The spore surface of intestinal isolates ofBacillus subtilis

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.

Bacterial Spore-Based Delivery System: 20 Years of a Versatile Approach for Innovative Vaccines

Mucosal vaccines offer several advantages over injectable conventional vaccines, such as the induction of adaptive immunity, with secretory IgA production at the entry site of most pathogens, and needle-less vaccinations. Despite their potential, only a few mucosal vaccines are currently used. Developing new effective mucosal vaccines strongly relies on identifying innovative antigens, efficient adjuvants, and delivery systems. Several approaches based on phages, bacteria, or nanoparticles have been proposed to deliver antigens to mucosal surfaces. Bacterial spores have also been considered antigen vehicles, and various antigens have been successfully exposed on their surface. Due to their peculiar structure, spores conjugate the advantages of live microorganisms with synthetic nanoparticles. When mucosally administered, spores expressing antigens have been shown to induce antigen-specific, protective immune responses. This review accounts for recent progress in the formulation of spore-based mucosal vaccines, describing a spore's structure, specifically the spore surface, and the diverse approaches developed to improve its efficiency as a vehicle for heterologous antigen presentation.

Different effects of Bacillus coagulans vegetative cells and spore isolates on constipation-induced gut microbiota dysbiosis in mice

Bacillus coagulans (B. coagulans) can improve and prevent functional gastrointestinal disorders. However, there has been little discussion in the literature on the difference between spores and vegetative cells for relieving constipation. The purpose of this study was to determine the efficacy of Bacillus coagulans (B. coagulans) vegetative cells and spores against loperamide-induced constipation in mice. According to our findings, B. coagulans vegetative cells and spores differ in their ability to relieve loperamide-induced constipation. Two of the three strains of B. coagulans spores used in this experiment, B. coagulans GBI-30 6086 and B. coagulans 90, were significantly different from the model group in relieving constipation. This mainly manifested as a decreased time required for first black stool defecation (by 52 and 79 min, respectively), and increased counts of the first black stools in 5 h (by 15 and 8, respectively), the small intestine transit rate (by 23.31% and 20.52%, respectively), and the concentration of SCFAs. While the administration of vegetative cells could only relieve some indicators of intestinal transit disorders and dysbacteriosis caused by constipation. Spores of B. coagulans GBI-30 6086 and B. coagulans 90 had higher survival rates in the simulated gastrointestinal tract environment, which indicated that the functional modes of the three strains were different and had a strong relationship with the morphology of the bacteria. B. coagulans GBI-30 6086 and B. coagulans 90 spores alleviate constipation by increasing the abundances of Actinobacteria, Deferribacteres, and Lachnospiraceae UCG-006 (which were positively correlated with SCFAs) and decreasing the abundances of Cyanobateria and Rikenellaceae_RC9_gut group (which were negatively correlated with SCFAs) and the levels of Ruminococcaceae UGC-014 and Alistipes. In this study, the effects of probiotics in the form of spore or vegetative cell were compared, and the optimal preparation form was determined, providing a theoretical basis for the application of probiotics of B. coagulans to relieve constipation.

Flagellotropic Bacteriophages: Opportunities and Challenges for Antimicrobial Applications

Bacteriophages (phages) are the most abundant biological entities in the biosphere. As viruses that solely infect bacteria, phages have myriad healthcare and agricultural applications including phage therapy and antibacterial treatments in the foodservice industry. Phage therapy has been explored since the turn of the twentieth century but was no longer prioritized following the invention of antibiotics. As we approach a post-antibiotic society, phage therapy research has experienced a significant resurgence for the use of phages against antibiotic-resistant bacteria, a growing concern in modern medicine. Phages are extraordinarily diverse, as are their host receptor targets. Flagellotropic (flagellum-dependent) phages begin their infection cycle by attaching to the flagellum of their motile host, although the later stages of the infection process of most of these phages remain elusive. Flagella are helical appendages required for swimming and swarming motility and are also of great importance for virulence in many pathogenic bacteria of clinical relevance. Not only is bacterial motility itself frequently important for virulence, as it allows pathogenic bacteria to move toward their host and find nutrients more effectively, but flagella can also serve additional functions including mediating bacterial adhesion to surfaces. Flagella are also a potent antigen recognized by the human immune system. Phages utilizing the flagellum for infections are of particular interest due to the unique evolutionary tradeoff they force upon their hosts: by downregulating or abolishing motility to escape infection by a flagellotropic phage, a pathogenic bacterium would also likely attenuate its virulence. This factor may lead to flagellotropic phages becoming especially potent antibacterial agents. This review outlines past, present, and future research of flagellotropic phages, including their molecular mechanisms of infection and potential future applications.

Spore Formers as Beneficial Microbes for Humans and Animals

Microorganisms efficiently colonize the external and internal surfaces of the animal body establishing mutually beneficial interactions and forming site- and individual-specific microbiota. The degradation of complex polysaccharides in the animal gut, the production of useful compounds, protection against pathogenic microorganisms and contribution to the development of an efficient immune system are the main beneficial effects of a balanced microbiota. A dysbiosis, an imbalanced composition of the microbiota, has been associated with a large number of diseases from gastro-intestinal or urogenital disorders to allergies, cardiovascular and autoimmune diseases and even to the onset of certain cancers. A growing body of evidence has indicated that probiotic treatments, aimed at maintaining or rebalancing the microbiota, are useful to treat/prevent those illnesses. Lactic Acid Bacteria and Bifidobacteria are the most common microbes used in probiotic preparations; however, other bacteria and yeast cells are also widely used in commercial products. Here we focus on the use of bacterial spore formers as probiotics. Spore formers have been marketed as probiotics for over 50 years and are now extensively used for the treatment of intestinal disorders and as dietary supplements in humans, as growth promoters and competitive exclusion agents in animals.

Spore-adsorption: Mechanism and applications of a non-recombinant display system

Surface display systems have been developed to express target molecules on almost all types of biological entities from viruses to mammalian cells and on a variety of synthetic particles. Various approaches have been developed to achieve the display of many different target molecules, aiming at several technological and biomedical applications. Screening of libraries, delivery of drugs or antigens, bio-catalysis, sensing of pollutants and bioremediation are commonly considered as fields of potential application for surface display systems. In this review, the non-recombinant approach to display antigens and enzymes on the surface of bacterial spores is discussed. Examples of molecules displayed on the spore surface and their potential applications are summarized and a mechanism of display is proposed.

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.

Importance of the gastrointestinal life cycle of Bacillus for probiotic functionality

Bacillus spp. are widely used in animal production for their probiotic properties. In many animal species, feed supplementation with specific Bacillus strains can provide numerous benefits including improvement in digestibility, the gut microbiota and immune modulation, and growth performance. Bacilli are fed to animals as spores that can sustain the harsh feed processing and long storage. However, the spores are metabolically quiescent and it is widely accepted that probiotics should be in a metabolically active state to perform certain probiotic functions like secretion of antimicrobial compounds and enzymes, synthesis of short chain fatty acids, and competition for essential nutrients. These functions should become active in the host gastrointestinal tract (GIT) soon after digestion of spores in order to contribute to microbiota and host metabolism. Considering that bacterial spores are metabolically dormant and many health benefits are provided by vegetative cells, it is of particular interest to discuss the life cycle of Bacillus in animal GIT. This review aims to capture the main characteristics of spores and vegetative cells and to discuss the latest knowledge in the life cycle of beneficial Bacillus in various intestinal environments. Furthermore, we review how the life cycle may influence probiotic functions of Bacillus and their benefits for human and animal health.

Zinc oxide induces the stringent response and major reorientations in the central metabolism of Bacillus subtilis

Microorganisms, such as bacteria, are one of the first targets of nanoparticles in the environment. In this study, we tested the effect of two nanoparticles, ZnO and TiO2, with the salt ZnSO4 as the control, on the Gram-positive bacterium Bacillus subtilis by 2D gel electrophoresis-based proteomics. Despite a significant effect on viability (LD50), TiO2 NPs had no detectable effect on the proteomic pattern, while ZnO NPs and ZnSO4 significantly modified B. subtilis metabolism. These results allowed us to conclude that the effects of ZnO observed in this work were mainly attributable to Zn dissolution in the culture media. Proteomic analysis highlighted twelve modulated proteins related to central metabolism: MetE and MccB (cysteine metabolism), OdhA, AspB, IolD, AnsB, PdhB and YtsJ (Krebs cycle) and XylA, YqjI, Drm and Tal (pentose phosphate pathway). Biochemical assays, such as free sulfhydryl, CoA-SH and malate dehydrogenase assays corroborated the observed central metabolism reorientation and showed that Zn stress induced oxidative stress, probably as a consequence of thiol chelation stress by Zn ions. The other patterns affected by ZnO and ZnSO4 were the stringent response and the general stress response. Nine proteins involved in or controlled by the stringent response showed a modified expression profile in the presence of ZnO NPs or ZnSO4: YwaC, SigH, YtxH, YtzB, TufA, RplJ, RpsB, PdhB and Mbl. An increase in the ppGpp concentration confirmed the involvement of the stringent response during a Zn stress. All these metabolic reorientations in response to Zn stress were probably the result of complex regulatory mechanisms including at least the stringent response via YwaC.