Isolation and characterization of a high molecular mass β-glucan from Lactobacillus fermentum Lf2 and evaluation of its immunomodulatory activity

Exploring probiotic effector molecules and their mode of action in gut-immune interactions

Probiotics, live microorganisms that confer health benefits when consumed in adequate amounts, have gained significant attention for their potential therapeutic applications. The beneficial effects of probiotics are believed to stem from their ability to enhance intestinal barrier function, inhibit pathogens, increase beneficial gut microbes, and modulate immune responses. However, clinical studies investigating the effectiveness of probiotics have yielded conflicting results, potentially due to the wide variety of probiotic species and strains used, the challenges in controlling the desired number of live microorganisms, and the complex interactions between bioactive substances within probiotics. Bacterial cell wall components, known as effector molecules, play a crucial role in mediating the interaction between probiotics and host receptors, leading to the activation of signaling pathways that contribute to the health-promoting effects. Previous reviews have extensively covered different probiotic effector molecules, highlighting their impact on immune homeostasis. Understanding how each probiotic component modulates immune activity at the molecular level may enable the prediction of immunological outcomes in future clinical studies. In this review, we present a comprehensive overview of the structural and immunological features of probiotic effector molecules, focusing primarily on Lactobacillus and Bifidobacterium. We also discuss current gaps and limitations in the field and propose directions for future research to enhance our understanding of probiotic-mediated immunomodulation.

Exopolysaccharide is the potential effector of Lactobacillus fermentum PS150, a hypnotic psychobiotic strain

Psychobiotics are a class of probiotics that confer beneficial effects on the mental health of the host. We have previously reported hypnotic effects of a psychobiotic strain, Lactobacillus fermentum PS150 (PS150), which significantly shortens sleep latency in experimental mice, and effectively ameliorate sleep disturbances caused by either caffeine consumption or a novel environment. In the present study, we discovered a L. fermentum strain, GR1009, isolated from the same source of PS150, and found that GR1009 is phenotypically distinct but genetically similar to PS150. Compared with PS150, GR1009 have no significant hypnotic effects in the pentobarbital-induced sleep test in mice. In addition, we found that heat-killed PS150 exhibited hypnotic effects and altered the gut microbiota in a manner similar to live bacteria, suggesting that a heat-stable effector, such as exopolysaccharide (EPS), could be responsible for these effects. Our comparative genomics analysis also revealed distinct genetic characteristics in EPS biosynthesis between GR1009 and PS150. Furthermore, scanning electron microscopy imaging showed a sheet-like EPS structure in PS150, while GR1009 displayed no apparent EPS structure. Using the phenol-sulfate assay, we found that the sugar content value of the crude extract containing EPS (C-EPS) from PS150 was approximately five times higher than that of GR1009, indicating that GR1009 has a lower EPS production activity than PS150. Through the pentobarbital-induced sleep test, we confirmed the hypnotic effects of the C-EPS isolated from PS150, as evidenced by a significant reduction in sleep latency and recovery time following oral administration in mice. In summary, we utilized a comparative approach to delineate differences between PS150 and GR1009 and proposed that EPS may serve as a key factor that mediates the observed hypnotic effect.

Synthesis of the Hexasaccharide Related to the Exopolysaccharide from Lactobacillus mucosae VG1 through Regioselective Glycosylation

Chemical synthesis of the hexasaccharide repeating unit associated with the exopolysaccharide of Lactobacillus mucosae VG1 is reported. The total synthesis is accomplished through a convergent [2 + 2 + 2] strategy using rationally protected monosaccharide derivatives. Chemoselective activation of the glycosyl donors and regioselective nucleophilicity of the acceptors were successfully employed throughout the chemical synthesis.

Lactic acid bacteria-derived exopolysaccharide: Formation, immunomodulatory ability, health effects, and structure-function relationship

Exopolysaccharides (EPSs) synthesized by lactic acid bacteria (LAB) have implications for host health and act as food ingredients. Due to the variability of LAB-EPS (lactic acid bacteria-derived exopolysaccharide) gene clusters, especially the glycosyltransferase genes that determine monosaccharide composition, the structure of EPS is very rich. EPSs are synthesized by LAB through the extracellular synthesis pathway and the Wzx/Wzy-dependent pathway. LAB-EPS has a strong immunomodulatory ability. The EPSs produced by different genera of LAB, especially Lactobacillus, Leuconostoc, and Streptococcus, have different immunomodulatory abilities because of their specific structures. LAB-EPS possesses other health effects, including antitumor, antioxidant, intestinal barrier repair, antimicrobial, antiviral, and cholesterol-lowering activities. The bioactivities of LAB-EPS are tightly related to their structures such us monosaccharide composition, glycosidic bonds, and molecular weight (MW). For the excellent physicochemical property, LAB-EPS acts as product improvers in dairy, bakery food, and meat in terms of stability, emulsification, thickening, and gelling. We systematically summarize the detailed process of EPS from synthesis to application, with emphasis on physiological mechanisms of EPS, and specific structure-function relationship, which provides theoretical support for the potential commercial value in the pharmaceutical, chemical, food, and cosmetic industries.

Screening and Molecular Identification of Lactic Acid Bacteria Producing β-Glucan in Boza and Cider

The goal of this study was screening and molecular identification of Lactic Acid Bacteria (LAB) producing β-glucan from different species isolated from boza and cider compared to a standard strain for Lactobacillus rhamnosus NRRL 1937 (LGG). From 48 unknown isolates, four LAB strains were selected. Based on the NCBI database, their nomenclature was A3, B6, and C9 for Limosilactobacillus fermentum SH1, SH2, and SH3 along with D6 for Leuconostoc mesenteroides SH4. Also, their similarity values were 100%, 99.8%, 100%, and 100%, respectively. The potential of Exopolysaccharide (EPS) (as β-glucan) production for selected LAB strains by gtf gene, conventional PCR and gene expression using both LGG as a control and LAB 16S rRNA gene as a house-keeping gene was investigated. In addition, EPS (mg/100 mL), cell mass (mg/100 mL), pH, total carbohydrate%, total protein% and β-glucan% by the HPLC for all selected LAB isolates were studied. All results of genetic and chemical tests proved the superiority of B6 treatment for L. fermentum SH2. The results showed the superiority of B6 treatment in gtf gene expression (14.7230 ± 0.070-fold) followed by C9 and A3 treatments, which were 10.1730 ± 0.231-fold and 8.6139 ± 0.320-fold, respectively. while D6 treatment recorded the lowest value of gene expression (0.8566 ± 0.040-fold) compared to the control LGG (one-fold). The results also demonstrated that B6 treatment was superior to the other treatments in terms of EPS formation, with a value of 481 ± 1.00 mg/100 mL, followed by the C9 treatment at 440 ± 2.00 mg/100 mL, compared to the LGG (control) reaching 199.7 ± 3.51 mg/100 mL. Also, the highest % of quantitative and qualitative β-glucan in EPS was observed in B6 followed by C9, D6 and A3 which were 5.56 ± 0.01%, 4.46 ± 0.01%, 0.25 ± 0.008% and 0.12 ± 0.008%, respectively compared to control (0.31 ± 0.01%). Finally, the presented results indicate the importance of screening the local LAB isolates to obtain a superior strain for β-glucan production which will be introduced in a subsequent study under optimum conditions.

The modulation and mechanism of probiotic-derived polysaccharide capsules on the immune response in allergic diseases

Allergic diseases, derived from the dysregulation of immune tolerance mechanisms, have been rising in the last two decades. Recently, increasing evidence has shown that probiotic-derived polysaccharide capsules exhibit a protective effect against allergic diseases, involving regulation of Th1/Th2 balance, induction of differentiation of T regulatory cells and activation of dendritic cells (DCs). DCs have a central role in controlling the immune response through their interaction with gut microbiota via their pattern recognition receptors, including Toll-like receptors and C-type-lectin receptors. This review discusses the effects and critical mechanism of probiotic-derived polysaccharide capsules in regulating the immune system to alleviate allergic diseases. We first describe the development of immune response in allergic diseases and recent relevant findings. Particular emphasis is placed on the effects of probiotic-derived polysaccharide capsules on allergic immune response. Then, we discuss the underlying mechanism of the impact of probiotic-derived polysaccharide capsules on DCs-mediated immune tolerance induction.

The anti-cancer effects and mechanisms of lactic acid bacteria exopolysaccharides in vitro: A review

Probiotic lactic acid bacteria (LAB) are a particular group of gram-positive bacteria that are usually involved in natural ferments and widely used in food manufacture industry. Most of them can produce exopolysaccharides (EPS), surface carbohydrate polymers with diverse biological functions. LAB EPS are potentially complementary and alternative medicines against cancer. EPS show anti-proliferative effects on a variety of tumor cells from intestine, liver, breast, etc. They modulate the development of tumors through various mechanisms including promoting apoptosis, inducing cell cycle arrest as well as anti-mutagenic, anti-oxidative, anti-angiogenesis and anti-inflammatory effects. Bacterial origin, existence form, chemical structure, purity et al. are important factors affecting the anticancer effects of EPS. The future challenge lies in elucidating the precise structure-function relationship of LAB EPS. Besides, more in vivo studies and further clinical trials are indispensable to confirm the anticancer effects.

Structural characterisation of two medium molecular mass exopolysaccharides produced by the bacterium Lactobacillus fermentum Lf2

Under optimized conditions, the lactic acid bacterium Lactobacillus fermentum Lf2 secretes up to 2 gL^-1 of a mixture of polysaccharides into the fermentation medium when grown on sucrose. Earlier studies had shown that the mixture is biologically active and work was undertaken to characterise the polysaccharides. Preparative size exclusion chromatography was used to separate a high molecular mass β-glucan (weight average mass of 1.23 × 10⁶ gmol^-1) from two medium molecular mass polysaccharides (weight average mass of 8.8 × 10⁴ gmol^-1). Under optimized growth conditions, the medium molecular mass polysaccharides accounted for more than 75% of the mixture by weight. Monomer, linkage analysis and NMR spectroscopy of the medium molecular mass polysaccharides, and material isolated after their Smith degradation, was used to identify the structure of the component polysaccharides. The mixture contains two novel polysaccharides. The first has a main chain of β-1,6-linked galactofuranoses which is non-stoichiometrically 2-O-glucosylated. The degree of substitution at the 2-position, with α-D-Glcp, depends on the fermentation conditions; under optimized conditions greater than 80% 2-O-α-D-glucosylation was observed. The second polysaccharide is a heteroglycan with four monosaccharides in the repeat unit: residual signals in the NMR suggest that the sample also contains trace amounts (<3%) of cell wall polysaccharides.