High-Level Production of Bacillus subtilis Glycine Oxidase by Fed-Batch Cultivation of Recombinant Escherichia coli Rosetta (DE3)

Black glucose-releasing silicon elastomer rings for fed-batch operation allow measurement of the oxygen transfer rate from the top and optical signals from the bottom for each well of a microtiter plate

BACKGROUND

In industrial microbial biotechnology, fed-batch processes are frequently used to avoid undesirable biological phenomena, such as substrate inhibition or overflow metabolism. For targeted process development, fed-batch options for small scale and high throughput are needed. One commercially available fed-batch fermentation system is the FeedPlate^®, a microtiter plate (MTP) with a polymer-based controlled release system. Despite standardisation and easy incorporation into existing MTP handling systems, FeedPlates^® cannot be used with online monitoring systems that measure optically through the transparent bottom of the plate. One such system that is broadly used in biotechnological laboratories, is the commercial BioLector. To allow for BioLector measurements, while applying the polymer-based feeding technology, positioning of polymer rings instead of polymer disks at the bottom of the well has been proposed. This strategy has a drawback: measurement requires an adjustment of the software settings of the BioLector device. This adjustment modifies the measuring position relative to the wells, so that the light path is no longer blocked by the polymer ring, but, traverses through the inner hole of the ring. This study aimed at overcoming that obstacle and allowing for measurement of fed-batch cultivations using a commercial BioLector without adjustment of the relative measurement position within each well.

RESULTS

Different polymer ring heights, colours and positions in the wells were investigated for their influence on maximum oxygen transfer capacity, mixing time and scattered light measurement. Several configurations of black polymer rings were identified that allow measurement in an unmodified, commercial BioLector, comparable to wells without rings. Fed-batch experiments with black polymer rings with two model organisms, E. coli and H. polymorpha, were conducted. The identified ring configurations allowed for successful cultivations, measuring the oxygen transfer rate and dissolved oxygen tension, pH, scattered light and fluorescence. Using the obtained online data, glucose release rates of 0.36 to 0.44 mg/h could be determined. They are comparable to formerly published data of the polymer matrix.

CONCLUSION

The final ring configurations allow for measurements of microbial fed-batch cultivations using a commercial BioLector without requiring adjustments of the instrumental measurement setup. Different ring configurations achieve similar glucose release rates. Measurements from above and below the plate are possible and comparable to measurements of wells without polymer rings. This technology enables the generation of a comprehensive process understanding and target-oriented process development for industrial fed-batch processes.

An auto-inducible expression and high cell density fermentation of Beefy Meaty Peptide with Bacillus subtilis

Currently, some cases about the expression of flavor peptides with microorganisms were reported owing to the obvious advantages of biological expression over traditional methods. However, beefy meaty peptide (BMP), the focus of umami peptides, has neither been concerned in its safe expression nor its overproduction in fermenter. In this study, multi-copy BMP (8BMP) was successfully auto-inducibly expressed and efficiently produced in Bacillus subtilis 168. First, 8BMP was successfully auto-inducibly expressed with srfA promoter in B. subtilis 168. Further, the efficient production of 8BMP was researched in a 5-L fermenter: the fermentation optimized by Pontryagin's maximum principle obtained the highest 8BMP yield (3.16 g/L), which was 1.2 times and 1.8 times than that of two-stage feeding cultivation (2.67 g/L) and constant-rate feeding cultivation (1.75 g/L), respectively. Overall, the auto-inducible expression of 8BMP in B. subtilis and fermentation with Pontryagin's maximum principle are conductive for overproduction of BMP and other peptides.

High-level expression of Thermobifida fusca glucose isomerase for high fructose corn syrup biosynthesis

Glucose isomerase (GIase), an efficient enzyme in the isomerization of d-glucose to d-fructose, has been widely used in food processing. In this study, an efficient expression system for a Thermobifida fusca GIase (GIase_Tfus) in Escherichia coli was firstly designed via a two-stage feeding strategy for improving expression level. The cultivation strategy was performed at an exponential feeding rate during the pre-induction phase, followed by a gradient-decreasing feeding rate at the induction phase in a 3-L fermenter. During this process, the effect of induction conditions and the complex nitrogen supplementation in feeding solutions on GIase_Tfus production were investigated and optimized. Under the optimal conditions, the yield of GIase_Tfus reached 124.1 U/mL, which is the highest expression level of GIase by recombinant E. coli reported to date. Additionally, the obtained GIase_Tfus was performed to produce high fructose corn syrup (HFCS) with conversion approacing 55 % from glucose (45 %, w/v) to fructose. According to the molecular dynamic simulation, a number of hydrogen bonds existed in the enzyme-substrate complex could stablilize the transient states, and a appreciate reaction distance of M1 catalytic site and oxygen atom of glucose make the reaction proceed easily, thus resulting in the efficient biosynthesis of HFCS. The function of GIase_Tfus renders it a valuable catalyst for HFCS-55 (containing 55 % d-fructose) manufacturing, the most favorable industrial product of HFCS. The efficient expression of GIase_Tfus and its efficient HFCS production lays the foundation for its proming industrial application.

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.

Enhanced production of human full-length immunoglobulin G1 in the periplasm of Escherichia coli

Monoclonal antibodies are currently the most important pharmaceutical proteins, and the economic production of functional immunoglobulin G (IgG) is an important issue in biotechnology. Recent successes in the development of aglycosylated IgG variants that do not require glycosylation for effector functions have increased the use of Escherichia coli as an alternative host for economic production of IgG, instead of traditional mammalian host expression systems. Here, we have developed a new E. coli host-vector system for the high-level production of full-length IgG1 by examining (1) E. coli strains, (2) modification of 5' untranslated region sequences, and (3) co-expression of periplasmic foldase. With the engineered host-vector system, fed-batch cultivations were conducted at two different conditions, and under optimized conditions, up to 362 mg/L of full-length IgG1 could be produced in a relatively short-time (22 h) cultivation. The fully assembled IgG1 from fed-batch cultivation was purified with high purity and yield. With the purified IgG1, the specific bindings to an antigen, anthrax toxin PA, and to human neonatal Fc receptor were successfully demonstrated.

High-level extracellular production of D-Psicose-3-epimerase with recombinant Escherichia coli by a two-stage glycerol feeding approach

The aim of this study is to achieve high-level extracellular production of D-Psicose-3-epimerase (DPE) with recombinant Escherichia coli. High-level production of DPE is one of the key factors in D-Psicose production. In the present study, the gene AAL45544.1 from Agrobacterium tumefaciens str. C58 was modified by artificial synthesis for overexpression in E. coli. The total DPE activity reached 3.96 U mL(-1) after optimization of the media composition, induction temperature, and concentration of inducer. Furthermore, it was found that addition of glycine had a positive effect on the extracellular production of DPE, which reached 3.5 U mL(-1). Finally, a two-stage glycerol feeding strategy based on both the specific growth rate before induction and the amount of glycerol residues after induction was applied in a 3-L fermenter. After a series of optimal strategies in the 3-L fermenter, the total and extracellular DPE activity were 5.08- and 3.11-fold higher than that noted in the shake flask. The extracellular and intracellular DPE activity reached 10.9 and 13.2 U mL(-1), achieving 25.5 and 31.1 % conversion of D-fructose to D-psicose, respectively. The systemic strategies presented in this study provide valuable novel information for the industrial application of DPE.

Overproduction of alkaline polygalacturonate lyase in recombinant Escherichia coli by a two-stage glycerol feeding approach

This work aims to achieve the overproduction of alkaline polygalacturonate lyase (PGL) with recombinant Escherichia coli by a two-stage glycerol feeding approach. First, the PGL coding gene from Bacillus subtilis WSHB04-02 was expressed in E. coli BL21 (DE3) under the strong inducible T7 promoter of the pET20b (+) vector. And then the influence of media composition, induction temperature, and inducer isopropyl β-D-1-thiogalactopyranoside (IPTG) concentration on cell growth and PGL production was investigated. Finally, a two-stage glycerol feeding strategy was proposed and applied in a 3-L fermenter, where cultivation was conducted at a controlled specific growth rate (μset=0.2) during pre-induction phase, followed by a constant glycerol feeding rate of 12 ml h(-1) at post-induction phase. The total PGL yield reached 371.86 U mL(-1), which is the highest PGL production by recombinant E. coli expression system.

Increasing recombinant protein production in Escherichia coli through metabolic and genetic engineering

Different hosts have been used for recombinant protein production, ranging from simple bacteria, such as Escherichia coli and Bacillus subtilis, to more advanced eukaryotes as Saccharomyces cerevisiae and Pichia pastoris, to very complex insect and animal cells. All have their advantages and drawbacks and not one seems to be the perfect host for all purposes. In this review we compare the characteristics of all hosts used in commercial applications of recombinant protein production, both in the area of biopharmaceuticals and industrial enzymes. Although the bacterium E. coli remains a very often used organism, several drawbacks limit its possibility to be the first-choice host. Furthermore, we show what E. coli strains are typically used in high cell density cultivations and compare their genetic and physiological differences. In addition, we summarize the research efforts that have been done to improve yields of heterologous protein in E. coli, to reduce acetate formation, to secrete the recombinant protein into the periplasm or extracellular milieu, and to perform post-translational modifications. We conclude that great progress has been made in the incorporation of eukaryotic features into E. coli, which might allow the bacterium to regain its first-choice status, on the condition that these research efforts continue to gain momentum.

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

High-level production of α-cyclodextrin glycosyltransferase (CGTase) is one of the key factors in α-cyclodextrin (CD) preparation. In the present study, a fed-batch fermentation strategy for high-cell-density cultivation of Escherichia coli and the extracellular production of recombinant α-CGTase from Paenibacillus macerans JFB05-01 was established. A combined feeding strategy based on both specific growth rate before induction and the amount of glycerol residues after induction was used to control cell growth, acetate production, and glycerol consumption. When induced by lactose, a feeding solution with complex nitrogen was found beneficial for α-CGTase production. In addition, different induction temperatures and induction points were investigated, and the results indicated that these factors played an important role in α-CGTase production. When induced at 25 °C and at a dry cell weight of 30 g L(-1), the extracellular activity of α-CGTase could reach 275.3 U mL(-1).

Calorimetric control for high cell density cultivation of a recombinant Escherichia coli strain

In order to achieve maximum productivity of recombinant proteins in Escherichia coli high cell density cultivation (HCDC) strategies have been the subject of many studies. The aim of this work was the application of calorimetric methods to HCDC. The specific growth rate of a recombinant E. coli strain producing green fluorescent protein (GFP) was controlled during fed-batch cultivations by estimating the specific growth rate from the measured heat flow produced by the cells. For the cultivation a standard 30 l laboratory bioreactor was used, which was extended in such a way that heat balancing is possible. The feed rate was adjusted by an adaptive controller such that the specific growth rate was kept on the desired set point value. On the basis of experimental investigations with a recombinant E. coli strain using glucose as limiting C-source it was demonstrated that the specific growth rate can be kept on a given set point value and biomass concentrations of up to 120 g l(-1) can be obtained, reproducibly.

Implication of a mutation in the flavin binding site on the specific activity and substrate specificity of glycine oxidase from Bacillus subtilis produced by directed evolution

Directed evolution was used to expand the substrate specificity and functionality of glycine oxidase by using a high-throughput screening assay based on the 4-aminoantipyrine peroxidase system, with a coefficient of variance below 4%. After screening the library, one mutant with the desired changes was found. The mutant was purified and characterized, showing important changes compared to the wild-type, especially towards cyclic d-amino acids. Amino acid substitution of Ile15 for Val, where the consensus sequence for flavin binding site is placed, seems to be responsible for these changes in specific activity and substrate specificity. The effect of this mutation was explained by using a computer-based three-dimensional model.

Characterization and structural modeling of a novel thermostable glycine oxidase from Geobacillus kaustophilus HTA426

Glycine oxidase from Geobacillus kaustophilus HTA426 (GOXK) is a 43 kDa monomer flavoenzyme containing noncovalently bound FAD. The induction of the enzyme resulted in the expression of a fully soluble protein with higher specific activity than those previously reported for GOX from B. subtilis (GOXB). A study of the kinetic properties of this novel GOXK revealed the lowest KM values for most of the substrates analyzed, with the exception of D-proline which kept a similar value and had the highest Vmax value reported. The Vmax/KM ratio maintained a substrate preference of GOXK for amines of small size, like glycine, sarcosine, N-ethyl-glycine, and glycine-ethyl-ester. GOXK presented good stability at 60-70 degrees C and in alkaline media (pH 6-9.5). The putative tridimensional structure was modeled by sequence alignment and by comparing the changes between GOXK and GOXB, and the residues that could be responsible for the substrate specificity as well as those essential for the catalytic activity were found. The comparison between the possible topology of GOXK with that of GOXB showed changes at the putative interactions between monomers for the building of the tetrameric oligomerization.