Heterologous expression of antigenic peptides in Bacillus subtilis biofilms

The P4' Peptide-Carrying Bacillus subtilis in Cottonseed Meal Improves the Chinese Mitten Crab Eriocheir sinensis Innate Immunity, Redox Defense, and Growth Performance

This study developed a recombinant Bacillus subtilis to carry the LGSPDVIVIR peptide (cmP4) isolated from the hydrolyzed products of cottonseed meal with excellent antioxidant and immune-enhancing properties in vitro. It was carried as a tandem of five cmP4 peptides (cmP4') to be stably expressed on a large scale. Then, its effectiveness was evaluated in Chinese mitten crab (Eriocheir sinensis) based on growth performance, redox defense, and innate immunity. A total of 280 crabs (mean body weight: 41.40 ± 0.14) were randomly assigned to seven diets including a control one (without B. subtilis) and six experimental ones with different doses (107,108, and 109 CFU/kg) of unmodified and recombinant B. subtilis, respectively, for 12 weeks. Each diet was tested in four tanks of crabs (10/tank). In terms of bacterial dosages, the final weight (FW), weight gain (WG), hemolymph and hepatopancreatic activities of superoxide dismutase (SOD), catalase (CAT), lysosome (LZM), acid phosphatase (ACP) and alkaline phosphatase (AKP), and hepatopancreatic transcriptions of cat, mitochondrial manganese superoxide dismutase (mtmnsod), thioredoxin-1 (trx1), and prophenoloxidase (propo) all increased significantly with increasing B. subtilis dosages, while hemolymph and hepatopancreatic malondialdehyde (MDA) content and the transcriptions of toll like receptors (tlrs), NF-κB-like transcription factor (relish), and lipopolysaccharide-induced TNF-α factor (litaf) all decreased remarkably. In terms of bacterial species, the recombinant B. subtilis group obtained significantly high values of FW, WG, hemolymph, and hepatopancreatic activities of SOD, CAT, LZM, ACP, and AKP, and the transcriptions of mtmnsod, peroxiredoxin 6 (prx6), and propo compared with the unmodified B. subtilis, while opposite results were noted in hemolymph and hepatopancreatic MDA content and the transcriptions of tlrs, relish, and litaf. These results indicated that dietary supplementation with 109 CFU/kg of recombinant B. subtilis can improve the growth performance, redox defense, and nonspecific immunity of E. sinensis.

Bacillus subtilis expressing duck Tembusu virus E protein induces immune protection in ducklings

Duck Tembusu virus (DTMUV) is an infectious disease that emerged in China in 2010. It has caused serious economic losses to the poultry industry and may pose a threat to public health. We aimed to develop a new Bacillus subtilis (B. subtilis)-based oral vaccine to control DTMUV transmission among poultry; to this end, we constructed a B. subtilis strain that can secrete DTMUV E protein. Ducklings were orally immunized, and serum antibodies, mucosal antibodies, and splenic cytokines were detected. The results showed that, in addition to high levels of specific IgG, there were also high levels of specific secretory immunoglobulin A (sIgA) in ducklings orally treated with recombinant B. subtilis. In addition, the levels of IFN-γ, IL-2, IL-4, and IL-10 in spleens were significantly boosted by recombinant B. subtilis. Recombinant B. subtilis could effectively enhance ducklings resistance to DTMUV and significantly reduce viral load (p<0.01), along with pathological damage in the brain, heart, and spleen. This is the first study to apply a B. subtilis live-vector vaccine platform for DTMUV disease prevention and control, and our results suggest that B. subtilis expressing DTMUV E protein may be a candidate vaccine against DTMUV.

A Selective Review on the Novel Approaches and Potential Control Agents of Anti-biofouling and Anti-biofilming

Specific aggregates of bacterial colonies, which, when embedded in a self-produced matrix, are known to cause biofouling. These complex structures are highly resistant to extreme stress conditions like antibiotics, complex cleaning strategies, or even the human immune system. The formation of biofilm matrices and biofouling is chosen as the preferred microbial environment owing to the advantages offered for the embedded cells for their long-term survival. This increased resistance and virulence emphasizes the urgency of finding newer alternatives for its complete eradication. Combined approaches using enzymes, biomimetic surface modification, and a fusion of physical and chemical methods are gaining more prominence. In brief, this review discusses the structure and biology of biofilms, their mechanism of action, and the new-age anti-biofilm and biofouling agents in food industries, bioelectric, and medical devices. Current anti-biofouling methods, including engineered polymers, surface coatings to antimicrobials, and antibiotics, have also been described.

The Bacterial Spore as a Mucosal Vaccine Delivery System

The development of efficient mucosal vaccines is strongly dependent on the use of appropriate vectors. Various biological systems or synthetic nanoparticles have been proposed to display and deliver antigens to mucosal surfaces. The Bacillus spore, a metabolically quiescent and extremely resistant cell, has also been proposed as a mucosal vaccine delivery system and shown able to conjugate the advantages of live and synthetic systems. Several antigens have been displayed on the spore by either recombinant or non-recombinant approaches, and antigen-specific immune responses have been observed in animals immunized by the oral or nasal route. Here we review the use of the bacterial spore as a mucosal vaccine vehicle focusing on the advantages and drawbacks of using the spore and of the recombinant vs. non-recombinant approach to display antigens on the spore surface. An overview of the immune responses induced by antigen-displaying spores so far tested in animals is presented and discussed.

Oral administration of recombinant Bacillus subtilis expressing a multi-epitope protein induces strong immune responses against Salmonella Enteritidis

The S. Enteritidis causes serious economic losses to the poultry industry every year. Vaccines that induce a mucosal immune response may be successful against an S. Enteritidis infection because mucosa plays an important role in preventing S. Enteritidis from entering the body. In order to develop novel and potent oral vaccines based on Bacillus subtilis (B. subtilis) to control the spread of S. Enteritidis in the poultry industry, we constructed a B. subtilis that can secrete a multi-epitope protein (OmpC-FliC-SopF-SseB-IL-18). Oral immunization of chickens was performed, and serum antibodies, mucosal antibodies, specific cellular immunity and serum cytokines were detected. Immunizing chicks with S. Enteritidis was evaluated. The results showed high levels of specific IgG in addition to high levels of specific secretory immunoglobulin A (sIgA) in chickens who received oral administrations of recombinant B. subtilis. Additionally, recombinant B. subtilis may significantly increase the levels of IL-2 and T cell-mediated immunity. Recombinant B. subtilis effectively protected chickens against S. Enteritidis and reduced pathological damage to the spleen and jejunum. Our study's outcomes indicate that the expression of the multi-epitope protein OmpC-FliC-SopF-SseB-IL-18 by B. subtilis could generate a mucosal vaccine candidate for animals to defend against S. Enteritidis in the future.

Advances on Bacterial and Fungal Biofilms for the Production of Added-Value Compounds

Simple Summary

The production of bio-based materials, including organic acids, antibiotics, enzymes, ethanol, and hydrogen, is generally done by the cultivation of suspended cells rather than using immobilized cells. However, several studies suggest the application of productive biofilms as a reliable alternative for biocatalysis, with many advantages over suspended-growth systems. This review gives an overview of the breakthrough in the application of biofilm platforms for the sustainable production of valuable compounds, with particular insight into the latest advances in the production of recombinant proteins. Productive biofilms are shown to improve production rates and product yields, demonstrating great potential for industrial applications.

Abstract

In recent years, abundant research has been performed on biofilms for the production of compounds with biotechnological and industrial relevance. The use of biofilm platforms has been seen as a compelling approach to producing fine and bulk chemicals such as organic acids, alcohols, and solvents. However, the production of recombinant proteins using this system is still scarce. Biofilm reactors are known to have higher biomass density, operational stability, and potential for long-term operation than suspended cell reactors. In addition, there is an increasing demand to harness industrial and agricultural wastes and biorefinery residues to improve process sustainability and reduce production costs. The synthesis of recombinant proteins and other high-value compounds is mainly achieved using suspended cultures of bacteria, yeasts, and fungi. This review discusses the use of biofilm reactors for the production of recombinant proteins and other added-value compounds using bacteria and fungi.

Hydrodynamic Effects on Biofilm Development and Recombinant Protein Expression

Hydrodynamics play an important role in the rate of cell attachment and nutrient and oxygen transfer, which can affect biofilm development and the level of recombinant protein production. In the present study, the effects of different flow conditions on the development of Escherichia coli biofilms and the expression of a model recombinant protein (enhanced green fluorescent protein, eGFP) were examined. Planktonic and biofilm cells were grown at two different flow rates in a recirculating flow cell system for 7 days: 255 and 128 L h−1 (corresponding to a Reynolds number of 4600 and 2300, respectively). The fluorometric analysis showed that the specific eGFP production was higher in biofilms than in planktonic cells under both hydrodynamic conditions (3-fold higher for 255 L h−1 and 2-fold higher for 128 L h−1). In the biofilm cells, the percentage of eGFP-expressing cells was on average 52% higher at a flow rate of 255 L h−1. Furthermore, a higher plasmid copy number (PCN) was obtained for the highest flow rate for both planktonic (244 PCN/cell versus 118 PCN/cell) and biofilm cells (43 PCN/cell versus 29 PCN/cell). The results suggested that higher flow velocities promoted eGFP expression in E. coli biofilms.

Display of Heterologous Proteins in Bacillus Subtilis Biofilms for Enteric Immunization

One of the foremost goals in vaccine development is the design of effective, heat-stable vaccines that simplify the distribution and delivery while conferring high levels of protective immunity. Here, we describe a method for developing a live, oral vaccine that relies on the biofilm-forming properties of the spore-former bacterium Bacillus subtilis. The amyloid protein TasA is an abundant component of the extracellular matrix of the biofilms formed by B. subtilis that can be genetically fused to an antigen of interest. Spores of the recombinant strain are then prepared and applied via the oral route in an animal model. Due to the intrinsic resistance of the spores, they can bypass the stomach barrier, germinate, and subsequently colonize the gut, where they develop into biofilms, expressing the antigen of interest. We describe here the steps necessary to produce spores, immunization, and downstream analysis of the vaccine efficacy.

New Bacterial Surface Display System Development and Application Based on Bacillus subtilis YuaB Biofilm Component as an Anchoring Motif

Bacterial surface display system has been adopted in various biotechnological applications. In the case of Bacillus subtilis, most of the studies have been developed using spore based surface display system utilizing the inherent rigidity of spore against heat, alkali, and shear stress. But, spore harvest, purification and separation need additional cost and labor. To eliminate this procedure and to use the gram-positive nature of B. subtilis, YuaB, which is one of the major B. subtilis biofilm components and locates in the cell wall, based cell surface display system, is developed. P43 promoter driven overexpression of YuaB-His₆ tag does not hamper bacterial cell growth and promoted biofilm formation of recombinant strain. Flow cytometry of recombinant strain and its protoplast using FITC-Anti His₆ antibody, verified that YuaB locate in plasma membrane and protrude to the outside of cell wall, which means YuaB can be used as very efficient anchoring motif. Using surface expressed YuaB-His₆ tag, removal of divalent metal ion, Cu²⁺ and Ni²⁺, was tried to test its possibility for the environmental application of developed system.

Mammalian orthoreovirus core protein μ2 reorganizes host microtubule-organizing center components

Filamentous mammalian orthoreovirus (MRV) viral factories (VFs) are membrane-less cytosolic inclusions in which virus transcription, replication of dsRNA genome segments, and packaging of virus progeny into newly synthesized virus cores take place. In infected cells, the MRV μ2 protein forms punctae in the enlarged region of the filamentous VFs that are co-localized with γ-tubulin and resistant to nocodazole treatment, and permitted microtubule (MT)-extension, features common to MT-organizing centers (MTOCs). Using a previously established reconstituted VF model, we addressed the functions of MT-components and MTOCs concerning their roles in the formation of filamentous VFs. Indeed, the MTOC markers γ-tubulin and centrin were redistributed within the VF-like structures (VFLS) in a μ2-dependent manner. Moreover, the MT-nucleation centers significantly increased in numbers, and γ-tubulin was pulled-down in a binding assay when co-expressed with histidine-tagged-μ2 and μNS. Thus, μ2, by interaction with γ-tubulin, can modulate MTOCs localization and function according to viral needs.

Immunization of mice against alpha, beta, and epsilon toxins of Clostridium perfringens using recombinant rCpa-b-x expressed by Bacillus subtilis

The anaerobic pathogen Clostridium perfringens is the most potent cause of intestinal diseases, such as enterotoxemia, hemorrhagic enteritis, and lamb dysentery, in sheep. Three toxinotypes (B, C, and D) are usually the cause of these diseases and are mainly mediated via three important exotoxins: alpha toxin (CPA), beta toxin (CPB), and epsilon toxin (ETX). We have designed a chimeric protein, rCpa-b-x, that contains the C-terminal binding region of CPA, partial sequence of CPB, and ETX (Cpa^247-370, Cpb^108-305, and Etx^H118P, respectively) according to the principle of structural vaccinology. The rCpa-b-x protein was then expressed by pHT43 plasmid in vivo using Bacillus subtilis as a delivery vector (Bs-pHT43-Cpa-b-x). The immunological activity of the rCpa-b-x protein was verified by western blot and its immunological efficacy was evaluated in a murine model. Oral administration with a recombinant agent caused local mucosal and systemic immune responses, and serum lgG and intestinal mucosal secretory IgA (sIgA) antibody titers were significantly increased. Levels of IL-2, IL-4, and IFN-γ were significantly higher in lymphocytes isolated from the Bs-pHT43-Cpa-b-x group compared with levels from the control groups. The percentages of CD4⁺ and CD8⁺ T lymphocytes in the Bs-pHT43-Cpa-b-x and inactivated vaccine (IV) groups were in the normal range. Mice of vaccine groups and control groups were challenged with 1x LD₁₀₀ unit filtrate containing alpha, beta, and epsilon toxins. Mice in the Bs-pHT43-Cpa-b-x group were found to have lower rates of morbidity. The active immunization of mice with Bs-pHT43-Cpa-b-x still maintained 85% to 90% survival at the end of the 10-day observation period, whereas mice of control groups died within two to five days. The results of this study demonstrate the effectiveness of Bs-pHT43-Cpa-b-x in preventing C. perfringens infection in mice, and that Bs-pHT43-Cpa-b-x could be considered a potential vaccine against C. perfringens.

Progress in research and application development of surface display technology using Bacillus subtilis spores

Bacillus subtilis is a widely distributed aerobic Gram-positive species of bacteria. As a tool in the lab, it has the advantages of nonpathogenicity and limited likelihood of becoming drug resistant. It is a probiotic strain that can be directly used in humans and animals. It can be induced to produce spores under nutrient deficiency or other adverse conditions. B. subtilis spores have unique physical, chemical, and biochemical characteristics. Expression of heterologous antigens or proteins on the surface of B. subtilis spores has been successfully performed for over a decade. As an update and supplement to previously published research, this paper reviews the latest research on spore surface display technology using B. subtilis. We have mainly focused on the regulation of spore coat protein expression, display and application of exogenous proteins, and identification of developing research areas of spore surface display technology.

Recombinant protein expression in biofilms

Biofilm research is usually focused on the prevention or control of biofilm formation. Recently, the significance of the biofilm mode of growth in biotechnological applications received increased attention. Since biofilm reactors show many advantages over suspended cell reactors, especially in their higher biomass density and operational stability, bacterial biofilms have emerged as an interesting approach for the expression of specific proteins. Despite the potential of biofilm systems, recombinant protein production using biofilms has been scarcely investigated for the past 25 years. Our group has demonstrated that E. coli biofilms were able to produce a model recombinant protein, the enhanced green fluorescent protein (eGFP), at much higher levels than their planktonic counterparts. Even without optimization of cultivation conditions, an attractive productivity was obtained, indicating that biofilm cultures can be used as an alternative form of high cell density cultivation (HCDC). E. coli remains one of the favorite hosts for recombinant protein production and it has been successfully used in metabolic engineering for the synthesis of high value products. This review presents the advantages and concerns of using biofilms for the production of recombinant proteins and summarizes the different biofilm systems which have been described for this purpose. The relative advantages and disadvantages of the four microbial hosts tested for recombinant protein production in biofilms (two bacteria and two filamentous fungi) are also discussed.

Targeting ideal oral vaccine vectors based on probiotics: a systematical view

Probiotics have great potential to be engineered into oral vaccine delivery systems, which can facilitate elicitation of mucosal immunity without latent risks of pathogenicity. Combined with the progressive understanding of probiotics and the mucosal immune system as well as the advanced biotechniques of genetic engineering, the development of promising oral vaccine vectors based on probiotics is available while complicated and demanding. Therefore, a systematical view on the design of practical probiotic vectors is necessary, which will help to logically analyze and resolve the problems that might be neglected during our exploration. Here, we attempt to systematically summarize several fundamental issues vital to the effectiveness of the vector of probiotics, including the stability of the engineered vectors, the optimization of antigen expression, the improvement of colonization, and the enhancement of immunoreactivity. We also compared the existent strategies and some developing ones, attempting to figure out an optimal strategy that might deserve to be referred in the future development of oral vaccine vectors based on probiotics.

Biological Engineered Living Materials: Growing Functional Materials with Genetically Programmable Properties

Natural biological materials exhibit remarkable properties: self-assembly from simple raw materials, precise control of morphology, diverse physical and chemical properties, self-repair, and the ability to sense-and-respond to environmental stimuli. Despite having found numerous uses in human industry and society, the utility of natural biological materials is limited. But, could it be possible to genetically program microbes to create entirely new and useful biological materials? At the intersection between microbiology, material science, and synthetic biology, the emerging field of biological engineered living materials (ELMs) aims to answer this question. Here we review recent efforts to program cells to produce living materials with novel functional properties, focusing on microbial systems that can be engineered to grow materials and on new genetic circuits for pattern formation that could be used to produce the more complex systems of the future.

Mouse intestinal microbiota reduction favors local intestinal immunity triggered by antigens displayed in Bacillus subtilis biofilm

BACKGROUND

We previously engineered Bacillus subtilis to express an antigen of interest fused to TasA in a biofilm. B. subtilis has several properties such as sporulation, biofilm formation and probiotic ability that were used for the oral application of recombinant spores harboring Echinococcus granulosus paramyosin and tropomyosin immunogenic peptides that resulted in the elicitation of a specific humoral immune response in a dog model.

RESULTS

In order to advance our understanding of the research in oral immunization practices using recombinant B. subtilis spores, we describe here an affordable animal model. In this study, we show clear evidence indicating that a niche is required for B. subtilis recombinant spores to colonize the densely populated mice intestinal microbiota. The reduction of intestinal microbiota with an antibiotic treatment resulted in a positive elicitation of local humoral immune response in BALB/c mice after oral application of recombinant B. subtilis spores harboring TasA fused to E. granulosus (102-207) EgTrp immunogenic peptide. Our results were supported by a lasting prevalence of spores in mice feces up to 50 days after immunization and by the presence of specific secretory IgA, isolated from feces, against E. granulosus tropomyosin.

CONCLUSIONS

The reduction of mouse intestinal microbiota allowed the elicitation of a local humoral immune response in mice after oral application with spores of B. subtilis harboring immunogenic peptides against E. granulosus.

Oral Application of Recombinant Bacillus subtilis Spores to Dogs Results in a Humoral Response against Specific Echinococcus granulosus Paramyosin and Tropomyosin Antigens

Bacillus subtilis is known as an endospore- and biofilm-forming bacterium with probiotic properties. We have recently developed a method for displaying heterologous proteins on the surface of B. subtilis biofilms by introducing the coding sequences of the protein of interest into the bacterial genome to generate a fusion protein linked to the C terminus of the biofilm matrix protein TasA. Although B. subtilis is a regular component of the gut microflora, we constructed a series of recombinant B. subtilis strains that were tested for their ability to be used to immunize dogs following oral application of the spores. Specifically, we tested recombinant spores of B. subtilis carrying either the fluorescent protein mCherry or else selected antigenic peptides (tropomyosin and paramyosin) from Echinococcus granulosus, a zoonotic intestinal tapeworm of dogs and other carnivores. The application of the recombinant B. subtilis spores led to the colonization of the gut with recombinant B. subtilis but did not cause any adverse effect on the health of the animals. As measured by enzyme-linked immunosorbent assay and immunoblotting, the dogs were able to develop a humoral immune response against mCherry as well as against E. granulosus antigenic peptides. Interestingly, the sera of dogs obtained after immunization with recombinant spores of E. granulosus peptides were able to recognize E. granulosus protoscoleces, which represent the infective form of the head of the tapeworms. These results represent an essential step toward the establishment of B. subtilis as an enteric vaccine agent.

Actinobacillus pleuropneumoniae biofilms: Role in pathogenicity and potential impact for vaccination development

Actinobacillus pleuropneumoniae is a Gram-negative bacterium that belongs to the family Pasteurellaceae. It is the causative agent of porcine pleuropneumonia, a highly contagious respiratory disease that is responsible for major economic losses in the global pork industry. The disease may present itself as a chronic or an acute infection characterized by severe pathology, including hemorrhage, fibrinous and necrotic lung lesions, and, in the worst cases, rapid death. A. pleuropneumoniae is transmitted via aerosol route, direct contact with infected pigs, and by the farm environment. Many virulence factors associated with this bacterium are well characterized. However, much less is known about the role of biofilm, a sessile mode of growth that may have a critical impact on A. pleuropneumoniae pathogenicity. Here we review the current knowledge on A. pleuropneumoniae biofilm, factors associated with biofilm formation and dispersion, and the impact of biofilm on the pathogenesis A. pleuropneumoniae. We also provide an overview of current vaccination strategies against A. pleuropneumoniae and consider the possible role of biofilms vaccines for controlling the disease.

Synthetic biology engineering of biofilms as nanomaterials factories

Bottom-up fabrication of nanoscale materials has been a significant focus in materials science for expanding our technological frontiers. This assembly concept, however, is old news to biology — all living organisms fabricate themselves using bottom-up principles through a vast self-organizing system of incredibly complex biomolecules, a marvelous dynamic that we are still attempting to unravel. Can we use what we have gleaned from biology thus far to illuminate alternative strategies for designer nanomaterial manufacturing? In the present review article, new synthetic biology efforts toward using bacterial biofilms as platforms for the synthesis and secretion of programmable nanomaterials are described. Particular focus is given to self-assembling functional amyloids found in bacterial biofilms as re-engineerable modular nanomolecular components. Potential applications and existing challenges for this technology are also explored. This novel approach for repurposing biofilm systems will enable future technologies for using engineered living systems to grow artificial nanomaterials.