IPTG Concentration Research Articles

Enhancing Soluble Expression of Phospholipase B for Efficient Catalytic Synthesis of L-Alpha-Glycerylphosphorylcholine

Phospholipase B (PLB) harbors three distinct activities with broad substrate specificities and application fields. Its hydrolyzing of sn-1 and sn-2 acyl ester bonds enables it to catalyze the production of L-alpha-glycerylphosphorylcholine (L-α-GPC) from phosphatidylcholine (PC) without speed-limiting acyl migration. This work was intended to obtain high-level active PLB and apply it to establish an efficient system for L-α-GPC synthesis. PLB from Pseudomonas fluorescens was co-expressed with five different molecular chaperones, including trigger factor (Tf), GroEL-GroES (GroELS), DnaK-DnaJ-GrpE (DnaKJE), GroELS and DnaKJE, or GroELS and Tf or fused with maltose binding protein (MBP) in Escherichia coli BL21(DE3) to improve PLB expression. PLB with DnaKJE-assisted expression exhibited the highest catalytic activity. Further optimization of the expression conditions identified an optimal induction OD600 of 0.8, IPTG concentration of 0.3 mmol/L, induction time of 9 h, and temperature of 25 °C. The PLB activity reached a maximum of 524.64 ± 3.28 U/mg under optimal conditions. Subsequently, to establish an efficient PLB-catalyzed system for L-α-GPC synthesis, a series of organic-aqueous mixed systems and surfactant-supplemented aqueous systems were designed and constructed. Furthermore, the factors of temperature, reaction pH, metal ions, and substrate concentration were further systematically identified. Finally, a high yield of 90.50 ± 2.21% was obtained in a Span 60-supplemented aqueous system at 40 °C and pH 6.0 with 0.1 mmol/L of Mg2+. The proposed cost-effective PLB production and an environmentally friendly PLB-catalyzed system offer a candidate strategy for the industrial production of L-α-GPC.

Heterologous expression of a papain-like protease inhibitor (SnuCalCpI17) in the E. coli and its mode of inhibition.

The effect of the Escherichia coli (E. coli) Rosetta (DE3) system on the expression of recombinant papain-like cysteine protease inhibitors (SnuCalCpIs) was evaluated, and the inhibition mode of the expressed inhibitor was determined. SnuCalCpI08 and SnuCalCpI17, which previously had not been expressed in the E. coli BL21 (DE3) system due to rare codons of more than 10%, were successfully expressed in E. coli Rosetta (DE3) since the strain provides tRNAs for six rare codons. Initially, both inhibitors were expressed as inclusion bodies; however, the water solubility of SnuCalCpI17 could be improved by lowering the incubation temperature, reducing the IPTG concentration, and increasing the induction time. In contrast, the other inhibitor could not be solubilized in water. To validate whether the inhibitor was expressed with correct protein folding, a papain inhibition assay was performed with SnuCalCpI17. SnuCalCpI17 showed a half-maximal inhibitory concentration (IC50) of 105.671 ± 9.857µg/mL and a slow-binding inhibition mode against papain at pH 7.0 with a Kiapp of 75.80μg/mL. The slow-binding inhibitor has a slow dissociation from the inhibitor-target complex, resulting in a long residence time in vivo, and thus can effectively inhibit the target at doses far below the IC50 of the inhibitor. KEY POINTS: • Propeptide inhibitor (SnuCalCpI17) containing rare codons was expressed in E. coli Rosetta (DE3). • The slow-binding inhibition was shown by plotting the apparent first-order rate constant (kobs). • Protein-protein interaction between SnuCalCpIs and papain was verified by docking simulation.

Bacterial over-expression of functionally active human CT2 (SLC22A16) carnitine transporter.

Escherichia coli is a widely used tool for the over-expression of human proteins for studying structure and function. The toxicity of human proteins for E. coli often hampers the expression. This study aims to find conditions for the expression of a membrane transporter known as the carnitine transporter CT2. The knowledge on this transporter is scarce, thus obtaining the recombinant protein is very important for further studies. The cDNAs coding for human CT2 (hCT2) was cloned in the pH6EX3 vector and different transformed E. coli strains were cultured in absence or in presence of glucose. hCT2 expression was obtained. The protein was purified and reconstituted into proteoliposomes in a functionally active state. Using the appropriate IPTG concentration, together with the addition of glucose, hCT2 has been expressed in E. coli. The protein is active and shows capacity to transport carnitine in proteoliposomes. The results have a great interest in basic biochemistry of membrane transporters and applications to human health since hCT2 is involved in human pathology.

Expression, Purification, and In Silico Characterization of Mycobacterium smegmatis Alternative Sigma Factor SigB.

Sigma factor B (SigB), an alternative sigma factor (ASF), is very similar to primary sigma factor SigA (σ70) but dispensable for growth in both Mycobacterium smegmatis (Msmeg) and Mycobacterium tuberculosis (Mtb). It is involved in general stress responses including heat, oxidative, surface, starvation stress, and macrophage infections. Despite having an extremely short half-life, SigB tends to operate downstream of at least three stress-responsive extra cytoplasmic function (ECF) sigma factors (SigH, SigE, SigL) and SigF involved in multiple signaling pathways. There is very little information available regarding the regulation of SigB sigma factor and its interacting protein partners. Hence, we cloned the SigB gene into pET28a vector and optimized its expression in three different strains of E. coli, viz., (BL21 (DE3), C41 (DE3), and CodonPlus (DE3)). We also optimized several other parameters for the expression of recombinant SigB including IPTG concentration, temperature, and time duration. We achieved the maximum expression of SigB at 25°C in the soluble fraction of the cell which was purified by affinity chromatography using Ni-NTA and further confirmed by Western blotting. Further, structural characterization demonstrates the instability of SigB in comparison to SigA that is carried out using homology modeling and structure function relationship. We have done protein-protein docking of RNA polymerase (RNAP) of Msmeg and SigB. This effort provides a platform for pulldown assay, structural, and other studies with the recombinant protein to deduce the SigB interacting proteins, which might pave the way to study its signaling networks along with its regulation.

Expression of eg9 gene encoding endoglucanase GH8 derived from metagenomic DNA data of bacteria in humus around white rot fungi degrading woods, in Escherichia coli

Endoglucanase is an important enzyme participating in the hydrolysis of cellulose into oligosaccharides or glucoses can be used in a variety of industrial fields. A gene (code GL0183420 designated as eg9) of 1398 bp encoding for endoglucanase family GH8 was identified from metagenomic DNA data of bacteria in the humus surrounding wood hydrolyzed by white rot fungi. The 126 terminal nucleotides at 5' terminal of the gene encode for a signal peptide in gram-negative bacteria and the next 1269 nucleotides encode the endoglucanase GH8. In this study, the eg9 gene (lack of sequence encoding the signal peptid) coding for the mature endoglucanase was codon optimized for expression in E. coli, artificical synthesized, then inserted into pET22b(+) for gene expression in E. coli strains. Through a survey of 5 expressive strains, EG9 was overexpressed in Rosetta and C43 strains. However, at 30oC in LB medium, most of EG9 were expressed in the insoluble fraction, in which Rosetta was the best strain for synthesis of EG9. The enzyme EG9 can be overexpressed in Rosetta strain at a large range of OD600 from 0.2 to 1. After reducing the culture temperature to 25°C, 50% of EG9 was expressed in soluble fraction and exhibited good hydrolysis activity in CMC substrate on agar plate. The investigation of media showed that PE was the most suitable medium for the recombinant Rosetta strain grow and synthesize endoglucanase EG9. EG9 was well expressed at various IPTG concentrations from 0.05 to 0.9 mM. These results offer great potential for production of recombinant EG9 for enzyme properties research.

Heterologous Production of Human Papillomavirus L1 Capsid Protein: Systematic Review and Meta-analysis

The coverage of HPV vaccination in Indonesia remains low due to the high-cost vaccination. The vaccine prices were affected by the production rate of L1, the active substance of HPV vaccines. L1 has been produced using various organisms with varying L1 production rates and immunogenicity. A systematic review and meta-analysis were conducted to determine the organism producing L1 with the highest production, treatments affecting the L1 expression rate, and immunogenicity (represented by anti-L1 IgG titer in mice). The data of L1 titer, induction period, and IgG titer were extracted from 19 articles that have passed the articles screening. The L1 titer and induction period data were used to calculate the L1 production rate, while the IgG titer was used in the immunogenicity analysis. On a 95% confidence level, the meta-analysis revealed weak evidence that E. coli produced L1 at the highest rate. The highest IgG titer was induced using L1 expressed in Saccharomyces cerevisiae, albeit insufficient evidence on 95% confidence level. Pearson’s correlation analysis showed that the concentration of glucose, IPTG, NH4+, K+, Ca2+, Mn2+, Fe2+, Zn2+, B4O72−, H2PO4−, HPO42−, Mo7O246−, and citric acid had a positive correlation with L1 production rate in E. coli. The treatment injection doses positively correlated with IgG titer in S. cerevisiae. This study reveals the mineral salts as the potential treatments to increase L1 production rates.

Comparative expression of soluble, active human kinases in specialized bacterial strains.

Kinases act as molecular switches for cellular functions and are involved in multiple human pathogeneses, most notably cancer. There is a continuous need for soluble and active kinases for in-vitro drug discovery and structural biology purposes. Kinases remain challenging to express using Escherichia coli, the most widely utilized host for heterologous expression. In this work, four bacterial strains, BL21 (DE3), BL21 (DE3) pLysS, Rosetta, and Arctic Express, were chosen for parallel expression trials along with BL21 (DE3) complemented with folding chaperones DnaJ/K and GroEL/ES to compare their performance in producing soluble and active human kinases. Three representative diverse kinases were studied, Epidermal Growth Factor Receptor kinase domain, Aurora Kinase A kinase domain, and Mitogen-activated protein Kinase Kinase. The genes encoding the kinases were subcloned into pET15b bacterial plasmid and transformed into the bacterial strains. Soluble kinase expression was tested using different IPTG concentrations (1–0.05 mM) at varying temperatures (37°C– 10°C) and induction times (3–24 hours). The optimum conditions for each kinase in all strains were then used for 1L large scale cultures from which each kinase was purified to compare yield, purity, oligomerization status, and activity. Although using specialized strains achieved improvements in yield and/or activity for the three kinases, none of the tested strains was universally superior, highlighting the individuality in kinase expression.

Expression of beta glucosidase mined from metagenomic DNA data of bacteria in Vietnamese goats’ rumen in \(\textit{Escherichia coli}\) system

Screening and expression of new β-glucosidase genes (bgc) have attracted much attention because of their valuable application in a wide range of industrial areas such as bioethanol production, food and animal feed processing, paper making, and biotechnological processes. Previously, we mined a new bgc gene coding for its mature enzyme (BGC) from metagenomic DNA data of bacteria in Vietnamese goats’ rumen. Based on the NCBI database, the BGC sequence was found to be the highest similarity with β-glucosidase of Bacteroidales bacterium (60.52%). The BGC enzyme was previously annotated to have two domains GH3 and GH31 and highly expressed in E. coli. The aim of this work was to experimentally confirm the predicted gene by expressing and assessing the activity of recombinant BGC from E. coli strains of BL21, Rosetta 1, C43, and SoluBL21. Furthermore, the expression level and solubility of the BGC were also investigated by varying fermentation conditions such as temperature, medium components, and IPTG concentration. The activity of the crude enzyme was identified through substrates including esculin and p-Nitrophenyl-β-D-glucopyranoside (pNPG). The new BGC could be used as potential material for further enzyme characterization.

Construction of cell factory capable of efficiently converting l-tryptophan into 5-hydroxytryptamine

Backgroundl-Tryptophan (l-Trp) derivatives such as 5-hydroxytryptophan (5-HTP) and 5-hydroxytryptamine (5-HT), N-Acetyl-5-hydroxytryptamine and melatonin are important molecules with pharmaceutical interest. Among, 5-HT is an inhibitory neurotransmitter with proven benefits for treating the symptoms of depression. At present, 5-HT depends on plant extraction and chemical synthesis, which limits its mass production and causes environmental problems. Therefore, it is necessary to develop an efficient, green and sustainable biosynthesis method to produce 5-HT.ResultsHere we propose a one-pot production of 5-HT from l-Trp via two enzyme cascades for the first time. First, a chassis cell that can convert l-Trp into 5-HTP was constructed by heterologous expression of tryptophan hydroxylase from Schistosoma mansoni (SmTPH) and an artificial endogenous tetrahydrobiopterin (BH4) module. Then, dopa decarboxylase from Harminia axyridis (HaDDC), which can specifically catalyse 5-HTP to 5-HT, was used for 5-HT production. The cell factory, E. coli BL21(DE3)△tnaA/BH4/HaDDC-SmTPH, which contains SmTPH and HaDDC, was constructed for 5-HT synthesis. The highest concentration of 5-HT reached 414.5 ± 1.6 mg/L (with conversion rate of 25.9 mol%) at the optimal conditions (substrate concentration,2 g/L; induced temperature, 25℃; IPTG concentration, 0.5 mM; catalysis temperature, 30℃; catalysis time, 72 h).ConclusionsThis protocol provided an efficient one-pot method for converting. l-Trp into 5-HT production, which opens up possibilities for the practical biosynthesis of natural 5-HT at an industrial scale.

Development of an indirect enzyme-linked immunosorbent assay for the detection of novel chicken orthoreovirus.

A novel avian orthoreovirus (N-ARV) variant characterized with obvious arthritis and synovial inflammation, was isolated from Shandong, China in May 2016. It caused chicken poor growth and enormous economic losses to the poultry industry of China. However, there are few effective methods for detecting the antibody levels of N-ARV. In this study, a viral structural protein σC was expressed using the prokaryotic expression vector pET32a (+). The target protein was obtained by inducing for 6 hours at an IPTG concentration of 0.6mM. The optimal dilution of the coating antigen and serum antibody were determined to be 1000 fold and 10 fold respectively. A specificity test showed that there was no positive reactivity between N-ARV and other pathogens, and when the positive serum was diluted 100 times detection results were still checkable. The repeatability of this method was determined by the inter assay and intra assay tests with variability ranging from 4.85% to 7.93%. In conclusion, this indirect enzyme linked immunosorbent assay (ELISA) will be useful for large-scale serological surveys and monitoring antibody levels in N-ARV infection.

RECOMBINANT ANTIBODY PRODUCTION BY CLONING OF Pepper yellow leaf curl Indonesia virus (PepYLCIV) COAT PROTEIN GENE

Pepper yellow leaf curl Indonesia virus (PepYLCIV) is an important pathogen on chili cultivation and is transmitted through the seed. Serological tests are sensitive, accurate, efficient and it has been widely used for the detection of seed-transmitted plant viruses. This study aimed to produce PepYLCIV recombinant protein as a material to produce recombinant antibodies PepYLCIV. DNA was extracted from infected chili leaves collected from Congkrang, Muntilan, Central Java verified using primer PepYLCIV-BamHI and PepYLCIV-EcoRI and produced an amplicon at 840 bp. The amplified fragments were cloned into the pET32a then transformed to Escherichia coli BL21. The percentage of nucleotide sequence identity and sequence of amino acid, PepYLCIV CK-6 isolates had the highest similarity of nucleotide and amino acid sequences to of chili isolates from Bandung. The expressed recombinant protein was obtained with IPTG concentration 0,5 mM and harvested at 6 hours after IPTG induction. SDS PAGE analysis of the recombinant plasmid Begomovirus CK-6 showed that the coat protein size was about 29 kDa. Immunization was carried out on rabbits by injecting 150 µg of recombinant protein 4 times with an interval of 1 week to produce crude antiserum and pure antiserum capable of detecting PepYLCIV in chili and Ageratum conyzoides using I-ELISA and DIBA tests.

Heterologous expression, on-column refolding and characterization of gamma-glutamyl transpeptidase gene from Bacillus altitudinis IHB B1644: A microbial bioresource from Western Himalayas

Several γ-glutamyl compounds produced from gamma-glutamyltranspeptidase (GGT) have alluring features for food, pharmaceutical, and biotechnology applications. GGT from Bacillus altitudinis IHB B1644 was cloned, followed by an expression in pET-47b(+) Escherichia coli BL21(DE3). Recombinant GGT (BaGGT) gene subsisted of 1755 bp encoding protein with 585 amino acids, predicted molecular weight, and theoretical pI of 63.3 kDa, and 4.92, respectively. Ectopic expression resulted in inclusion bodies formation at 37 °C. The protein was solubilized and different strategies like dialysis, rapid dilution, and on-column refolding were tried to get active recombinant protein (BaGGT1). To get protein in soluble fraction, GGT was over expressed at low temperature (20 °C), and IPTG concentration (0.025 mM) (BaGGT2). The heterodimeric enzyme consisted of molecular weight of 40, and 22 kDa for large and small subunits, respectively. The specific activities for BaGGT1 and BaGGT2 were 263.9, and 497.45 U mg−1, respectively. BaGGT1 and BaGGT2 showed optimum temperature, and pH at 37 °C and 9, respectively. Km values of 0.8 and 0.2 mM, and Vmax of 666.67 and 333.33 U mg−1 of protein, were calculated for BaGGT1and BaGGT2, respectively. The results demonstrate potential of BaGGT in biosynthesis of γ-glutamyl compounds with industrial application.

Molecular Cloning of DARPins G3 in pET28b Expression Vector and Optimization of the Expression of This Protein in Escherichia Coli

Background: Human epidermal growth factor receptor 2 (HER2) is over-expressed in breast, ovarian, gastric, and prostate cancers and is used as a tumor marker in the diagnosis of cancer. Monoclonal antibodies have been used as a diagnostic and therapeutic tool against HER2. Because of the difficulties associated with the stability and complexity of the construct and the high cost of antibody production, we aimed to investigate, cloning, and expression of HER2- binding DARPins genes to identify, HER2-positive tumor markers, we aimed to investigate. Materials and Methods: After synthesis, the DARPins peptide gene was cloned into the M13 vector and sub-cloned into the TOP10 pet28b bacterial vector. After culturing the bacteria on an agarose plate containing antibiotics, the transfected bacteria expressing the DARPins gene were selected. To ensure gene cloning, we used enzymatic digestion and recombinant plasmid delivery for sequencing. Isopropyl β-d-1-thiogalactopyranosideIPTG was used for the induction of recombinant protein expression and the SDS-PAGE method and Western blot for expression confirmation. Results: The polymerase chain reaction (PCR) amplification product of DARPins was analyzed using agarose gel electrophoresis. Plasmid was purified from the positive clone by PCR cloning, sequenced and gene cloning was confirmed. After culturing from competent cells, protein expression was obtained from positive colonies. SDS- PAGE results showed the effect of different conditions including temperature, IPTG concentration, and time on the pET-DARPins expression. Conclusion: We were succeeded to express a new codon-optimized DARPins gene in Escherichia coli and HEK293t system.

Overproduction, Purification and Refolding of codon-optimized Hepatitis B Virus X Protein Subgenotype B3 in Escherichia coli BL21(DE3)

Hepatitis B virus (HBV) infects human and causes chronic liver infection, leading to liver cirrhosis and hepatocellular carcinoma. HBV X (Hbx) protein is known to interact with tumor suppressor protein p53 and block its translocation into the nucleus. This study outlines the overproduction of Hbx protein from HBV subgenotype B3 in Escherichia coli BL21(DE3), including its purification and refolding. The gene encoding Hbx was first codon-optimized and inserted into pET16b. The recombinant plasmid was then transformed into E. coli BL21(DE3) as an expression host. Optimization of Hbx expression was performed with variation of IPTG concentration and overproduction temperature. The results showed that Hbx protein was optimally induced by 0.075 mM IPTG and overproduction of Hbx at 17, 25, and 37°C exhibited no difference in protein level and location. The optimal refolding of Hbx was obtained using 0.1 M arginine prior to elution from Nickel column using 100 mM imidazole and 0.25 M arginine. Hbx migrates differently in SDS-PAGE reducing and non-reducing, while the melting curve pattern in TSA analysis changed after the refolding step. Essentially, this purified Hbx protein could potentially be used for interaction study with p53 and the inhibitor candidate of the protein.

Co-Expression of Chaperones for Improvement of Soluble Expression and Purification of An Anti-HER2 scFv in Escherichia Coli.

Single-chain fragment variable (scFv) is one of the most commonly used antibody fragments. They offer some advantages over full-length antibodies, including better penetration to target tissues. However, their functional production has been a challenge for manufacturers due to the potential misfolding and formation of inclusion bodies. Here we evaluated the soluble expression and purification of molecular chaperone co-expression. E. coli BL21(DE3) cells were co-transformed with the mixture of plasmids pKJE7 and pET22b-scFv by the electroporation method. First, L-arabinose was added to induce the expression of molecular chaperones, and then IPTG was used as an inducer to start the expression of anti-HER2 scFv. The effect of cultivation temperature and IPTG concentration on soluble expression of the protein with or without chaperones was evaluated. The soluble expressed protein was subjected to native purification using the Ni-NTA affinity column. SDS-PAGE analysis confirmed the successful co-expression of anti-HER2-scFv and DnaK/DnaJ/GrpE chaperones. Co-expression with chaperones and low-temperature cultivation synergistically improved the soluble expression of anti-HER2 scFv. Co-expression with chaperone also exhibited an approximately four-fold increase in the final yield of purified soluble protein. The combination of co-expression with chaperones and low temperature presented in this work may be useful for the improvement of commercial production of other scFvs in E. coli as functionally bioactive and soluble form.

Optimization of Expression and Purification of Recombinant Mouse plac1.

Background:Placenta-specific 1 (PLAC1) is one of the recently-discovered Cancer-Testis-Placenta (CTP) antigen with restricted normal tissue and ectopic expression in a wide range of cancer cells from different histological origins. The production of recombinant human PLAC1 has already been optimized; however, no study has been reported so far on the production and purification of mouse plac1. In this study, mouse plac1 expression and purification was optimized in a prokaryotic system and the effects of the generated proteins on inducing humoral responses in mice were investigated.Methods:A fusion protein containing full extracellular domain of mouse plac1, immunostimulatory peptides, tetanus toxin P2P30 and PADRE and KDEL3 signal (main plac1), and the same fragment without immunostimulatory peptides (control plac1) was produced. To optimize production and purification steps, different parameters including bacterial strain, cultivation temperature, cultivation time, IPTG concentration, culture medium, and also different buffers for purification of the recombinant proteins were tested. After confirming the identity of recombinant plac1 proteins with Western Blotting (WB) and ELISA assays, these proteins were subcutaneously injected in mice with Freund's adjuvant and the anti-plac1 antibody response was detected by ELISA.Results:The optimal expression level of main and control plac1 was obtained in BL21 (DE3) and TB culture medium in the presence of 0.25 mM IPTG after 24 hr of induction at 15°C. The buffer containing 2% sarkosyl produced higher yield and purity. Our results showed specific reactivity of anti-human recombinant plac1 polyclonal antibody with both main and control plac1 recombinant proteins in WB and ELISA analysis. Both proteins induced humoral responses in mice; however, anti-plac1 antibody titer was significantly higher in sera of mice immunized with main compared to control plac1.Conclusion:In this study, an optimized protocol for production and purification of mouse plac1 was reported and it was shown that insertion of immunostimulatory peptides in gene construct could efficiently enhance humoral immune responses against mouse plac1, which could potentially augment cellular immune responses against plac1 leading to more effective anti-cancer responses.

Model-based dynamic engineering of Escherichia coli for N-acetylglucosamine overproduction

N-acetylglucosamine (GlcNAc), a glucosamine derivative, has a wide range of applications in pharmaceutical fields, and there is an increasing interest in the efficient production of GlcNAc genetic engineered bacteria. In this work, Escherichia coli ATCC 25947 (DE3) strain was engineered by a model-based dynamic regulation strategy achieving GlcNAc overproduction. First, the GlcNAc synthetic pathway was introduced into E. coli, and through flux balance analysis of the genome-scale metabolic network model, metabolic engineering strategies were generated to further increase GlcNAc yield. Knock-out of genes poxB and ldhA, encoding pyruvate oxidase and lactate dehydrogenase, increased GlcNAc titer by 5.1%. Furthermore, knocking out N-acetylmuramic acid 6-phosphate etherase encoded by murQ and enhancing glutamine synthetase encoded by glnA gene further increased GlcNAc titer to 130.8 g/L. Analysis of metabolic flux balance showed that GlcNAc production maximization requires the strict dynamic restriction of the reactions catalyzed by pfkA and zwf to balance cell growth and product synthesis. Hence, a dynamic regulatory system was constructed by combining the CRISPRi (clustered regularly interspaced short palindromic repeats interference) system with the lactose operon lacI and the transcription factor pdhR, allowing the cell to respond to the concentration of pyruvate and IPTG to dynamically repress pfkA and zwf transcription. Finally, the engineered bacteria with the dynamic regulatory system produced 143.8 g/L GlcNAc in a 30-L bioreactor in 55 h with a yield reaching 0.539 g/g glucose. Taken together, this work significantly enhanced the GlcNAc production of E. coli. Moreover, it provides a systematic, effective, and universal way to improve the synthetic ability of other engineered strains.

Characterization and application of a recombinant dopa decarboxylase from Harmonia axyridis for the efficient biosynthesis of dopamine

Here, a dopa decarboxylase (DDC) from Harmonia axyridis was heterogeneously expressed in Escherichia coli for the efficient biosynthesis of dopamine. For the production of recombinant DDC, the cultivation conditions including IPTG concentration, temperature and induction time were optimized and obtained an optimal specific enzyme activity of 51.72 U·mg−1 crude extracts. After the purification of DDC with a recovery yield of 68.79%, its activity was further characterized. The Vmax, Km, Kcat, and Kcat/Km of DDC for dihydroxyphenylalanine (dopa) were 0.02 mmol·ml−1·s−1, 2.328 mmol·ml−1, 10435.90 s−1 and 4482.77 ml·mmol−1·s−1, respectively. The highest DDC activity was observed at the condition of pH 7.5 and 45 °C. With the purified DDC, the feasibility to produce dopamine from L-dopa was evaluated. The optimal yield was determined at the following bioconversion conditions: pH of 7.0, the reaction temperature of 40 °C, 0.4 mmol·L−1 of PLP and 4 g·L−1 of L-dopa. Subsequently, a fed-batch process for the production of dopamine was developed and the effect of oxygen was evaluated. The titer, yield and productivity of dopamine reached up to 21.99 g·L−1, 80.88% and 14.66 g·L−1·h−1 at 90 min under anaerobic condition.

Artificial Consortium of Three E. coli BL21 Strains with Synergistic Functional Modules for Complete Phenanthrene Degradation.

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic and persistent organic pollutions that can accumulate in the environment. In this study, an aromatic ring cleavage module, a salicylic acid synthesis module, and a catechol metabolism module were respectively constructed in three Escherichia coli BL21 strains. Subsequently, the engineered strains were cocultured as an artificial consortium for the biodegradation of phenanthrene, a typical PHA. Single factor experiments and response surface methodology were used to identify the optimal degradation conditions, including an inoculation interval of 6 h, inoculation ratio of 1:1:1, and IPTG concentration of 2 mM. Under these conditions, the 7-day degradation ratio of 100 mg/L phenanthrene reached 72.67%. Moreover, the engineered Escherichia coli BL21 strains showed good phenanthrene degradation ability at substrate concentrations 10 mg/L up to 500 mg/L. Enzyme activity assays combined with gas chromatography-mass spectrometry measurements confirmed that the three engineered strains behaved as a synergistic consortium in the phenanthrene degradation process. Based on the analysis of the key metabolites, the engineered bacteria were supplemented at 7-day intervals in batches so that each engineered strain maintained its optimal degradation ability. The 21-day degradation ratio finally reached 90.66%, which was much higher than what was observed with simultaneous inoculation. These findings suggest that the three engineered strains with separate modules constructed in this study offer an attractive solution for removing PAHs from the environment.

Heat shock transformation and expression of the plasmid containing cytolethal distending toxin of Campylobacter fetus subsp venerealis in Escherichia coli

The cytolethal distending toxins (cdt) is a multi-subunit toxin consisted of three subunit encoded cdtA, cdtB and cdtC. The cdt played an important role as a virulence factor of Campylobacter infection, including C. fetus subsp venerealis. The cdtA which responsible for binding the cdt to cell membrane, was cloned in plasmid expression and inserted into bacterial cells of Escherichia coli BL21(DE3). The research was conducted to evaluate the transformation using the heat shock method of a plasmid containing cdtA3 gene and the protein expression induced by various concentration of IPTG. Transformation was done using the heat shock method at 42oC for 90 second. Evaluation of the transformation was observed on the presence of E. coli BL21(DE3) colonies on Luria Bertani agar containing Ampicillin antibiotic with 100 µg/mL dosage. The recombinant protein was expressed using IPTG-induction with various concentration (0.1mM, 0.25mM, 0.5mM, 0.75mM and 1 mM). The result showed that the transformation and IPTG-induction 0.1 mM produced higher concentration of protein than other concentration applied. The protein characterization was observed with SDS PAGE and cdtA3 protein was detected on 23,4 kDa.