Construction of a food-grade cell surface display system for Lactobacillus casei

Production of recombinant glycosidases fused with Usp45 and SpaX to avoid the purification and immobilization stages

The elucidation of the physicochemical properties of glycosidases is essential for their subsequent technological application, which may include saccharide hydrolysis processes and oligosaccharide synthesis. As the application of cloning, purification and enzymatic immobilization methods can be time consuming and require a heavy financial investment, this study has validated the recombinant production of the set of Lacticaseibacillus rhamnosus fucosidases fused with Usp45 and SpaX anchored to the cell wall of Lacticaseibacillus cremoris subsp cremoris MG1363, with the aim of avoiding the purification and stabilization steps. The cell debris harboring the anchored AlfA, AlfB and AlfC fucosidases showed activity against p-nitrophenyl α-L-fucopyranoside of 6.11 ± 0.36, 5.81 ± 0.29 and 9.90 ± 0.58 U/mL, respectively, and exhibited better thermal stability at 50 °C than the same enzymes in their soluble state. Furthermore, the anchored AlfC fucosidase transfucosylated different acceptor sugars, achieving fucose equivalent concentrations of 0.94 ± 0.09 mg/mL, 4.11 ± 0.21 mg/mL, and 4.08 ± 0.15 mg/mL of fucosylgalatose, fucosylglucose and fucosylsucrose, respectively.

TonB-Dependent Receptor Protein Displayed on Spores of Bacillus subtilis Stimulates Protective Immune Responses against Acinetobacter baumannii

The emergence of antibiotic-resistant Acinetobacter baumannii strains with limited treatment options has become a significant global health concern. Efforts to develop vaccines against the bacteria have centred on several potential protein targets, including the TonB-dependent receptors (TBDRs). In the present study, TBDRs from A. baumannii were displayed on the surface of Bacillus subtilis spores. The immunogenicity of the recombinant spores was evaluated in orally vaccinated mice. None of the immunized mice demonstrated signs of illness and were observed to be healthy throughout the study. Sera and the intestinal secretions from the recombinant spores-treated mice demonstrated mucosal and humoral antibody responses to the vaccine antigen. In addition, bactericidal activities of the sera against A. baumannii clinical isolates were demonstrated. These observations suggest that the B. subtilis spore-displayed TBDRs should be further explored as much-needed potential oral vaccine candidates against A. baumannii.

Mucosal immunization with lactiplantibacillus plantarum-displaying recombinant SARS-CoV-2 epitopes on the surface induces humoral and mucosal immune responses in mice

BACKGROUND

The use of probiotic lactic acid bacteria as a mucosal vaccine vector is considered a promising alternative compared to the use of other microorganisms because of its "Generally Regarded as Safe" status, its potential adjuvant properties, and its tolerogenicity to the host. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease (COVID-19), is highly transmissible and pathogenic. This study aimed to determine the potential of Lactiplantibacillus plantarum expressing SARS-CoV-2 epitopes as a mucosal vaccine against SARS-CoV-2.

RESULTS

In this study, the possible antigenic determinants of the spike (S1-1, S1-2, S1-3, and S1-4), membrane (ME1 and ME2), and envelope (E) proteins of SARS-CoV-2 were predicted, and recombinant L. plantarum strains surface-displaying these epitopes were constructed. Subsequently, the immune responses induced by these recombinant strains were compared in vitro and in vivo. Most surface-displayed epitopes induced pro-inflammatory cytokines [tumor necrosis factor alpha (TNF-α and interleukin (IL)-6] and anti-inflammatory cytokines (IL-10) in lipopolysaccharide-induced RAW 264.7, with the highest anti-inflammatory to pro-inflammatory cytokine ratio in the S1-1 and S1-2 groups, followed by that in the S1-3 group. When orally administered of recombinant L. plantarum expressing SARS-CoV-2 epitopes in mice, all epitopes most increased the expression of IL-4, along with induced levels of TNF-α, interferon-gamma, and IL-10, specifically in spike protein groups. Thus, the surface expression of epitopes from the spike S1 protein in L. plantarum showed potential immunoregulatory effects, suggesting its ability to potentially circumvent hyperinflammatory states relevant to monocyte/macrophage cell activation. At 35 days post immunization (dpi), serum IgG levels showed a marked increase in the S1-1, S1-2, and S1-3 groups. Fecal IgA levels increased significantly from 21 dpi in all the antigen groups, but the boosting effect after 35 dpi was explicitly observed in the S1-1, S1-2, and S1-3 groups. Thus, the oral administration of SARS-CoV-2 antigens into mice induced significant humoral and mucosal immune responses.

CONCLUSION

This study suggests that L. plantarum is a potential vector that can effectively deliver SARS-CoV-2 epitopes to intestinal mucosal sites and could serve as a novel approach for SARS-CoV-2 mucosal vaccine development.

Engineering Components of the Lactobacillus S-Layer for Biotherapeutic Applications

Lactic acid bacteria (LAB) are frequently harnessed for the delivery of biomolecules to mucosal tissues. Several species of Lactobacillus are commonly employed for this task, of which a subset are known to possess surface-layers (S-layers). S-layers are two-dimensional crystalline arrays of repeating proteinaceous subunits that form the outermost coating of many prokaryotic cell envelopes. Their periodicity and abundance have made them a target for numerous biotechnological applications. In the following review, we examine the multi-faceted S-layer protein (Slp), and its use in both heterologous protein expression systems and mucosal vaccine delivery frameworks, through its diverse genetic components: the strong native promoter, capable of synthesizing as many as 500 Slp subunits per second; the signal peptide that stimulates robust secretion of recombinant proteins; and the structural domains, which can be harnessed for both cell surface display of foreign peptides or adhesion enhancement of a host bacterium. Although numerous studies have established vaccine platforms based on one or more components of the Lactobacillus S-layer, this area of research still remains largely in its infancy, thus this review is meant to not only highlight past works, but also advocate for the future usage of Slps in biotherapeutic research.

Clinical detection of Hepatitis C viral infection by yeast-secreted HCV-core:Gold-binding-peptide

Access to affordable and field deployable diagnostics are key barriers to the control and eradication of many endemic and emerging infectious diseases. While cost, accuracy, and usability have all improved in recent years, there remains a pressing need for even less expensive and more scalable technologies. To that end, we explored new methods to inexpensively produce and couple protein-based biosensing molecules (affinity reagents) with scalable electrochemical sensors. Previous whole-cell constructs resulted in confounding measurements in clinical testing due to significant cross-reactivity when probing for host-immune (antibody) response to infection. To address this, we developed two complimentary strategies based on either the release of surface displayed or secretion of fusion proteins. These dual affinity biosensing elements couple antibody recognition (using antigen) and sensor surface adhesion (using gold-binding peptide-GBP) to allow single-step reagent production, purification, and biosensor assembly. As a proof-of-concept, we developed Hepatitis C virus (HCV)-core antigen-GBP fusion proteins. These constructs were first tested and optimized for consistent surface adhesion then the assembled immunosensors were tested for cross-reactivity and evaluated for performance in vitro. We observed loss of function of the released reagents while secreted constructs performed well in in vitro testing with 2 orders of dynamic range, and a limit of detection of 32 nM. Finally, we validated the secreted platform with clinical isolates (n = 3) with statistically significant differentiation of positive vs. non-infected serum (p < 0.0001) demonstrating the ability to clearly distinguish HCV positive and negative clinical samples.

Bioengineered probiotics as a new hope for health and diseases: an overview of potential and prospects

Despite the use of microorganisms as therapeutics for over a century, the scientific and clinical admiration of their potential is a recent phenomenon. Genome sequencing and genetic engineering has enabled researchers to develop novel strategies, such as bioengineered probiotics or pharmabiotics, which may become a therapeutic strategy. Bioengineered probiotics with multiple immunogenic or antagonistic properties could be a viable option to improve human health. The bacteria are tailored to deliver drugs, therapeutic proteins or gene therapy vectors with precision and a higher degree of site specificity than conventional drug administration regimes. This article provides an overview of methodological concepts, thereby encouraging research and interest in this topic, with the ultimate goal of using designer probiotics as therapeutics in clinical practice.

Construction and characterization of three protein-targeting expression system in Lactobacillus casei

We previously reported that the β-1,4-Mannanase (manB) gene from Bacillus pumilus functions as a good reporter gene in Lactobacillus casei. Two vectors were constructed. One carries the signal peptide of secretion protein Usp45 (SPUsp45) from Lactococcus lactis (pELSH), and the other carries the full-length S-layer protein, SlpA, from L. acidophilus (pELWH). In this work, another vector, pELSPH, was constructed to include the signal peptide of protein SlpA (SPSlpA), and the capacity of all three vectors to drive expression of the manB gene in L. casei was evaluated. The results showed that SPUsp45 is functionally recognized and processed by the L. casei secretion machinery. The SPUsp45-mediated secretion efficiency was ∼87%, and SPSlpA drove the export of secreted ManB with ∼80% efficiency. SPSlpA secretion was highly efficient, and expressed SlpA was anchored to the cell wall by an unknown secretion mechanism. Full-length SlpA drove the cell wall-anchored expression of an SlpA-ManB fusion protein but at a much lower level than that of protein SlpA.

Characterization of a new Lactobacillus salivarius strain engineered to express IBV multi-epitope antigens by chromosomal integration

To obtain adhesive and safe lactic acid bacteria (LAB) strains for expressing heterologous antigens, we screened LAB inhabitants in intestine of Tibetan chickens by analyzing their adhesion and safety properties and the selected LAB was engineered to express heterologous antigen (UTEpi C-A) based on chromosomal integration strategy. We demonstrated that a new Lactobacillu salivarius TCMM17 strain is strongly adhesive to chicken intestinal epithelial cells, contains no endogenous plasmids, is susceptible to tested antimicrobials, and shows no toxicities. In order to examine the potential of TCMM17 strain as heterogenous antigen delivering vehicle, we introduced a UTEpi C-A expression cassette in its chromosome by constructing a non-replicative plasmid (pORI280-UUTEpi C-AD). The recombinant TCMM17 strain (∆TCMM17) stably was found to keep the gene cassette through 50 generations, and successfully displayed EpiC encoded by the cassette on its surface. This work provides a universal platform for development of novel oral vaccines and expression of further antigens of avian pathogens.

Expression and Purification of the Uropathogenic Escherichia coli PapG Protein and its Surface Absorption on Lactobacillus reuteri: Implications for Surface Display System Vaccines

Background:

Uropathogenic Escherichia coli (UPEC) is one of the most common bacteria that can cause urinary tract infections (UTIs). Unfortunately, no human vaccine against UTIs has been developed. Therefore, it is necessary to develop an efficient and safe vaccine that is able to induce mucosal and systemic immune responses. The use of lactic acid bacteria as a delivery system is a promising method to induce the immune system.

Objectives:

The aim of this study was to establish Lactobacillus reuteri harboring the E. coli PapG antigen on its surface.

Materials and Methods:

In this study, the gene encoding PapG was fused to the AcmA gene (which encodes an anchor protein in Lactobacillus) and cloned into the pEX A vector. The PapG.AcmA fusion gene was digested with BamHI and NdeI and sub-cloned into the pET21a expression vector at the digestion sites. Subsequently, the recombinant plasmids (pET21a-PapG.AcmA and pET21a-PapG) were transformed into the E. coli Origami strain using the calcium chloride method and the fusion protein was expressed under 1 mM IPTG induction. The expression of the fusion protein was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting. Purification of the PapG and PapG.AcmA proteins was carried out using a Ni-NTA column, and surface adsorption was estimated on Lactobacillus. Finally, surface localization of the fusion protein was verified by an enzyme-linked immunosorbent assay (ELISA).

Results:

The PapG.AcmA fusion was successfully sub-cloned in the pET21a expression vector. The expression of PapG and PapG.AcmA proteins in the E. coli Origami strain was indicated as protein bands in SDS-PAGE and confirmed by western blotting. In addition, the fusion protein was displayed on the surface of L. reuteri.

Conclusions:

In conclusion, we developed a method to express the PapG.AcmA protein on the surface of Lactobacillus. This is the first report on the successful application of lactic acid bacteria displaying the PapG.AcmA fusion protein. It will be interesting to determine the immune responses against the PapG protein in near future using this surface display strategy.