Mucosal vaccines offer several advantages over injectable conventional vaccines, such as adaptive immunity induction, secretory IgA production at the entry site of most pathogens, and needleless vaccinations. Despite their potential, only a few mucosal vaccines are currently used. Developing new effective mucosal vaccines strongly relies on identifying innovative anti-gens, 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, the spores conjugate the advantages of live microorganisms with synthetic nanoparticles. When mucosally administered, spores expressing anti-gens 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 the spore's structure, specifically the spore surface, and the diverse approaches developed to improve its efficiency as a vehicle for heterologous antigen presentation.

A total of thirty-two aerobic spore former strains were isolated from intestinal samples of healthy children and analyzed for their hemolytic and antibiotic-resistance activities. Four strains selected as non-hemolytic and sensitive to all antibiotics recommended as relevant by regulatory agencies were short-listed and evaluated for their in silico and in vitro probiotic potentials. The four selected strains were assigned to the Bacillus velenzensis (MV4 and MV11), B. subtilis (MV24) and Priestia megaterium (formerly Bacillus megaterium) (MV30) species. A genomic analysis indicated that MV4, MV11 and MV24 contained a homolog of the gene coding for the fibrinolytic enzyme nattokinase while only MV30 encoded for a glutamic acid decarboxylase essential to synthesize the neurotransmitter GABA. All four strains showed a strong antioxidant activity, formed biofilm and produced/secreted quorum sensing peptides able to induce a cytoprotective stress response in a model of human intestinal (HT29) cells. Altogether, genomic and physiological data indicate that the analyzed strains do not pose safety concerns and have in vitro probiotic potentials.

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.

In the last decades, intensive crop management has involved excessive use of pesticides or fertilizers, compromising environmental integrity and public health. Accordingly, there has been worldwide pressure to find an eco-friendly and safe strategy to ensure agricultural productivity. Recently, Plant Growth-Promoting (PGP) rhizobacteria are receiving increasing attention as suitable biocontrol agents against agricultural pests. In the present study, 22 spore-forming bacteria were selected among a salt-pan rhizobacteria collection for their PGP traits and their antagonistic activity against the plant pathogen fungus Macrophomina phaseolina. Based on the higher antifungal activity, strain RHFS10, identified as Bacillus vallismortis, was furtherly examined and cell-free supernatants assays, column purification, and tandem mass spectrometry employed to purify and preliminarily identify the antifungal metabolites. Interestingly, the minimum inhibitory concentration assessed for the fractions active against M. phaseolina, resulted 10 times lower and more stable than the one estimated for the commercial fungicide pentachloronitrobenzene. These results suggest the use of B. vallismortis strain RHFS10 as a potential Plant Growth Promoting Rhizobacteria to efficiently control phytopathogenic fungus M. phaseolina, in alternative to chemical pesticides.

This lack of information is due to the primary role of HSTs in fungal pathogenesis, which often masks the functions of NSTs and CWDEs. So, the toxic effects of A. alternata metabolites due to NSTs and CWDEs have received minor attention than those reported for HSTs mycotoxins [11]. A wider study of the activity of isolated fungal metabolites can allow the identification of compounds directly related to the pathogenic activity of the fungus, making it possible to create chemo libraries that facilitate the linking of the structure of the compounds with the species that produce it and its effect on host and non-host crops, as well as with biosynthetic features [12]. In this context, our work reports a study focused on NSTs and CWDEs used by an A. alternata strain isolated from infected pears in Italy. To this aim, the characterization of hydrolytic enzyme activities of A. alternata and the identification of the metabolites produced in vitro were performed. Furthermore, the phytotoxic activity of the isolated compounds was evaluated on pear (host and non-host varieties) and lemon fruits [13]. Finally, the competition of A. alternata with other pathogens was evaluated to investigate the role of NSTs on co-infections.