Extractable Bacterial Surface Proteins in Probiotic-Host Interaction

Understanding the nutritional benefits through plant proteins-probiotics interactions: mechanisms, challenges, and perspectives

The nutritional benefits of combining probiotics with plant proteins have sparked increasing research interest and drawn significant attention. The interactions between plant proteins and probiotics demonstrate substantial potential for enhancing the functionality of plant proteins. Fermented plant protein foods offer a unique blend of bioactive components and beneficial microorganisms that can enhance gut health and combat chronic diseases. Utilizing various probiotic strains and plant protein sources opens doors to develop innovative probiotic products with enhanced functionalities. Nonetheless, the mechanisms and synergistic effects of these interactions remain not fully understood. This review aims to delve into the roles of promoting health through the intricate interplay of plant proteins and probiotics. The regulatory mechanisms have been elucidated to showcase the synergistic effects, accompanied by a discussion on the challenges and future research prospects. It is essential to recognize that the interactions between plant proteins and probiotics encompass multiple mechanisms, highlighting the need for further research to address challenges in achieving a comprehensive understanding of these mechanisms and their associated health benefits.

Propionibacterium freudenreichii CIRM-BIA 129 mitigates colitis through S layer protein B-dependent epithelial strengthening

The growing incidence of human diseases involving inflammation and increased gut permeability makes the quest for protective functional foods more crucial than ever. Propionibacterium freudenreichii (P. freudenreichii) is a beneficial bacterium used in the dairy and probiotic industries. Selected strains exert anti-inflammatory effects, and the present work addresses whether the P. freudenreichii CIRM-BIA129, consumed daily in a preventive way, could protect mice from acute colitis induced by dextran sodium sulfate (DSS), and more precisely, whether it could protect from intestinal epithelial breakdown induced by inflammation. P. freudenreichii CIRM-BIA129 mitigated colitis severity and inhibited DSS-induced permeability. It limited crypt length reduction and promoted the expression of zonula occludens-1 (ZO-1), without reducing interleukin-1β mRNA (il-1β) expression. In vitro, P. freudenreichii CIRM-BIA129 prevented the disruption of a Caco-2 monolayer induced by proinflammatory cytokines. It increased transepithelial electrical resistance (TEER) and inhibited permeability induced by inflammation, along with an increased ZO-1 expression. Extracellular vesicles (EVs) from P. freudenreichii CIRM-BIA129, carrying the surface layer protein (SlpB), reproduced the protective effect of P. freudenreichii CIRM-BIA129. A mutant strain deleted for slpB (ΔslpB), or EVs from this mutant strain, had lost their protective effects and worsened both DSS-induced colitis and inflammation in vivo. These results shown that P. freudenreichii CIRM-BIA129 daily consumption has the potential to greatly alleviate colitis symptoms and, particularly, to counter intestinal epithelial permeability induced by inflammation by restoring ZO-1 expression through mechanisms involving S-layer protein B. They open new avenues for the use of probiotic dairy propionibacteria and/or postbiotic fractions thereof, in the context of gut permeability.NEW & NOTEWORTHY Propionibacterium freudenreichii reduces dextran sodium sulfate (DSS)-induced intestinal permeability in vivo. P. freudenreichii does not inhibit inflammation but damages linked to inflammation. P. freudenreichii inhibits intestinal epithelial breakdown through S-layer protein B. The protective effects of P. freudenreichii depend on S-layer protein B. Extracellular vesicles from P. freudenreichii CB 129 mimic the protective effect of the probiotic.

Single-cell phenotyping of bacteria combined with deep sequencing for improved contextualization of microbiome analyses

Great effort was made to characterize the bacterial communities inhabiting the human body as a factor in disease, resulting in the realization that a wide spectrum of diseases is associated with an altered composition of the microbiome. However, the identification of disease-relevant bacteria has been hindered by the high cross-sectional diversity of individual microbiomes, and in most cases, it remains unclear whether the observed alterations are cause or consequence of disease. Hence, innovative analysis approaches are required that enable inquiries of the microbiome beyond mere taxonomic cataloging. This review highlights the utility of microbiota flow cytometry, a single-cell analysis platform to directly interrogate cellular interactions, cell conditions, and crosstalk with the host's immune system within the microbiome to take into consideration the role of microbes as critical interaction partners of the host and the spectrum of microbiome alterations, beyond compositional changes. In conjunction with advanced sequencing approaches it could reveal the genetic potential of target bacteria and advance our understanding of taxonomic diversity and gene usage in the context of the microenvironment. Single-cell bacterial phenotyping has the potential to change our perspective on the human microbiome and empower microbiome research for the development of microbiome-based therapy approaches and personalized medicine.

Milk phospholipids protect Bifidobacterium longum subsp. infantis during in vitro digestion and enhance polysaccharide production

Bifidobacterium longum subsp. infantis is associated with the gut microbiota of breast-fed infants. Bifidobacterium infantis promotes intestinal barrier and immune function through several proposed mechanisms, including interactions between their surface polysaccharides, the host, and other gut microorganisms. Dairy foods and ingredients are some of the most conspicuous food-based niches for this species and may provide benefits for their delivery and efficacy in the gut. Milk phospholipid (MPL)-rich ingredients have been increasingly recognized for their versatile benefits to health, including interactions with the gut microbiota and intestinal cells. Therefore, our objective was to investigate the capacity for MPL to promote survival of B. infantis during simulated digestion and to modulate bacterial polysaccharide production. To achieve these aims, B. infantis was incubated with or without 0.5% MPL in de Man, Rogosa, and Sharpe (MRS) media at 37°C under anaerobiosis. Survival across the oral, gastric, and intestinal phases using in vitro digestion was measured using plate count, along with adhesion to goblet-like intestinal cells. MPL increased B. infantis survival at the end of the intestinal phase by at least 7% and decreased adhesion to intestinal cells. The bacterial surface characteristics, which may contribute to these effects, were assessed by ζ-potential, changes in surface proteins using comparative proteomics, and production of bound polysaccharides. MPL decreased the surface charge of the bifidobacteria from -17 to -24 mV and increased a 50 kDa protein (3-fold) that appears to be involved in protection from stress. The production of bound polysaccharides was measured using FTIR, HPLC, and TEM imaging. These techniques all suggest an increase in bound polysaccharide production at least 1.7-fold in the presence of MPL. Our results show that MPL treatment increases B. infantis survival during simulated digestion, induces a stress resistance surface protein, and yields greater bound polysaccharide production, suggesting its use as a functional ingredient to enhance probiotic and postbiotic effects.

Oral Administration of Lactobacillus sakei CVL-001 Improves Recovery from Dextran Sulfate Sodium-Induced Colitis in Mice by Microbiota Modulation

Inflammatory bowel disease (IBD) is an intestinal chronic inflammatory disease, and its incidence is steadily increasing. IBD is closely related to the intestinal microbiota, and probiotics are known to be a potential therapeutic agent for IBD. In our study, we evaluated the protective effect of Lactobacillus sakei CVL-001, isolated from Baechu kimchi, on dextran sulfated sodium (DSS)-induced colitis in mice. The oral administration of L. sakei CVL-001 according to the experimental schedule alleviated weight loss and disease activity in the mice with colitis. Furthermore, the length and histopathology of the colon improved. The expression of tumor necrosis factor (TNF)-α and interleukin (IL)-1β genes decreased in the colons of mice that were administered L. sakei CVL-001, whereas that of IL-10 increased. The expressions of genes coding for E-cadherin, claudin3, occludin, and mucin were also restored. In co-housed conditions, L. sakei CVL-001 administration did not improve disease activity, colon length, and histopathology. Microbiota analysis revealed that L. sakei CVL-001 administration increased the abundance of microbiota and altered Firmicutes/Bacteroidetes ratio, and decreased Proteobacteria. In conclusion, L. sakei CVL-001 administration protects mice from DSS-induced colitis by regulating immune response and intestinal integrity via gut microbiota modulation.

S-layer proteins as immune players: tales from pathogenic and non-pathogenic bacteria

In bacteria, as in other microorganisms, surface compounds interact with different pattern recognition receptors expressed by host cells, which usually triggers a variety of cellular responses that result in immunomodulation. The S-layer is a two-dimensional macromolecular crystalline structure formed by (glyco)-protein subunits that covers the surface of many species of Bacteria and almost all Archaea. In Bacteria, the presence of S-layer has been described in both pathogenic and non-pathogenic strains. As surface components, special attention deserves the role that S-layer proteins (SLPs) play in the interaction of bacterial cells with humoral and cellular components of the immune system. In this sense, some differences can be predicted between pathogenic and non-pathogenic bacteria. In the first group, the S-layer constitutes an important virulence factor, which in turn makes it a potential therapeutic target. For the other group, the growing interest to understand the mechanisms of action of commensal microbiota and probiotic strains has prompted the studies of the role of the S-layer in the interaction between the host immune cells and bacteria bearing this surface structure. In this review, we aim to summarize the main latest reports and the perspectives of bacterial SLPs as immune players, focusing on those from pathogenic and commensal/probiotic most studied species.

Interactions between the gut microbiota-derived functional factors and intestinal epithelial cells - implication in the microbiota-host mutualism

Mutual interactions between the gut microbiota and the host play essential roles in maintaining human health and providing a nutrient-rich environment for the gut microbial community. Intestinal epithelial cells (IECs) provide the frontline responses to the gut microbiota for maintaining intestinal homeostasis. Emerging evidence points to commensal bacterium-derived components as functional factors for the action of commensal bacteria, including protecting intestinal integrity and mitigating susceptibility of intestinal inflammation. Furthermore, IECs have been found to communicate with the gut commensal bacteria to shape the composition and function of the microbial community. This review will discuss the current understanding of the beneficial effects of functional factors secreted by commensal bacteria on IECs, with focus on soluble proteins, metabolites, and surface layer components, and highlight the impact of IECs on the commensal microbial profile. This knowledge provides a proof-of-concept model for understanding of mechanisms underlying the microbiota-host mutualism.

Surface Layer Protein Pattern of Levilactobacillus brevis Strains Investigated by Proteomics

The outermost constituent of many bacterial cells is represented by an S-layer, i.e., a semiporous lattice-like layer composed of self-assembling protein subunits called S-layer proteins (Slps). These proteins are involved in several processes, such as protecting against environmental stresses, mediating bacterial adhesion to host cells, and modulating gut immune response. Slps may also act as a scaffold for the external display of additional cell surface proteins also named S-layer associated proteins (SLAPs). Levilactobacillus brevis is an S-layer forming lactic acid bacterium present in many different environments, such as sourdough, milk, cheese, and the intestinal tract of humans and animals. This microorganism exhibits probiotic features including the inhibition of bacterial infection and the improvement of human immune function. The potential role of Slps in its probiotic and biotechnological features was documented. A shotgun proteomic approach was applied to identify in a single experiment both the Slps and the SLAPs pattern of five different L. brevis strains isolated from traditional sourdoughs of the Southern Italian region. This study reveals that these closely related strains expressed a specific pattern of surface proteins, possibly affecting their peculiar properties.

Factors Affecting Spontaneous Endocytosis and Survival of Probiotic Lactobacilli in Human Intestinal Epithelial Cells

Mutualistic bacteria have different forms of interaction with the host. In contrast to the invasion of pathogenic bacteria, naturally occurring internalization of commensal bacteria has not been studied in depth. Three in vitro methods, gentamicin protection, flow cytometry and confocal laser scanning microscopy, have been implemented to accurately assess the internalization of two lactobacillus strains—Lacticaseibacillus paracasei BL23 and Lacticaseibacillus rhamnosus GG—in Caco-2 and T84 intestinal epithelial cells (IECs) under a variety of physiological conditions and with specific inhibitors. First and most interesting, internalization occurred at a variable rate that depends on the bacterial strain and IEC line, and the most efficient was BL23 internalization by T84 and, second, efficient internalization required active IEC proliferation, as it improved naturally at the early confluence stages and by stimulation with epidermal growth factor (EGF). IFN-γ is bound to innate immune responses and autolysis; this cytokine had a significant effect on internalization, as shown by flow cytometry, but increased internalization was not perceived in all conditions, possibly because it was also stimulating autolysis and, as a consequence, the viability of bacteria after uptake could be affected. Bacterial uptake required actin polymerization, as shown by cytochalasin D inhibition, and it was partially bound to clathrin and caveolin dependent endocytosis. It also showed partial inhibition by ML7 indicating the involvement of cholesterol lipid rafts and myosin light chain kinase (MLCK) activation, at least in the LGG uptake by Caco-2. Most interestingly, bacteria remained viable inside the IEC for as long as 72 h without damaging the epithelial cells, and paracellular transcytosis was observed. These results stressed the fact that internalization of commensal and mutualistic bacteria is a natural, nonpathogenic process that may be relevant in crosstalk processes between the intestinal populations and the host, and future studies could determine its connection to processes such as commensal tolerance, resilience of microbial populations or transorganic bacterial migration.

Bacillus amyloliquefaciens Enriched Camel Milk Attenuated Colitis Symptoms in Mice Model

Fermented camel’s milk has various health beneficial prebiotics and probiotics. This study aimed to evaluate the preventive efficacy of Bacillus amyloliquefaciens enriched camel milk (BEY) in 2-, 4- and 6-Trinitrobenzenesulfonic acid (TNBS)-induced colitis mice models. To this end, the immune modulatory effects of Bacillus amyloliquefaciens (BA) on TNF-α challenged HT29 colon cells were estimated using the cell proliferation and cytokines ELISA method. BEY was prepared using the incubation method and nutritional value was quantified by comparing it to commercial yogurt. Furthermore, TNBS-induced colitis was established and the level of disease index, pathological scores, and inflammatory markers of BEY-treated mice using macroscopic and microscopic examinations, qPCR and immunoblot were investigated. The results demonstrate that BA is non-toxic to HT29 colon cells and balanced the inflammatory cytokines. BEY reduced the colitis disease index, and improved the body weight and colon length of the TNBS-induced mice. Additionally, Myeloperoxidase (MPO) and pro-inflammatory cytokines (IL1β, IL6, IL8 and TNF-α) were attenuated by BEY treatment. Moreover, the inflammatory progress mRNA and protein markers nuclear factor kappa B (NFκB), phosphatase and tensin homolog (PTEN), proliferating cell nuclear antigen (PCNA), cyclooxygenase-2 (COX-2) and occludin were significantly down-regulated by BEY treatment. Interestingly, significant suppression of PCNA was observed in colonic tissues using the immunohistochemical examination. Treatment with BEY increased the epigenetic (microRNA217) interactions with PCNA. In conclusion, the BEY clearly alleviated the colitis symptoms and in the future could be used to formulate a probiotic-based diet for the host gut health and control the inflammatory bowel syndrome in mammals.

In Vitro Anti-Inflammatory Activity of Peptides Obtained by Tryptic Shaving of Surface Proteins of Streptococcus thermophilus LMD-9

Streptococcus thermophilus, a lactic acid bacterium widely used in the dairy industry, is consumed regularly by a significant proportion of the population. Some strains show in vitro anti-inflammatory activity which is not fully understood. We hypothesized that peptides released from the surface proteins of this bacterium during digestion could be implied in this activity. Consequently, we prepared a peptide hydrolysate by shaving and hydrolysis of surface proteins using trypsin, and the origin of peptides was checked by liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis. Most of the identified peptides originated from bacterial cell surface proteins. The anti-inflammatory activity of peptide hydrolysate was investigated under inflammatory conditions in two cell models. Peptide hydrolysate significantly decreased secretion of pro-inflammatory cytokine IL-8 in lipopolysaccharide (LPS)-stimulated human colon epithelial HT-29 cells. It also reduced the production of pro-inflammatory cytokines IL-8, IL-1β and the protein expression levels of Pro-IL-1β and COX-2 in LPS-stimulated THP-1 macrophages. The results showed that peptides released from bacterial surface proteins by a pancreatic protease could therefore participate in an anti-inflammatory activity of S. thermophilus LMD-9 and could prevent low-grade inflammation.

Gut health benefit and application of postbiotics in animal production

Gut homeostasis is of importance to host health and imbalance of the gut usually leads to disorders or diseases for both human and animal. Postbiotics have been applied in manipulating of gut health, and utilization of postbiotics threads new lights into the host health. Compared with the application of probiotics, the characteristics such as stability and safety of postbiotics make it a potential alternative to probiotics. Studies have reported the beneficial effects of components derived from postbiotics, mainly through the mechanisms including inhibition of pathogens, strengthen gut barrier, and/or regulation of immunity of the host. In this review, we summarized the characteristics of postbiotics, main compounds of postbiotics, potential mechanisms in gut health, and their application in animal production.

Discovery and delivery strategies for engineered live biotherapeutic products

Genetically engineered microbes that secrete therapeutics, sense and respond to external environments, and/or target specific sites in the gut fall under an emergent class of therapeutics, called live biotherapeutic products (LBPs). As live organisms that require symbiotic host interactions, LBPs offer unique therapeutic opportunities, but also face distinct challenges in the gut microenvironment. In this review, we describe recent approaches (often demonstrated using traditional probiotic microorganisms) to discover LBP chassis and genetic parts utilizing omics-based methods and highlight LBP delivery strategies, with a focus on addressing physiological challenges that LBPs encounter after oral administration. Finally, we share our perspective on the opportunity to apply an integrated approach, wherein discovery and delivery strategies are utilized synergistically, towards tailoring and optimizing LBP efficacy.

Organoid technologies for the study of intestinal microbiota–host interactions

Postbiotics have recently emerged as critical effectors of the activity of probiotics and, because of their safety profile, they are considered potential therapeutics for the treatment of fragile patients. Here, we present recent studies on probiotics and postbiotics in the context of novel discovery tools, such as organoids and organoid-based platforms, and nontransformed preclinical models, that can be generated from intestinal stem cells. The implementation of organoid-related techniques is the next gold standard for unraveling the effect of microbial communities on homeostasis, inflammation, idiopathic diseases, and cancer in the gut. We also summarize recent studies on biotics in organoid-based models and offer our perspective on future directions.

SlpB Protein Enhances the Probiotic Potential of L. lactis NCDO 2118 in Colitis Mice Model

Bacteria used in the production of fermented food products have been investigated for their potential role as modulators of inflammation in gastrointestinal tract disorders such as inflammatory bowel diseases (IBD) that cause irreversible changes in the structure and function of gut tissues. Ulcerative colitis (UC) is the most prevalent IBD in the population of Western countries, and it is marked by symptoms such as weight loss, rectal bleeding, diarrhea, shortening of the colon, and destruction of the epithelial layer. The strain Propionibacterium freudenreichii CIRM-BIA 129 recently revealed promising immunomodulatory properties that greatly rely on surface-layer proteins (Slp), notably SlpB. We, thus, cloned the sequence encoding the SlpB protein into the pXIES-SEC expression and secretion vector, and expressed the propionibacterial protein in the lactic acid bacterium Lactococcus lactis NCDO 2118. The probiotic potential of L. lactis NCDO 2118 harboring pXIES-SEC:slpB (L. lactis-SlpB) was evaluated in a UC-mice model induced by Dextran Sulfate Sodium (DSS). During colitis induction, mice receiving L. lactis-SlpB exhibited reduced severity of colitis, with lower weight loss, lower disease activity index, limited shortening of the colon length, and reduced histopathological score, with significant differences, compared with the DSS group and the group treated with L. lactis NCDO 2118 wild-type strain. Moreover, L. lactis-SlpB administration increased the expression of genes encoding tight junction proteins zo-1, cln-1, cln-5, ocln, and muc-2 in the colon, increased IL-10 and TGF-β, and decreased IL-17, TNF-α, and IL-12 cytokines in the colon. Therefore, this work demonstrates that SlpB recombinant protein is able to increase the probiotic potential of the L. lactis strain to alleviate DSS-induced colitis in mice. This opens perspectives for the development of new approaches to enhance the probiotic potential of strains by the addition of SlpB protein.

Lactobacillus johnsonii activates porcine monocyte derived dendritic cells maturation to modulate Th cellular immune response

Lactobacilli are abundant in the intestinal tract where they constantly regulate immune system via interacting with a great diversity of immune cells, such as dendritic cells (DCs). Notably, DCs are powerful antigen-presenting cells and they are capable of initiating primary immune responses. In this study, we studied the effects of Lactobacillus johnsonii (L. johnsonii) and Lactobacillus johnsonii cell-free supernatant (L. johnsonii-CFS) on the activation of porcine monocyte-derived dendritic cells (MoDCs) and their regulation of Th cellular immune responses in vitro. The MoDCs generated from porcine peripheral blood monocytes were stimulated by L. johnsonii and L. johnsonii-CFS, respectively. Pre-incubation with L. johnsonii increased expression of CD172a, CD80, major histocompatibility complex class II (MHCII) in MoDCs, and enhanced the ability of MoDCs to induce the proliferation of CD4⁺ T cell, while pre-incubation with L. johnsonii-CFS merely upregulated the expression of MHCII. Analysis of the cytokines showed that L. johnsonii stimulated up-regulation of Th1-type cytokines (IL-12p40, IFN-γ, TNF-α), pro-inflammatory cytokine IL-1β, chemokine CCL20, and Treg-type / anti-inflammatory cytokines IL-10 in MoDCs. Notably, a high production of IL-10 was observed in the MoDCs treated with L. johnsonii-CFS, indicating L. johnsonii-CFS exerted anti-inflammatory effects. Furthermore, L. johnsonii induced up-regulation of TLR2 and TLR6, but L. johnsonii-CFS not. Moreover, MoDCs stimulated by L. johnsonii mainly promoted T cell differentiate into Th1/Th2/Treg cells and plays an important role in improving the balance between Th1/Th2/Treg-type cells, whereas MoDCs stimulated by L. johnsonii-CFS mainly directed T cell to Th2/Treg subset polarization. In conclusion, L. johnsonii and L. johnsonii-CFS exhibited the ability of modulating innate immunity by regulating immunological functions of MoDCs in vitro, suggesting their potential ability to use as microecological preparations and medicines.

Extractable surface proteins of indigenous probiotic strains confer anti-adhesion knack and protect against methicillin-resistant Staphylococcus aureus induced epithelial hyperpermeability in HT-29 cell line

Probiotic intervention has been long believed to have beneficial effects on human health by curbing the intestinal colonization of pathogens. However, the application of live probiotics therapy may not be an ideal approach to circumvent the infections of superbug origin due to the risk of horizontal antibiotic resistance genes transfer. In this study, the anti-adhesion ability of extractable cell surface proteins from two indigenous potential probiotic strains (Lactiplantibacillus plantarum A5 and Limosilactobacillus fermentum Lf1) and two standard reference strains (Lactobacillus acidophilus NCFM and Lacticaseibacillus rhamnosus LGG) was evaluated against clinical isolates of Methicillin-Resistant Staphylococcus aureus (MRSA) on porcine gastric mucin and HT-29 cells. The surface proteins from the probiotic strains were extracted by treatment with 5 M lithium chloride. The surface protein quantification and SDS-PAGE profiling indicated that the yield and protein patterns were strain-specific. Surface proteins significantly hampered the mucoadhesion of MRSA isolates via protective, competitive, and displacement. Similarly, the treatment with surface proteins probiotic strains displayed anti-adhesion against MRSA isolates on HT-29 cells without affecting the viability of the cell line. Surface proteins treatment to the confluent monolayer of HT-29 cells maintained the epithelial integrity; however, MRSA isolates (10⁹ cells/mL) showed considerable alteration in the epithelial integrity by exacerbating the FITC-dextran transflux. Contrarily, the co-treatment with surface proteins with MRSA isolates significantly lowered the FITC-dextran transflux across the differentiated HT-29 monolayer. Overall, the findings of this study suggest that probiotic-derived surface proteins could be the novel biotherapeutics to combat the MRSA colonization and their concomitant intestinal infections.

Receptor-targeted engineered probiotics mitigate lethal Listeria infection

Probiotic bacteria reduce the intestinal colonization of pathogens. Yet, their use in preventing fatal infection caused by foodborne Listeria monocytogenes (Lm), is inconsistent. Here, we bioengineered Lactobacillus probiotics (BLP) to express the Listeria adhesion protein (LAP) from a non-pathogenic Listeria (L. innocua) and a pathogenic Listeria (Lm) on the surface of Lactobacillus casei. The BLP strains colonize the intestine, reduce Lm mucosal colonization and systemic dissemination, and protect mice from lethal infection. The BLP competitively excludes Lm by occupying the surface presented LAP receptor, heat shock protein 60 and ameliorates the Lm-induced intestinal barrier dysfunction by blocking the nuclear factor-κB and myosin light chain kinase-mediated redistribution of the major epithelial junctional proteins. Additionally, the BLP increases intestinal immunomodulatory functions by recruiting FOXP3+T cells, CD11c+ dendritic cells and natural killer cells. Engineering a probiotic strain with an adhesion protein from a non-pathogenic bacterium provides a new paradigm to exclude pathogens and amplify their inherent health benefits.

Differential Adaptation of Propionibacterium freudenreichii CIRM-BIA129 to Cow's Milk Versus Soymilk Environments Modulates Its Stress Tolerance and Proteome

Propionibacterium freudenreichii is a beneficial bacterium that modulates the gut microbiota, motility and inflammation. It is traditionally consumed within various fermented dairy products. Changes to consumer habits in the context of food transition are, however, driving the demand for non-dairy fermented foods, resulting in a considerable development of plant-based fermented products that require greater scientific knowledge. Fermented soymilks, in particular, offer an alternative source of live probiotics. While the adaptation of lactic acid bacteria (LAB) to such vegetable substrates is well documented, little is known about that of propionibacteria. We therefore investigated the adaptation of Propionibacterium freudenreichii to soymilk by comparison to cow's milk. P. freudenreichii grew in cow's milk but not in soymilk, but it did grow in soymilk when co-cultured with the lactic acid bacterium Lactobacillus plantarum. When grown in soymilk ultrafiltrate (SUF, the aqueous phase of soymilk), P. freudenreichii cells appeared thinner and rectangular-shaped, while they were thicker and more rounded in cow's milk utltrafiltrate (MUF, the aqueous phase of cow milk). The amount of extractable surface proteins (SlpA, SlpB, SlpD, SlpE) was furthermore reduced in SUF, when compared to MUF. This included the SlpB protein, previously shown to modulate adhesion and immunomodulation in P. freudenreichii. Tolerance toward an acid and toward a bile salts challenge were enhanced in SUF. By contrast, tolerance toward an oxidative and a thermal challenge were enhanced in MUF. A whole-cell proteomic approach further identified differential expression of 35 proteins involved in amino acid transport and metabolism (including amino acid dehydrogenase, amino acid transporter), 32 proteins involved in carbohydrate transport and metabolism (including glycosyltransferase, PTS), indicating metabolic adaptation to the substrate. The culture medium also modulated the amount of stress proteins involved in stress remediation: GroEL, OpuCA, CysK, DnaJ, GrpE, in line with the modulation of stress tolerance. Changing the fermented substrate may thus significantly affect the fermentative and probiotic properties of dairy propionibacteria. This needs to be considered when developing new fermented functional foods.

Lactobacillus Cell Surface Proteins Involved in Interaction with Mucus and Extracellular Matrix Components

The gut microbiota is a complex microbial ecosystem where bacteria, through mutual interactions, cooperate in maintaining of wellbeing and health. Lactobacilli are among the most important constituents of human and animal intestinal microbiota and include many probiotic strains. Their presence ensures protection from invasion of pathogens, as well as stimulation of the immune system and protection of the intestinal flora, often exerted through the ability to interact with mucus and extracellular matrix components. The main factors responsible for mediating adhesion of pathogens and commensals to the gut are cell surface proteins that recognize host targets, as mucus layer and extracellular matrix proteins. In the last years, several adhesins have been reported to be involved in lactobacilli–host interaction often miming the same mechanism used by pathogens.

Postbiotics against Pathogens Commonly Involved in Pediatric Infectious Diseases

The Sustainable Development goals for 2020 included reducing all causes associated with infant and perinatal mortality in their priorities. The use of compounds with bioactive properties has been proposed as a therapeutic strategy due to their stimulating effect on the host's immune system. Additionally, biotherapeutic products such as postbiotics, tentatively defined as compounds produced during a fermentation process that support health and well-being, promote intestinal barrier integrity without posing considerable risks to children's health. Although this is a concept in development, there are increasing studies in the field of nutrition, chemistry, and health that aim to understand how postbiotics can help prevent different types of infections in priority populations such as minors under the age of five. The present review aims to describe the main mechanisms of action of postbiotics. In addition, it presents the available current evidence regarding the effects of postbiotics against pathogens commonly involved in pediatric infections. Postbiotics may constitute a safe alternative capable of modulating the cellular response and stimulating the host's humoral response.

Cell adherence efficacy of probiotic Pediococcus pentosaceus GS4 (MTCC 12683) and demonstrable role of its surface layer protein (Slp)

The current study examined the cell adherence property of probiotic Pediococcus pentosaceus GS4 (MTCC12683) with the characterization and functionality in adherence of its surface layer protein (GS4-Slp). The Slp of P. pentosaceus GS4 was extracted purified and detected using SDS-PAGE (98 kDa) and size exclusion chromatography. The cell adherence property of probiotic GS4 (Slp⁺/Slp^-) was evaluated on buccal cells and HCT-116. Purified Slp was found neutralized with raised anti-Slp showing reduced adherence to HCT-116 as evident from SEM analysis. The structure of GS4-Slp was determined by MALDI-TOF analysis, CD analysis, atomic force microscopy (AFM), and FT-IR spectrometry. In Silico approach revealed its indirect similarity with cell membrane protein of Helicobacter pylori. Results thus reveal that GS4 has the potential of the production of 98 kDa Slp which facilitates the cell adherence property. This added probiotic attribute will enhance the probiotic potentials of P. pentosaceus GS4 to use it biotechnologically. SIGNIFICANCE: Probiotic Pediococcus pentosaceus GS4 facilitates demonstrable colonization by the elaboration of Slp. This property imparts a value to the strain and claims to be more useful biotechnologically.

Regulating colonic dendritic cells by commensal glycosylated large surface layer protein A to sustain gut homeostasis against pathogenic inflammation

Microbial interaction with the host through sensing receptors, including SIGNR1, sustains intestinal homeostasis against pathogenic inflammation. The newly discovered commensal Propionibacterium strain, P. UF1, regulates the intestinal immunity against pathogen challenge. However, the molecular events driving intestinal phagocytic cell response, including colonic dendritic cells (DCs), by this bacterium are still elusive. Here, we demonstrate that the glycosylation of bacterial large surface layer protein A (LspA) by protein O-mannosyltransferase 1 (Pmt1) regulates the interaction with SIGNR1, resulting in the control of DC transcriptomic and metabolomic machineries. Programmed DCs promote protective T cell response to intestinal Listeria infection and resist chemically induced colitis in mice. Thus, our findings may highlight a novel molecular mechanism by which commensal surface glycosylation interacting with SIGNR1 directs the intestinal homeostasis to potentially protect the host against proinflammatory signals inducing colonic tissue damage.

Probiotic Propionibacterium freudenreichii requires SlpB protein to mitigate mucositis induced by chemotherapy

Propionibacterium freudenreichii CIRM-BIA 129 (P. freudenreichii wild type, WT) is a probiotic bacterium, which exerts immunomodulatory effects. This strain possesses extractable surface proteins, including SlpB, which are involved in anti-inflammatory effect and in adhesion to epithelial cells. We decided to investigate the impact of slpB gene mutation on immunomodulation in vitro and in vivo. In an in vitro assay, P. freudenreichii WT reduced expression of IL-8 (p<0.0001) and TNF-α (p<0.0001) cytokines in LPS-stimulated HT-29 cells. P. freudenreichii ΔslpB, lacking the SlpB protein, failed to do so. Subsequently, both strains were investigated in vivo in a 5-FU-induced mucositis mice model. Mucositis is a common side effect of cytotoxic chemotherapy with 5-FU, characterized by mucosal injury, inflammation, diarrhea, and weight loss. The WT strain prevented weight loss, reduced inflammation and consequently histopathological scores. Furthermore, it regulated key markers, including Claudin-1 (cld1, p<0.0005) and IL-17a (Il17a, p<0.0001) genes, as well as IL-12 (p<0.0001) and IL-1β (p<0.0429) cytokines levels. Mutant strain displayed opposite regulatory effect on cld1 expression and on IL-12 levels. This work emphasizes the importance of SlpB in P. freudenreichii ability to reduce mucositis inflammation. It opens perspectives for the development of probiotic products to decrease side effects of chemotherapy using GRAS bacteria with immunomodulatory surface protein properties.

Exploring lectin-like activity of the S-layer protein of Lactobacillus acidophilus ATCC 4356

The surface layer (S-layer) protein of Lactobacillus acidophilus is a crystalline array of self-assembling, proteinaceous subunits non-covalently bound to the outmost bacterial cell wall envelope and is involved in the adherence of bacteria to host cells. We have previously described that the S-layer protein of L. acidophilus possesses anti-viral and anti-bacterial properties. In this work, we extracted and purified S-layer proteins from L. acidophilus ATCC 4356 cells to study their interaction with cell wall components from prokaryotic (i.e., peptidoglycan and lipoteichoic acids) and eukaryotic origin (i.e., mucin and chitin), as well as with viruses, bacteria, yeast, and blood cells. Using chimeric S-layer fused to green fluorescent protein (GFP) from different parts of the protein, we analyzed their binding capacity. Our results show that the C-terminal part of the S-layer protein presents lectin-like activity, interacting with different glycoepitopes. We further demonstrate that lipoteichoic acid (LTA) serves as an anchor for the S-layer protein. Finally, a structure for the C-terminal part of S-layer and possible binding sites were predicted by a homology-based model.

Proteomics for the Investigation of Surface-Exposed Proteins in Probiotics

Probiotics are commensal microorganisms that are present in the intestinal tract and in many fermented foods and positively affect human health, promoting digestion and uptake of dietary nutrients, strengthening intestinal barrier function, modulating immune response, and enhancing antagonism toward pathogens. The proteosurfaceome, i.e., the complex set of proteins present on the bacterial surface, is directly involved as leading actor in the dynamic communication between bacteria and host. In the last decade, the biological relevance of surface-exposed proteins prompted research activities exploiting the potentiality of proteomics to define the complex network of proteins that are involved in the molecular mechanisms at the basis of the adaptation to gastrointestinal environment and the probiotic effects. These studies also took advantages of the recent technological improvements in proteomics, mass spectrometry and bioinformatics that triggered the development of ad hoc designed innovative strategies to characterize the bacterial proteosurfaceome. This mini-review is aimed at describing the key role of proteomics in depicting the cell wall protein architecture and the involvement of surface-exposed proteins in the intimate and dynamic molecular dialogue between probiotics and intestinal epithelial and immune cells.

Review: Adaptation of Beneficial Propionibacteria, Lactobacilli, and Bifidobacteria Improves Tolerance Toward Technological and Digestive Stresses

This review deals with beneficial bacteria, with a focus on lactobacilli, propionibacteria, and bifidobacteria. As being recognized as beneficial bacteria, they are consumed as probiotics in various food products. Some may also be used as starters in food fermentation. In either case, these bacteria may be exposed to various environmental stresses during industrial production steps, including drying and storage, and during the digestion process. In accordance with their adaptation to harsh environmental conditions, they possess adaptation mechanisms, which can be induced by pretreatments. Adaptive mechanisms include accumulation of compatible solutes and of energy storage compounds, which can be largely modulated by the culture conditions. They also include the regulation of energy production pathways, as well as the modulation of the cell envelop, i.e., membrane, cell wall, surface layers, and exopolysaccharides. They finally lead to the overexpression of molecular chaperones and of stress-responsive proteases. Triggering these adaptive mechanisms can improve the resistance of beneficial bacteria toward technological and digestive stresses. This opens new perspectives for the improvement of industrial processes efficiency with regard to the survival of beneficial bacteria. However, this bibliographical survey evidenced that adaptive responses are strain-dependent, so that growth and adaptation should be optimized case-by-case.

Lactobacillus casei expressing Internalins A and B reduces Listeria monocytogenes interaction with Caco-2 cells in vitro

Listeria monocytogenes has been implicated in a number of outbreaks including the recent largest outbreak in South Africa. Current methods for prevention of foodborne L. monocytogenes infection are inadequate, thus raising a need for an alternative strategy. Probiotic bioengineering is considered a prevailing approach to enhance the efficacy of probiotics for targeted control of pathogens. Here, the ability of Lactobacillus casei expressing the L. monocytogenes invasion proteins Internalins A and B (inlAB) to prevent infection was investigated. The inlAB operon was cloned and surface‐expressed on L. casei resulting in a recombinant strain, Lbc^InlAB, and subsequently, its ability to inhibit adhesion, invasion and translocation of L. monocytogenes through enterocyte‐like Caco‐2 cells was examined. Cell surface expression of InlAB on the Lbc^InlAB was confirmed by Western blotting and immunofluorescence staining. The Lbc^InlAB strain showed significantly higher (P < 0.0001) adherence, invasion and translocation of Caco‐2 cells than the wild‐type L. casei strain (Lbc^WT), as well as reduced L. monocytogenes adhesion, invasion and transcellular passage through the cell monolayer than Lbc^WT. Furthermore, pre‐exposure of Caco‐2 cells to Lbc^InlAB significantly reduced L. monocytogenes‐induced cell cytotoxicity and epithelial barrier dysfunction. These results suggest that InlAB‐expressing L. casei could be a potential practical approach for prevention of listeriosis.

The Cheese Matrix Modulates the Immunomodulatory Properties of Propionibacterium freudenreichii CIRM-BIA 129 in Healthy Piglets

Propionibacterium freudenreichii is a beneficial bacterium, used as a cheese starter, which presents versatile probiotic properties. These properties are strain-dependent. We hypothesized they may also be delivery vehicle-dependent. In this study, we thus explored in healthy piglets how the cheese matrix affects the immunomodulatory properties of P. freudenreichii. During 2 weeks, three groups of weaned piglets consumed, respectively, P. freudenreichii as a liquid culture (PF-culture), P. freudenreichii under the form of a cheese (PF-cheese), or a control sterile cheese matrix (Cheese-matrix). The in vivo metabolic activity of P. freudenreichii was assessed by determining short chain fatty acids (SCFA) concentration and bifidobacteria population in feces. Whatever the delivery vehicle, P. freudenreichii was metabolically active in piglets' colon and enhanced both bifidobacteria and SCFA in feces. P. freudenreichii consumption decreased the secretion of TNFα and of IL-10 by peripheral blood mononuclear cells (PBMC). It did not alter IL-10, IFNγ, IL-17, and TNFα secretion in mesenteric lymph node immune cells (MLNC). PF-cheese enhanced significantly Treg phenotype, while PF-culture decreased significantly Th17 phenotype in PBMC and MLNC. Remarkably, only PF-cheese induced an increase of Th2 phenotype in PBMC and MLNC. Ex vivo stimulation of PBMC and MLNC by Lipopolysaccharides and Concanavalin A emphasized the difference in the immunomodulatory responses between PF-culture and PF-cheese group, as well as between PBMC and MLNC. This study shows the importance to consider the delivery vehicle for probiotic administration. It confirms the anti-inflammatory potential of P. freudenreichii. It opens new perspectives for the use propionibacteria-fermented products as preventive agents for inflammatory bowel diseases and intestinal infectious diseases.

Mutation of the Surface Layer Protein SlpB Has Pleiotropic Effects in the Probiotic Propionibacterium freudenreichii CIRM-BIA 129

Propionibacterium freudenreichii is a beneficial Gram-positive bacterium, traditionally used as a cheese-ripening starter, and currently considered as an emerging probiotic. As an example, the P. freudenreichii CIRM-BIA 129 strain recently revealed promising immunomodulatory properties. Its consumption accordingly exerts healing effects in different animal models of colitis, suggesting a potent role in the context of inflammatory bowel diseases. This anti-inflammatory effect depends on surface layer proteins (SLPs). SLPs may be involved in key functions in probiotics, such as persistence within the gut, adhesion to host cells and mucus, or immunomodulation. Several SLPs coexist in P. freudenreichii CIRM-BIA 129 and mediate immunomodulation and adhesion. A mutant P. freudenreichii CIRM-BIA 129ΔslpB (CB129ΔslpB) strain was shown to exhibit decreased adhesion to intestinal epithelial cells. In the present study, we thoroughly analyzed the impact of this mutation on cellular properties. Firstly, we investigated alterations of surface properties in CB129ΔslpB. Surface extractable proteins, surface charges (ζ-potential) and surface hydrophobicity were affected by the mutation. Whole-cell proteomics, using high definition mass spectrometry, identified 1,288 quantifiable proteins in the wild-type strain, i.e., 53% of the theoretical proteome predicted according to P. freudenreichii CIRM-BIA 129 genome sequence. In the mutant strain, we detected 1,252 proteins, including 1,227 proteins in common with the wild-type strain. Comparative quantitative analysis revealed 97 proteins with significant differences between wild-type and mutant strains. These proteins are involved in various cellular process like signaling, metabolism, and DNA repair and replication. Finally, in silico analysis predicted that slpB gene is not part of an operon, thus not affecting the downstream genes after gene knockout. This study, in accordance with the various roles attributed in the literature to SLPs, revealed a pleiotropic effect of a single slpB mutation, in the probiotic P. freudenreichii. This suggests that SlpB may be at a central node of cellular processes and confirms that both nature and amount of SLPs, which are highly variable within the P. freudenreichii species, determine the probiotic abilities of strains.