High-level expression of recombinant beta-galactosidases in Lactobacillus plantarum and Lactobacillus sakei using a Sakacin P-based expression system

PEARL: Protein Eluting Alginate with Recombinant Lactobacilli

Engineered living materials (ELMs) made of bacteria in hydrogels have shown considerable promise for therapeutic applications through controlled and sustained release of complex biopharmaceuticals at low costs and with reduced wastage. While most therapeutic ELMs use E. coli due to its large genetic toolbox, most live biotherapeutic bacteria in development are lactic acid bacteria due to native health benefits they offer. Among these, lactobacilli form the largest family of probiotics with therapeutic potential in almost all sites of the body with a microbiome. A major factor limiting the use of lactobacilli in ELMs is their limited genetic toolbox. This study expands on recent work to expand the genetic programmability of probiotic Lactiplantibacillus plantarum WCFS1 for protein secretion and encapsulate it in a simple, cost-effective, and biocompatible core-shell alginate bead to develop an ELM. The controlled release of recombinant proteins is demonstrated, even up to 14 days from this ELM, thereby terming it PEARL - Protein Eluting Alginate with Recombinant Lactobacilli. Notably, lactobacillus encapsulation offered benefits like bacterial containment, protein release profile stabilization, and metabolite-induced cytotoxicity prevention. These findings demonstrate the mutual benefits of combining recombinant lactobacilli with alginate for the controlled and sustained release of proteins.

Discovery of a high-performance phage-derived promoter/repressor system for probiotic lactobacillus engineering

BACKGROUND

The Lactobacillaceae family comprises many species of great importance for the food and healthcare industries, with numerous strains identified as beneficial for humans and used as probiotics. Hence, there is a growing interest in engineering these probiotic bacteria as live biotherapeutics for animals and humans. However, the genetic parts needed to regulate gene expression in these bacteria remain limited compared to model bacteria like E. coli or B. subtilis. To address this deficit, in this study, we selected and tested several bacteriophage-derived genetic parts with the potential to regulate transcription in lactobacilli.

RESULTS

We screened genetic parts from 6 different lactobacilli-infecting phages and identified one promoter/repressor system with unprecedented functionality in Lactiplantibacillus plantarum WCFS1. The phage-derived promoter was found to achieve expression levels nearly 9-fold higher than the previously reported strongest promoter in this strain and the repressor was able to almost completely repress this expression by reducing it nearly 500-fold.

CONCLUSIONS

The new parts and insights gained from their engineering will enhance the genetic programmability of lactobacilli for healthcare and industrial applications.

Lactiplantibacillus plantarum as a novel platform for production and purification of integral membrane proteins using RseP as the benchmark

The present study describes a detailed procedure for expressing and purifying the integral membrane protein RseP using the pSIP system and Lactiplantibacillus plantarum as an expression host. RseP is a membrane-bound site-2-protease and a known antibacterial target in multiple human pathogens. In the present study, we screened five RseP orthologs from Gram-positive bacteria and found RseP from Enterococcus faecium (EfmRseP) to yield the highest protein levels. The production conditions were optimized and EfmRseP was purified by immobilized metal ion affinity chromatography followed by size-exclusion chromatography. The purification resulted in an overall yield of approximately 1 mg of pure protein per 3 g of wet-weight cell pellet. The structural integrity of the purified protein was confirmed using circular dichroism. We further assessed the expression and purification of RseP from E. faecium in the Gram-negative Escherichia coli. Detection of soluble protein failed in two of the three E. coli strains tested. Purification of EfmRseP expressed in E. coli C43(DE3) resulted in a protein with lower purity compared to EfmRseP expressed in L. plantarum. To our knowledge, this is the first time L. plantarum and the pSIP expression system have been applied for the production of membrane proteins.

Plasmid-Based Gene Expression Systems for Lactic Acid Bacteria: A Review

Lactic acid bacteria (LAB) play a very vital role in food production, preservation, and as probiotic agents. Some of these species can colonize and survive longer in the gastrointestinal tract (GIT), where their presence is crucially helpful to promote human health. LAB has also been used as a safe and efficient incubator to produce proteins of interest. With the advent of genetic engineering, recombinant LAB have been effectively employed as vectors for delivering therapeutic molecules to mucosal tissues of the oral, nasal, and vaginal tracks and for shuttling therapeutics for diabetes, cancer, viral infections, and several gastrointestinal infections. The most important tool needed to develop genetically engineered LABs to produce proteins of interest is a plasmid-based gene expression system. To date, a handful of constitutive and inducible vectors for LAB have been developed, but their limited availability, host specificity, instability, and low carrying capacity have narrowed their spectrum of applications. The current review discusses the plasmid-based vectors that have been developed so far for LAB; their functionality, potency, and constraints; and further highlights the need for a new, more stable, and effective gene expression platform for LAB.

Heterologous Protein Production in Lactobacillus (plantarum) Using pSIP Vectors

While lactobacilli are not generally regarded as efficient cell factories for heterologous proteins, these food-grade Gram-positive bacteria are attractive as expression hosts for medicinal proteins. Furthermore, tools have been developed not only to secrete the protein of interest, but also to anchor the protein to the cell membrane or the cell wall. Research efforts aimed at the production and surface display of complex vaccine proteins have shown that lactobacilli are capable of producing heterologous proteins that are otherwise difficult to produce in soluble form. Many recent studies on expressing a wide variety of proteins in lactobacilli have employed the pSIP vector system, which offers a wide range of possibilities for inducible expression, including various options for secretion and surface anchoring. The modular nature of the pSIP vectors allows for rapid screening of multiple expression strategies. This chapter describes the pSIP vector system and how it can be used to accomplish protein expression in lactobacilli.

Recombinant Protein Production and Purification of Insoluble Proteins

Proteins are synthesized in heterologous systems because of the impossibility to obtain satisfactory yields from natural sources. The efficient production of soluble and functional recombinant proteins is among the main goals in the biotechnological field. In this context, it is important to point out that under stress conditions, protein folding machinery is saturated and this promotes protein misfolding and, consequently, protein aggregation. Thus, the selection of the optimal expression organism and its growth conditions to minimize the formation of insoluble protein aggregates should be done according to the protein characteristics and downstream requirements. Escherichia coli is the most popular recombinant protein expression system despite the great development achieved so far by eukaryotic expression systems. Besides, other prokaryotic expression systems, such as lactic acid bacteria and psychrophilic bacteria, are gaining interest in this field. However, it is worth mentioning that prokaryotic expression system poses, in many cases, severe restrictions for a successful heterologous protein production. Thus, eukaryotic systems such as mammalian cells, insect cells, yeast, filamentous fungus, and microalgae are an interesting alternative for the production of these difficult-to-express proteins.

Efficient Secretion and Recombinant Production of a Lactobacillal α-amylase in Lactiplantibacillus plantarum WCFS1: Analysis and Comparison of the Secretion Using Different Signal Peptides

Lactic acid bacteria (LAB) have been used as starter cultures and producers of enzymes, antimicrobial peptides or metabolites that contribute to the flavor, texture and safety of food products. Lactiplantibacillus plantarum, one of the best-studied LAB, is considered as safe and effective cell factory for food applications. In this study, our aim was to use L. plantarum as the producer for high levels of a food-grade lactobacillal α-amylase, which has potential applications in food, fermentation and feed industries. The native form of an α-amylase (AmyL) from L. plantarum S21, an amylolytic LAB isolated from Thai fermented rice noodles, was expressed in L. plantarum WCFS1 using the pSIP expression system. The secretion of the α-amylase was driven by the native signal peptides of the α-amylases from L. plantarum S21 (SP_AmyL) and Lactobacillus amylovorus NRRL B-4549 (SP_AmyA), as well as by three Sec-type signal peptides derived from L. plantarum WCFS1; Lp_2145, Lp_3050, and Lp_0373. Among the tested signal peptides, Lp_2145 appears to be the best signal peptide giving the highest total and extracellular enzymatic activities of α-amylase AmyL from L. plantarum S21, which were 13.1 and 8.1 kU/L of fermentation, respectively. These yields were significantly higher than the expression and secretion in L. plantarum WCFS1 using the native signal peptide SP_AmyL, resulting in 6.2- and 5.4-fold increase in total and extracellular activities of AmyL, respectively. In terms of secretion efficiency, Lp_0373 was observed as the most efficient signal peptide among non-cognate signal peptides for the secretion of AmyL. Real-time reverse-transcriptase quantitative PCR (RT-qPCR) was used to estimate the mRNA levels of α-amylase transcript in each recombinant strain. Relative quantification by RT-qPCR indicated that the strain with the Lp_2145 signal peptide-containing construct had the highest mRNA levels and that the exchange of the signal peptide led to a change in the transcript level of the target gene.

Construction and Evaluation of Peptide-Linked Lactobacillus brevis β-Galactosidase Heterodimers

BACKGROUND

β-galactosidases are enzymes that are utilized to hydrolyze lactose into galactose and glucose, and are is widely used in the food industry.

OBJECTIVE

We describe the recombinant expression of an unstudied, heterodimeric β-galactosidase originating from Lactobacillus brevis ATCC 367 in Escherichia coli. Furthermore, six different constructs, in which the two protein subunits were fused with different peptide linkers, were also investigated.

METHODS

The heterodimeric subunits of the β-galactosidase were cloned in expressed in various expression constructs, by using either two vectors for the independent expression of each subunit, or using a single Duet vector for the co-expression of the two subunits.

RESULTS

The co-expression in two independent expression vectors only resulted in low β-galactosidase activities, whereas the co-expression in a single Duet vector of the independent and fused subunits increased the β-galactosidase activity significantly. The recombinant β-galactosidase showed comparable hydrolyzing properties towards lactose, N-acetyllactosamine, and pNP-β-D-galactoside.

CONCLUSION

The usability of the recombinant L. brevis β-galactosidase was further demonstrated by the hydrolysis of human, bovine, and goat milk samples. The herein presented fused β-galactosidase constructs may be of interest for analytical research as well as in food- and biotechnological applications.

β-Galactosidase: From its source and applications to its recombinant form

Carbohydrate-active enzymes are a group of important enzymes playing a critical role in the degradation and synthesis of carbohydrates. Glycosidases can hydrolyze glycosides into oligosaccharides, polysaccharides, and glycoconjugates via a cost-effective approach. Lactase is an important member of β-glycosidases found in higher plants, animals, and microorganisms. β-Galactosidases can be used to degrade the milk lactose for making lactose-free milk, which is sweeter than regular milk and is suitable for lactose-intolerant people. β-Galactosidase is employed by many food industries to degrade lactose and improve the digestibility, sweetness, solubility, and flavor of dairy products. β-Galactosidase enzymes have various families and are applied in the food-processing industries such as hydrolyzed-milk products, whey, and galactooligosaccharides. Thus, this enzyme is a valuable protein which is now produced by recombinant technology. In this review, origins, structure, recombinant production, and critical modifications of β-galactosidase for improving the production process are discussed. Since β-galactosidase is a valuable enzyme in industry and health care, a study of its various aspects is important in industrial biotechnology and applied biochemistry.

Safety Aspects of Genetically Modified Lactic Acid Bacteria

Lactic acid bacteria (LAB) have a long history of use in the food industry. Some species are part of the normal human microbiota and have beneficial properties for human health. Their long-standing use and considerable biotechnological potential have led to the development of various systems for their engineering. Together with novel approaches such as CRISPR-Cas, the established systems for engineering now allow significant improvements to LAB strains. Nevertheless, genetically modified LAB (GM-LAB) still encounter disapproval and are under extensive regulatory requirements. This review presents data on the prospects for LAB to obtain 'generally recognized as safe' (GRAS) status. Genetic modification of LAB is discussed, together with problems that can arise from their engineering, including their dissemination into the environment and the spread of antibiotic resistance markers. Possible solutions that would allow the use of GM-LAB are described, such as biocontainment, alternative selection markers, and use of homologous DNA. The use of GM-LAB as cell factories in closed systems that prevent their environmental release is the least problematic aspect, and this is also discussed.

Characterization of three novel β-galactosidases from Akkermansia muciniphila involved in mucin degradation

The gut microbe Akkermansia (A.) muciniphila becomes increasingly important as its prevalence is inversely correlated with different human metabolic disorders and diseases. This organism is a highly potent degrader of intestinal mucins and the hydrolyzed glycan compounds can then serve as carbon sources for the organism itself or other members of the gut microbiota via cross-feeding. Despite its importance for the hosts' health and microbiota composition, exact mucin degrading mechanisms are still mostly unclear. In this study, we identified and characterized three extracellular β-galactosidases (Amuc_0771, Amuc_0824, and Amuc_1666) from A. muciniphila ATCC BAA-835. The substrate spectrum of all three enzymes was analyzed and the results indicated a preference for different galactosidic linkages for each hydrolase. All preferred target structures are prevalent within mucins of the colonic habitat of A. muciniphila. To check a potential function of the enzymes for the degradation of mucosal glycan structures, porcine stomach mucin was applied as a model substrate. In summary, we could confirm the involvement of all three β-galactosidases from A. muciniphila in the complex mucin degradation machinery of this important gut microbe. These findings could contribute to the understanding of the molecular interactions between A. muciniphila and its host on a molecular level.

A New β-Galactosidase from the Antarctic Bacterium Alteromonas sp. ANT48 and Its Potential in Formation of Prebiotic Galacto-Oligosaccharides

As an important medical enzyme, β-galactosidases catalyze transgalactosylation to form prebiotic Galacto-Oligosaccharides (GOS) that assist in improving the effect of intestinal flora on human health. In this study, a new glycoside hydrolase family 2 (GH2) β-galactosidase-encoding gene, galA, was cloned from the Antarctic bacterium Alteromonas sp. ANT48 and expressed in Escherichia coli. The recombinant β-galactosidase GalA was optimal at pH 7.0 and stable at pH 6.6–7.0, which are conditions suitable for the dairy environment. Meanwhile, GalA showed most activity at 50 °C and retained more than 80% of its initial activity below 40 °C, which makes this enzyme stable in normal conditions. Molecular docking with lactose suggested that GalA could efficiently recognize and catalyze lactose substrates. Furthermore, GalA efficiently catalyzed lactose degradation and transgalactosylation of GOS in milk. A total of 90.6% of the lactose in milk could be hydrolyzed within 15 min at 40 °C, and the GOS yield reached 30.9%. These properties make GalA a good candidate for further applications.

Construction of a Lactobacillus plantarum Strain Expressing the Capsid Protein of Porcine Circovirus Type 2d (PCV2d) as an Oral Vaccine

Porcine circovirus type 2 (PCV2) is a pathogenic virus that causes high rates of porcine death, resulting in severe economic losses to the swine industry. In recent years, the prevalence of PCV2d genotype infection in pigs has increased, but most commercially available vaccines were developed against the PCV2a strain and do not ensure complete protection from PCV2d. Here, we first constructed an expression vector for the antigenic ORF2-encoded capsid protein of PCV2d (pLp3050-His₆-tag-capsid). We then utilized Lactobacillus plantarum to express the protein at mucosal sites in orally vaccinated mice. After transducing L. plantarum with pLp3050-His₆-tag-capsid, the expressed protein could be found in cell wall and cell-free supernatant fractions by Western blotting. Using flow cytometry, we found that L. plantarum cells with surface-displayed capsid protein increased with time after SppIP induction. Finally, mice that were orally immunized 18 times with capsid-expressing L. plantarum showed increased levels of capsid-specific sIgA and virus neutralizing activity at mucosal sites, suggesting mucosal immunity had been stimulated by the vaccine. Overall, our findings demonstrate the feasibility and utility of a PCV2d-based vaccine, which may be of great value in porcine agriculture.

Constitutive expression and cell-surface display of a bacterial β-mannanase in Lactobacillus plantarum

BACKGROUND

Lactic acid bacteria (LAB) are important microorganisms in the food and beverage industry. Due to their food-grade status and probiotic characteristics, several LAB are considered as safe and effective cell-factories for food-application purposes. In this present study, we aimed at constitutive expression of a mannanase from Bacillus licheniformis DSM13, which was subsequently displayed on the cell surface of Lactobacillus plantarum WCFS1, for use as whole-cell biocatalyst in oligosaccharide production.

RESULTS

Two strong constitutive promoters, Pgm and SlpA, from L. acidophilus NCFM and L. acidophilus ATCC4356, respectively, were used to replace the inducible promoter in the lactobacillal pSIP expression system for the construction of constitutive pSIP vectors. The mannanase-encoding gene (manB) was fused to the N-terminal lipoprotein anchor (Lp_1261) from L. plantarum and the resulting fusion protein was cloned into constitutive pSIP vectors and expressed in L. plantarum WCFS1. The localization of the protein on the bacterial cell surface was confirmed by flow cytometry and immunofluorescence microscopy. The mannanase activity and the reusability of the constructed L. plantarum displaying cells were evaluated. The highest mannanase activities on the surface of L. plantarum cells obtained under the control of the Pgm and SlpA promoters were 1200 and 3500 U/g dry cell weight, respectively, which were 2.6- and 7.8-fold higher compared to the activity obtained from inducible pSIP anchoring vectors. Surface-displayed mannanase was shown to be able to degrade galactomannan into manno-oligosaccharides (MOS).

CONCLUSION

This work demonstrated successful displaying of ManB on the cell surface of L. plantarum WCFS1 using constitutive promoter-based anchoring vectors for use in the production of manno-oligosaccharides, which are potentially prebiotic compounds with health-promoting effects. Our approach, where the enzyme of interest is displayed on the cell surface of a food-grade organism with the use of strong constitutive promoters, which continuously drive synthesis of the recombinant protein without the need to add an inducer or change the growth conditions of the host strain, should result in the availability of safe, stable food-grade biocatalysts.

β-Galactosidase from Lactobacillus helveticus DSM 20075: Biochemical Characterization and Recombinant Expression for Applications in Dairy Industry

β-Galactosidase encoding genes lacLM from Lactobacillus helveticus DSM 20075 were cloned and successfully overexpressed in Escherichia coli and Lactobacillus plantarum using different expression systems. The highest recombinant β-galactosidase activity of ∼26 kU per L of medium was obtained when using an expression system based on the T7 RNA polymerase promoter in E. coli, which is more than 1000-fold or 28-fold higher than the production of native β-galactosidase from L. helveticus DSM 20075 when grown on glucose or lactose, respectively. The overexpression in L. plantarum using lactobacillal food-grade gene expression system resulted in ∼2.3 kU per L of medium, which is approximately 10-fold lower compared to the expression in E. coli. The recombinant β-galactosidase from L. helveticus overexpressed in E. coli was purified to apparent homogeneity and subsequently characterized. The K_m and v_max values for lactose and o-nitrophenyl-β-d-galactopyranoside (oNPG) were 15.7 ± 1.3 mM, 11.1 ± 0.2 µmol D-glucose released per min per mg protein, and 1.4 ± 0.3 mM, 476 ± 66 µmol o-nitrophenol released per min per mg protein, respectively. The enzyme was inhibited by high concentrations of oNPG with K_i,s = 3.6 ± 0.8 mM. The optimum pH for hydrolysis of both substrates, lactose and oNPG, is pH 6.5 and optimum temperatures for these reactions are 60 and 55 °C, respectively. The formation of galacto-oligosaccharides (GOS) in discontinuous mode using both crude recombinant enzyme from L. plantarum and purified recombinant enzyme from E. coli revealed high transgalactosylation activity of β-galactosidases from L. helveticus; hence, this enzyme is an interesting candidate for applications in lactose conversion and GOS formation processes.

Catalytic activity, structure and stability of proteinase K in the presence of biosynthesized CuO nanoparticles

Here, CuO nanoparticles were synthesized using Sambucus nigra (elderberry) fruit extract. Further, the binding of proteinase K, as a model enzyme with green synthesized nanoparticles was investigated. The results demonstrated that the structural changes in enzyme were induced by the binding of nanoparticles. These changes were accompanied by the decrease in the Michaelis-Menten constant at 298 K. This means that the enzyme affinity for the substrate was increased. Thermodynamic parameters of protein stability and protein-ligand binding were estimated from the spectroscopic measurements at 298-333 K. Depending on the temperature, CuO nanoparticles showed a dual effect on the thermodynamic stability and binding affinity of enzyme. Nanoparticles increase the stability of the native state of enzyme at room temperature. On the other hand, nanoparticles stabilize the unfolded state of enzyme at 310-333 K. An overall favorable Gibbs energy change was observed for the binding process at 298-333 K. The enzyme-nanoparticle binding is enthalpically driven at room temperature. It was concluded that hydrogen bonding plays a key role in the interaction of enzyme with nanoparticles at 298-310 K. At higher temperatures, the protein-ligand binding is entropically driven. This means that hydrophobic association plays a major role in the proteinase K-CuO binding at 310-333 K.

Immobilization of β-Galactosidases from Lactobacillus on Chitin Using a Chitin-Binding Domain

Two β-galactosidases from Lactobacillus, including a heterodimeric LacLM type enzyme from Lactobacillus reuteri L103 and a homodimeric LacZ type β-galactosidase from Lactobacillus bulgaricus DSM 20081, were studied for immobilization on chitin using a carbohydrate-binding domain (chitin-binding domain, ChBD) from a chitinolytic enzyme. Three recombinant enzymes, namely, LacLM-ChBD, ChBD-LacLM, and LacZ-ChBD, were constructed and successfully expressed in Lactobacillus plantarum WCFS1. Depending on the structure of the enzymes, either homodimeric or heterodimeric, as well as the positioning of the chitin-binding domain in relation to the catalytic domains, that is, upstream or downstream of the main protein, the expression in the host strain and the immobilization on chitin beads were different. Most constructs showed a high specificity for the chitin in immobilization studies; thus, a one-step immobilizing procedure could be performed to achieve up to 100% yield of immobilization without the requirement of prior purification of the enzyme. The immobilized-on-chitin enzymes were shown to be more stable than the corresponding native enzymes; especially the immobilized LacZ from L. bulgaricus DSM20081 could retain 50% of its activity when incubated at 37 °C for 48 days. Furthermore, the immobilized enzymes could be recycled for conversion up to eight times with the converting ability maintained at 80%. These results show the high potential for application of these immobilized enzymes in lactose conversion on an industrial scale.

Immunogenic Properties of Lactobacillus plantarum Producing Surface-Displayed Mycobacterium tuberculosis Antigens

Tuberculosis (TB) remains among the most deadly diseases in the world. The only available vaccine against tuberculosis is the bacille Calmette-Guérin (BCG) vaccine, which does not ensure full protection in adults. There is a global urgency for the development of an effective vaccine for preventing disease transmission, and it requires novel approaches. We are exploring the use of lactic acid bacteria (LAB) as a vector for antigen delivery to mucosal sites. Here, we demonstrate the successful expression and surface display of a Mycobacterium tuberculosis fusion antigen (comprising Ag85B and ESAT-6, referred to as AgE6) on Lactobacillus plantarum The AgE6 fusion antigen was targeted to the bacterial surface using two different anchors, a lipoprotein anchor directing the protein to the cell membrane and a covalent cell wall anchor. AgE6-producing L. plantarum strains using each of the two anchors induced antigen-specific proliferative responses in lymphocytes purified from TB-positive donors. Similarly, both strains induced immune responses in mice after nasal or oral immunization. The impact of the anchoring strategies was reflected in dissimilarities in the immune responses generated by the two L. plantarum strains in vivo The present study comprises an initial step toward the development of L. plantarum as a vector for M. tuberculosis antigen delivery.

IMPORTANCE

This work presents the development of Lactobacillus plantarum as a candidate mucosal vaccine against tuberculosis. Tuberculosis remains one of the top infectious diseases worldwide, and the only available vaccine, bacille Calmette-Guérin (BCG), fails to protect adults and adolescents. Direct antigen delivery to mucosal sites is a promising strategy in tuberculosis vaccine development, and lactic acid bacteria potentially provide easy, safe, and low-cost delivery vehicles for mucosal immunization. We have engineered L. plantarum strains to produce a Mycobacterium tuberculosis fusion antigen and to anchor this antigen to the bacterial cell wall or to the cell membrane. The recombinant strains elicited proliferative antigen-specific T-cell responses in white blood cells from tuberculosis-positive humans and induced specific immune responses after nasal and oral administrations in mice.

From by-product to valuable components: Efficient enzymatic conversion of lactose in whey using β-galactosidase from Streptococcus thermophilus

β-Galactosidase from Streptococcus thermophilus was overexpressed in a food-grade organism, Lactobacillus plantarum WCFS1. Laboratory cultivations yielded 11,000 U of β-galactosidase activity per liter of culture corresponding to approximately 170 mg of enzyme. Crude cell-free enzyme extracts obtained by cell disruption and subsequent removal of cell debris showed high stability and were used for conversion of lactose in whey permeate. The enzyme showed high transgalactosylation activity. When using an initial concentration of whey permeate corresponding to 205 g L^-1 lactose, the maximum yield of galacto-oligosaccharides (GOS) obtained at 50°C reached approximately 50% of total sugar at 90% lactose conversion, meaning that efficient valorization of the whey lactose was obtained. GOS are of great interest for both human and animal nutrition; thus, efficient conversion of lactose in whey into GOS using an enzymatic approach will not only decrease the environmental impact of whey disposal, but also create additional value.

Lactobacillus plantarum displaying CCL3 chemokine in fusion with HIV-1 Gag derived antigen causes increased recruitment of T cells

Background

Chemokines are attractive candidates for vaccine adjuvants due to their ability to recruit the immune cells. Lactic acid bacteria (LAB)-based delivery vehicles have potential to be used as a cheap and safe option for vaccination. Chemokine produced on the surface of LAB may potentially enhance the immune response to an antigen and this approach can be considered in development of future mucosal vaccines.

Results

We have constructed strains of Lactobacillusplantarum displaying a chemokine on their surface. L. plantarum was genetically engineered to express and anchor to the surface a protein called CCL3Gag. CCL3Gag is a fusion protein comprising of truncated HIV-1 Gag antigen and the murine chemokine CCL3, also known as MIP-1α. Various surface anchoring strategies were explored: (1) a lipobox-based covalent membrane anchor, (2) sortase-mediated covalent cell wall anchoring, (3) LysM-based non-covalent cell wall anchoring, and (4) an N-terminal signal peptide-based transmembrane anchor. Protein production and correct localization were confirmed using Western blotting, flow cytometry and immunofluorescence microscopy. Using a chemotaxis assay, we demonstrated that CCL3Gag-producing L. plantarum strains are able to recruit immune cells in vitro.

Conclusions

The results show the ability of engineered L. plantarum to produce a functional chemotactic protein immobilized on the bacterial surface. We observed that the activity of surface-displayed CCL3Gag differed depending on the type of anchor used. The chemokine which is a part of the bacteria-based vaccine may increase the recruitment of immune cells and, thereby, enhance the reaction of the immune system to the vaccine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0360-z) contains supplementary material, which is available to authorized users.

Cloning strategies for heterologous expression of the bacteriocin enterocin A by Lactobacillus sakei Lb790, Lb. plantarum NC8 and Lb. casei CECT475

Background

Bacteriocins produced by lactic acid bacteria (LAB) attract considerable interest as natural and nontoxic food preservatives and as therapeutics whereas the bacteriocin-producing LAB are considered potential probiotics for food, human and veterinary applications, and in the animal production field. Within LAB the lactobacilli are increasingly used as starter cultures for food preservation and as probiotics. The lactobacilli are also natural inhabitants of the gastrointestinal (GI) tract and attractive vectors for delivery of therapeutic peptides and proteins, and for production of bioactive peptides. Research efforts for production of bacteriocins in heterologous hosts should be performed if the use of bacteriocins and the LAB bacteriocin-producers is ever to meet the high expectations deposited in these antimicrobial peptides. The recombinant production and functional expression of bacteriocins by lactobacilli would have an additive effect on their probiotic functionality.

Results

The heterologous production of the bacteriocin enterocin A (EntA) was evaluated in different Lactobacillus spp. after fusion of the versatile Sec-dependent signal peptide (SP_usp45) to mature EntA plus the EntA immunity gene (entA + entiA) (fragment UAI), and their cloning into plasmid vectors that permitted their inducible (pSIP409 and pSIP411) or constitutive (pMG36c) production. The amount, antimicrobial activity (AA) and specific antimicrobial activity (SAA) of the EntA produced by Lactobacillus sakei Lb790, Lb. plantarum NC8 and Lb. casei CECT475 transformed with the recombinant plasmids pSIP409UAI, pSIP411UAI and pMGUAI varied depending of the expression vector and the host strain. The Lb. casei CECT475 recombinant strains produced the largest amounts of EntA, with the highest AA and SAA. Supernatants from Lb. casei CECT (pSIP411UAI) showed a 4.9-fold higher production of EntA with a 22.8-fold higher AA and 4.7-fold higher SAA than those from Enterococcus faecium T136, the natural producer of EntA. Moreover, supernatants from Lb. casei CECT475 (pSIP411UAI) showed a 15.7- to 59.2-fold higher AA against Listeria spp. than those from E. faecium T136.

Conclusion

Lb. casei CECT457 (pSIP411UAI) may be considered a promising recombinant host and cell factory for the production and functional expression of the antilisterial bacteriocin EntA.

Shape-Dependent Biomimetic Inhibition of Enzyme by Nanoparticles and Their Antibacterial Activity

Enzyme inhibitors are ubiquitous in all living systems, and their biological inhibitory activity is strongly dependent on their molecular shape. Here, we show that small zinc oxide nanoparticles (ZnO NPs)-pyramids, plates, and spheres-possess the ability to inhibit activity of a typical enzyme β-galactosidase (GAL) in a biomimetic fashion. Enzyme inhibition by ZnO NPs is reversible and follows classical Michaelis-Menten kinetics with parameters strongly dependent on their geometry. Diverse spectroscopic, biochemical, and computational experimental data indicate that association of GAL with specific ZnO NP geometries interferes with conformational reorganization of the enzyme necessary for its catalytic activity. The strongest inhibition was observed for ZnO nanopyramids and compares favorably to that of the best natural GAL inhibitors while being resistant to proteases. Besides the fundamental significance of this biomimetic function of anisotropic NPs, their capacity to serve as degradation-resistant enzyme inhibitors is technologically attractive and is substantiated by strong shape-specific antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), endemic for most hospitals in the world.

Plasmids from Food Lactic Acid Bacteria: Diversity, Similarity, and New Developments

Plasmids are widely distributed in different sources of lactic acid bacteria (LAB) as self-replicating extrachromosomal genetic materials, and have received considerable attention due to their close relationship with many important functions as well as some industrially relevant characteristics of the LAB species. They are interesting with regard to the development of food-grade cloning vectors. This review summarizes new developments in the area of lactic acid bacteria plasmids and aims to provide up to date information that can be used in related future research.

Heterologous expression of a recombinant lactobacillal β-galactosidase in Lactobacillus plantarum: effect of different parameters on the sakacin P-based expression system

Background

Two overlapping genes lacL and lacM (lacLM) encoding for heterodimeric β-galactosidase from Lactobacillus reuteri were previously cloned and over-expressed in the food-grade host strain Lactobacillus plantarum WCFS1, using the inducible lactobacillal pSIP expression system. In this study, we analyzed different factors that affect the production of recombinant L. reuteri β-galactosidase.

Results

Various factors related to the cultivation, i.e. culture pH, growth temperature, glucose concentration, as well as the induction conditions, including cell concentration at induction point and inducer concentration, were tested. Under optimal fermentation conditions, the maximum β-galactosidase levels obtained were 130 U/mg protein and 35–40 U/ml of fermentation broth corresponding to the formation of approximately 200 mg of recombinant protein per litre of fermentation medium. As calculated from the specific activity of the purified enzyme (190 U/mg), β-galactosidase yield amounted to roughly 70% of the total soluble intracellular protein of the host organism. It was observed that pH and substrate (glucose) concentration are the most prominent factors affecting the production of recombinant β-galactosidase.

Conclusions

The over-expression of recombinant L. reuteri β-galactosidase in a food-grade host strain was optimized, which is of interest for applications of this enzyme in the food industry. The results provide more detailed insight into these lactobacillal expression systems and confirm the potential of the pSIP system for efficient, tightly controlled expression of enzymes and proteins in lactobacilli.

Production of Recombinant β-Galactosidase in Lactobacillus plantarum, Using a pSIP-Based Food-Grade Expression System

Food-grade expression systems based on using food-grade microorganisms have been developed for the production of recombinant enzymes used in food applications. Lactic acid bacteria (LAB), especially Lactobacilli, have been widely used for various purposes in food and recognized as a promising host of food-grade enzyme production. In this study, the pSIP409 vectors, originally containing the erm gene, were used to replace this selection marker by the alr gene resulting in the production of the pSIP609 expression vector in L. planatarum. This vector could express high amounts of β-galactosidases, showing both high volumetric as well a specific enzymatic activity. Thus, the food-grade recombinant enzyme production in L. planatarum harboring pSIP609 was very fruitful and useful for food industries.

Heterologous protein secretion in Lactobacilli with modified pSIP vectors

We describe new variants of the modular pSIP-vectors for inducible gene expression and protein secretion in lactobacilli. The basic functionality of the pSIP system was tested in Lactobacillus strains representing 14 species using pSIP411, which harbors the broad-host-range Lactococcus lactis SH71rep replicon and a β-glucuronidase encoding reporter gene. In 10 species, the inducible gene expression system was functional. Based on these results, three pSIP vectors with different signal peptides were modified by replacing their narrow-host-range L. plantarum 256rep replicon with SH71rep and transformed into strains of five different species of Lactobacillus. All recombinant strains secreted the target protein NucA, albeit with varying production levels and secretion efficiencies. The Lp_3050 derived signal peptide generally resulted in the highest levels of secreted NucA. These modified pSIP vectors are useful tools for engineering a wide variety of Lactobacillus species.

Secretion of biologically active heterologous oxalate decarboxylase (OxdC) in Lactobacillus plantarum WCFS1 using homologous signal peptides

Current treatment options for patients with hyperoxaluria and calcium oxalate stone diseases are limited and do not always lead to sufficient reduction in urinary oxalate excretion. Oxalate degrading bacteria have been suggested for degrading intestinal oxalate for the prevention of calcium oxalate stone. Here, we reported a recombinant Lactobacillus plantarum WCFS1 (L. plantarum) secreting heterologous oxalate decarboxylase (OxdC) that may provide possible therapeutic approach by degrading intestinal oxalate. The results showed secretion and functional expression of OxdC protein in L. plantarum driven by signal peptides Lp_0373 and Lp_3050. Supernatant of the recombinant strain containing pLp_0373sOxdC and pLp_3050sOxdC showed OxdC activity of 0.05 U/mg and 0.02 U/mg protein, while the purified OxdC from the supernatant showed specific activity of 18.3 U/mg and 17.5 U/mg protein, respectively. The concentration of OxdC protein in the supernatant was 8–12 μg/mL. The recombinant strain showed up to 50% oxalate reduction in medium containing 10 mM oxalate. In conclusion, the recombinant L. plantarum harboring pLp_0373sOxdC and pLp_3050sOxdC can express and secrete functional OxdC and degrade oxalate up to 50% and 30%, respectively.

A novel manganese starvation-inducible expression system for Lactobacillus plantarum

A novel expression system for Lactobacillus plantarum was developed. This system is based on the manganese starvation-inducible promoter from specific manganese transporter of L. plantarum NC8, which was cloned for the first time. The expression of a β-glucosidase from Pyrococcus furiosus (CelB) was achieved by cultivating L. plantarum NC8 at low manganese concentrations with MRS medium and the pmntH2-CelB expression vector. A CelB activity of 8.52 μkatoNPGal L(-1) was produced in a bioreactor (4 L). The advantages of the novel expression system are that no addition of an external inducing agent was required, and additionally, no further introduction of regulatory genes was necessary. The new promoter meets the general demands of a food-grade expression system.

Recombinant production of hyperthermostable CelB from Pyrococcus furiosus in Lactobacillus sp

Lactic acid bacteria (LAB) are used widespread in the food industry as traditional starters for various fermented foods. For recombinant protein production, LAB would be superior with view from the food safety demands since most of them are Generally Recognized As Safe organisms. We investigated the two pSIP expression systems, pSIP403 and pSIP409 (Sørvig et al. 2005), to produce a hyper-thermophilic β-glycosidase (CelB) from Pyrococcus furiosus in Lactobacillus plantarum NC8 and Lactobacillus casei as hosts, respectively. Both lactobacilli harboring the pSIP409-celB vector produced active CelB in batch bioreactor cultivations (MRS medium) while the specific CelB activity of the cell free extract was about 44 % higher with L. plantarum (1,590 ± 90 nkat/mg(protein)) than with L. casei (1,070 ± 66 nkat/mg(protein)) using p-nitrophenyl-β-galactoside (pNPGal) as the substrate. A fed-batch bioreactor cultivation of L. plantarum NC8 pSIP409-celB resulted in a specific CelB activity of 2,500 ± 120 nkat ( pNPGal)/mg(protein) after 28 h. A repeated dosage of the inducer spp-IP did not increase the enzyme expression further. As alternative for the cost intensive MRS medium, a basal whey medium with supplements (yeast extract, Tween 80, NH(4)-citrate) was developed. In bioreactor cultivations using this medium, about 556 ± 29 nkat ( pNPGal)/mg(protein) of CelB activity was achieved. It was shown that both LAB were potential expression hosts for recombinant enzyme production. The pSIP expression system can be applied in L. casei.

Surface display of N-terminally anchored invasin by Lactobacillus plantarum activates NF-κB in monocytes

The probiotic lactic acid bacterium Lactobacillus plantarum is a potential delivery vehicle for mucosal vaccines because of its generally regarded as safe (GRAS) status and ability to persist at the mucosal surfaces of the human intestine. However, the inherent immunogenicity of vaccine antigens is in many cases insufficient to elicit an efficient immune response, implying that additional adjuvants are needed to enhance the antigen immunogenicity. The goal of the present study was to increase the proinflammatory properties of L. plantarum by expressing a long (D1 to D5 [D1-D5]) and a short (D4-D5) version of the extracellular domain of invasin from the human pathogen Yersinia pseudotuberculosis. To display these proteins on the bacterial surface, four different N-terminal anchoring motifs from L. plantarum were used, comprising two different lipoprotein anchors, a transmembrane signal peptide anchor, and a LysM-type anchor. All these anchors mediated surface display of invasin, and several of the engineered strains were potent activators of NF-κB when interacting with monocytes in cell culture. The most distinct NF-κB responses were obtained with constructs in which the complete invasin extracellular domain was fused to a lipoanchor. The proinflammatory L. plantarum strains constructed here represent promising mucosal delivery vehicles for vaccine antigens.

Heterologous expression of Oenococcus oeni malolactic enzyme in Lactobacillus plantarum for improved malolactic fermentation

Lactobacillus plantarum is involved in a multitude of food related industrial fermentation processes including the malolactic fermentation (MLF) of wine. This work is the first report on a recombinant L. plantarum strain successfully conducting MLF. The malolactic enzyme (MLE) from Oenococcus oeni was cloned into the lactobacillal expression vector pSIP409 which is based on the sakacin P operon of Lactobacillus sakei and expressed in the host strain L. plantarum WCFS1. Both recombinant and wild-type L. plantarum strains were tested for MLF using a buffered malic acid solution in absence of glucose. Under the conditions with L-malic acid as the only energy source and in presence of Mn²⁺ and NAD⁺, the recombinant L. plantarum and the wild-type strain converted 85% (2.5 g/l) and 51% (1.5 g/l), respectively, of L-malic acid in 3.5 days. Furthermore, the recombinant L. plantarum cells converted in a modified wine 15% (0.4 g/l) of initial L-malic acid concentration in 2 days. In conclusion, recombinant L. plantarum cells expressing MLE accelerate the malolactic fermentation.

Homodimeric β-galactosidase from Lactobacillus delbrueckii subsp. bulgaricus DSM 20081: expression in Lactobacillus plantarum and biochemical characterization

The lacZ gene from Lactobacillus delbrueckii subsp. bulgaricus DSM 20081, encoding a β-galactosidase of the glycoside hydrolase family GH2, was cloned into different inducible lactobacillal expression vectors for overexpression in the host strain Lactobacillus plantarum WCFS1. High expression levels were obtained in laboratory cultivations with yields of approximately 53000 U of β-galactosidase activity per liter of medium, which corresponds to ~170 mg of recombinant protein per liter and β-galactosidase levels amounting to 63% of the total intracellular protein of the host organism. The wild-type (nontagged) and histidine-tagged recombinant enzymes were purified to electrophoretic homogeneity and further characterized. β-Galactosidase from L. bulgaricus was used for lactose conversion and showed very high transgalactosylation activity. The maximum yield of galacto-oligosaccharides (GalOS) was approximately 50% when using an initial concentration of 600 mM lactose, indicating that the enzyme can be of interest for the production of GalOS.

Disulfide bond formation and activation of Escherichia coli β-galactosidase under oxidizing conditions

Escherichia coli β-galactosidase is probably the most widely used reporter enzyme in molecular biology, cell biology, and biotechnology because of the easy detection of its activity. Its large size and tetrameric structure make this bacterial protein an interesting model for crystallographic studies and atomic mapping. In the present study, we investigate a version of Escherichia coli β-galactosidase produced under oxidizing conditions, in the cytoplasm of an Origami strain. Our data prove the activation of this microbial enzyme under oxidizing conditions and clearly show the occurrence of a disulfide bond in the β-galactosidase structure. Additionally, the formation of this disulfide bond is supported by the analysis of a homology model of the protein that indicates that two cysteines located in the vicinity of the catalytic center are sufficiently close for disulfide bond formation.

Chitinase from Bacillus licheniformis DSM13: expression in Lactobacillus plantarum WCFS1 and biochemical characterisation

The gene chi, coding for a GH18 chitinase from the Gram-positive bacterium Bacillus licheniformis DSM13 (ATCC 14580), was cloned into the inducible lactobacillal expression vectors pSIP403 and pSIP409, derived from the sakacin-P operon of Lactobacillus sakei, and expressed in the host strain Lactobacillus plantarum WCFS1. Both the complete chi gene including the original bacillal signal sequence as well as the mature chi gene were compared, however, no extracellular chitinase activity was detected with any of the constructs. The chitinase gene was expressed intracellularly as an active enzyme with these different systems, at levels of approximately 5mg of recombinant protein per litre of cultivation medium. Results obtained for the two different expression vectors that only differ in the promoter sequence were well comparable. To further verify the suitability of this expression system, recombinant, His-tagged chitinase Chi was purified from cell extracts of L. plantarum and characterised. The monomeric 65-kDa enzyme can degrade both chitin and chitosan, and shows properties that are very similar to those reported for the native chitinase purified from other B. licheniformis isolates. It shows good thermostability (half lives of stability of 20 and 8.4 days at 37 and 50°C, respectively), and good stability in the pH range of 5-10. The results presented lead the way to overproduction of chitinase in a food-grade system, which is of interest for the food and feed industry.

Food-grade gene expression in lactic acid bacteria

In the 1990s, significant efforts were invested in the research and development of food-grade expression systems in lactic acid bacteria (LAB). At this time, Lactococcus lactis in particular was demonstrated to be an ideal cell factory for the food-grade production of recombinant proteins. Steady progress has since been made in research on LAB, including Lactococcus, Lactobacillus and Streptococcus, in the areas of recombinant enzyme production, industrial food fermentation, and gene and metabolic pathway regulation. Over the past decade, this work has also led to new approaches on chromosomal integration vectors and host/vector systems. These newly constructed food-grade gene expression systems were designed with specific attention to self-cloning strategies, food-grade selection markers, plasmid replication and chromosomal gene replacements. In this review, we discuss some well-characterized chromosomal integration and food-grade host/vector systems used in LAB, with a special focus on sustainability, stability and overall safety, and give some attractive examples of protein expression that are based on these systems.

Quantitative transcript analysis of the inducible expression system pSIP: comparison of the overexpression of Lactobacillus spp. β-galactosidases in Lactobacillus plantarum

BACKGROUND

Two sets of overlapping genes, lacLMReu and lacLMAci, encoding heterodimeric β-galactosidases from Lactobacillus reuteri and Lactobacillus acidophilus, respectively, have previously been cloned and expressed using the pSIP vector system and Lactobacillus plantarum WCSF1 as host. Despite the high similarity between these lacLM genes and the use of identical cloning and expression strategies, strains harboring lacLMReu produced about twenty-fold more β-galactosidase than strains containing lacLMAci.

RESULTS

In this study, the plasmid copy numbers (PCN) of expression vectors pEH9R (lacLMReu) and pEH9A (lacLMAci) as well as the transcription levels of both lacLM genes were compared using quantitative PCR methods. Analyses of parallel fermentations of L. plantarum harboring either pEH9R or pEH9A showed that the expression plasmids were present in similar copy numbers. However, transcript levels of lacLM from L. reuteri (pEH9R) were up to 18 times higher than those of lacLM from L. acidophilus (pEH9A). As a control, it was shown that the expression levels of regulatory genes involved in pheromone-induced promoter activation were similar in both strains.

CONCLUSION

The use of identical expression strategies for highly similar genes led to very different mRNA levels. The data indicate that this difference is primarily caused by translational effects that are likely to affect both mRNA synthesis rates and mRNA stability. These translational effects thus seem to be a dominant determinant for the success of gene expression efforts in lactobacilli.

A food-grade system for inducible gene expression in Lactobacillus plantarum using an alanine racemase-encoding selection marker

Food-grade gene expression systems for lactic acid bacteria are useful for applications in the food industry. We describe a new food-grade host/vector system for Lactobacillus plantarum based on pSIP expression vectors and the use of the homologous alanine racemase gene (alr) as selection marker. A new series of expression vectors were constructed by exchanging the erythromycin resistance gene (erm) in pSIP vectors by the L. plantarum WCFS1 alr gene. The vectors were applied for the overexpression of β-galactosidase genes from L. reuteri L103 and L. plantarum WCFS1 in an alr deletion mutant of L. plantarum WCFS1. The expression levels obtained in this way, i.e. without the use of antibiotics, were comparable to the levels obtained with the conventional system based on selection for erythromycin resistance. The new system is suitable for the production of ingredients and additives for the food industry.

Characterization of a heterodimeric GH2 β-galactosidase from Lactobacillus sakei Lb790 and formation of prebiotic galacto-oligosaccharides

The lacLM genes from Lactobacillus sakei Lb790, encoding a heterodimeric β-galactosidase that belongs to glycoside hydrolase family GH2, were cloned and heterologously expressed in Escherichia coli . Subsequently, the recombinant β-galactosidase LacLM was purified to apparent homogeneity and characterized. The enzyme is a β-galactosidase with narrow substrate specificity because o-nitrophenyl-β-D-galactopyranoside (oNPG) was efficiently hydrolyzed, whereas various structurally related oNP analogues were not. The K(m) and k(cat) values for oNPG and lactose were 0.6 mM and 180 s(-1) and 20 mM and 43 s(-1), respectively. The enzyme is inhibited competitively by its two end-products D-galactose and D-glucose (K(i) values of 180 and 475 mM, respectively). As judged by the ratio of the inhibition constant to the Michaelis constant, K(i)/K(m), this inhibition is only very moderate and much less pronounced than for other microbial β-galactosidases. β-Galactosidase from L. sakei possesses high transgalactosylation activity and was used for the synthesis of galacto-oligosaccharides (GalOS), employing lactose at a concentration of 215 g/L. The maximum GalOS yield was 41% (w/w) of total sugars at 77% lactose conversion and contained mainly non-lactose disaccharides, trisaccharides, and tetrasaccharides with approximately 38, 57, and 5% of total GalOS formed, respectively. The enzyme showed a strong preference for the formation of β-(1→6)-linked transgalactosylation products, whereas β-(1→3)-linked compounds were formed to a lesser extent and β-(1→4)-linked reaction products could not be detected.

Beta-galactosidase from Lactobacillus pentosus: purification, characterization and formation of galacto-oligosaccharides

A novel heterodimeric beta-galactosidase with a molecular mass of 105 kDa was purified from crude cell extracts of the soil isolate Lactobacillus pentosus KUB-ST10-1 using ammonium sulphate fractionation followed by hydrophobic interaction and affinity chromatography. The electrophoretically homogenous enzyme has a specific activity of 97 U(oNPG)/mg protein. The K(m), k(cat) and k(cat)/K(m) values for lactose and o-nitrophenyl-beta-D-galactopyranoside (oNPG) were 38 mM, 20 s(-1), 530 M(-1).s(-1) and 1.67 mM, 540 s(-1), 325 000 M(-1).s(-1), respectively. The temperature optimum of beta-galactosidase activity was 60-65 degrees C for a 10-min assay, which is considerably higher than the values reported for other lactobacillal beta-galactosidases. Mg(2+) ions enhanced both activity and stability significantly. L. pentosus beta-galactosidase was used for the production of prebiotic galacto-oligosaccharides (GOS) from lactose. A maximum yield of 31% GOS of total sugars was obtained at 78% lactose conversion. The enzyme showed a strong preference for the formation of beta-(1-->3) and beta-(1-->6) linkages, and the main transgalactosylation products identified were the disaccharides beta-D-Galp-(1-->6)-D-Glc, beta-D-Galp-(1-->3)-D-Glc, beta-D-Galp-(1-->6)-D-Gal, beta-D-Galp-(1-->3)-D-Gal, and the trisaccharides beta-D-Galp-(1-->3)-D-Lac, beta-D-Galp-(1-->6)-D-Lac.