Production of cholera toxin B subunit in Lactobacillus

Development of Heterologous Expression System and Optimization of the Method of Cholera Toxin β-Subunit Production in E. coli

Cholera is a deadly infection disease, which is usually associated with low hygiene levels and limited access to high-quality drinking water. An effective way to prevent cholera is the use of vaccines. Among active vaccine components there is the CtxB protein (cholera toxin β-subunit). In the current work, we have developed a genetic system for production of the recombinant CtxB in E. coli cells and studied conditions for synthesis and purification of the target product at the laboratory scale. It has been found that the optimal algorithm for isolation of the recombinant protein is to grow E. coli culture in the synthetic M9 medium with glycerol, followed by CtxB purification out of the spent culture medium using Ni2+-chelate affinity chromatography techniques. Forty-eight hours after induction of CtxB expression, concentration of the target product could be up to 50 mg/liter in the culture medium. The CtxB protein retains its pentameric structure during expression and through purification. The latter makes it possible to consider the developed system as a promising tool for the industrial-level production of recombinant CtxB for medical and research purposes.

A single point mutation within the coding sequence of cholera toxin B subunit will increase its expression yield

Background: Cholera toxin B subunit (CTB) has been extensively considered as an immunogenic and adjuvant protein, but its yield of expression is not satisfactory in many studies. The aim of this study was to compare the expression of native and mutant recombinant CTB (rCTB) in pQE vector. Methods: ctxB fragment from Vibrio cholerae O₁ ATCC14035 containing the substitution of mutant ctxB for amino acid S128T was amplified by PCR and cloned in pGETM-T easy vector. It was then transformed to E. coli Top 10F' and cultured on LB agar plate containing ampicillin. Sequence analysis confirmed the mature ctxB gene sequence and the mutant one in both constructs which were further subcloned to pQE-30 vector. Both constructs were subsequently transformed to E. coli M15 (pREP4) for expression of mature and mutant rCTB. Results: SDS-PAGE analysis showed the maximum expression of rCTB in both systems at 5 hours after induction and Western-blot analysis confirmed the presence of rCTB in blotting membranes. The expression of mutant rCTB was much higher than mature rCTB, which may be the result of serine-to-threonine substitution at position 128 of mature rCTB amino acid sequence created by PCR mutagenesis. The mutant rCTB retained pentameric stability and its ability to bind to anti- cholera toxin IgG antibodies. Conclusion: Point mutation in ctxB sequence resulted in over-expression of rCTB, probably due to the increase of solubility of produced rCTB. Consequently, this expression system can be used to produce rCTB in high yield.

The B subunits of cholera and Escherichia coli heat-labile toxins enhance the immune responses in mice orally immunised with a recombinant live P-fimbrial vaccine for avian pathogenic E. coli

This study aimed to investigate the adjuvant effect of recombinant attenuated Salmonella expressing cholera toxin B subunit (CTB) and Escherichia coli heat-labile enterotoxin B subunit (LTB) for the P-fimbriae subunit-based vaccine of avian pathogenic E. coli (APEC) in a murine model. The PapA-specific sIgA and IgG responses were significantly enhanced after immunisation with the Salmonella-PapA vaccine in the presence of CTB or LTB. The group immunised with the Salmonella-LTB strain promoted Th1-type immunity, whereas that immunised with the Salmonella-CTB strain produced Th2-type immunity. We concluded that both Salmonella-CTB and -LTB strains can enhance the immune response to PapA, and that the LTB strain may be a more effective adjuvant for APEC vaccination, which requires higher Th1-type immunity for protection. Thus, our findings provide evidence that immunisation with an adjuvant, LTB, is one of the strategies of developing effective vaccines against P-fimbriated APEC.

Effect of pressure on refolding of recombinant pentameric cholera toxin B

The production of recombinant proteins is an essential tool for the expansion of modern biological research and biotechnology. The expression of heterologous proteins in Escherichia coli often results in an incomplete folding process that leads to the accumulation of inclusion bodies (IB), aggregates that hold a certain degree of native-like secondary structure. High hydrostatic pressure (HHP) impairs intermolecular hydrophobic and electrostatic interactions, leading to dissociation of aggregates under non-denaturing conditions and is therefore a useful tool to solubilize proteins for posterior refolding. Cholera toxin (CT) is composed of a non-toxic pentamer of B subunits (CTB), a useful adjuvant in vaccines, and a toxic subunit A (CTA). We studied the process of refolding of CTB using HHP. HHP was shown to be effective for dissociation of CTB monomers from IB. Posterior incubation at atmospheric pressure of concentrated CTB (1mg/ml) is necessary for the association of the monomers. Pentameric CTB was obtained when suspensions of CTB IB were compressed at 2.4kbar for 16h in the presence of Tween 20 and incubated at 1bar for 120h. Soluble and biologically active pentameric CTB was obtained, with a yield of 213mg CTB/liter of culture. The experience gained in this study can be important to improve the refolding of proteins with quaternary structure.

The hows and whys of constructing a native recombinant cholera vaccine

Emergence of different ctxB genotypes within virulent Vibrio cholerae populations accentuates the need to develop a vaccine that has the potential to protect against all cholera toxin genotypes. Oral administration of rCTB-alone and in combination with 2 dominant domestic killed whole cells of V. cholerae (O1 Ogawa El Tor and O1 Inaba El Tor) plus one standard V. cholerae (O1 Ogawa classic ATCC 14035)-has shown satisfactory protection as a potent vaccine candidate against toxigenic V. cholerae.

Comparison of two recombinant systems for expression of cholera toxin B subunit from Vibrio cholerae

PURPOSE

The aim of this study was to assess the production of recombinant cholera toxin B subunit (rCTB) protein in two different expression systems (pAE_ctxB and pQE_ctxB constructs) in Escherichia coli BL21 (DE3).

MATERIALS AND METHODS

The ctxB fragment was amplified from Vibrio cholerae O 1 ATCC14035 and cloned in pGETM-T easy vector after which it was transformed to E. coli Top 10F' and grown on LB-ampicillin agar medium. Sequence analysis confirmed the complete ctxB gene sequence in the construct which was further subcloned to pQE-30 vector. The construct was subsequently transformed to E. coli M15 (pREP4). The recombinant pAE_ctxB and pQE_ctxB were transformed to competent E. coli BL21 (DE3) cells to express CTB protein.

RESULT

Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed the maximum expression of rCTB in both systems at 5 h after induction and western blot analysis confirmed the presence of recombinant CTB in blotting membranes.

CONCLUSION

Expression of rCTB in pAE_ctxB construct was more efficient (15-fold) than pQE_ctxB, and it seems that Lac UV5 in E. coli BL21 (DE3) is more compatible with the former construct. This expression system can be used to produce recombinant CTB in high yield which may enable us to study the oral tolerance or mucosal adjuvant properties of rCTB using animal models.

Rapid and scalable plant-based production of a cholera toxin B subunit variant to aid in mass vaccination against cholera outbreaks

INTRODUCTION

Cholera toxin B subunit (CTB) is a component of an internationally licensed oral cholera vaccine. The protein induces neutralizing antibodies against the holotoxin, the virulence factor responsible for severe diarrhea. A field clinical trial has suggested that the addition of CTB to killed whole-cell bacteria provides superior short-term protection to whole-cell-only vaccines; however, challenges in CTB biomanufacturing (i.e., cost and scale) hamper its implementation to mass vaccination in developing countries. To provide a potential solution to this issue, we developed a rapid, robust, and scalable CTB production system in plants.

METHODOLOGY/PRINCIPAL FINDINGS

In a preliminary study of expressing original CTB in transgenic Nicotiana benthamiana, the protein was N-glycosylated with plant-specific glycans. Thus, an aglycosylated CTB variant (pCTB) was created and overexpressed via a plant virus vector. Upon additional transgene engineering for retention in the endoplasmic reticulum and optimization of a secretory signal, the yield of pCTB was dramatically improved, reaching >1 g per kg of fresh leaf material. The protein was efficiently purified by simple two-step chromatography. The GM1-ganglioside binding capacity and conformational stability of pCTB were virtually identical to the bacteria-derived original B subunit, as demonstrated in competitive enzyme-linked immunosorbent assay, surface plasmon resonance, and fluorescence-based thermal shift assay. Mammalian cell surface-binding was corroborated by immunofluorescence and flow cytometry. pCTB exhibited strong oral immunogenicity in mice, inducing significant levels of CTB-specific intestinal antibodies that persisted over 6 months. Moreover, these antibodies effectively neutralized the cholera holotoxin in vitro.

CONCLUSIONS/SIGNIFICANCE

Taken together, these results demonstrated that pCTB has robust producibility in Nicotiana plants and retains most, if not all, of major biological activities of the original protein. This rapid and easily scalable system may enable the implementation of pCTB to mass vaccination against outbreaks, thereby providing better protection of high-risk populations in developing countries.

Oral vaccination with the porcine rotavirus VP4 outer capsid protein expressed by Lactococcus lactis induces specific antibody production

The objective of this study to design a delivery system resistant to the gastrointestinal environment for oral vaccine against porcine rotavirus. Lactococcus lactis NZ9000 was transformed with segments of vP4 of the porcine rotavirus inserted into the pNZ8112 surface-expression vector, and a recombinant L. lactis expressing VP4 protein was constructed. An approximately 27 kDa VP4 protein was confirmed by SDS-PAGE , Western blot and immunostaining analysis. BALB/c mice were immunized orally with VP4-expression recombinant L. lactis and cellular, mucosal and systemic humoral immune responses were examined. Specific anti-VP4 secretory IgA and IgG were found in feces, ophthalmic and vaginal washes and in serum. The induced antibodies demonstrated neutralizing effects on porcine rotavirus infection on MA104 cells. Our findings suggest that oral immunization with VP4-expressing L. lactis induced both specific local and systemic humoral and cellular immune responses in mice.

Genome-wide analysis of signal peptide functionality in Lactobacillus plantarum WCFS1

Background

Lactobacillus plantarum is a normal, potentially probiotic, inhabitant of the human gastrointestinal (GI) tract. The bacterium has great potential as food-grade cell factory and for in situ delivery of biomolecules. Since protein secretion is important both for probiotic activity and in biotechnological applications, we have carried out a genome-wide experimental study of signal peptide (SP) functionality.

Results

We have constructed a library of 76 Sec-type signal peptides from L. plantarum WCFS1 that were predicted to be cleaved by signal peptidase I. SP functionality was studied using staphylococcal nuclease (NucA) as a reporter protein. 82% of the SPs gave significant extracellular NucA activity. Levels of secreted NucA varied by a dramatic 1800-fold and this variation was shown not to be the result of different mRNA levels. For the best-performing SPs all produced NucA was detected in the culture supernatant, but the secretion efficiency decreased for the less well performing SPs. Sequence analyses of the SPs and their cognate proteins revealed four properties that correlated positively with SP performance for NucA: high hydrophobicity, the presence of a transmembrane helix predicted by TMHMM, the absence of an anchoring motif in the cognate protein, and the length of the H+C domain. Analysis of a subset of SPs with a lactobacillal amylase (AmyA) showed large variation in production levels and secretion efficiencies. Importantly, there was no correlation between SP performance with NucA and the performance with AmyA.

Conclusion

This is the first comprehensive experimental study showing that predicted SPs in the L. plantarum genome actually are capable of driving protein secretion. The results reveal considerable variation between the SPs that is at least in part dependent on the protein that is secreted. Several SPs stand out as promising candidates for efficient secretion of heterologous proteins in L. plantarum. The results for NucA provide some hints as to the sequence-based prediction of SP functionality, but the general conclusion is that such prediction is difficult. The vector library generated in this study is based on exchangeable cassettes and provides a powerful tool for rapid experimental screening of SPs.

Heterologous protein secretion by Lactobacillus plantarum using homologous signal peptides

AIMS

To test seven selected putative signal peptides from Lactobacillus plantarum WCFS1 in terms of their ability to drive secretion of two model proteins in Lact. plantarum, and to compare the functionality of these signal peptides with that of well-known heterologous signal peptides (Usp45, M6).

METHODS AND RESULTS

Signal peptide functionality was assessed using a series of modular derivatives of the pSIP vectors for peptide pheromone-controlled high-level gene expression in lactobacilli. Several of the constructs with homologous signal peptides yielded similar or higher reporter protein activities than constructs with heterologous signal peptides. Two of the homologous signal peptides (Lp_0373 and Lp_0600) appeared as especially promising candidates for directing secretion, as they were among the best performing with both reporter proteins.

CONCLUSIONS

We have identified homologous signal peptides for high-level secretion of heterologous proteins in Lact. plantarum. With the model proteins, some of these performed better than commonly used heterologous signal peptides.

SIGNIFICANCE AND IMPACT OF THE STUDY

The homologous signal peptides tested out, in this study, could be useful in food-grade systems for secretion of interesting proteins in Lact. plantarum. The constructed modular secretion vectors are easily accessible for rapid signal peptide screening.

Construction of recombinant Lactobacillus casei efficiently surface displayed and secreted porcine parvovirus VP2 protein and comparison of the immune responses induced by oral immunization

Lactobacillus casei ATCC 393 was selected as a bacterial carrier for the development of mucosal vaccine against porcine parvovirus (PPV) infection. The PPV major structural polypeptide VP2 was used as the model parvovirus antigen. Two inducible expression systems, namely pPG611.1 of the cell-surface expression system and pPG612.1 of the secretion expression system based on the xylose operon promoter were used to express the VP2 protein. The immunogenicity of recombinant strains producing VP2 protein in two cellular locations, cell-surface exposed and secreted, was compared to each other by immunizing mice through the intragastric administration. The two types of constructs were able to induce strong specific immune responses against VP2 via intragastric administration and maximum titres of IgA and IgG were attained on days 46 post oral immunization, while the highest antibody levels were obtained with the strain producing the VP2 protein in extracellular milieu. The induced antibodies demonstrated neutralizing effects on PPV infection.

Mice protected by oral immunization with Lactobacillus reuteri secreting fusion protein of Escherichia coli enterotoxin subunit protein

A green fluorescent protein (gfp) gene was ligated to the Lactobacillus reuteri‐specific nisin‐inducible expression‐secretion vector pNIES, generating a pNIES‐GFP vector capable of secreting the cloned gene as a GFP‐fusion protein with fluorescent activity. To develop this system as a live vehicle carrying the heat‐stable enterotoxin (ST) and heat‐labile enterotoxin B (LT_B) of the enterotoxigenic Escherichia coli (ETEC), a recombinant 5′‐ST‐LT_B‐3′ DNA fragment was cloned into pNIES‐GFP. The resulting L. reuteri/pNIES‐GFP:STLT_B system was found to possess the capability of adhering to the mice gut, secreting GFP:STLT_B product at 0.14 and 0.026 pgcell⁻¹ under induced and noninduced conditions, respectively. Further analysis of the GFP:STLT_B product confirmed its ganglioside‐binding ability, LT_B antigenicity and relative freedom from the ST‐associated toxicity, making it suitable for use as an oral vaccine in mice. Oral inoculation of the L. reuteri/pNIES‐GFP:STLT_B culture in mice elicited significant (P<0.01) serum IgG and mucosal IgA antibodies against the STLT_B antigen. These immunized mice were subsequently challenged with ETEC and showed full protection against the fluid influx response in the gut. This is the first report of using L. reuteri as a vaccine carrier to induce complete immunologic protection against ETEC.

B subunit of E. coli enterotoxin as adjuvant and carrier in oral and skin vaccination

Mucosal sites are one of the main natural ports of entry into the body. Stimulation of a local response by antibodies as the systemic protection may enhance the efficacy of non-living vaccines, and allow for vaccination by subunit vaccines without the need for injection. Mucosal or skin vaccination necessitates a suitable adjuvant and carrier. Escherichia coli heat-labile enterotoxin (LT) and its B subunit (LTB) have been found to be effective adjuvants. The aim of this study was to efficiently produce and purify recombinant LTB (brLTB), and examine its adjuvant and carrier properties. The gene encoding LTB was cloned and expressed in E. coli, and the product was found to have a pentameric form with the ability to bind the cell receptor, GM1 ganglioside. A one-step method for efficient purification and concentration of brLTB was developed. Both oral and intramuscular vaccination with purified brLTB yielded high antibody titers, which detected the whole toxin. In an attempt to test its adjuvant characteristics, brLTB was mixed with either BSA or a recombinant protein (rKnob of egg drop syndrome adenovirus) and delivered intramuscularly, orally or transcutaneously. The addition of brLTB significantly elevated the antibody response in groups vaccinated orally and transcutaneously, but had no influence in injected groups. Vaccination with another recombinant protein, (viral protein 2 of infectious bursal disease virus) supplemented with brLTB did not elevate the antibody response, as compared to vaccination with the antigen alone. These results demonstrate that the addition of brLTB makes oral and transcutaneous vaccination with protein antigens possible.

Vaccine and adjuvant activity of recombinant subunit B of E. coli enterotoxin produced in yeast

Escherichia coli heat-labile enterotoxin (LT) and cholera toxin (CT) have been studied intensively as vaccines against diseases caused by those bacteria and as adjuvants for mucosal vaccination. Two major problems interfere with the use of these promising adjuvants: their toxicity and the residual bacterial endotoxins mixed with the desired LT. In this study, subunit B of LT was expressed in Pichia pastoris yeast cells (yrLTB) and the recombinant protein was purified and concentrated by ion-exchange chromatography. The final yield of the recombinant protein was 5-8 mg/l induction medium. The molecule is in pentameric form and binds to GM1 gangliosides. When given orally to chickens, anti-LTB antibodies were produced, exhibiting its ability to cross the digestive system and induce an immune response. The adjuvant activity of yrLTB was proven by fusing it to viral protein 2 (VP2) of infectious bursal disease virus. Birds intramuscularly vaccinated with this molecule exhibit 70-100% protection, in a dose-response-dependent manner. This method eliminated the bacterial endotoxins and enabled the production of large quantities of LTB. Expression in a eukaryotic system allows the production of fusion proteins that require post-translational modifications. This may allow oral vaccination with a protein fused to yrLTB. The approach described in this study will enable the efficient production of a non-toxic, eukaryotically expressed enterotoxin as a vaccine against the toxin itself or as a carrier or adjuvant for foreign vaccine molecules.

Expression of Streptococcus pneumoniae antigens, PsaA (pneumococcal surface antigen A) and PspA (pneumococcal surface protein A) by Lactobacillus casei

A number of recent research works in lactic acid bacteria aim towards the design of new strains that could be used as live vectors for the delivery of antigens for oral vaccination, or other therapeutic molecules. In this work, an inducible expression system based on the Lactobacillus casei lactose operon promoter was used to express three important surface antigens of Streptococcus pneumoniae in this lactic acid bacterium: a virulence-related pneumococcal surface antigen (PsaA) and two variants of the virulence factor PspA (pneumococcal surface protein A). Expression of the three proteins was induced upon growth on lactose and strongly repressed by glucose. These proteins were produced intracellularly. Also, secretion to the growth medium was achieved by means of a fusion to the secreting and processing signals from the L. casei surface proteinase. Interestingly, while secreted PspA proteins were found in the culture supernatants, PsaA remained trapped in the cell wall. Expression of pneumococcal antigens in a food-grade organism opens an alternative for mucosal vaccination against this important pathogen.

Peptide surface display and secretion using two LPXTG-containing surface proteins from Lactobacillus fermentum BR11

A locus encoding two repetitive proteins that have LPXTG cell wall anchoring signals from Lactobacillus fermentum BR11 has been identified by using an antiserum raised against whole L. fermentum BR11 cells. The first protein, Rlp, is similar to the Rib surface protein from Streptococcus agalactiae, while the other protein, Mlp, is similar to the mucus binding protein Mub from Lactobacillus reuteri. It was shown that multiple copies of mlp exist in the genome of L. fermentum BR11. Regions of Rlp, Mlp, and the previously characterized surface protein BspA were used to surface display or secrete heterologous peptides in L. fermentum. The peptides tested were 10 amino acids of the human cystic fibrosis transmembrane regulator protein and a six-histidine epitope (His(6)). The BspA promoter and secretion signal were used in combination with the Rlp cell wall sorting signal to express, export, and covalently anchor the heterologous peptides to the cell wall. Detection of the cell surface protein fusions revealed that Rlp was a significantly better surface display vector than BspA despite having lower cellular levels (0.7 mg per liter for the Rlp fusion compared with 4 mg per liter for the BspA fusion). The mlp promoter and encoded secretion signal were used to express and export large (328-kDa at 10 mg per liter) and small (27-kDa at 0.06 mg per liter) amino-terminal fragments of the Mlp protein fused to the His(6) and CFTR peptides or His(6) peptide, respectively. Therefore, these newly described proteins from L. fermentum BR11 have potential as protein production and targeting vectors.

Immune response induced by recombinant Mycobacterium bovis BCG producing the cholera toxin B subunit

The pentameric form of the cholera toxin B subunit (CTB) is known to be a strong mucosal adjuvant and stimulates antigen-specific secretory immunoglobulin A (IgA) and systemic antibody responses to antigens when given by mucosal routes. To deliver CTB for prolonged periods of time to the respiratory mucosa, we constructed a Mycobacterium bovis bacillus Calmette-Guérin (BCG) strain that produces and secretes assembled pentameric CTB. Mice immunized intranasally (i.n.) with recombinant BCG (rBCG) developed a stronger anti-BCG IgA response in bronchoalveolar lavage fluids (BALF) than mice immunized with nonrecombinant BCG. The total IgA response in the BALF of mice immunized with rBCG was also stronger than that in BALF of mice immunized with the nonrecombinant strain. The induction of IgA was well correlated with an increased production of transforming growth factor beta1. Simultaneous administration of intraperitoneally delivered ovalbumin and of i.n. delivered CTB-producing BCG induced a long-lasting ovalbumin-specific mucosal IgA response as well as a systemic IgG response, both of which were significantly higher than those in mice immunized with nonrecombinant BCG together with ovalbumin. These results suggest that the CTB-producing BCG may be a powerful adjuvant to be considered for future mucosal vaccine development.

Genetically modified lactic acid bacteria: applications to food or health and risk assessment

Lactic acid bacteria have a long history of use in fermented food products. Progress in gene technology allows their modification by introducing new genes or by modifying their metabolic functions. These modifications may lead to improvements in food technology (bacteria better fitted to technological processes, leading to improved organoleptic properties em leader ), or to new applications including bacteria producing therapeutic molecules that could be delivered by mouth. Examples in these two fields will be discussed, at the same time evaluating their potential benefit to society and the possible risks associated with their use. Risk assessment and expected benefits will determine the future use of modified bacteria in the domains of food technology and health.

Synthesis of cholera toxin B subunit gene: cloning and expression of a functional 6XHis-tagged protein in Escherichia coli

Cholera toxin B subunit (CTB) has been extensively studied as immunogen, adjuvant, and oral tolerance inductor depending on the antigen conjugated or coadministered. It has been already expressed in several bacterial and yeast systems. In this study, we synthesized a versatile gene coding a 6XHis-tagged CTB (359bp). The sequence was designed according to codon usage of Escherichia coli, Lactobacillus casei, and Salmonella typhimurium. The gene assembly was based on a polymerase chain reaction, in which the polymerase extends DNA fragments from a pool of overlapping oligonucleotides. The synthetic gene was amplified, cloned, and expressed in E. coli in an insoluble form, reaching levels about 13 mg of purified active pentameric rCTB per liter of induced culture. Western blot and ELISA analyses showed that recombinant CTB is strongly and specifically recognized by polyclonal antibodies against the cholera toxin. The ability to form the functional pentamers was observed in cell culture by the inhibition of cholera toxin activity on Y1 adrenal cells in the presence of recombinant CTB. The 6XHis-tagged CTB provides a simple way to obtain functional CTB through Ni(2+)-charged resin after refolding and also free of possible CTA contaminants as in the case of CTB obtained from Vibrio cholerae cultures.

Nasal vaccination using live bacterial vectors

Live recombinant bacteria represent an attractive means to induce both mucosal and systemic immune responses against heterologous antigens. Several models have now been developed and shown to be highly efficient following intranasal immunization. In this review, we describe the two main classes of live recombinant bacteria: generally recognized as safe bacteria and attenuated strains derived from pathogenic bacteria. Among the latter, we have differentiated the bacteria, which do not usually colonize the respiratory tract from those that are especially adapted to respiratory tissues. The strategies of expression of the heterologous antigens, the invasiveness and the immunogenicity of the recombinant bacteria are discussed.

Adaptation of the nisin-controlled expression system in Lactobacillus plantarum: a tool to study in vivo biological effects

The potential of lactic acid bacteria as live vehicles for the production and delivery of therapeutic molecules is being actively investigated today. For future applications it is essential to be able to establish dose-response curves for the targeted biological effect and thus to control the production of a heterologous biopeptide by a live lactobacillus. We therefore implemented in Lactobacillus plantarum NCIMB8826 the powerful nisin-controlled expression (NICE) system based on the autoregulatory properties of the bacteriocin nisin, which is produced by Lactococcus lactis. The original two-plasmid NICE system turned out to be poorly suited to L. plantarum. In order to obtain a stable and reproducible nisin dose-dependent synthesis of a reporter protein (beta-glucuronidase) or a model antigen (the C subunit of the tetanus toxin, TTFC), the lactococcal nisRK regulatory genes were integrated into the chromosome of L. plantarum NCIMB8826. Moreover, recombinant L. plantarum producing increasing amounts of TTFC was used to establish a dose-response curve after subcutaneous administration to mice. The induced serum immunoglobulin G response was correlated with the dose of antigen delivered by the live lactobacilli.

Pharmacokinetics of Lactobacillus plantarum NCIMB 8826, Lactobacillus fermentum KLD, and Lactococcus lactis MG 1363 in the human gastrointestinal tract

OBJECTIVES

Genetically modified lactic acid bacteria may be a way to deliver vaccinal epitopes in the gastrointestinal tract.

AIM

Three strains of lactic acid bacteria were studied for their pharmacokinetics in the human gastrointestinal tract.

METHODS

The survival of the strains was studied up to the ileum in six subjects each, after ingestion of 150 g of fermented milk. The strains and their concentrations in the products were Lactobacillus fermentum KLD (107 cfu/g), Lactobacillus plantarum NCIMB 8826 (108 cfu/g), and Lactococcus lactis MG 1363 (108 cfu/g). Ileal fluid was aspirated by intestinal intubation and immediately cultured. L. plantarum NCIMB 8826, which was found in high concentrations in the ileum, was studied for its survival in the faeces after consumption of 150 g of fermented milk three times daily for 7 days. Faecal samples were collected for culture.

RESULTS

The concentration of L. plantarum NCIMB 8826 in the ileum reached 108 cfu/mL after a single dose, with a survival of 7%. L. fermentum KLD and Lc. lactis MG 1363 had lower (0.5 and 1.0%, respectively) and shorter (4 h) survival in the ileum. During the 7-day ingestion period, L. plantarum NCIMB 8826 reached high concentrations (108 cfu/g) in the faeces, with a survival of 25 +/- 29%. None of the strains colonized.

CONCLUSIONS

L. plantarum NCIMB 8826 has a promising pharmacokinetic profile as a candidate vaccine vehicle.

Gene expression systems for lactic acid bacteria

Considerable advances have been made in the genetics and molecular biology of lactic acid bacteria, including Lactococcus, Lactobacillus, Leuconostoc, Pediococcus and Streptococcus spp. These have resulted in the construction of constitutive gene expression cassettes, inducible gene expression systems, and specific protein targeting systems for these bacteria. These developments are important in the food industry where lactic acid bacteria can be exploited as food-grade cell factories.