High-level extracellular production of α-cyclodextrin glycosyltransferase with recombinant Escherichia coli BL21 (DE3)

A holistic approach for process intensification of nicotinamide mononucleotide production via high cell density cultivation under exponential feeding strategy

Nicotinamide mononucleotide (NMN) subsists in all living organisms and has drawn tremendous attention as a nutraceutical and pharmaceutical product for several diseases such as Alzheimer's, cancer, aging, and vascular dysfunction. Here, NMN was produced intracellularly in a high cell density bioreactor using an engineered Escherichiacoli strain via exponential feeding of co-substrates. Fed-batch culture via exponential feeding of co-substrate (glucose) and continuous feeding of substrate (nicotinamide) were performed using different cumulative nicotinamide concentrations. The highest concentration of 19.3 g/L NMN with a dry cell weight of 117 g/L was acquired from a cumulative nicotinamide concentration of 7.2 g/L with a conversion of 98 % from nicotinamide in 28 h. Further, liquid chromatography-mass spectrometry analysis validated the NMN production. This approach will be beneficial in achieving simultaneously low cost and ensuring high quality and quantity of NMN production.

CRISPR-Based Construction of a BL21 (DE3)-Derived Variant Strain Library to Rapidly Improve Recombinant Protein Production

Escherichia coli BL21 (DE3) is the most widely used host for recombinant protein expression. However, not every protein can be highly expressed in BL21 (DE3), so individual optimization strategies are often required for different proteins, which is time-consuming and difficult to apply rapidly for industrial production. Constructing more hosts is a good choice to enrich protein expression selection. The expression level of T7 RNAP is the core control node of the pET expression system, so regulating its expression level is an effective way of improving the production of difficult-to-express proteins. Various BL21 (DE3)-derived variant hosts with different translation levels of T7 RNAP could be obtained by changing the ribosomal binding site (RBS) sequences of T7 RNAP in a genome. Here, a BL21 (DE3)-derived variant strain library with different RBS sequences of T7 RNAP was constructed using a base editor and CRISPR-Cas9. Notably, the CRISPR-Cas9 system combined with degenerate primers enabled the construction of an RBS library with 87.5% of the theoretical coverage in single editing, which is more convenient and efficient than the use of a base editor. The expression level of a target gene in the variant strain library ranged from 28 to 220% of the parental strain. Furthermore, a high-throughput host-screening platform for recombinant protein production was constructed, which enabled us to obtain the best expression host for certain target proteins in only 3 days. As a proof of concept, the production of all eight difficult-to-express proteins was greatly improved, including autolytic protein, membrane proteins, antimicrobial peptides, and hardly soluble proteins. Among them, the expression of glucose dehydrogenase in the best host exhibited a 298-fold increase compared to the parental strain. This strategy is simple and effective, requires no advanced equipment, and can be carried out in any laboratory.

Efficient secretory expression of Bacillus stearothermophilus α/β-cyclodextrin glycosyltransferase in Bacillus subtilis

Bacillus stearothermophilus α/β-cyclodextrin glycosyltransferase (α/β-CGTase) is an excellent transglycosylase with broad potential for food application, but its expression level is low in Bacillus subtilis. In this study, the optimal signal peptide for α/β-CGTase expression was screened from 173 signal peptides in B. subtilis WS11. The α/β-CGTase activity in a 3-L fermentor reached 151.93 U⋅ mL^-1, but substantial amounts of inclusion bodies were produced. The N-terminal 12 amino acids of α/β-CGTase were then replaced with the N-terminal 15 amino acids of a β-CGTase from the same family that has a high percentage of disorder-promoting amino acids. As a result, the inclusion bodies were significantly reduced, and the enzyme activity increased to 249.35 U mL^-1, 2.3 times that of the strain constructed previously. Finally, the ppsE and sfp genes of B. subtilis WS11, which are related to lipopeptide biosurfactant synthesis, were knocked out to produce B. subtilis WS13. When B. subtilis WS13 was used to produce α/β-CGTase in a 3-L fermentor, 70 % less defoaming agent was required than with B. subtilis WS11. Furthermore, enzyme production and growth of WS13 were equivalent to those of WS11. This study is of great significance for future research to efficiently scale-up production of α/β-CGTase.

Production of Enantiopure Chiral Epoxides with E. coli Expressing Styrene Monooxygenase

Styrene monooxygenases are a group of highly selective enzymes able to catalyse the epoxidation of alkenes to corresponding chiral epoxides in excellent enantiopurity. Chiral compounds containing oxirane ring or products of their hydrolysis represent key building blocks and precursors in organic synthesis in the pharmaceutical industry, and many of them are produced on an industrial scale. Two-component recombinant styrene monooxygenase (SMO) from Marinobacterium litorale was expressed as a fused protein (StyAL2StyB) in Escherichia coli BL21(DE3). By high cell density fermentation, 35 g_DCW/L of biomass with overexpressed SMO was produced. SMO exhibited excellent stability, broad substrate specificity, and enantioselectivity, as it remained active for months and converted a group of alkenes to corresponding chiral epoxides in high enantiomeric excess (˃95–99% ee). Optically pure (S)-4-chlorostyrene oxide, (S)-allylbenzene oxide, (2R,5R)-1,2:5,6-diepoxyhexane, 2-(3-bromopropyl)oxirane, and (S)-4-(oxiran-2-yl)butan-1-ol were prepared by whole-cell SMO.

Inhibition of E. coli Host RNA Polymerase Allows Efficient Extracellular Recombinant Protein Production by Enhancing Outer Membrane Leakiness

With the growing interest in continuous cultivation of Escherichia coli, secretion of product to the medium is not only a benefit, but a necessity in future bioprocessing. In this study, it is shown that induced decoupling of growth and heterologous gene expression in the E. coli X-press strain (derived from BL21(DE3)) facilitates extracellular recombinant protein production. The effect of the process parameters temperature and specific glucose consumption rate (q_S ) on growth, productivity, lysis and leakiness, is investigated, to find the parameter space allowing extracellular protein production. Two model proteins are used, Protein A (SpA) and a heavy-chain single-domain antibody (VHH), and performance is compared to the industrial standard strain BL21(DE3). It is shown that inducible growth repression in the X-press strain greatly mitigates the effect of metabolic burden under different process conditions. Furthermore, temperature and q_S are used to control productivity and leakiness. In the X-press strain, extracellular SpA and VHH titer reach up to 349 and 19.6 mg g^-1 , respectively, comprising up to 90% of the total soluble product, while keeping cell lysis at a minimum. The findings demonstrate that the X-press strain constitutes a valuable host for extracellular production of recombinant protein with E. coli.

Combined Optimization of Codon Usage and Glycine Supplementation Enhances the Extracellular Production of a β-Cyclodextrin Glycosyltransferase from Bacillus sp. NR5 UPM in Escherichia coli

Two optimization strategies, codon usage modification and glycine supplementation, were adopted to improve the extracellular production of Bacillus sp. NR5 UPM β-cyclodextrin glycosyltransferase (CGT-BS) in recombinant Escherichia coli. Several rare codons were eliminated and replaced with the ones favored by E. coli cells, resulting in an increased codon adaptation index (CAI) from 0.67 to 0.78. The cultivation of the codon modified recombinant E. coli following optimization of glycine supplementation enhanced the secretion of β-CGTase activity up to 2.2-fold at 12 h of cultivation as compared to the control. β-CGTase secreted into the culture medium by the transformant reached 65.524 U/mL at post-induction temperature of 37 °C with addition of 1.2 mM glycine and induced at 2 h of cultivation. A 20.1-fold purity of the recombinant β-CGTase was obtained when purified through a combination of diafiltration and nickel-nitrilotriacetic acid (Ni-NTA) affinity chromatography. This combined strategy doubled the extracellular β-CGTase production when compared to the single approach, hence offering the potential of enhancing the expression of extracellular enzymes, particularly β-CGTase by the recombinant E. coli.

Improved Activity of Sulfolobus acidocaldarius Maltooligosyltrehalose Synthase through Directed Evolution

Maltooligosyltrehalose synthase (MTSase) is a key enzyme for the production of trehalose from starch. Thermophilic MTSases offer advantages for trehalose production but suffer from low yield. In this study, directed evolution was used to increase the production of Sulfolobus acidocaldarius MTSase (SaMTSase) in Escherichia coli. Mutant libraries constructed using error-prone polymerase chain reaction were assessed using high-throughput activity assays. Three mutants with enhanced activities were obtained, the best of which (mutant D-4) exhibited 2.4 times greater activity than wild-type SaMTSase. The specific activity and catalytic efficiency of D-4 were also greater than those of wild-type SaMTSase. The D-4 activity (624.7 U·mL^-1) produced in a 3 L fermenter was 2.0 times greater than that of wild-type SaMTSase. Because the same trehalose yield was obtained using an equal amount of either D-4 or wild-type SaMTSase activity, using D-4 will significantly lower the cost of trehalose production. The activities of the individual mutations present in the three SaMTSase mutants obtained using directed evolution were analyzed. Mutants F284V and T439A exhibited the greatest increases in enzyme activity. Homology models suggested that the decreased side-chain size, weakened hydrophobicity, and decreased interaction might enhance the flexibility of the loop containing catalytic residue Asp443, which was conducive to catalysis.

High-level extracellular production of an alkaline pectate lyase in E. coli BL21 (DE3) and its application in bioscouring of cotton fabric

A high heterologous expression of an alkaline pectate lyase (APL) pelNK93I in E. coli was obtained through optimizing the lactose feeding and fed-batch fermentation. The highest soluble APL activity produced by E. coli BL21 (pET22b-pelNK93I) was 10,181 U/mL which is the highest level so far. On this basis, to improve the extracellular yield of APL, optimized glycine feeding was used to achieve elevated extracellular production of pelNK93I. The highest extracellular APL activity produced by E. coli BL21 (pET22b-pelNK93I) was 6357 U/mL which was also relatively higher than that in previous reports. The final productivity of APL was 282.8 U/mL/h in the fermentation of E. coli BL21 (pET22b-pelNK93I) in a 10 L fermenter. Thus the current study has provided a cost-effective method for the over-expression and preparation of alkaline pectate lyase pelNK93I for its industrial applications. Moreover, pelNK93I (4 U/mL) used for bioscouring increased cottonseed husk removal and radial capillary effect of cotton fabric by 37.63% and 47.06%, respectively, making it a promising enzyme in green textile technology.

High-level extracellular secretion and characterization of the thermophilic β-cyclodextrin glucanotranferase from Paenibacillus campinasensis in Escherichia coli

A strain CGT-1 producing β-cyclodextrin glucanotranferase (β-CGTase) was identified as Paenibacillus campinasensis by morphological analysis and 16s rDNA analysis. The gene coding for β-CGTase was cloned, sequenced, and expressed in Escherichia coli BL21(DE3). Recombinant β-CGTase was purified and its purity evaluated by SDS-PAGE, showing it encodes a mature protein with a molecular mass of 74 kDa. The β-CGTase was most active at pH 7.0 and 65 °C, respectively. More than 80% activity was retained after incubation at 55 °C for 5 h. The stability of the enzyme was in a pH range from 5.5 to 10.0. The K _m and V _max for the enzyme activity on CGTase were 3.75 mg/mL and 290.75 μmol/min, respectively. The recombinant plasmid pET28a-DacD-cgt-his, pET28a-OmpA-cgt-his, pET28a-OmpT-cgt-his, and pET28a-CGTase-cgt-his were constructed by cloning the signal peptide genes DacD, OmpA, OmpT, and signal peptide derived from cgtase gene into pET28a-cgt-his, respectively. The production of the recombinant β-CGTase with pET28a-DacD-cgt-his reached 60.89 U/mL after 72 h of culture, which produced an approximately 1.98, 2.93, 4.15 to 9.74-fold higher activity than those containing OmpA, CGTase, OmpT, and the control without signal peptide, respectively. The culture conditions for extracellular production of the recombinant β-CGTase in E. coli BL21(DE3) were optimized. The CGTase activity reached the highest level (37.67 U/mL) under the induction of 0.03 mM IPTG at OD₆₀₀ of 0.8 at 30 °C after 48 h of culture. Optimization of the extracellular secretion of the β-CGTase from Paenibacillus campinasensis in recombinant E. coli laid the foundation for further industrial production and application of β-CGTase.

Production of recombinant beta-amylase of Bacillus aryabhattai

In this study, the effects of carbon source, nitrogen source, and metal ions on cell growth and Bacillus aryabhattai β-amylase production in recombinant Brevibacillus choshinensis were investigated. The optimal medium for β-amylase production, containing glucose (7.5 g·L^-1), pig bone peptone (40.0 g·L^-1), Mg²⁺ (0.05 mol·L^-1), and trace metal elements, was determined through single-factor experiments in shake flasks. When cultured in the optimized medium, the β-amylase yield reached 925.4 U mL^-1, which was 7.2-fold higher than that obtained in the initial medium. Besides, a modified feeding strategy was proposed and applied in a 3-L fermentor fed with glucose, which achieved a dry cell weight of 15.4 g L^-1. Through this cultivation approached 30 °C with 0 g·L^-1 initial glucose concentration, the maximum β-amylase activity reached 5371.8 U mL^-1, which was 41.7-fold higher than that obtained with the initial medium in shake flask.

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.

Cyclodextrin enhanced the soluble expression of Bacillus clarkii γ-CGTase in Escherichia coli

BACKGROUND

Cyclodextrin glycosyltransferases (CGTases) catalyze the synthesis of cyclodextrins, which are circular α-(1,4)-linked glucans used in many applications in the industries related to food, pharmaceuticals, cosmetics, chemicals, and agriculture, among others. Economic use of these CGTases, particularly γ-CGTase, requires their efficient production. In this study, the effects of chemical chaperones, temperature and inducers on cell growth and the production of soluble γ-CGTase by Escherichia coli were investigated.

RESULTS

The yield of soluble γ-CGTase in shake-flask culture approximately doubled when β-cyclodextrin was added to the culture medium as a chemical chaperone. When a modified two-stage feeding strategy incorporating 7.5 mM β-cyclodextrin was used in a 3-L fermenter, a dry cell weight of 70.3 g·L^- 1 was achieved. Using this cultivation approach, the total yield of γ-CGTase activity (50.29 U·mL^- 1) was 1.71-fold greater than that observed in the absence of β-cyclodextrin (29.33 U·mL^- 1).

CONCLUSIONS

Since β-cyclodextrin is inexpensive and nontoxic to microbes, these results suggest its universal application during recombinant protein production. The higher expression of soluble γ-CGTase in a semi-synthetic medium showed the potential of the proposed process for the economical production of many enzymes on an industrial scale.

Efficient Expression of Maltohexaose-Forming α-Amylase from Bacillus stearothermophilus in Brevibacillus choshinensis SP3 and Its Use in Maltose Production

The maltohexaose-forming, Ca²⁺-independent α-amylase gene from Bacillus stearothermophilus (AmyMH) was efficiently expressed in Brevibacillus choshinensis SP3. To improve the production of AmyMH in B. choshinensis SP3, the temperature and initial pH of culture medium were optimized. In addition, single-factor and response surface methodologies were pursued to optimize culture medium. Addition of proline to the culture medium significantly improved the production of recombinant α-amylase in B. choshinensis SP3. This improvement may result from improved cellular integrity of recombinant B. choshinensis SP3 in existence of proline. Culture medium optimization resulted in an 8-fold improvement in α-amylase yield, which reached 1.72 × 10⁴ U·mL⁻¹. The recombinant α-amylase was applied to the production of maltose on a laboratory scale. A maltose content of 90.72%, which could be classified as an extremely high maltose syrup, could be achieved using 15% (m/v) corn starch as the substrate. This study demonstrated that the B. choshinensis SP3 expression system was able to produce substantial quantities of recombinant α-amylase that has potential application in the starch industry.

A Bacillus paralicheniformis Iron-Containing Urease Reduces Urea Concentrations in Rice Wine

Urease, a nickel-containing metalloenzyme, was the first enzyme to be crystallized and has a prominent position in the history of biochemistry. In the present study, we identified a nickel urease gene cluster, ureABCEFGDH, in Bacillus paralicheniformis ATCC 9945a and characterized it in Escherichia coli Enzymatic assays demonstrate that this oxygen-stable urease is also an iron-containing acid urease. Heterologous expression assays of UreH suggest that this accessory protein is involved in the transmembrane transportation of nickel and iron ions. Moreover, this iron-containing acid urease has a potential application in the degradation of urea in rice wine. The present study not only enhances our understanding of the mechanism of activation of urease but also provides insight into the evolution of metalloenzymes.IMPORTANCE An iron-containing, oxygen-stable acid urease from B. paralicheniformis ATCC 9945a with good enzymatic properties was characterized. This acid urease shows activities toward both urea and ethyl carbamate. After digestion with 6 U/ml urease, approximately 92% of the urea in rice wine was removed, suggesting that this urease has great potential in the food industry.

Efficient extracellular recombinant production and purification of a Bacillus cyclodextrin glucanotransferase in Escherichia coli

BACKGROUND

Cyclodextrin glucanotransferases (CGTases) catalyze the synthesis of cyclodextrins, cyclic oligosaccharides composed of glucose monomers that find applications in the pharmaceutical, food, and cosmetic industries. An economic application of these industrially important enzymes requires their efficient production and recovery. In this study, the effect of Sec-type signal peptides on the recombinant expression of a CGTase derived from Bacillus sp. G825-6 was investigated in Escherichia coli BL21(DE3) using a codon-adapted gene. In addition, a novel purification method for the CGTase using starch adsorption was developed.

RESULTS

Expression vectors encoding N-terminal PelB, DacD, and the native Bacillus sp. G825-6 CGTase signal peptides (SP) were constructed for the recombinant CGTase. With the DacD SP derived from E. coli, a 3.9- and 3.1-fold increase in total enzyme activity was obtained compared to using the PelB and the native CGTase SP, respectively. DacD enabled a 7.3-fold increase of activity in the extracellular fraction after induction for 24 h compared to the native CGTase SP. After induction for 48 h, 75% of the total activity was detected in the extracellular fraction. By a batch wise adsorption to starch, the extracellular produced CGTase could be purified to homogeneity with a yield of 46.5% and a specific activity of 1637 U/mg.

CONCLUSIONS

The signal peptide DacD promoted the high-level heterologous extracellular expression of a recombinant CGTase from Bacillus sp. G825-6 with a pET20b(+) vector in E. coli BL21(DE3). A protocol based on starch adsorption enabled a fast and efficient purification of the recombinant enzyme.

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.

Enhanced extracellular production of recombinant proteins in Escherichia coli by co-expression with Bacillus cereus phospholipase C

BACKGROUND

Our laboratory has reported a strategy for improving the extracellular production of recombinant proteins through co-expression with Thermobifida fusca cutinase, which increases membrane permeability via its phospholipid hydrolysis activity. However, the foam generated by the lysophospholipid product makes the fermentation process difficult to control in a fermentor. Phospholipase C (PLC) catalyzes the hydrolysis of phospholipids to produce sn1,2-diacylglycerides and organic phosphate, which do not induce foam formation. Therefore, co-expression with Bacillus cereus PLC was investigated as a method to improve the extracellular production of recombinant proteins.

RESULTS

When B. cereus PLC was expressed in Escherichia coli without its signal peptide, 95.3% of the total PLC activity was detected in the culture supernatant. PLC expression enhanced membrane permeability without obvious cell lysis. Then, six test enzymes, three secretory and three cytosolic, were co-expressed with B. cereus PLC. The enhancement of extracellular production correlated strongly with the molecular mass of the test enzyme. Extracellular production of Streptomyces sp. FA1 xylanase (43 kDa), which had the lowest molecular mass among the secretory enzymes, was 4.0-fold that of its individual expression control. Extracellular production of glutamate decarboxylase (51 kDa), which had the lowest molecular mass among the cytosolic enzymes, reached 26.7 U/mL; 88.3% of the total activity produced. This strategy was effectively scaled up using a 3-L fermentor. No obvious foam was generated during this fermentation process.

CONCLUSIONS

This is the first study to detail the enhanced extracellular production of recombinant proteins through co-expression with PLC. This new strategy, which is especially appropriate for lower molecular mass proteins, allows large-scale protein production in an easily controlled fermentation process.

Efficient Extracellular Expression of Metalloprotease for Z-Aspartame Synthesis

Metalloprotease PT121 and its mutant Y114S (Tyr114 was substituted to Ser) are effective catalysts for the synthesis of Z-aspartame (Z-APM). This study presents the selection of a suitable signal peptide for improving expression and extracellular secretion of proteases PT121 and Y114S by Escherichia coli. Co-inducers containing IPTG and arabinose were used to promote protease production and cell growth. Under optimal conditions, the expression levels of PT121 and Y114S reached >500 mg/L, and the extracellular activity of PT121/Y114S accounted for 87/82% of the total activity of proteases. Surprisingly, purer protein was obtained in the supernatant, because arabinose reduced cell membrane permeability, avoiding cell lysis. Comparison of Z-APM synthesis and caseinolysis between proteases PT121 and Y114S showed that mutant Y114S presented remarkably higher activity of Z-APM synthesis and considerably lower activity of caseinolysis. The significant difference in substrate specificity renders these enzymes promising biocatalysts.

Extracellular expression of glutamate decarboxylase B in Escherichia coli to improve gamma-aminobutyric acid production

Escherichia coli overexpressing glutamate decarboxylase GadB can produce gamma-aminobutyric acid with addition of monosodium glutamate. The yield and productivity of gamma-aminobutyric acid might be significantly improved if the overexpressed GadB in E. coli cells can be excreted outside, where it can directly transforms monosodium glutamate to gamma-aminobutyric acid. In this study, GadB was fused to signal peptides TorA or PelB, respectively, and overexpressed in E. coli BL21(DE3). It was found that TorA could facilitate GadB secretion much better than PelB. Conditions for GadB secretion and gamma-aminobutyric acid production were optimized in E. coli BL21(DE3)/pET20b-torA-gadB, leading the secretion of more than half of the overexpressed GadB. Fed-batch fermentation for GadB expression and gamma-aminobutyric acid production of BL21(DE3)/pET20b-torA-gadB was sequentially performed in one fermenter; 264.4 and 313.1 g/L gamma-aminobutyric acid were obtained with addition of monosodium glutamate after 36 and 72 h, respectively.

Efficient extracellular expression of Bacillus deramificans pullulanase in Brevibacillus choshinensis

In this study, the pullulanase gene from Bacillus deramificans was efficiently expressed in Brevibacillus choshinensis. The optimal medium for protein expression was determined through a combination of single-factor experiments and response surface methodology. The initial pH of the medium and the culture temperature were optimized. The pullulanase yield increased 10.8-fold through medium and condition optimization at the shake-flask level. From the results of these experiments, the dissolved oxygen level was optimized in a 3-L fermentor. Under these optimized conditions, the pullulanase activity and the specific pullulanase productivity reached 1005.8 U/mL and 110.5 × 103 U/g dry cell weight, respectively, with negligible intracellular expression. The Brevibacillus choshinensis expression system has proven to be valuable for the extracellular production of pullulanase.

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).

Enhanced extracellular production of recombinant Bacillus deramificans pullulanase in Escherichia coli through induction mode optimization and a glycine feeding strategy

Process optimization strategies were developed to improve extracellular production of recombinant Bacillus deramificans pullulanase in Escherichia coli. Cell growth and pullulanase production in shake-flask cultures were investigated as a function of the concentration of added glycine, and the type and concentration of inducer. From the results of these experiments, a fed-batch fermentation strategy for high-cell-density cultivation was applied in a 3-L fermentor. The gradual addition of lactose was utilized for the induction of protein expression. The optimal lactose feeding rate and induction point were 0.4gL(-1)h(-1) and a dry cell weight (DCW) of 15gL(-1), respectively. Furthermore, a glycine feeding strategy was formulated to promote the secretion of recombinant protein. The optimal total and extracellular pullulanase activity were 2523.5 and 1567.9UmL(-1), respectively, which represent 1.2 and 22.6-fold increases compared with those observed under unoptimized conditions.

Recent advances in discovery, heterologous expression, and molecular engineering of cyclodextrin glycosyltransferase for versatile applications

Cyclodextrin glycosyltransferase (CGTase) is an important enzyme with multiple functions, in particular the production of cyclodextrins. It is also widely applied in baking and carbohydrate glycosylation because it participates in various types of catalytic reactions. New applications are being found with novel CGTases being isolated from various organisms. Heterologous expression is performed for the overproduction of CGTases to meet the requirements of these applications. In addition, various directed evolution techniques have been applied to modify the molecular structure of CGTase for improved performance in industrial applications. In recent years, substantial progress has been made in the heterologous expression and molecular engineering of CGTases. In this review, we systematically summarize the heterologous expression strategies used for enhancing the production of CGTases. We also outline and discuss the molecular engineering approaches used to improve the production, secretion, and properties (e.g., product and substrate specificity, catalytic efficiency, and thermal stability) of CGTase.

Optimization of pullulanase production in Escherichia coli by regulation of process conditions and supplement with natural osmolytes

In this study, the effects of temperature, IPTG (Isopropyl β-D-1-thiogalactopyranoside) concentration, and osmolytes (proline, K-glutamate, and betaine) on cell growth and soluble pullulanase productivity of recombinant Escherichia coli were investigated. The yield of soluble pullulanase was found to be enhanced with decrease in cultivation temperature, lower IPTG concentration, and betaine supplementation in a shake flask. In addition, a modified two-stage feeding strategy was proposed and applied in a 3-L fermentor supplied with 20mM betaine, which achieved a dry cell weight of 59.3 g L(-1). Through this cultivation approach at 25 °C, the total soluble activity of pullulanase reached 963.9 U mL(-1), which was 8.3-fold higher than that observed without addition of betaine at 30 °C (115.8 U mL(-1)). The higher expression of soluble pullulanase in a scalable semisynthetic medium showed the potential of the proposed process for the industrial production of soluble enzyme.

Extracellular location of Thermobifida fusca cutinase expressed in Escherichia coli BL21(DE3) without mediation of a signal peptide

Cutinase is a multifunctional esterase with potential industrial applications. In the present study, a truncated version of the extracellular Thermobifida fusca cutinase without a signal peptide (referred to as cutinase(NS)) was heterologously expressed in Escherichia coli BL21(DE3). The results showed that the majority of the cutinase activity was located in the culture medium. In a 3-liter fermentor, the cutinase activity in the culture medium reached 1,063.5 U/ml (2,380.8 mg/liter), and the productivity was 40.9 U/ml/h. Biochemical characterization of the purified cutinase(NS) showed that it has enzymatic properties similar to those of the wild-type enzyme. In addition, E. coli cells producing inactive cutinase(NS)S130A were constructed, and it was found that the majority of the inactive enzyme was located in the cytoplasm. Furthermore, T. fusca cutinase was confirmed to have hydrolytic activity toward phospholipids, an important component of the cell membrane. Compared to the cells expressing the inactive cutinase(NS)S130A, the cells expressing cutinase(NS) showed increased membrane permeability and irregular morphology. Based on these results, a hypothesis of "cell leakage induced by the limited phospholipid hydrolysis of cutinase(NS)" was proposed to explain the underlying mechanism for the extracellular release of cutinase(NS).

Enhanced production of α-cyclodextrin glycosyltransferase in Escherichia coli by systematic codon usage optimization

Enhancing the production of α-cyclodextrin glycosyltransferase (α-CGTase) is a key aim in α-CGTase industries. Here, the mature α-cgt gene from Paenibacillus macerans JFB05-01 was redesigned with systematic codon optimization to preferentially match codon frequencies of Escherichia coli without altering the amino acid sequence. Following synthesis, codon-optimized α-cgt (coα-cgt) and wild-type α-cgt (wtα-cgt) genes were cloned into pET-20b(+) and expressed in E. coli BL21(DE3). The total protein yield of the synthetic gene was greater than wtα-cgt expression (1,710 mg L−1) by 2,520 mg L−1, with the extracellular enzyme activity being improved to 55.3 U mL−1 in flask fermentation. ΔG values at -3 to +50 of the pelB site of both genes were −19.10 kcal mol−1. Functionally, coα-CGTase was equally as effective as wtα-CGTase in forming α-cyclodextrin (α-CD). These findings suggest that preferred codon usage is advantageous for translational efficiency to increase protein expression. Finally, batch fermentation was applied, and the extracellular coα-CGTase enzyme activity was 326 % that of wtα-CGTase. The results suggest that codon optimization is a reasonable strategy to improve the yield of α-CGTase for industrial application.

Production of α-cyclodextrin glycosyltransferase in Bacillus megaterium MS941 by systematic codon usage optimization

α-Cyclodextrin glycosyltransferase is a key enzyme in the cyclodextrin industry. The Gram-positive bacterium Bacillus megaterium was chosen for production of recombinant α-CGTase for safety concerns. Successful production of heterologous α-CGTase was achieved by adapting the original α-cgt gene to the codon usage of B. megaterium by systematic codon optimization. This balanced the tRNA pool and reduced ribosomal traffic jams. Protein expression and secretion was ensured by using the strong inducible promoter P(xyl) and the signal peptide SP(LipA). The impact of culture medium composition and induction strategies on α-CGTase production was systematically analyzed. Production and secretion at 32 °C for 24 h using modified culture medium was optimal for α-CGTase yield. Batch- and simple fed-batch fermentation was applied to achieve a high yield of 48.9 U·mL(-1), which was the highest activity reported for a Bacillus species, making this production system a reasonable alternative to Escherichia coli.