Oscillospira is a class of organism that often appears in high-throughput sequencing data but has not been purely cultured and is widely present in the animal and human intestines. There is a strong association between variation in Oscillospira abundance and obesity, leanness, and human health. In addition, a growing body of studies has shown that Oscillospira is also implicated in other diseases, such as gallstones and chronic constipation, and has shown some correlation with the positive or negative changes in its course. Sequencing data combined with metabolic profiling indicate that Oscillospira is likely to be a genus capable of producing short-chain fatty acids (SCFAs) such as butyrate, which is an important reference indicator for screening “next-generation probiotics “. Considering the positive effects of Oscillospira in some specific diseases, such as obesity-related metabolic diseases, it has already been characterized as one of the next-generation probiotic candidates and therefore has great potential for development and application in the future food, health care, and biopharmaceutical products.

Endemic selenium (Se) deficiency is a major worldwide nutritional challenge. Organic Se can be synthesized through physical and chemical methods that are conducive to human absorption, but its high production cost and low output cannot meet the actual demand for Se supplementation. Some microbes are known to convert inorganic Se into organic forms of high nutritional value and Se-enriched probiotics are the main representatives. The aim of the present review is to describe the characteristics of Se-enriched yeast, lactic acid bacteria, bifidobacteria and discuss their Se enrichment mechanisms. Se products metabolized by Se-enriched probiotics have been classified, such as Se nanoparticles (SeNPs) and selenoprotein, and their bioactivities have been assessed. The factors affecting the Se enrichment capacity of probiotics and their application in animal feed, food additives, and functional food production have been summarized. Moreover, a brief summary and the development of Se-enriched probiotics, particularly their potential applications in the field of biomedicine have been provided. In conclusion, Se-enriched probiotics not just have a wide range of applications in the food industry but also have great potential for application in the field of biomedicine in the future. Graphical Abstract

Selenium (Se) is an essential trace element for human health and animal nutrition. The aim of this study was to evaluate the inhibitory activities of Se-enriched lactic acid bacteria (LAB), Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus, against pathogenic Salmonella typhimurium, Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes in vitro. The results indicated that the accumulation amount of Se by Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus reached 12.05 ± 0.43 µg/mL and 11.56 ± 0.25 µg/mL, respectively, accompanied by the relative maximum living cells when sodium selenite was 80 µg/mL. Oxford cup double plate assay showed that bacterial culture solution and cell-free culture supernatant (CFCS) from Se-enriched LAB exerted stronger antibacterial activity than those from the non-Se strains. The growth of pathogenic bacterial culture with CFCS at any growth stages was worse than that without CFCS; moreover, the inhibiting effect of CFCS of Se-enriched LAB was more significant than that of non-Se strains. Results from a scanning electron microscope equipped with energy dispersion X-ray spectrometry showed that elemental Se nanoparticles, which characteristically energy peak around 1.42 keV, were deposited on the cell surfaces of Lactobacillus delbrueckii ssp. bulgaricus. In addition, CFCS of Se-enriched LAB induced more serious cell structure damage of pathogenic bacteria than did non-Se LAB.

The gut microbiome is mainly composed of microbiota and mycobiota, both of which play important roles in the development of the host immune system, metabolic regulation, and maintenance of intestinal homeostasis. With the increasing awareness of the pathogenic essence of infectious, immunodeficiency, and tumor-related diseases, the interactions between gut bacteria, fungi, and host immunity have been shown to directly influence the disease process or final therapeutic outcome, and collaborative and antagonistic relationships are commonly found between bacteria and fungi. Interventions represented by probiotics, prebiotics, engineered probiotics, fecal microbiota transplantation (FMT), and drugs can effectively modulate the triple interactions. In particular, traditional probiotics represented by Bifidobacterium and Lactobacillus and next-generation probiotics represented by Akkermansia muciniphila and Faecalibacterium prausnitzii showed a high enrichment trend in the gut of patients with a high response to inflammation remission and tumor immunotherapy, which predicts the potential medicinal value of these beneficial microbial formulations. However, there are bottlenecks in all these interventions that need to be broken. Meanwhile, further unraveling the underlying mechanisms of the “triple interactions” model can guide precise interventions and ultimately improve the efficiency of interventions on the host gut microbiome and immune modulation, thus directly or indirectly improving anti-inflammatory and tumor immunotherapy effects. Graphical Abstract

Bifidobacterium breve (YH68) is widely used in the fields of food fermentation and biomedicine. In this study, we explored the antibacterial activity of the cell free culture supernatant (CFCS) of YH68 against Clostridioides difficile ATCC 9689 (CD) by measuring multiple indexes, including the growth, spores production, toxin A/B production, and the expression levels of the tcdA and tcdB genes of CD. In addition, we examined the changes in major cellular functional groups, structures, permeability, integrity, and the proton motive force (PMF) of the cytoplasmic membrane. The results showed that double-dilution ratio of YH68-CFCS (3 × 10⁹ CFU/mL) was the MIC value. The cell density, spores production, and the toxin production of CD treated with YH68-CFCS were lower than that of the control (p < 0.05). In addition, the gene expression levels of tcdA and tcdB in CD treated with YH68-CFCS were significant downregulated (p < 0.05). Marked differences were observed in the cell membrane and cell wall by a FT-IR spectroscopy and SEM. Analysis of the cell membrane permeability and integrity of the CD cells revealed that YH68-CFCS induced the leakage of a large amount of intracellular K⁺, inorganic phosphate, ATP, nucleic acids and proteinaceous substances. Furthermore, PMF analysis indicated that there was a significant change in Δψ and ΔpH. These findings demonstrated that the antibacterial activity of YH68-CFCS against CD involved the inhibition of growth, spore production, toxin production, and virulence genes expression; a consumption of PMF in the cytoplasmic membrane, the formation of pore in the cell membrane, together with the enhanced cell membrane permeability; and, eventually, cell completely disintegration.