Production of recombinant antibody fragments in Bacillus megaterium

Construction and Application of a Plasmid-Based Signal Peptide Library for Improved Secretion of Recombinant Proteins with Priestia megaterium

The secretion of recombinant proteins plays an important role in their economic production and purification. The secretion efficiency depends on the responsible signal peptide (SP) in combination with the target protein and the given host and cannot be predicted so far. Due to its high plasmid stability, the lack of alkaline extracellular proteases and only few contaminating extracellular host proteins, Priestia megaterium provides a promising alternative to common Bacillus species. For the development of an easy and fast cloning and screening system to identify the SP best suited to a distinct protein, a plasmid-based SP library containing all predicted 182 Sec-dependent SPs from P. megaterium was established. The splitting of the SPs into 10 groups of individual multi-SP plasmids (pMSPs) allows their grouped amplification and application in screening approaches. The functionality of the whole library was demonstrated by enhancing the amount of the already well-secreted α-amylase AmyE by 1.6-fold. The secretion of a novel penicillin G acylase, which remained as insoluble protein inside the cells, as its native SP is unsuitable for secretion in P. megaterium, could be enhanced even up to 29-fold. Overall, only around 170 recombinant P. megaterium clones based on 50 inserted SPs had to be screened to achieve sufficient amounts for further enzyme characterizations. Thus, this newly developed plasmid-based genetic tool applicable for P. megaterium and also other Bacillus species facilitates the identification of suitable SPs for secretion of recombinant proteins.

Designing and generating a single-chain fragment variable (scFv) antibody against IL2Rα (CD25): An in silico and in vitro study

OBJECTIVES

IL-2Rα plays a critical role in maintaining immune function. However, expression and secretion of CD25 in various malignant disorders and autoimmune diseases are now well established. Thus, CD25 is considered an important target candidate for antibody-based therapy. This study aimed to find the most suitable linker peptide to construct a functional anti-CD25 single-chain fragment variable (scFv) by bioinformatics studies and its production in a bacterial expression system.

MATERIALS AND METHODS

Here, the 3D structures of the scFvs with different linkers were predicted and molecular dynamics simulation was performed to compare their structures and dynamics. Then, interactions between five models of scFv and human CD25 were calculated via molecular docking. According to MD and docking results, the anti-CD25 scFvs with (Gly4Ser)3 linker were constructed and cloned into pET-22b(+). Then, recombinant plasmids were transformed into Escherichia coli Bl21 (DE3) for expression using IPTG and lactose as inducers. Anti-CD25 scFv was purified from the periplasm and detected by SDS-PAGE and Western blot. Afterward, functionality was evaluated using ELISA.

RESULTS

In silico analysis showed that the model containing (Gly4Ser)3 as a linker has more stability compared with other linkers. The results of SDS-PAGE, Western blot, and ELISA confirmed the accuracy of anti-CD25 scFv production and its ability to bind to the human CD25.

CONCLUSION

Conclusively, our work provides a theoretical and experimental basis for production of an anti-CD25 scFv, which may be applied for various malignant disorders and autoimmune diseases.

Manually curated genome-scale reconstruction of the metabolic network of Bacillus megaterium DSM319

Bacillus megaterium is a microorganism widely used in industrial biotechnology for production of enzymes and recombinant proteins, as well as in bioleaching processes. Precise understanding of its metabolism is essential for designing engineering strategies to further optimize B. megaterium for biotechnology applications. Here, we present a genome-scale metabolic model for B. megaterium DSM319, iJA1121, which is a result of a metabolic network reconciliation process. The model includes 1709 reactions, 1349 metabolites, and 1121 genes. Based on multiple-genome alignments and available genome-scale metabolic models for other Bacillus species, we constructed a draft network using an automated approach followed by manual curation. The refinements were performed using a gap-filling process. Constraint-based modeling was used to scrutinize network features. Phenotyping assays were performed in order to validate the growth behavior of the model using different substrates. To verify the model accuracy, experimental data reported in the literature (growth behavior patterns, metabolite production capabilities, metabolic flux analysis using ¹³C glucose and formaldehyde inhibitory effect) were confronted with model predictions. This indicated a very good agreement between in silico results and experimental data. For example, our in silico study of fatty acid biosynthesis and lipid accumulation in B. megaterium highlighted the importance of adopting appropriate carbon sources for fermentation purposes. We conclude that the genome-scale metabolic model iJA1121 represents a useful tool for systems analysis and furthers our understanding of the metabolism of B. megaterium.

Isolation, Development, and Genomic Analysis of Bacillus megaterium SR7 for Growth and Metabolite Production Under Supercritical Carbon Dioxide

Supercritical carbon dioxide (scCO2) is an attractive substitute for conventional organic solvents due to its unique transport and thermodynamic properties, its renewability and labile nature, and its high solubility for compounds such as alcohols, ketones, and aldehydes. However, biological systems that use scCO2 are mainly limited to in vitro processes due to its strong inhibition of cell viability and growth. To solve this problem, we used a bioprospecting approach to isolate a microbial strain with the natural ability to grow while exposed to scCO2. Enrichment culture and serial passaging of deep subsurface fluids from the McElmo Dome scCO2 reservoir in aqueous media under scCO2 headspace enabled the isolation of spore-forming strain Bacillus megaterium SR7. Sequencing and analysis of the complete 5.51 Mbp genome and physiological characterization revealed the capacity for facultative anaerobic metabolism, including fermentative growth on a diverse range of organic substrates. Supplementation of growth medium with L-alanine for chemical induction of spore germination significantly improved growth frequencies and biomass accumulation under scCO2 headspace. Detection of endogenous fermentative compounds in cultures grown under scCO2 represents the first observation of bioproduct generation and accumulation under this condition. Culturing development and metabolic characterization of B. megaterium SR7 represent initial advancements in the effort toward enabling exploitation of scCO2 as a sustainable solvent for in vivo bioprocessing.

Cost-effective batch production process of scFv antibody in Escherichia coli

BACKGROUND

Cost-effective production of antibody (Ab) fragments is of great interests of many pharmaceutical industries, in large part due to their high usages in research, diagnosis and therapy. Thus, the production of Abs necessitates accomplishment of the optimal strategies.

OBJECTIVE

In this study, based on the induction start time using arabinose, we implemented a novel strategy for the cost-effective production of single chain variable fragment (scFv) in Escherichia coli (E. coli).

METHODS

Complex and minimum media were used to investigate the batch fermentation in 50 mL batch tubes to find the optimum conditions for the production of a scFv in the Escherichia coli HB2151.

RESULTS

Arabinose was used as an appropriate economical alternative of isopropyl β-D-1-thiogalactopyranoside (IPTG) for the production of scFv antibody. The optimum concentration of arabinose as an inducer was 0.1% (w/w), while below this point the scFv production yield (YP/X) decreased significantly. The start time of the induction of E. coli HB2151 cells was adjusted to the stationary phase of the growth, and the results showed higher specific scFv production yields up to 0.9 mg scFv/g biomass in the minimum media. The optimum induction duration times for the complex and minimum media were about 12 and 24 hours, respectively.

CONCLUSIONS

We propose this method to possibly be used for the large-scale production of recombinant proteins/peptides such as scFv and Fab antibodies.

Optimizing antibody expression: The nuts and bolts

Antibodies are extensively utilized entities in biomedical research, and in the development of diagnostics and therapeutics. Many of these applications require high amounts of antibodies. However, meeting this ever-increasing demand of antibodies in the global market is one of the outstanding challenges. The need to maintain a balance between demand and supply of antibodies has led the researchers to discover better means and methods for optimizing their expression. These strategies aim to increase the volumetric productivity of the antibodies along with the reduction of associated manufacturing costs. Recent years have witnessed major advances in recombinant protein technology, owing to the introduction of novel cloning strategies, gene manipulation techniques, and an array of cell and vector engineering techniques, together with the progress in fermentation technologies. These innovations were also highly beneficial for antibody expression. Antibody expression depends upon the complex interplay of multiple factors that may require fine tuning at diverse levels to achieve maximum yields. However, each antibody is unique and requires individual consideration and customization for optimizing the associated expression parameters. This review provides a comprehensive overview of several state-of-the-art approaches, such as host selection, strain engineering, codon optimization, gene optimization, vector modification and process optimization that are deemed suitable for enhancing antibody expression.

Recombinant production of the antibody fragment D1.3 scFv with different Bacillus strains

Background

Different strains of the genus Bacillus are versatile candidates for the industrial production and secretion of heterologous proteins. They can be cultivated quite easily, show high growth rates and are usually non-pathogenic and free of endo- and exotoxins. They have the ability to secrete proteins with high efficiency into the growth medium, which allows cost-effective downstream purification processing. Some of the most interesting and challenging heterologous proteins are recombinant antibodies and antibody fragments. They are important and suitable tools in medical research for analytics, diagnostics and therapy. The smallest conventional antibody fragment with high-affinity binding to an antigen is the single-chain fragment variable (scFv). Here, different strains of the genus Bacillus were investigated using diverse cultivation systems for their suitability to produce and secret a recombinant scFv.

Results

Extracellular production of lysozyme-specific scFv D1.3 was realized by constructing a plasmid with a xylose-inducible promoter optimized for Bacillus megaterium and the D1.3scFv gene fused to the coding sequence of the LipA signal peptide from B. megaterium. Functional scFv was successfully secreted with B. megaterium MS941, Bacillus licheniformis MW3 and the three Bacillus subtilis strains 168, DB431 and WB800N differing in the number of produced proteases. Starting with shake flasks (150 mL), the bioprocess was scaled down to microtiter plates (1250 µL) as well as scaled up to laboratory-scale bioreactors (2 L). The highest extracellular concentration of D1.3 scFv (130 mg L⁻¹) and highest space–time-yield (8 mg L⁻¹ h⁻¹) were accomplished with B. subtilis WB800N, a strain deficient in eight proteases. These results were reproduced by the production and secretion of a recombinant penicillin G acylase (Pac).

Conclusions

The genus Bacillus provides high potential microbial host systems for the secretion of challenging heterologous proteins like antibody fragments and large proteins at high titers. In this study, the highest extracellular concentration and space–time-yield of a recombinant antibody fragment for a Gram-positive bacterium so far was achieved. The successful interspecies use of the here-designed plasmid originally optimized for B. megaterium was demonstrated by two examples, an antibody fragment and a penicillin G acylase in up to five different Bacillus strains.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0625-9) contains supplementary material, which is available to authorized users.

A Bacillus megaterium System for the Production of Recombinant Proteins and Protein Complexes

For many years the Gram-positive bacterium Bacillus megaterium has been used for the production and secretion of recombinant proteins. For this purpose it was systematically optimized. Plasmids with different inducible promoter systems, with different compatible origins, with small tags for protein purification and with various specific signals for protein secretion were combined with genetically improved host strains. Finally, the development of appropriate cultivation conditions for the production strains established this organism as a bacterial cell factory even for large proteins. Along with the overproduction of individual proteins the organism is now also used for the simultaneous coproduction of up to 14 recombinant proteins, multiple subsequently interacting or forming protein complexes. Some of these recombinant strains are successfully used for bioconversion or the biosynthesis of valuable components including vitamins. The titers in the g per liter scale for the intra- and extracellular recombinant protein production prove the high potential of B. megaterium for industrial applications. It is currently further enhanced for the production of recombinant proteins and multi-subunit protein complexes using directed genetic engineering approaches based on transcriptome, proteome, metabolome and fluxome data.

Expression of recombinant antibodies

Recombinant antibodies are highly specific detection probes in research, diagnostics, and have emerged over the last two decades as the fastest growing class of therapeutic proteins. Antibody generation has been dramatically accelerated by in vitro selection systems, particularly phage display. An increasing variety of recombinant production systems have been developed, ranging from Gram-negative and positive bacteria, yeasts and filamentous fungi, insect cell lines, mammalian cells to transgenic plants and animals. Currently, almost all therapeutic antibodies are still produced in mammalian cell lines in order to reduce the risk of immunogenicity due to altered, non-human glycosylation patterns. However, recent developments of glycosylation-engineered yeast, insect cell lines, and transgenic plants are promising to obtain antibodies with "human-like" post-translational modifications. Furthermore, smaller antibody fragments including bispecific antibodies without any glycosylation are successfully produced in bacteria and have advanced to clinical testing. The first therapeutic antibody products from a non-mammalian source can be expected in coming next years. In this review, we focus on current antibody production systems including their usability for different applications.

Getting the big beast to work--systems biotechnology of Bacillus megaterium for novel high-value proteins

The high industrial relevance of the soil bacterium Bacillus megaterium as host for recombinant proteins is driving systems-wide analyses of its metabolic and regulatory networks. The present review highlights novel systems biology tools available to unravel the various cellular components on the level of metabolic and regulatory networks. These provide a rational platform for systems metabolic engineering of B. megaterium. In line, a number of interesting studies have particularly focused on studying recombinant B. megaterium in its industrial bioprocess environment thus integrating systems metabolic engineering with systems biotechnology and providing the full picture toward optimal processes.

Biomedicals from a soil bug: expanding scFv production host range

Recombinant antibody fragments have a wide range of applications from research to diagnostics and therapy. Of special interest are small fragments like fragment antigen binding (Fab) or single chain fragment variables (scFv) fragments as they can be produced inexpensively in bacterial expression systems. However, recombinant production efficiencies from established production hosts vary significantly leading to inadequate yields. Gene sequences that have been synthetically adapted to match the codon preferences and respective genomic tRNA pool of the host have been used to improve yields but cannot resolve the principal problem. The development of inducible broad host range scFv expression plasmid constructs leads the way to an easy and efficient screening method for the identification of the optimal bacterial expression host.

Antibody production in Bacillus megaterium: strategies and physiological implications of scaling from microtiter plates to industrial bioreactors

Bacillus megaterium was used as an alternative high potential microbial production system for the production of antibody fragment D1.3 scFv. The aim of the study was to follow a holistic optimization approach from medium screening in small scale microtiter platforms, gaining deeper process understanding in the bioreactor scale and implementing advanced process strategies at larger scales (5-100 L). Screening and optimization procedures were supported by statistical design of experiments and a genetic algorithm approach. The process control relied on a soft-sensor for biomass estimation to establish a μ-oscillating time-dependent fed-batch strategy. Several cycles of growth phases and production phases, equal to starving phases, were performed in one production. Flow cytometry was used to monitor and characterize the dynamics of secretion and cell viability. Besides the biosynthesis of the product, secretion was optimized by an appropriate medium design considering different carbon sources, metal ions, (NH(4))(2)SO(4), and inductor concentrations. For bioprocess design, an adapted oscillating fed-batch strategy was conceived and successfully implemented at an industrially relevant scale of 100 L. In comparison to common methods for controlling fed-batch profiles, the developed process delivered increased overall productivities. Thereby measured process parameters such as growth stagnation or productivity fluctuations were directly linked to single cell or population behavior leading to a more detailed process understanding. Above all, the importance of single cell analysis as key scale-free tool to characterize and optimize recombinant protein production is highlighted, since this can be applied to all development stages independently of the cultivation platform.

Viability and membrane potential analysis of Bacillus megaterium cells by impedance flow cytometry

Single cell analysis is an important tool to gain deeper insights into microbial physiology for the characterization and optimization of bioprocesses. In this study a novel single cell analysis technique was applied for estimating viability and membrane potential (MP) of Bacillus megaterium cells cultured in minimal medium. Its measurement principle is based on the analysis of the electrical cell properties and is called impedance flow cytometry (IFC). Comparatively, state-of-the-art fluorescence-based flow cytometry (FCM) was used to verify the results obtained by IFC. Viability and MP analyses were performed with cells at different well-defined growth stages, focusing mainly on exponential and stationary phase cells, as well as on dead cells. This was done by PI and DiOC(2)(3) staining assays in FCM and by impedance measurements at 0.5 and 10 MHz in IFC. In addition, transition growth stages of long-term cultures and agar plate colonies were characterized with both methods. FCM and IFC analyses of all experiments gave comparable results, quantitatively and qualitatively, indicating that IFC is an equivalent technique to FCM for the study of physiological cell states of bacteria.

Development of a high-expression system for staphylococcal exfoliative toxin genes

We constructed a new expression system for staphylococcal exfoliative toxin (ET). The expression vector, pETA-exp2, was constructed based on Bacillus-Escherichia shuttle vector pHY300PLK. The pETA-exp2 vector includes the regulator of the ETA gene (eta), the promoter and Shine-Dalgarno (SD) sequences of eta, a SalI sequence at the end of the signal sequence of eta, a nucleotide sequence encoding mature ETA, an XhoI site, a 6x His sequence just before the stop codon and the end of the transcription sequence of eta. The nucleotide sequences coding for the mature proteins of ETB, ExhA, ExhB, ExhC, ExhD and SHETB were amplified by polymerase chain reaction (PCR) and inserted into pETA-exp2. These recombinant plasmids were transformed into Bacillus megaterium. The major protein in the culture supernatant of the transformant was recombinant ET (rET). The yields of all rETs were high, and all of them showed exfoliative activity in susceptible animals. The antigenicities of rETs and ETs were not distinguishable from each other.

Recombinant antibodies: engineering and production in yeast and bacterial hosts

After the appearance of the first FDA-approved antibody 25 years ago, antibodies have become major therapeutic agents in the treatment of many human diseases, including cancer and infectious diseases, and the use of antibodies as therapeutic/diagnostic agents is expected to increase in the future. So far, a variety of strategies have been devised for engineering of these fascinating molecules to develop superior properties and functions. Recent progress in systems biology has provided more information about the structures and cellular networks of antibodies, and, in addition, recent development of biotechnology tools, particularly in regard to high-throughput screening, has made it possible to perform more intensive engineering on these substances. Based on a sound understanding and new technologies, antibodies are now being developed as more powerful drugs. In this review, we highlight the recent, significant progress that has been made in antibody engineering, with a particular focus on Fc engineering and glycoengineering for improved functions, and cellular engineering for enhanced production of antibodies in yeast and bacterial hosts.

Single cell analysis applied to antibody fragment production with Bacillus megaterium: development of advanced physiology and bioprocess state estimation tools

BACKGROUND

Single cell analysis for bioprocess monitoring is an important tool to gain deeper insights into particular cell behavior and population dynamics of production processes and can be very useful for discrimination of the real bottleneck between product biosynthesis and secretion, respectively.

RESULTS

Here different dyes for viability estimation considering membrane potential (DiOC2(3), DiBAC4(3), DiOC6(3)) and cell integrity (DiBAC4(3)/PI, Syto9/PI) were successfully evaluated for Bacillus megaterium cell characterization. It was possible to establish an appropriate assay to measure the production intensities of single cells revealing certain product secretion dynamics. Methods were tested regarding their sensitivity by evaluating fluorescence surface density and fluorescent specific concentration in relation to the electronic cell volume. The assays established were applied at different stages of a bioprocess where the antibody fragment D1.3 scFv production and secretion by B. megaterium was studied.

CONCLUSIONS

It was possible to distinguish between live, metabolic active, depolarized, dormant, and dead cells and to discriminate between high and low productive cells. The methods were shown to be suitable tools for process monitoring at single cell level allowing a better process understanding, increasing robustness and forming a firm basis for physiology-based analysis and optimization with the general application for bioprocess development.

Efficient production of soluble recombinant single chain Fv fragments by a Pseudomonas putida strain KT2440 cell factory

Background

Recombinant antibody fragments have a wide range of applications in research, diagnostics and therapy. For many of these, small fragments like single chain fragment variables (scFv) function well and can be produced inexpensively in bacterial expression systems. Although Escherichia coli K-12 production systems are convenient, yields of different fragments, even those produced from codon-optimized expression systems, vary significantly. Where yields are inadequate, alternative production systems are needed. Pseudomonas putida strain KT2440 is a versatile biosafety strain known for good expression of heterologous genes, so we have explored its utility as a cell factory for production of scFvs.

Results

We have generated new broad host range scFv expression constructs and assessed their production in the Pseudomonas putida KT2440 host. Two scFvs bind either to human C-reactive protein or to mucin1, proteins of significant medical diagnostic and therapeutic interest, whereas a third is a model anti-lysozyme scFv. The KT2440 antibody expression systems produce scFvs targeted to the periplasmic space that were processed precisely and were easily recovered and purified by single-step or tandem affinity chromatography. The influence of promoter system, codon optimization for P. putida, and medium on scFv yield was examined. Yields of up to 3.5 mg/l of pure, soluble, active scFv fragments were obtained from shake flask cultures of constructs based on the original codon usage and expressed from the Ptac expression system, yields that were 2.5-4 times higher than those from equivalent cultures of an E. coli K-12 expression host.

Conclusions

Pseudomonas putida KT2440 is a good cell factory for the production of scFvs, and the broad host range constructs we have produced allow yield assessment in a number of different expression hosts when yields in one initially selected are insufficient. High cell density cultivation and further optimization and refinement of the KT2440 cell factory will achieve additional increases in the yields of scFvs.

Systems biology of recombinant protein production using Bacillus megaterium

The Gram-negative bacterium Escherichia coli is the most widely used production host for recombinant proteins in both academia and industry. The Gram-positive bacterium Bacillus megaterium represents an increasingly used alternative for high yield intra- and extracellular protein synthesis. During the past two decades, multiple tools including gene expression plasmids and production strains have been developed. Introduction of free replicating and integrative plasmids into B. megaterium is possible via protoplasts transformation or transconjugation. Using His(6)- and StrepII affinity tags, the intra- or extracellular produced proteins can easily be purified in one-step procedures. Different gene expression systems based on the xylose controlled promoter P(xylA) and various phage RNA polymerase (T7, SP6, K1E) driven systems enable B. megaterium to produce up to 1.25g of recombinant protein per liter. Biomass concentrations of up to 80g/l can be achieved by high cell density cultivations in bioreactors. Gene knockouts and gene replacements in B. megaterium are possible via an optimized gene disruption system. For a safe application in industry, sporulation and protease-deficient as well as UV-sensitive mutants are available. With the help of the recently published B. megaterium genome sequence, it is possible to characterize bottle necks in the protein production process via systems biology approaches based on transcriptome, proteome, metabolome, and fluxome data. The bioinformatical platform (Megabac, http://www.megabac.tu-bs.de) integrates obtained theoretical and experimental data.

Influence of culture medium on the production of eif antigen from Leishmania chagasi in recombinant Escherichia coli

With the advent of recombinant DNA technology, recombinant protein expression has become an important tool in the study of the structure, function and identification of new proteins, especially those with therapeutic functions. Escherichia coli has been the predominant prokaryote used in genetic engineering studies due to the abundance of information about its metabolism. Despite significant advances in molecular biology and immunology of infections, there are as yet no prophylactic drugs capable of preventing visceral leishmaniasis. It is therefore important to identify specific antigens in order to develop vaccines and diagnostic kits against this disease. The objective of this study was to evaluate the influence of culture medium on the production of eIF antigen from Leishmania chagasi in recombinant Escherichia coli. An induction procedure using IPTG was carried out in a series of trials, to observe the influence of culture medium (2xTY, TB) under expression of the recombinant eIF protein. Results showed that recombinant protein expression was associated to growth and that the highest eIF antigen expression was obtained in the 2xTY medium.

A short story about a big magic bug

Bacillus megaterium, the "big beast," is a Gram-positive bacterium with a size of 4 × 1.5 µm. During the last years, it became more and more popular in the field of biotechnology for its recombinant protein production capacity. For the purpose of intra- as well as extracellular protein synthesis several vectors were constructed and commercialized (MoBiTec GmbH, Germany). On the basis of two compatible vectors, a T7 RNA polymerase driven protein production system was established. Vectors for chromosomal integration enable the direct manipulation of the genome. The vitamin B(12) biosynthesis of B. megaterium served as a model for the systematic development of a production strain using these tools. For this purpose, the overexpression of chromosomal and plasmid encoded genes and operons, the synthesis of anti-sense RNA for gene silencing, the removal of inhibitory regulatory elements in combination with the utilization of strong promoters, directed protein design, and the recombinant production of B(12) binding proteins to overcome feedback inhibition were successfully employed. For further system biotechnology based optimization strategies the genome sequence will provide a closer look into genomic capacities of B. megaterium. DNA arrays are available. Proteome, fluxome and metabolome analyses are possible. All data can be integrated by using a novel bioinformatics platform. Finally, the size of the "big beast" B. megaterium invites for cell biology research projects. All these features provide a solid basis for challenging biotechnological approaches.

Systems biology of recombinant protein production in Bacillus megaterium

Over the last two decades the Gram-positive bacterium Bacillus megaterium was systematically developed to a useful alternative protein production host. Multiple vector systems for high yield intra- and extracellular protein production were constructed. Strong inducible promoters were combined with DNA sequences for optimised ribosome binding sites, various leader peptides for protein export and N- as well as C-terminal affinity tags for affinity chromatographic purification of the desired protein. High cell density cultivation and recombinant protein production were successfully tested. For further system biology based control and optimisation of the production process the genomes of two B. megaterium strains were completely elucidated, DNA arrays designed, proteome, fluxome and metabolome analyses performed and all data integrated using the bioinformatics platform MEGABAC. Now, solid theoretical and experimental bases for primary modeling attempts of the production process are available.

Antibody production by the gram-positive bacterium Bacillus megaterium

The increasing demand for recombinant antibodies as detection reagents in research, diagnostics, and therapy requires appropriate production systems. In contrast to antibody therapies, small recombinant antibody fragments like Fab and scFv are sufficient for most applications in research and diagnostics. These antibody fragments can also be produced in bacterial hosts. Gram-negative bacteria, particularly Escherichia coli, were extensively studied for the recombinant antibody production but they showed only a limited capacity to secrete antibody fragments into the medium--a prerequisite for easy downstream processing. Gram-positive bacteria are known to efficiently secrete recombinant proteins into the medium. Recently, we demonstrated the production of scFv and scFab fragments in Bacillus megaterium. Here, we describe the process in detail from transformation of B. megaterium to production and purification of scFv fragments.

Purification and characterization of keratinase from recombinant Pichia and Bacillus strains

The keratinase gene from Bacillus licheniformis MKU3 was cloned and successfully expressed in Bacillus megaterium MS941 as well as in Pichia pastoris X33. Compared with parent strain, the recombinant B. megaterium produced 3-fold increased level of keratinase while the recombinant P. pastoris strain had produced 2.9-fold increased level of keratinase. The keratinases from recombinant P. pastoris (pPZK3) and B. megaterium MS941 (pWAK3) were purified to 67.7- and 85.1-folds, respectively, through affinity chromatography. The purified keratinases had the specific activity of 365.7 and 1277.7 U/mg, respectively. Recombinant keratinase from B. megaterium was a monomeric protein with an apparent molecular mass of 30 kDa which was appropriately glycosylated in P. pastoris to have a molecular mass of 39 kDa. The keratinases from both recombinant strains had similar properties such as temperature and pH optimum for activity, and sensitivity to various metal ions, additives and inhibitors. There was considerable enzyme stability due to its glycosylation in yeast system. At pH 11 the glycosylated keratinase retained 95% of activity and 75% of its activity at 80 degrees C. The purified keratinase hydrolyzed a broad range of substrates and displayed effective degradation of keratin substrates. The K(m) and V(max) of the keratinase for the substrate N-succinyl-Ala-Ala-Pro-Phe-pNA was found to be 0.201 mM and 61.09 U/s, respectively. Stability in the presence of detergents, surfactants, metal ions and solvents make this keratinase suitable for industrial processes.

A sucrose-inducible promoter system for the intra- and extracellular protein production in Bacillus megaterium

A sucrose-inducible promoter system (P(sacB)) from Bacillus megaterium was identified using a secretome approach. It was successfully employed for the extracellular production of the homologous levansucrase SacB (4252.4 U l(-1)) and the heterologous green fluorescent protein GFP (7.9 mg g(CDW)(-1)). Mutational analysis of B. megaterium P(sacB) allowed the identification of important promoter elements. The sucrose-inducible promoter provides a useful alternative to the established xylose-inducible promoter system (P(xylA)) for recombinant gene expression in B. megaterium.

Production of single chain Fab (scFab) fragments in Bacillus megaterium

Background

The demand on antigen binding reagents in research, diagnostics and therapy raises questions for novel antibody formats as well as appropriate production systems. Recently, the novel single chain Fab (scFab) antibody format combining properties of single chain Fv (scFv) and Fab fragments was produced in the Gram-negative bacterium Escherichia coli. In this study we evaluated the Gram-positive bacterium Bacillus megaterium for the recombinant production of scFab and scFvs in comparison to E. coli.

Results

The lysozyme specific D1.3 scFab was produced in B. megaterium and E. coli. The total yield of the scFab after purification obtained from the periplasmic fraction and culture supernatant of E. coli was slightly higher than that obtained from culture supernatant of B. megaterium. However, the yield of functional scFab determined by analyzing the antigen binding activity was equally in both production systems. Furthermore, a scFv fragment with specificity for the human C reactive protein was produced in B. megaterium. The total yield of the anti-CRP scFv produced in B. megaterium was slightly lower compared to E. coli, whereas the specific activity of the purified scFvs produced in B. megaterium was higher compared to E. coli.

Conclusion

B. megaterium allows the secretory production of antibody fragments including the novel scFab antibody format. The yield and quality of functional antibody fragment is comparable to the periplasmic production in E. coli.