Statistical optimization of seed and induction conditions to enhance phytase production by recombinant Escherichia coli

Microbial phytase: Impact of advances in genetic engineering in revolutionizing its properties and applications

Phytases are enzymes that increase the availability of phosphorous in monogastric diet and reduces the anti-nutrition effect of phytate. This review highlights contributions of recombinant technology to phytase research during the last decade with specific emphasis on new generation phytases. Application of modern molecular tools and genetic engineering have aided the discovery of novel phytase genes, facilitated its commercial production and expanded its applications. In future, by adopting most recent gene improvement techniques, more efficient next generation phytases can be developed for specific applications.

Expression of nattokinase in Escherichia coli and renaturation of its inclusion body

Nattokinase is an important fibrinolytic enzyme with therapeutic applications for cardiovascular diseases. The full-length and mature nattokinase genes were cloned from Bacillus subtilis var. natto and expressed in pQE30 vector in Escherichia coli. The full-length gene expressed low nattokinase activity in the intracellular soluble and the medium fractions. The mature gene expressed low soluble nattokinase activity and large amount insoluble protein in inclusion bodies without enzyme activity. Large amount of refolding solutions (RSs) at different pH values were screening and RS-10 and RS-11 at pH 9 were selected to refold nattokinase inclusion bodies. The recombinant cells were lysed with 0.1mg/mL lysozyme and ultrasonic treatment. After centrifugation, the pellete was washed twice with 20mM Tris-HCl buffer (pH 7.5) containing 1% Triton X-100 to purify the inclusion bodies. The inclusion bodies were dissolved in water at pH 12.0 and refolded with RS-10. The refolded proteins showed 42.8IU/mg and 79.3IU/mg fibrinolytic activity by the traditional dilution method (20-fold dilution into RS-10) and the directly mixing the protein solution with equal volume RS-10, respectively, compared to the 52.0IU/mg of total water-soluble proteins from B. subtilis var. natto. This work demonstrated that the inclusion body of recombinant nattokinase expressed in E. coli could be simply refolded to the natural enzyme activity level by directly mixing the protein solution with equal volume refolding solution.

Evaluation of pre-induction temperature, cell growth at induction and IPTG concentration on the expression of a leptospiral protein in E. coli using shaking flasks and microbioreactor

Background

Leptospirosis is a zoonose that is increasingly endemic in built-up areas, especially where there are communities living in precarious housing with poor or non-existent sanitation infrastructure. Leptospirosis can kill, for its symptoms are easily confused with those of other diseases. As such, a rapid diagnosis is required so it can be treated effectively. A test for leptospirosis diagnosis using Leptospira Immunoglobulin-like (Lig) proteins is currently at final validation at Fiocruz.

Results

In this work, the process for expression of LigB (131-645aa) in E. coli BL21 (DE3)Star™/pAE was evaluated. No significant difference was found for the experiments at two different pre-induction temperatures (28°C and 37°C). Then, the strain was cultivated at 37°C until IPTG addition, followed by induction at 28°C, thereby reducing the overall process time. Under this condition, expression was assessed using central composite design for two variables: cell growth at which LigB (131-645aa) was induced (absorbance at 600 nm between 0.75 and 2.0) and inducer concentration (0.1 mM to 1 mM IPTG). Both variables influenced cell growth and protein expression. Induction at the final exponential growth phase in shaking flasks with Abs_ind  = 2.0 yielded higher cell concentrations and LigB (131-645aa) productivities. IPTG concentration had a negative effect and could be ten-fold lower than the concentration commonly used in molecular biology (1 mM), while keeping expression at similar levels and inducing less damage to cell growth. The expression of LigB (131-645aa) was associated with cell growth. The induction at the end of the exponential phase using 0.1 mM IPTG at 28°C for 4 h was also performed in microbioreactors, reaching higher cell densities and 970 mg/L protein. LigB (131-645aa) was purified by nickel affinity chromatography with 91% homogeneity.

Conclusions

It was possible to assess the effects and interactions of the induction variables on the expression of soluble LigB (131-645aa) using experimental design, with a view to improving process productivity and reducing the production costs of a rapid test for leptospirosis diagnosis.

Efficient production of mutant phytase (phyA-7) derived from Selenomonas ruminantium using recombinant Escherichia coli in pilot scale

A mutant gene of rumen phytase (phyA-7) was cloned into pET23b(+) vector and expressed in the Escherichia coli BL21 under the control of the T7 promoter. The study of fermentation conditions includes the temperature impacts of mutant phytase expression, the effect of carbon supplements over induction stage, the inferences of acetic acid accumulation upon enzyme expression and the comparison of one-stage and two-stage operations in batch mode. The maximum value of phytase activity was reached 107.0 U mL(-1) at induction temperature of 30°C. Yeast extract supplement demonstrated a significant increase on both protein concentration and phytase activity. The acetic acid (2 g L(-1)) presented in the modified synthetic medium demonstrated a significant decrease on expressed phytase activity. A two-stage batch operation enhanced the level of phytase activity from 306 to 1204 U mL(-1) in the 20 L of fermentation scale. An overall 3.7-fold improvement in phytase yield (35,375.72-1,31,617.50 U g(-1) DCW) was achieved in the two-stage operation.

Cultivation Conditions for Phytase Production from Recombinant Escherichia coli DH5α

Response surface methodology (RSM) was used to optimize the cultivation conditions for the production of phytase by recombinant Escherichia coli DH5α. The optimum predicted cultivation conditions for phytase production were at 3 hours seed age, a 2.5% inoculum level, an L-arabinose concentration of 0.20%, a cell concentration of 0.3 (as measured at 600 nm) and 17 hours post-induction time with a predicted phytase activity of 4194.45 U/mL. The model was validated and the results showed no significant difference between the experimental and the predicted phytase activity (P = 0.305). Under optimum cultivation conditions, the phytase activity of the recombinant E. coli DH5α was 364 times higher compared to the phytase activity of the wild-type producer, Enterobacter sakazakii ASUIA279. Hence, optimization of the cultivation conditions using RSM positively increased phytase production from recombinant E. coli DH5α.

Enhanced production of a novel cyclic hexapeptide antibiotic (NW-G01) by Streptomyces alboflavus 313 using response surface methodology

NW-G01, produced by Streptomyces alboflavus 313, is a novel cyclic hexapeptide antibiotic with many potential applications, including antimicrobial activity and antitumor agents. This study developed a system for optimizing medium components in order to enhance NW-G01 production. In this study, Plackett-Burman design (PBD) was used to find the key ingredients of medium components, and then response surface methodology (RSM) was implemented to determine their optimal concentrations. The results of PBD revealed that the crucial ingredients related to the production of NW-G01 were (NH(4))(2)SO(4), peptone and CaCO(3). A prediction model has been built in the experiments of central composite design and response surface methodology, and its validation has been further verified. The optimal medium composition was determined (g/L): corn starch 15, glucose 15, peptone 3.80, (NH(4))(2)SO(4) 0.06, NaCl 1.5, CaCO(3) 1.30, MgSO(4)·7H(2)O 0.015, K(2)HPO(4)·3H(2)O 0.015, MnCl(2)·4H(2)O 0.015, FeSO(4)·7H(2)O 0.015, and ZnSO(4)·7H(2)O 0.015. Compared with NW-G01 production (5.707 mg/L) in non-optimized fermentation medium, the production of NW-G01 (15.564 mg/L) in optimized fermentation medium had a 2.73-fold increase.

Optimization of medium formulation and seed conditions for expression of mature PsaA (pneumococcal surface adhesin A) in Escherichia coli using a sequential experimental design strategy and response surface methodology

PsaA, a candidate antigen for a vaccine against pneumonia, is well-conserved in all Streptococcus pneumoniae serotypes. A sequence of two-level experimental designs was used to evaluate medium composition and seed conditions to optimize the expression of soluble mature PsaA in E. coli. A face-centered central composite design was first used to evaluate the effects of yeast extract (5 and 23.6 g/L), tryptone (0 and 10 g/L), and glucose (1 and 10 g/L), with replicate experiments at the central point (14.3 g/L yeast extract, 5 g/L tryptone, 5.5 g/L glucose). Next, a central composite design was used to analyze the influence of NaCl concentration (0, 5, and 10 g/L) compared with potassium salts (9.4 g/L K(2)HPO(4)/2.2 g/L KH(2)PO(4)), and seed growth (7 and 16 h). Tryptone had no significant effect and was removed from the medium. Yeast extract and glucose were optimized at their intermediate concentrations, resulting in an animal-derived material-free culture medium containing 15 g/L yeast extract, 8 g/L glucose, 50 μg/mL kanamycin, and 0.4% glycerol, yielding 1 g/L rPsaA after 16 h induction at 25°C in shake flasks at 200 rpm. All the seed age and salt conditions produced similar yields, indicating that no variation had a statistically significant effect on expression. Instead of growing the seed culture for 16 h (until saturation), the process can be conducted with 7 h seed growth until the exponential phase. These results enhanced the process productivity and reduced costs, with 5 g/L NaCl being used rather than potassium salts.

Analyzing the metabolic stress response of recombinant Escherichia coli cultures expressing human interferon-beta in high cell density fed batch cultures using time course transcriptomic data

Fed batch cultures expressing recombinant interferon beta under the T7 promoter were run with different exponential feeding rates of a complex substrate and induced at varying cell densities. Post-induction profiles of the specific product formation rates showed a strong dependence on the specific growth rate with the maximum product yield obtained at 0.2 h(-1). A study of the relative transcriptomic profiles as a function of pre-induction μ was therefore done to provide insight into the role of cellular physiology in enhancing recombinant protein expression. Hierarchical clustering analysis of the significantly regulated genes allowed us to identify biologically important groups of genes which fall under specific master regulators. The groups were: rpoH, ArcB, CreB, Lrp, RelA, Fis and Hfq. The response of these regulators, which exert a feedback control on the growth and product formation rates correlated well with the expression levels obtained. Thus at the optimum pre-induction μ, the alternative sigma factors and ribosomal machinery genes did not get depressed till the 6th hour post-induction unlike at other specific growth rates, demonstrating a critical role for the genes in sustaining recombinant protein expression.

Cloning and expression of protease ClpP from Streptococcus pneumoniae in Escherichia coli: study of the influence of kanamycin and IPTG concentration on cell growth, recombinant protein production and plasmid stability

Infections caused by Streptococcus pneumoniae are one of the main causes of death around the world. In order to address this problem, investigations are being made into the development of a protein-based vaccine. The aims of this study were to clone and express ClpP, a protein from S. pneumoniae serotype 14 in Escherichia coli, to optimize protein expression by using experimental design and to study plasmid segregation in the system. ClpP was cloned into the pET28b vector and expressed in E. coli BL21 Star (DE3). Protein expression was optimized by using central composite design, varying the inducer (IPTG) and kanamycin concentration, with a subsequent analysis being made of the concentration of heterologous protein, cell growth and the fraction of plasmid-bearing cells. In all the experiments, approximately the same concentration of ClpP was expressed in its soluble form, with a mean of 240.4mg/L at the center point. Neither the IPTG concentration nor the kanamycin concentration was found to have any statistically significant influence on protein expression. Also, higher IPTG concentrations were found to have a negative effect on cell growth and plasmid stability. Plasmid segregation was identified in the system under all the concentrations studied. Using statistical analysis, it was possible to ascertain that the procedures for determining plasmid stability (serial dilution and colony counting) were reproducible. It was concluded that the inducer concentration could be reduced tenfold and the antibiotic eliminated from the system without significantly affecting expression levels and with the positive effect of reducing costs.

Influence of induction conditions on the expression of carbazole dioxygenase components (CarAa, CarAc, and CarAd) from Pseudomonas stutzeri in recombinant Escherichia coli using experimental design

Carbazole 1,9a-dioxygenase (CarA), the first enzyme in the carbazole degradation pathway used by Pseudomonas sp., was expressed in E. coli under different conditions defined by experimental design. This enzyme depends on the coexistence of three components containing [2Fe-2S] clusters: CarAa, CarAc, and CarAd. The catalytic site is present in CarAa. The genes corresponding to components of carbazole 1,9a-dioxygenase from P. stutzeri were cloned and expressed by salt induction in E. coli BL21-SI (a host that allows the enhancement of overexpressed proteins in the soluble fraction), using the vector pDEST™14. The expression of these proteins was performed under different induction conditions (cell concentration, temperature, and time), with the help of two-level factorial design. Cell concentration at induction (measured by absorbance at 600 nm) was tested at 0.5 and 0.8. After salt induction, expression was performed at 30 and 37°C, for 4 h and 24 h. Protein expression was evaluated by densitometry analysis. Expression of CarAa was enhanced by induction at a lower cell concentration and temperature and over a longer time, according to the analysis of the experimental design results. The results were validated at Abs (ind) = 0.3, 25°C, and 24 h, at which CarAa expression was three times higher than under the standard condition. The behavior of CarAc and CarAd was the inverse, with the best co-expression condition tested being the standard one (Abs (ind) = 0.5, T = 37°C, and t = 4 h). The functionality of the proteins expressed in E. coli was confirmed by the degradation of 20 ppm carbazole.

Production enhancement and refolding of caprine growth hormone expressed in Escherichia coli

This study describes comparison between IPTG and lactose induction on expression of caprine growth hormone (cGH), enhancing cell densities of Escherichia coli cultures and refolding the recombinant cGH, produced as inclusion bodies, to biologically active state. 2-3 times higher cell densities were obtained in shake flask cultures when induction was done with lactose showing almost same level of expression as in case of IPTG induction. With lactose induction highest cell densities were achieved in TB (OD(600) 16.3) and M9NG (OD(600) 16.1) media, producing 885 and 892 mg cGH per liter of the culture, respectively. Lactose induction done at mid-exponential stage resulted in a higher cell density and thus higher product yield. cGH over-expressed as inclusion bodies was solubilized in 50 mM Tris-Cl buffer (pH 12.5) containing 2 M urea, followed by dilution and lowering the pH in a step-wise manner to obtain the final solution in 50mM Tris-Cl (pH 9.5). The cGH was purified by Q-Sepharose chromatography followed by gel filtration with a recovery yield of 39% on the basis of total cell proteins. The product thus obtained showed a single band by SDS-PAGE analysis. MALDI-TOF analysis showed a single peak with a mass of 21,851 dalton, which is very close to its calculated molecular weight. A bioassay based on proliferation of Nb2 rat lymphoma cells showed that the purified cGH was biologically active.

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).