1

Recombinant human interferon-β (rhIFN-β) is therapeutically important and new commercially viable approaches are needed for its increased production. In this study, a codon-optimized gene encoding for rhIFN-β_(C17S) protein was designed and expressed in E. coli SE1. As a first step of medium optimization, growth of E. coli as a function of different media components was studied. Subsequently, to optimize the media composition, a response surface methodology (RSM) was used. Our results show that optimized medium (15.0 g/L tryptone, 12.3 g/L meat extract, 1.0 g/L MgSO₄ and 0.5 g/L thiamine along with minimal medium) obtained in this study provide better growth of recombinant cells and the expression level of recombinant protein was ~ 1.7-fold more than Luria-Bertani medium. The optimized medium may be utilized for the large-scale production of rhIFN-β.

A dynamic method for the investigation of induced state metabolic capacities as a function of temperature

Background

Science-based recombinant bioprocess designs as well as the design of statistical experimental plans for process optimization (Design of Experiments, DoE) demand information on physiological bioprocess boundaries, such as the onset of acetate production, adaptation times, mixed feed metabolic capabilities or induced state maximum metabolic rates as at the desired cultivation temperature. Dynamic methods provide experimental alternatives to determine this information in a fast and efficient way. Information on maximum metabolic capabilities as a function of temperature is needed in case a reduced cultivation temperature is desirable (e.g. to avoid inclusion body formation) and an appropriate feeding profile is to be designed.

Results

Here, we present a novel dynamic method for the determination of the specific growth rate as a function of temperature for induced recombinant bacterial bioprocesses. The method is based on the control of the residual substrate concentration at non-limiting conditions with dynamic changes in cultivation temperature. The presented method was automated in respect to information extraction and closed loop control by means of in-line Fourier Transformation Infrared Spectroscopy (FTIR) residual substrate measurements and on-line first principle rate-based soft-sensors. Maximum induced state metabolic capabilities as a function of temperature were successfully extracted for a recombinant E. coli C41 fed-batch bioprocess without the need for sampling in a time frame of 20 hours.

Conclusions

The presented method was concluded to allow the fast and automated extraction of maximum metabolic capabilities (specific growth rate) as a function of temperature. This complements the dynamic toolset necessary for science-based recombinant bacterial bioprocess design and DoE design.

Non-conventional induction strategies for production of subunit swine erysipelas vaccine antigen in rE. coli fed-batch cultures

In spite of the large number of reports on fed-batch cultivation of E. coli, alternative cultivation/induction strategies remain to be more deeply exploited. Among these strategies, it could be mentioned the use of complex media with combination of different carbon sources, novel induction procedures and feed flow rate control matching the actual cell growth rate. Here, four different carbon source combinations (glucose, glycerol, glucose + glycerol and auto-induction) in batch media formulation were compared. A balanced combination of glucose and glycerol in a complex medium formulation led to: fast growth in the batch-phase; reduced plasmid instability by preventing early expression leakage; and protein volumetric productivity of 0.40 g.L^-1.h^-1. Alternative induction strategies were also investigated. A mixture of lactose and glycerol as supplementary medium fully induced a high biomass population, reaching a good balance between specific protein production (0.148 g_prot.g_DCW^-1) and volumetric productivity (0.32 g.L^-1.h^-1). The auto-induction protocol showed excellent results on specific protein production (0.158 g_prot.g_DCW^-1) in simple batch cultivations. An automated feed control based on the on-line estimated growth rate was implemented, which allowed cells to grow at higher rates than those generally used to avoid metabolic overflow, without leading to acetate accumulation. Some of the protocols described here may provide a useful alternative to standard cultivation and recombinant protein production processes, depending on the performance index that is expected to be optimized. The protocols using glycerol as carbon source and induction by lactose feeding, or glycerol plus glucose in batch medium and induction by lactose pulse led to rSpaA production in the range of 6 g.L^-1, in short fed-batch processes (16 to 20 h) with low accumulation of undesired side metabolites.

Identification and Optimization of Recombinant E. coli Fed-Batch Fermentation Producing γ-Interferon Protein

A novel approach to identification of fed-batch cultivation of E. coli BL21 (DE3) has been presented. The process has been identified in the system that is designed for maximum production of γ-interferon protein. Dynamic order of the process has been determined by Lipschitz test. Multilayer Perceptron neural network has been used to process identification by experimental data. The optimal brain surgeon method is used to reduce the model complexity that can be easily implemented. Validation results base on autocorrelation function of the residuals, show good performance of neural network and make it possible to use of it in process analyses.

Molecular cloning, expression and purification of recombinant soluble mouse endostatin as an anti-angiogenic protein in Escherichia coli

Inhibition of angiogenesis has become a particular interest for treatment of solid tumors. Endostatin, a C-terminal fragment of collagen XVIII, has been reported to exhibit potent inhibitory effect on endothelial cells proliferation, migration and tube formation. In this research, the cDNA library of endostatin was synthesized from mouse liver and inserted into the SacI and SalI enzyme-cutting sites of pUC18 cloning vector. The recombinant vector was transferred into Escherichia coli DH5a and the recombinant clone was selected on LB agar plate plus ampicillin. PCR analysis and DNA sequencing proved the presence of intact endostatin gene in pUC18. The endostatin gene subcloned into pET32a expression vector and the competent bacterial cells of E. coli BL21 were transformed by the vector harboring endostatin gene. In the optimum conditions, expression plasmid was induced with IPTG and recombinant soluble endostatin as a fusion with thioredoxin was purified with Ni-NTA (Ni(2+)-nitrilotriacetate) resin. The results showed that soluble recombinant endostatin as a fusion protein with thioredoxin is a homogenous polypeptide that inhibits angiogenesis (capillary tube formation) in human umbilical vein endothelial cells by 200 ng/ml.

Industrial production of recombinant therapeutics in Escherichia coli and its recent advancements

Nearly 30% of currently approved recombinant therapeutic proteins are produced in Escherichia coli. Due to its well-characterized genetics, rapid growth and high-yield production, E. coli has been a preferred choice and a workhorse for expression of non-glycosylated proteins in the biotech industry. There is a wealth of knowledge and comprehensive tools for E. coli systems, such as expression vectors, production strains, protein folding and fermentation technologies, that are well tailored for industrial applications. Advancement of the systems continues to meet the current industry needs, which are best illustrated by the recent drug approval of E. coli produced antibody fragments and Fc-fusion proteins by the FDA. Even more, recent progress in expression of complex proteins such as full-length aglycosylated antibodies, novel strain engineering, bacterial N-glycosylation and cell-free systems further suggests that complex proteins and humanized glycoproteins may be produced in E. coli in large quantities. This review summarizes the current technology used for commercial production of recombinant therapeutics in E. coli and recent advances that can potentially expand the use of this system toward more sophisticated protein therapeutics.

Expression of recombinant human interferon-γ with antiviral activity in the bi-cistronic baculovirus-insect/larval system

A bi-cistronic baculovirus-insect/larval system containing a polyhedron promoter, an internal ribosome entry site (IRES), and an egfp gene was developed as a cost-effective platform for the production of recombinant human interferon gamma (rhIFN-γ). There was no significant difference between the amounts of rhIFN-γ produced in the baculovirus-infected Spodoptera frugiferda 21 cells grown in serum-free medium and the serum-supplemented medium, while the Trichoplusia ni (T. ni) and Spodoptera exigua (S. exigua) larvae afforded rhIFN-γ amounting to 1.08±0.04 and 9.74±0.35 µg/mg protein respectively. The presence of non-glycosylated and glycosylated rhIFN-γ was confirmed by immunoblot and lectin blot. The immunological activity of purified rhIFN-γ, with 96% purity by Nickel (II)-nitrilotriacetic acid (Ni-NTA) affinity chromatography, was similar to that commercially available. Moreover, the rhIFN-γ protein from T. ni had more potent antiviral activity. These findings suggest that this IRES-based expression system is a simple and inexpensive alternative for large-scale protein production in anti-viral research.

Enhancement of human granulocyte-colony stimulating factor production in recombinant E. coli using batch cultivation

Development of inexpensive and simple culture media is always favorable for recombinant protein over-expression in E. coli. The effects of medium composition on the production of recombinant human granulocyte-colony stimulating factor (rh-GCSF) were investigated in batch culture of E. coli BL21 (DE3) [pET23a-hgcsf]. First, the optimum medium for production of rh-GCSF was determined; and, then it was shown that mixture of amino acid addition at induction time, which was determined on the basis of amino acids frequency in the recombinant protein, increases recombinant protein expression level significantly. Furthermore, the effect of glucose concentration on productivity of rh-GCSF was investigated; 20 g/l of glucose will result in maximum attainable biomass and rh-GCSF in this process. At optimum conditions, a cell dry weight of 10.5 g/l, an expression level of about 35% of total cellular protein, rh-GCSF concentration of 1.75 +/- 0.1 g/l, and overall rh-GCSF yield of 165 +/- 5 mg/g were obtained.

Kinetic studies of recombinant human interferon-gamma expression in continuous cultures of E. coli

A series of continuous cultures was performed to understand the product formation kinetics of recombinant human interferon gamma (rhIFN-gamma) in Escherichia coli at different dilution rates ranging from 0.1 to 0.3 h(-1) in different media. A T7 promoter-based vector was used for expression of IFN-gamma in E. coli BL21 (DE3) cells. The recombinant protein was produced as inclusion bodies, thus allowing a rapid buildup of rhIFN-gamma inside the cell, with the specific product yield (Y(p/X)) reaching a maximum value of 182 mg g(-1) dry cell weight (DCW). In all the media tested, the specific product formation rate (q(p)) was found to be strongly correlated with the specific growth rate (mu), demonstrating the growth-associated nature of product formation. The q(p) values show no significant decline with time postinduction, even though the recombinant protein has been over produced inside the cell. The maximum q(p) level of 75.5 mg g(-1) h(-1) was achieved at the first hour of induction at the dilution rate of 0.3 h(-1). Also, this correlation between q(p) and mu was not critically dependent on media composition, which would made it possible to grow cells in defined media in the growth phase and then push up the specific growth rate just before induction by pulse addition of glucose and yeast extract. This would ensure the twin objectives of high biomass and high specific productivities, leading to high volumetric product concentration.

Overproduction of human interleukin-2 in recombinant Escherichia coli BL21 high-cell-density culture by the determination and optimization of essential amino acids using a simple stoichiometric model

In order to increase the productivity of human IL-2 (interleukin-2), a stoichiometric model has been used to determine the most essential amino acids and precise values of their amounts to be added to the culture during expression of human IL-2 (as a model protein) by recombinant Escherichia coli BL21 (pET21a-hil2). Experiments were performed to investigate the effect of chosen amino acids and their interactions on expression of human IL-2. Glutamine, a mixture of leucine, aspartic acid and glycine, and a mixture of leucine, glutamine and aspartic acid, were the most effective for the expression of IL-2. The most promising amino acids were then chosen for further experiments at three different levels to determine whether altering their stoichiometry can lead to better expression levels. The optimized value of glutamine in the flask was 0.316 g/l; a mixture of leucine, glutamine and aspartic acid at concentrations of 0.124, 0.316 and 0.212 g/l respectively and of leucine, aspartic acid and glycine in concentrations of 0.124, 0.212, 0.111 g/l respectively were chosen to be added to the flask. The effect of glutamine, as one of the amino acids most influencing the expression of IL-2 in batch and fed-batch high-cell-density cultures, was studied. The results revealed that the amount of expressed IL-2 compared with the control culture increased from 81 to 195 mg/l in the shake flask, 403 to 594 mg/l in the fermentor and 5.15 to 10.01 g/l in the fermentor under fed-batch cultivation.