Process strategies to improve heterologous protein production in Escherichia coli under lactose or IPTG induction

Constructing an Antibiotic-Free Protein Expression System for Ovalbumin Biosynthesis in Probiotic Escherichia coli Nissle 1917

Ovalbumin (OVA) is the principal protein constituent of eggs. As an alternative to eggs, cell-cultured OVA can reduce the environmental impact of global warming and land use. Escherichia coli Nissle 1917 (EcN), a probiotic with specific endogenous cryptic plasmids that stably exist in cells without the addition of antibiotics, was chosen as the host for the efficient heterologous expression of the OVA. OVA yield reached 20 mg·L-1 in shake flasks using the OVA expression cassette containing a tac promoter (Ptac) upstream of the OVA-coding sequences on the endogenous plasmid pMUT2. Subsequently, we improved the level of the expression of the OVA by employing a dual promoter (PP5 combined with Ptac via a sigma factor binding site 24) and ribosome binding site (RBS) substitution. These enhancements increased the level of production of OVA in shake flasks to 30 and 42 mg·L-1, respectively. OVA by EcNP-P28 harboring plasmid L28 equipped with both dual promoter and the strong RBS8 reached 3.70 g·L-1 in a 3 L bioreactor. Recombinant OVA and natural OVA showed similar biochemical characteristics, including secondary structure, isoelectric point, amino acid composition, and thermal stability. This is currently the highest OVA production reported among prokaryotes. We successfully constructed an antibiotic-free heterologous protein expression system for EcN.

The advent of plant cells in bioreactors

Ever since agriculture started, plants have been bred to obtain better yields, better fruits, or sustainable products under uncertain biotic and abiotic conditions. However, a new way to obtain products from plant cells emerged with the development of recombinant DNA technologies. This led to the possibility of producing exogenous molecules in plants. Furthermore, plant chemodiversity has been the main source of pharmacological molecules, opening a field of plant biotechnology directed to produce high quality plant metabolites. The need for different products by the pharma, cosmetics agriculture and food industry has pushed again to develop new procedures. These include cell production in bioreactors. While plant tissue and cell culture are an established technology, beginning over a hundred years ago, plant cell cultures have shown little impact in biotechnology projects, compared to bacterial, yeasts or animal cells. In this review we address the different types of bioreactors that are currently used for plant cell production and their usage for quality biomolecule production. We make an overview of Nicotiana tabacum, Nicotiana benthamiana, Oryza sativa, Daucus carota, Vitis vinifera and Physcomitrium patens as well-established models for plant cell culture, and some species used to obtain important metabolites, with an insight into the type of bioreactor and production protocols.

Production of recombinant scorpion antivenoms in E. coli: current state and perspectives

Scorpion envenomation is a serious health problem in tropical and subtropical zones. The access to scorpion antivenom is sometimes limited in availability and specificity. The classical production process is cumbersome, from the hyper-immunization of the horses to the IgG digestion and purification of the F(ab)'₂ antibody fragments. The production of recombinant antibody fragments in Escherichia coli is a popular trend due to the ability of this microbial host to produce correctly folded proteins. Small recombinant antibody fragments, such as single-chain variable fragments (scFv) and nanobodies (V_HH), have been constructed to recognize and neutralize the neurotoxins responsible for the envenomation symptoms in humans. They are the focus of interest of the most recent studies and are proposed as potentially new generation of pharmaceuticals for their use in immunotherapy against scorpion stings of the Buthidae family. This literature review comprises the current status on the scorpion antivenom market and the analyses of cross-reactivity of commercial scorpion anti-serum against non-specific scorpion venoms. Recent studies on the production of new recombinant scFv and nanobodies will be presented, with a focus on the Androctonus and Centruroides scorpion species. Protein engineering-based technology could be the key to obtaining the next generation of therapeutics capable of neutralizing and cross-reacting against several types of scorpion venoms. KEY POINTS: • Commercial antivenoms consist of predominantly purified equine F(ab)'₂fragments. • Nanobody-based antivenom can neutralize Androctonus venoms and have a low immunogenicity. • Affinity maturation and directed evolution are used to obtain potent scFv families against Centruroides scorpions.

A combination fermentation strategy for simultaneously increasing cellular NADP(H) level, biomass, and enzymatic activity of glufosinate dehydrogenase in Escherichia coli

Oxidoreductase is one of the most important biocatalysts for the synthesis of various chiral compounds. However, their whole-cell activity is frequently affected by an insufficient supply of expensive nicotinamide cofactors. This study aimed to overcome such shortcomings by developing a combination fermentation strategy for simultaneously increasing intracellular NADP(H) level, biomass, and glufosinate dehydrogenase activity in E. coli. The results showed that the feeding mode of NAD(H) synthesis precursor and lactose inducer had essential effects on the accumulation level of intracellular NADPH. Adding 40 mg L^-1 of L-aspartic acid to the medium increased the intracellular NADP(H) concentration by 36.3%. Under the pH-stat feeding mode and adding 0.4 g L^-1 h^-1 lactose, the NADP(H) concentration, biomass, and GluDH activity in the 5-L fermenter reached 445.7 μmol L^-1, 21.7 gDCW L^-1, and 8569.3 U L^-1, respectively. As far as we know, this is the highest reported activity of GluDH in the fermentation broth. Finally, the 5000-L fermenter was successfully scaled up to use this fermentation approach. The combination fermentation strategy might serve as a useful approach for the high-activity fermentation of other NADPH-dependent oxidoreductases.

High-Level Production of Recombinant Lipase by Fed-Batch Fermentation in Escherichia coli and Its Application in Biodiesel Synthesis from Waste Cooking Oils

The enzymatic production of biodiesel from waste cooking oils (WCOs) offers a green and sustainable solution for the liquid fuel manufacture as well as waste resource recovery. In present study, liquid lipase was used to simplify the catalysis process, thereby reducing biodiesel production costs. An engineered Escherichia coli expressing Geobacillus thermocatenulatus lipase 2 (GTL2) was screened at an enzyme activity of 6.96 U/mg, after evaluating the propagating stability of the recombinant plasmids exceeding 86.11%. Through the beneficial feeding strategy and effective pH control, high-level production of GTL2 by fed-batch fermentation was achieved with an enzyme activity of 434.32 U/mg, which was almost 62 times that of shake flask fermentation. In addition, liquid GTL2 was used to prepare fatty acid methyl esters (FAMEs) using WCOs. The effects of the reaction time, catalyst loading, temperature, and methanol-to-oil molar ratio on FAMEs production using WCOs were explored, and a maximum FAMEs yield of 96.62% was achieved under optimized conditions. These results indicate that liquid GTL2 is a promising biocatalyst for efficient utilization of WCOs in the synthesis of biodiesel and provide a novel enzymatic process for biodiesel reducing the cost of production.

Biosynthesis of a Therapeutically Important Nicotinamide Mononucleotide through a Phosphoribosyl Pyrophosphate Synthetase 1 and 2 Engineered Strain of Escherichia coli

Nicotinamide mononucleotide (NMN), a precursor of NAD⁺, can be synthesized by the conversion of nicotinamide with the help of nicotinamide phosphoribosyl transferase (NAMPT) via the salvage pathway. NMN has recently gained great attention as an excellent therapeutic option due to its long-term effective pharmacological activities. In this study, we constructed a recombinant strain of Escherichia coli by inserting NAMPT and phosphoribosyl pyrophosphate synthetase 1 (PRPS1) and PRPS2 (from Homo sapiens) genes to investigate the effect of PRPS1 and PRPS2 on NMN synthesis. The metabolically engineered strain of E. coli BL21 (DE3) exhibited 1.57 mM NMN production in the presence of Mg²⁺ and phosphates in batch fermentation studies. For further improvement in NMN production levels, effects of different variables were studied using a response surface methodology approach. A significant increment was achieved with a maximum of 2.31 mM NMN production when supplemented with 1% ribose, 1 mM Mg²⁺ and phosphate, and 0.5% nicotinamide in the presence of a lactose (1%) inducer. Additionally, insertion of the PRPS1 and PRPS2 genes in the phosphoribosyl pyrophosphate synthesis pathway and individual gene expression studies facilitated a higher NMN production at the intracellular level than the reported studies. The strain exhibited intracellular production of NMN from cheap substrates such as glucose, lactose, and nicotinamide. Hence, the overall optimized process can be further scaled up for the economical production of NMN using a recombinant strain of E. coli BL21 (DE3), which is the future perspective of the current study.

Construction and potential application of bacterial superoxide dismutase expressed in Bacillus subtilis against mycotoxins

Oxidative stress, which could be evoked by numerous inducements including mycotoxins like deoxynivalenol (DON), cause severe damages to organisms. Antioxidants are promising protectants against oxidative stress that could be applied in pharmaceutical, cosmetic, and food and feed industries. In this study, a thermostable and acidophilic superoxide dismutase (AaSOD) was used to develop an antioxidant product that can potentially protect organisms from oxidative stress related damages. The enzyme was successfully expressed as an extracelluar protein in Bacillus subtilis with a high yield. To obtain a feasible protocol for industrial production of AaSOD, the fermentation mediums that are commonly used for culturing B. subtilis were screened, the feasibility of expressing AaSOD without antibiotic as selection pressure was confirmed, and the effect of using lactose as an inducer instead of isopropyl-β-d-thiogalactoside (IPTG) was investigated. Batch fermentation was conducted to validate the optimized conditions for AaSOD production, and 6530 U mL^-1 of SOD activity was obtained in the fermentation broth. The dry powder product of AaSOD with an activity of 22202 U g^-1 was prepared by spray-drying and was administrated on zebrafish to test its function as a protectant against DON, and thus gained a significant redress of the reactive oxygen species (ROS) accumulation induced by DON. Taken together, this study provides a feasible protocol to prepare the AaSOD-based antioxidant product that is potentially applied in livestock industry.

Robotic integration enables autonomous operation of laboratory scale stirred tank bioreactors with model-driven process analysis

Given its geometric similarity to large-scale production plants and the excellent possibilities for precise process control and monitoring, the classic stirred tank bioreactor (STR) still represents the gold standard for bioprocess development at a laboratory scale. However, compared to microbioreactor technologies, bioreactors often suffer from a low degree of process automation and deriving key performance indicators (KPIs) such as specific rates or yields often requires manual sampling and sample processing. A widely used parallelized STR setup was automated by connecting it to a liquid handling system and controlling it with a custom-made process control system. This allowed for the setup of a flexible modular platform enabling autonomous operation of the bioreactors without any operator present. Multiple unit operations like automated inoculation, sampling, sample processing and analysis, and decision making, for example for automated induction of protein production were implemented to achieve such functionality. The data gained during application studies was used for fitting of bioprocess models to derive relevant KPIs being in good agreement with literature. By combining the capabilities of STRs with the flexibility of liquid handling systems, this platform technology can be applied to a multitude of different bioprocess development pipelines at laboratory scale.

Comparison of E. coli based self-inducible expression systems containing different human heat shock proteins

IPTG-inducible promoter is popularly used for the expression of recombinant proteins. However, it is not suitable at the industrial scale due to the high cost and toxicity on the producing cells. Recently, a Self-Inducible Expression (SILEX) system has developed to bypass such problems using Hsp70 as an autoinducer. Herein, the effect of other heat shock proteins on the autoinduction of green fluorescent protein (EGFP), romiplostim, and interleukin-2 was investigated. For quantitative measurements, EGFP expression was monitored after double-transformation of pET28a-EGFP and pET21a-(Hsp27/Hsp40/Hsp70) plasmids into E. coli using fluorimetry. Moreover, the expression level, bacterial growth curve, and plasmid and expression stability were compared to an IPTG- inducible system using EGFP. Statistical analysis revealed a significant difference in EGFP expression between autoinducible and IPTG-inducible systems. The expression level was higher in Hsp27 system than Hsp70/Hsp40 systems. However, the highest amount of expression was observed for the inducible system. IPTG-inducible and Hsp70 systems showed more lag-time in the bacterial growth curve than Hsp27/Hsp40 systems. A relatively stable EGFP expression was observed in SILEX systems after several freeze-thaw cycles within 90 days, while, IPTG-inducible system showed a decreasing trend compared to the newly transformed bacteria. Moreover, the inducible system showed more variation in the EGFP expression among different clones than clones obtained by SILEX systems. All designed SILEX systems successfully self-induced the expression of protein models. In conclusion, Hsp27 system could be considered as a suitable autoinducible system for protein expression due to less metabolic burden, lower variation in the expression level, suitable plasmid and expression stability, and a higher expression level.

Optimization of bacterial cytokine protein production by response surface methodology for environmental bioremediation

In natural and engineered systems, most microorganisms would enter a state of dormancy termed as “viable but non-culturable” (VBNC) state when they are exposed to unpredictable environmental stress. One of the major advances in resuscitating from such a state is the discovery of a kind of bacterial cytokine protein called resuscitation-promoting factor (Rpf), which is secreted from Micrococcus luteus. In this study, the optimization of Rpf production was investigated by the response surface methodology (RSM). Results showed that an empirical quadratic model well predicted the Rpf yield, and the highest Rpf protein yield could be obtained at the optimal conditions of 59.56 mg L⁻¹ IPTG, cell density 0.69, induction temperature 20.82 °C and culture time 7.72 h. Importantly, Phyre2 web portal characterized the structure of the Rpf domain to have a shared homology with lysozymes, and the highest lysozyme activity was at pH 5 and 50 °C. This study broadens the knowledge of Rpf production and provided potential strategies to apply Rpf as a bioactivator for environmental bioremediation.

A group of secreted proteins from M. luteus, recognized as resuscitation promoting factors (Rpf) can resuscitate the viable but non-culturable (VBNC) state bacteria which have the potential function of environmental bioremediation.

Development of recombinant human granulocyte colony-stimulating factor (nartograstim) production process in Escherichia coli compatible with industrial scale and with no antibiotics in the culture medium

The granulocyte colony-stimulating factor (G-CSF) is a hematopoietic cytokine that has important clinical applications for treating neutropenia. Nartograstim is a recombinant variant of human G-CSF. Nartograstim has been produced in Escherichia coli as inclusion bodies (IB) and presents higher stability and biological activity than the wild type of human G-CSF because of its mutations. We developed a production process of nartograstim in a 10-L bioreactor using auto-induction or chemically defined medium. After cell lysis, centrifugation, IB washing, and IB solubilization, the following three refolding methods were evaluated: diafiltration, dialysis, and direct dilution in two refolding buffers. Western blot and SDS-PAGE confirmed the identity of 18.8-kDa bands as nartograstim in both cultures. The auto-induction medium produced 1.17 g/L and chemically defined medium produced 0.95 g/L. The dilution method yielded the highest percentage of refolding (99%). After refolding, many contaminant proteins precipitated during pH adjustment to 5.2, increasing purity from 50 to 78%. After applying the supernatant to cation exchange chromatography (CEC), nartograstim recovery was low and the purity was 87%. However, when the refolding solution was applied to anion exchange chromatography followed by CEC, 91%-98% purity and 2.2% recovery were obtained. The purification process described in this work can be used to obtain nartograstim with high purity, structural integrity, and the expected biological activity. KEY POINTS: • Few papers report the final recovery of the purification process from inclusion bodies. • The process developed led to high purity and reasonable recovery compared to literature. • Nartograstim biological activity was demonstrated in mice using a neutropenia model.

Microaerobic fermentation alters lactose metabolism in Escherichia coli

Microaerobic fermentation has been shown to improve lactose transport and recombinant protein production in Escherichia coli. Mechanistic correlation between lactose and dissolved oxygen has been studied and it has been demonstrated that E. coli can switch its genetic machinery upon fluctuations in dissolved oxygen levels and thereby impact lactose transport, resulting in product formation. Continuous induction of lactose in microaerobic fermentation led to a 3.3-fold improvement in product titre of rLTNF oligomer and a 1.8-fold improvement in product titre of rSymlin oligomer as compared with traditional aerobic fermentation. Transcriptome profiling indicated that ribosome synthesis, lactose transport and amino acid synthesis genes were upregulated during microaerobic fermentation. Besides, novel lactose transporter setB was examined and it was observed that lactose uptake rate was 1.4-fold higher in microaerobic fermentation. The results indicate that microaerobic fermentation can offer a superior alternative for industrial production of recombinant therapeutics, industrial enzymes and metabolites in E. coli. KEY POINTS: • Microaerobic fermentation results in significantly improved protein production • Lactose transport, ribosome synthesis and amino acid synthesis are enhanced • Product titre improves by 1.8-3.3-fold.

Optimization of fermentation conditions for the production of recombinant feruloyl esterase from Burkholderia pyrrocinia B1213

Statistical experimental designs were used to optimize conditions for recombinant Burkholderia pyrrocinia feruloyl esterase (BpFae) production in bacteria under lactose induction. After optimization by single factor design, Plackett-Burman design, steepest ascent design and the response surface method, the optimal conditions for BpFae production were: 6 g/L lactose, pH 5.5, pre-induced period 5 h, 23 °C, shaker rotational speed of 240 rpm, medium volume of 50 mL/250 mL, inoculum size 0.2% (v/v), and a post-induced period of 32 h in a Luria-Bertani culture. The produced BpFae activity was 7.43 U/mL, which is 2.92 times higher than that obtained under optimal conditions using IPTG as the inducer. BpFae activity was 4.82 U/mL in a 5 L fermenter under the abovementioned optimal conditions. BpFae produced a small amount of ethyl acetate but had no effect on the synthesis of other important esters in Baijiu. The results underpin further investigations into BpFae characterization and potential applications.

Permeabilized TreS-Expressing Bacillus subtilis Cells Decorated with Glucose Isomerase and a Shell of ZIF-8 as a Reusable Biocatalyst for the Coproduction of Trehalose and Fructose

Metal-organic frameworks (MOFs) are a class of porous materials with versatile properties. In this study, ZIF-8 was employed to establish a two-enzyme system by encapsulating permeabilized Bacillus subtilis cells coated with glucose isomerase. B. subtilis was constructed by introducing the shuttle plasmid PMA5 associated with the overexpression of trehalose synthase. Using this two-enzyme system, trehalose was produced by trehalose synthase and the byproduct glucose was converted to fructose with the help of glucose isomerase. The decrease in glucose production not only relieved the inhibition of the entire reaction chain but also increased the final yield of trehalose. The highest trehalose production rate reached 67.7% and remained above 50% after 20 batches. In addition, the toxicity of the ZIF-8 coating for B. subtilis was investigated by fluorescence microscopy and was found to be negligible. By simulating an extreme environment, the ZIF-8 coating was demonstrated to have a protective effect on the cells and enzymes. This study provides a theoretical basis for the application of MOFs in the immobilization of microorganisms and enzymes.

Improving the heterologous expression of human β-defensin 2 (HBD2) using an experimental design

At present, expressing antimicrobial peptides in bacterial models is considered a routine lab bench work. However, low expression yields of these types of proteins are usually obtained. In this work, the antimicrobial peptide human β-defensin 2 (HBD2) was obtained in low expression yields in Escherichia coli BL21(DE3). To improve the expression yields of HBD2, some variables such as cell density, temperature, and length of induction, as well as the inducer concentration, were investigated using a 2⁴-factorial design of experiments (DoE). This approach allowed us to identify the identification of critical variables (main effects and interactions among factors) affecting bacterial HBD2 expression. After the evaluation of 19 different combination, the best condition to express HBD2 had a pre-induction temperature of 37 °C, a cell density of 1.0 U (600 nm), an induction temperature of 20 °C and a 0.1 mM of gene expression inducer (IPTG) over four hours. Under such conditions, the expression yield of the HBD2 peptide was one order of magnitude higher than the peptide expression performed initially.

Pilot-scale production of a highly thermostable α-amylase enzyme from Thermotoga petrophila cloned into E. coli and its application as a desizer in textile industry

In this study, the industrial applications of a highly thermostable α-amylase as a desizer in the textile industry was evaluated. The cloned gene was expressed in different media (ZBM, LB, ZYBM9, and ZB) with IPTG (isopropyl β-d-1-thiogalactopyranoside) used as an inducer. Lactose was also used as an alternate inducer for the T7 promoter system in E. coli. For the large-scale production of the enzyme, different parameters were optimized. The maximum enzyme production was achieved when the volume of medium was 70% of the total volume of fermenter with a 2.0 vvm air supply and 20% dissolved oxygen at a 200 rpm agitation rate. Under all the optimized conditions, the maximum enzyme production was 22.08 U ml⁻¹ min⁻¹ with lactose (200 mM) as an inducer in ZBM medium. The desizing potential of the purified α-amylase enzyme was calculated with different enzyme concentrations (50–300 U ml⁻¹) at different temperatures (50–100 °C), and pHs (4–9) with varying time intervals (30–120 min). The highest desizing activity was found when 150 U ml⁻¹ enzyme units were utilized at 85 °C and at 6.5 pH for 1 h.

Thermostable recombinant α-amylase was produced in a large scale for the desizing of cotton cloth in the textile industry.

High-efficiency expression of Sulfolobus acidocaldarius maltooligosyl trehalose trehalohydrolase in Escherichia coli through host strain and induction strategy optimization

Maltooligosyl trehalose trehalohydrolase (MTHase, EC 3.2.1.141) catalyzes the release of trehalose, a novel food ingredient, by splitting the α-1,4-glucosidic linkage adjacent to the α-1,1-glucosidic linkage of maltooligosyl trehalose. However, the high-yield preparation of recombinant MTHase has not yet been reported. In this study, a codon-optimized synthetic gene encoding Sulfolobus acidocaldarius MTHase was expressed in Escherichia coli. In initial expression experiments conducted using pET-24a (+) and E. coli BL21 (DE3), the MTHase activity was 10.4 U/mL and a large amount of the expression product formed inclusion bodies. The familiar strategies, including addition of additives, co-expression with molecular chaperones, and expression with a fusion partner, failed to enhance soluble MTHase expression. Considering the intermolecular disulfide bond of MTHase, expression was investigated using a system comprising plasmid pET-32a (+) and host E. coli Origami (DE3), which is conducive to cytoplasmic disulfide bond formation. The MTHase activity increased to 55.0 U/mL, a 5.3-fold increase. Optimization of the induction conditions in a 3-L fermentor showed that when the lactose was fed at 0.2 g/L/h beginning at an OD₆₀₀ of 40 and the induction temperature was maintained at 30 °C, the MTHase activity reached a maximum of 204.6 U/mL. This is the first report describing a systematic effort to obtain high-efficiency MTHase production. The high yield obtained using this process provides the basis for the industrial-scale production of trehalose. This report is also expected to be valuable in the production of other enzymes containing disulfide bonds.

Enhanced production, overexpression and characterization of a hyperthermophilic multimodular GH family 2 β‑glucuronidase (TpGUS) cloned from Thermotoga petrophila RKU-1T in a mesophilic host

A multimodular hyperthermophilic β‑glucuronidase (TpGUS) from Thermotoga petrophila RKU-1^T, belongs to glycoside hydrolase family 2 (GH2), was cloned and overexpressed in Escherichia coli BL21 CodonPlus (DE3)-RIPL. Expression and production of extracellular TpGUS was enhanced through various specific cultivation and induction strategies. Extracellular TpGUS activity was improved by 3.44 and 7 fold in 4 × ZB medium induced with 0.5 mM IPTG and 100 mM lactose, respectively. The enzyme was purified to homogeneity with a single band of 65.6 kDa on SDS-PAGE, using two subsequent steps of anion exchange and hydrophobic interaction chromatography after heat precipitation (70 °C, 1 h). Optimal activity of TpGUS was observed at 95 °C and pH 6.0; and it displayed prodigious thermal stability over a temperature range of 50-85 °C for 12 h at pH 6.0-7.5. K_m, V_max, V_maxK_m^-1, k_cat, and k_catK_m^-1 were calculated to be 0.7 mM, 227 mmol mg^-1 min^-1, 324.3 min^-1, 164,492.7 s^-1 and 234,989.6 mM^-1 s^-1, respectively using pNPGU as a substrate. Recombinant TpGUS exhibited favorable properties which make this a promising candidate for various biotechnological and pharmacological applications.

A new vector for heterologous gene expression in Escherichia coli with increased stability in the absence of antibiotic

Expression vectors for industrial production should be stable and allow tight control of protein synthesis. This is necessary to ensure plasmid transmission to daughter cells in order to achieve a stable population capable of synthesizing high amounts of the target protein. A high-copy-number plasmid, pAE, was previously used for laboratory-scale production of recombinant human granulocyte colony-stimulating factor (rhG-CSF) and the Schistosoma mansoni fatty acid binding protein (rSm14), but it was unstable for large-scale production. Therefore, here we evaluated a new expression vector derived from pAE, pAR-KanI, which combines two plasmid replication strategies: a high-copy plasmid pUC origin of replication as pAE, and a par locus sequence derived from pSC101, which is typical of low copy plasmids, for rhG-CSF and rSm14 production in Escherichia coli. Clones bearing these constructs were cultivated in two complex media (2YT and auto-induction) and both yielded higher-than-95% resistant colonies, before and after induction, either with or without antibiotics. In 2YT medium, we obtained 244 μg/mL of rSm14, 181 μg/mL and 392 μg/mL for rhG-CSF, with and without glucose, respectively. In auto-induction medium without antibiotics, 147 μg/mL of rSm14 and 162 μg/mL of rhG-CSF were obtained. The new vector presented high stability for the production of both recombinant proteins in complex media in Escherichia coli, even in the absence of antibiotics, making the pAR-KanI a promising vector for industrial production of recombinant proteins.

Enhanced Production of a Recombinant Multidomain Thermostable GH9 Processive Endo-1,4-β-Glucanase (CenC) from Ruminiclostridium thermocellum in a Mesophilic Host Through Various Cultivation and Induction Strategies

Commonly, unintentional induction and inadvertently preparing medium for engineered Escherichia coli BL21 CodonPlus (DE3)-RIPL, give poor or variable yields of heterologous proteins. Therefore, to enhance the activity and production of an industrially relevant recombinant processive endo-1,4-β-glucanase (CenC) propagated in Escherichia coli BL21 CodonPlus(DE3)-RIPL through various cultivation and induction strategies. Investigation of various growth media and induction parameters revealed that high-cell-density and optimal CenC expression were obtained in ZYBM9 medium induced either with 0.5 mM IPTG/150 mM lactose, after 6 h induction at 37 °C; and before induction, bacterial cells were given heat shock (42 °C) for 1 h when culture density (OD_600nm) reached at 0.6. Intracellular enzyme activity was enhanced by 6.67 and 3.20-fold in ZYBM9 and 3×ZYBM9 medium, respectively, under optimal conditions. Using YNG auto-induction medium, activity was 2.5-fold increased after 10 h incubation at 37 °C. Approximately similar results were obtained by transferring the optimized process at the bioreactor level. Results showed that the effective process strategy is essential to enhance recombinant bacterial cell mass and enzyme production from small to large-scale. To the best of our knowledge, this is the first ever report on enhanced production of thermostable processive endo-1,4-β-glucanase cloned from Ruminiclostridium thermocellum, which is a suitable candidate for industrial applications. Graphical Abstract Flow Chart Summary of Enhanced Production of a Recombinant Multidomain Thermostable GH9 Processive Endo-1,4-β-glucanase from Ruminiclostridium thermocellum.

Full-Length cDNA, Prokaryotic Expression, and Antimicrobial Activity of UuHb-F-I from Urechis unicinctus

Hemoglobin, which widely exists in all vertebrates and in some invertebrates, is possibly a precursor of antimicrobial peptides (AMPs). However, AMPs in the hemoglobin of invertebrates have been rarely investigated. This study is the first to report the full-length cDNA, prokaryotic expression, and antimicrobial activity of UuHb-F-I from Urechis unicinctus. The full-length cDNA sequence of UuHb-F-I was 780 bp with an open-reading frame of 429 bp encoding 142 amino acids. MALDI-TOF-MS suggested that the recombinant protein of UuHb-F-I (rUuHb-F-I) yielded a molecular weight of 15,168.01 Da, and its N-terminal amino acid sequence was MGLTGAQIDAIK. rUuHb-F-I exhibited different antimicrobial activities against microorganisms. The lowest minimum inhibitory concentration against Micrococcus luteus was 2.78–4.63 μM. Our results may help elucidate the immune defense mechanism of U. unicinctus and may provide insights into new AMPs in drug discovery.

Exacerbation of substrate toxicity by IPTG in Escherichia coli BL21(DE3) carrying a synthetic metabolic pathway

BACKGROUND

Heterologous expression systems based on promoters inducible with isopropyl-β-D-1-thiogalactopyranoside (IPTG), e.g., Escherichia coli BL21(DE3) and cognate LacI(Q)/P(lacUV5)-T7 vectors, are commonly used for production of recombinant proteins and metabolic pathways. The applicability of such cell factories is limited by the complex physiological burden imposed by overexpression of the exogenous genes during a bioprocess. This burden originates from a combination of stresses that may include competition for the expression machinery, side-reactions due to the activity of the recombinant proteins, or the toxicity of their substrates, products and intermediates. However, the physiological impact of IPTG-induced conditional expression on the recombinant host under such harsh conditions is often overlooked.

RESULTS

The physiological responses to IPTG of the E. coli BL21(DE3) strain and three different recombinants carrying a synthetic metabolic pathway for biodegradation of the toxic anthropogenic pollutant 1,2,3-trichloropropane (TCP) were investigated using plating, flow cytometry, and electron microscopy. Collected data revealed unexpected negative synergistic effect of inducer of the expression system and toxic substrate resulting in pronounced physiological stress. Replacing IPTG with the natural sugar effector lactose greatly reduced such stress, demonstrating that the effect was due to the original inducer's chemical properties.

CONCLUSIONS

IPTG is not an innocuous inducer; instead, it exacerbates the toxicity of haloalkane substrate and causes appreciable damage to the E. coli BL21(DE3) host, which is already bearing a metabolic burden due to its content of plasmids carrying the genes of the synthetic metabolic pathway. The concentration of IPTG can be effectively tuned to mitigate this negative effect. Importantly, we show that induction with lactose, the natural inducer of P lac , dramatically lightens the burden without reducing the efficiency of the synthetic TCP degradation pathway. This suggests that lactose may be a better inducer than IPTG for the expression of heterologous pathways in E. coli BL21(DE3).

Enhanced production of recombinant Escherichia coli glutamate decarboxylase through optimization of induction strategy and addition of pyridoxine

This report describes the optimization of recombinant Escherichia coli glutamate decarboxylase (GAD) production from engineered E. coli BL21(DE3) in a 3-L fermentor. Investigation of different induction strategies revealed that induction was optimal when the temperature was maintained at 30°C, the inducer (lactose) was fed at a rate of 0.2 g L(-1)h(-1), and protein expression was induced when the cell density (OD600) reached 50. Under these conditions, the GAD activity of 1273.8 U mL(-1) was achieved. Because GAD is a pyridoxal 5'-phosphate (PLP)-dependent enzyme, the effect of supplementing the medium with pyridoxine hydrochloride (PN), a cheap and stable PLP precursor, on GAD production was also investigated. When the culture medium was supplemented with PN to a concentration of 2mM at the initiation of protein expression, and then again 10h later, the GAD activity reached 3193.4 U mL(-1), which represented the highest GAD production ever reported.

Extracellular expression of natural cytosolic arginine deiminase from Pseudomonas putida and its application in the production of L-citrulline

The Pseudomonas putida arginine deiminase (ADI), a natural cytosolic enzyme, and Thermobifida fusca cutinase were co-expressed in Escherichia coli, and the optimized cutinase gene was used for increasing its expression level. 90.9% of the total ADI protein was released into culture medium probably through a nonspecific leaking mechanism caused by the co-expressed cutinase. The enzymatic properties of the extracellular ADI were found to be similar to those of ADI prepared by conventional cytosolic expression. Extracellular production of ADI was further scaled up in a 3-L fermentor. When the protein expression was induced by IPTG (25.0μM) and lactose (0.1gL(-1)h(-1)) at 30°C, the extracellular ADI activity reached 101.2UmL(-1), which represented the highest ADI production ever reported. In addition, the enzymatic synthesis of l-citrulline was performed using the extracellularly expressed ADI, and the conversion rate reached 100% with high substrate concentration at 650gL(-1).

Acetate: friend or foe? Efficient production of a sweet protein in Escherichia coli BL21 using acetate as a carbon source

BACKGROUND

Escherichia coli is, to date, the most used microorganism for the production of recombinant proteins and biotechnologically relevant metabolites. High density cell cultures allow efficient biomass and protein yields. However, their main limitation is the accumulation of acetate as a by-product of unbalanced carbon metabolism. Increased concentrations of acetate can inhibit cellular growth and recombinant protein production, and many efforts have been made to overcome this problem. On the other hand, it is known that E. coli is able to grow on acetate as the sole carbon source, although this mechanism has never been employed for the production of recombinant proteins.

RESULTS

By optimization of the fermentation parameters, we have been able to develop a new acetate containing medium for the production of a recombinant protein in E. coli BL21(DE3). The medium is based on a buffering phosphate system supplemented with 0.5% yeast extract for essential nutrients and sodium acetate as additional carbon source, and it is compatible with lactose induction. We tested these culture conditions for the production of MNEI, a single chain derivative of the sweet plant protein monellin, with potential for food and beverage industries. We noticed that careful oxygenation and pH control were needed for efficient protein production. The expression method was also coupled to a faster and more efficient purification technique, which allowed us to obtain MNEI with a purity higher than 99%.

CONCLUSIONS

The method introduced represents a new strategy for the production of MNEI in E. coli BL21(DE3) with a simple and convenient process, and offers a new perspective on the capabilities of this microorganism as a biotechnological tool. The conditions employed are potentially scalable to industrial processes and require only low-priced reagents, thus dramatically lowering production costs on both laboratory and industrial scale. The yield of recombinant MNEI in these conditions was the highest to date from E. coli cultures, reaching on average ~180 mg/L of culture, versus typical LB/IPTG yields of about 30 mg/L.

Cold-adapted RTX lipase from antarctic Pseudomonas sp. strain AMS8: isolation, molecular modeling and heterologous expression

A new strain of psychrophilic bacteria (designated strain AMS8) from Antarctic soil was screened for extracellular lipolytic activity and further analyzed using molecular approach. Analysis of 16S rDNA showed that strain AMS8 was similar to Pseudomonas sp. A lipase gene named lipAMS8 was successfully isolated from strain AMS8, cloned, sequenced and overexpressed in Escherichia coli. Sequence analysis revealed that lipAMS8 consist of 1,431 bp nucleotides that encoded a polypeptide consisting of 476 amino acids. It lacked an N-terminal signal peptide and contained a glycine- and aspartate-rich nonapeptide sequence at the C-terminus, which are known to be the characteristics of repeats-in-toxin bacterial lipases. Furthermore, the substrate binding site of lipAMS8 was identified as S(207), D(255) and H(313), based on homology modeling and multiple sequence alignment. Crude lipase exhibited maximum activity at 20 °C and retained almost 50 % of its activity at 10 °C. The molecular weight of lipAMS8 was estimated to be 50 kDa via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimal expression level was attained using the recombinant plasmid pET32b/BL21(DE3) expressed at 15 °C for 8 h, induced by 0.1 mM isopropyl β-D thiogalactoside (IPTG) at E. coli growth optimal density of 0.5.

Efficient feeding profile optimization for recombinant protein production using physiological information

A multivariate study was performed aiming at the optimization of a recombinant rhamnose inducible E. coli induction system with alkaline phosphatase as target product. The effects of typical factors with impact on post- as well as pre-induction feeding rates were investigated with respect to the space–time yield of the target product. The goal was increased understanding as well as quantitative characterization of these factors with respect to their physiological impact on the model system. The optical density (OD) at which the culture was induced had a strong positive effect on the space–time yield. Pre-induction growth rate (k) had a second-order effect, while induction feed rate drop (J), a factor defining the linear post-induction feed rate, was interacting with (k). However, explanation of the observed effects to acquire more understanding regarding their effect on cell metabolism was not straight forward. Hence, the original process parameters were transformed into physiological more meaningful parameters and served as the basis for a multivariate data analysis. The observed variance with respect to observed volumetric activity was fully explained by the specific substrate uptake rate (q_s) and induction OD, merging the process parameters pre-induction growth rate (k) and feed rate drop (J) into the physiological parameter specific substrate uptake rate (q_s). After transformation of the response volumetric activity (U/ml) into the biomass specific activity (U/g_biomass), the observed variance was fully explained solely by the specific substrate uptake rate (q_s). Due to physiological multivariate data analysis, the interpretation of the results was facilitated and factors were reduced. On the basis of the obtained results, it was concluded that the physiological parameter q_s rather than process parameters (k, J, induction OD) should be used for process optimization with respect to the feeding profile.

Process development and cGMP manufacturing of a recombinant ricin vaccine: an effective and stable recombinant ricin A-chain vaccine-RVEc™

Ricin is a potent toxin and a potential bioterrorism weapon with no specific countermeasures or vaccines available. The holotoxin is composed of two polypeptide chains linked by a single disulfide bond: the A-chain (RTA), which is an N-glycosidase enzyme, and the B-chain (RTB), a lectin polypeptide that binds galactosyl moieties on the surface of the mammalian target cells. Previously (McHugh et al.), a recombinant truncated form of RTA (rRTA1-33/44-198 protein, herein denoted RVEa™) expressed in Escherichia coli using a codon-optimized gene was shown to be non-toxic, stable, and protective against a ricin challenge in mice. Here, we describe the process development and scale-up at the 12 L fermentation scale, and the current Good Manufacturing Practice (cGMP)-compliant production of RVEc™ at the 40 L scale. The average yield of the final purified bulk RVEc™ is approximately 16 g/kg of wet cell weight or 1.2 g/L of fermentation broth. The RVEc™ was >99% pure by three HPLC methods and SDS-PAGE. The intact mass and peptide mapping analysis of RVEc™ confirmed the identity of the product and is consistent with the absence of posttranslational modifications. Potency assays demonstrated that RVEc™ was immunoprotective against lethal ricin challenge and elicited neutralizing anti-ricin antibodies in 95-100% of the vaccinated mice.

High cell density cultivation of Escherichia coli with surface anchored transglucosidase for use as whole-cell biocatalyst for alpha-arbutin synthesis

A fed-batch culture strategy for the production of recombinant Escherichia coli cells anchoring surface-displayed transglucosidase for use as a whole-cell biocatalyst for alpha-arbutin synthesis was developed. Lactose was used as an inducer of the recombinant protein. In fed-batch cultures, dissolved oxygen was used as the feed indicator for glucose, thus accumulation of glucose and acetate that affected the cell growth and recombinant protein production was avoided. Fed-batch fermentation with lactose induction yielded a biomass of 18 g/L, and the cells possessed very high transglucosylation activity. In the synthesis of alpha-arbutin by hydroquinone glucosylation, the whole-cell biocatalysts showed a specific activity of 501 nkat/g cell and produced 21 g/L of arbutin, which corresponded to 76% molar conversion. A sixfold increased productivity of whole cell biocatalysts was obtained in the fed-batch culture with lactose induction, as compared to batch culture induced by IPTG.

Improved expression of a soluble single chain antibody fusion protein containing tumor necrosis factor in Escherichia coli

The immunocytokine scFvMEL/TNF is a fusion protein composed of tumor necrosis factor (TNF-alpha) and a single-chain Fv antibody scFvMEL targeting the melanoma-associated gp240 antigen. The fusion protein containing thioredoxin and a hexa-histidine tag was expressed in two Escherichia coli host cells, AD494 (DE3) pLysS and T7 Express I (q). The cell growth and expression level of target protein, His-tagged scFvMEL/TNF, were highly dependent on the induction temperature, inducer types and host strains. The ratio of insoluble to soluble target proteins was found to be controllable and could be minimized using cold shock conditions at less than 18 degrees C. The total productivity of soluble target protein was further improved by high cell density cultivation using a DO-STAT feeding strategy. The scFvMEL/TNF purified under their conditions was specifically cytotoxic to gp240-antigen positive melanoma A375-M cells as previously described.

Lactose-induced production of human soluble B lymphocyte stimulator (hsBLyS) in E. coli with different culture strategies

Over-production of human soluble B lymphocyte stimulator (hsBLyS) was carried out with four different fed-batch culture strategies using lactose as inducer, instead of IPTG, in a fed-batch culture of Escherichia coli. As lactose acted as both inducer and carbon source, the best and simplest culture strategy was direct feeding of lactose after batch culture, thereby giving hsBLyS at 3.7 g l(-1) and a productivity of 0.11 g l(-1) h(-1).