The effect of moonlighting proteins on the adhesion and aggregation ability of Lactobacillus helveticus

Characterization and Assessment of Native Lactic Acid Bacteria from Broiler Intestines for Potential Probiotic Properties

Probiotics are the most promising alternative to antibiotics for improving animal production and controlling pathogenic infections, while strains derived from natural hosts are considered highly desirable due to their good adaptation to the gastrointestinal tract. The aim of this study was to screen Lactobacillus with broad-spectrum antibacterial activity from broilers fed an antibiotic-free diet and evaluate their potential as poultry probiotics. A total of 44 lactic acid bacteria (LAB) strains were isolated from the intestines of healthy broilers, among which 3 strains exhibited outstanding antimicrobial activity and were subsequently identified through 16S rRNA sequencing as Enterococcus faecium L8, Lactiplantibacillus plantarum L10, and Limosilactobacillus reuteri H11. These three isolates demonstrated potent bacteriostatic activity against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella cholerae, with inhibition zones ranging from 15.67 ± 1.53 to 21.33 ± 0.58 mm. The selected LAB strains exhibited high tolerance to acid and bile salts, with L. reuteri H11 displaying the highest survival rate (ranging from 34.68% to 110.28%) after exposure to 0.3% (w/v) bile salts for 6 h or a low pH environment (pH 2, 2.5, and 3) for 3 h. Notably, L. reuteri H11 outperformed other strains in terms of hydrophobicity (84.31%), auto-aggregation (53.12%), and co-aggregation with E. coli ATCC 25922 (36.81%) and S. aureus ATCC 6538 (40.20%). In addition, the three LAB isolates were either fully or moderately susceptible to the tested antibiotics, except for strain L8, which resisted gentamycin and vancomycin. Consequently, these three LAB strains, especially L. reuteri H11, isolated from the intestines of broiler chickens, represent promising probiotic candidates that can be employed as feed additives to enhance production performance and control poultry pathogens.

Host-microbe interaction and pathogen exclusion mediated by an aggregation-prone surface layer protein of Lactobacillus helveticus

Probiotic surface layer proteins (Slps) have multiple functions and bacterial adhesion to host cells is one of them. The precise role of Slps in cellular adhesion is not well understood due to its low native protein yield and self-aggregative nature. Here, we report the recombinant expression and purification of biologically active Slp of Lactobacillus helveticus NCDC 288 (SlpH) in high yield. SlpH is a highly basic protein (pI = 9.4), having a molecular weight of 45 kDa. Circular Dichroism showed a prevalence of beta-strands in SlpH structure and resistance to low pH. SlpH showed binding to human intestinal tissue, enteric Caco-2 cell line, and porcine gastric mucin, but not with fibronectin, collagen type IV and laminin. SlpH inhibited the binding of the enterotoxigenic E. coli by 70 % and 76 % and that of Salmonella Typhimurium SL1344 by 71 % and 75 % to enteric Caco-2 cell line in the exclusion and competition assays, respectively. The pathogen exclusion and competition activity and tolerance to harsh gastrointestinal conditions show the potential for developing SlpH as a prophylactic or therapeutic agent against enteric pathogens.

Lactobacilli extracellular vesicles: potential postbiotics to support the vaginal microbiota homeostasis

Background

Lactobacillus species dominate the vaginal microflora performing a first-line defense against vaginal infections. Extracellular vesicles (EVs) released by lactobacilli are considered mediators of their beneficial effects affecting cellular communication, homeostasis, microbial balance, and host immune system pathways. Up to now, very little is known about the role played by Lactobacillus EVs in the vaginal microenvironment, and mechanisms of action remain poorly understood.

Results

Here, we hypothesized that EVs can mediate lactobacilli beneficial effects to the host by modulating the vaginal microbiota colonization. We recovered and characterized EVs produced by two vaginal strains, namely Lactobacillus crispatus BC5 and Lactobacillus gasseri BC12. EVs were isolated by ultracentrifugation and physically characterized by Nanoparticle Tracking Analysis (NTA) and Dynamic Light Scattering (DLS). EVs protein and nucleic acids (DNA and RNA) content was also evaluated. We explored the role of EVs on bacterial adhesion and colonization, using a cervical cell line (HeLa) as an in vitro model. Specifically, we evaluated the effect of EVs on the adhesion of both vaginal beneficial lactobacilli and opportunistic pathogens (i.e., Escherichia coli, Staphylococcus aureus, Streptococcus agalactiae, and Enterococcus faecalis). We demonstrated that EVs from L. crispatus BC5 and L. gasseri BC12 significantly enhanced the cellular adhesion of all tested lactobacilli, reaching the maximum stimulation effect on strains belonging to L. crispatus species (335% and 269% of average adhesion, respectively). At the same time, EVs reduced the adhesion of all tested pathogens, being EVs from L. gasseri BC12 the most efficient.

Conclusions

Our observations suggest for the first time that EVs released by symbiotic Lactobacillus strains favor healthy vaginal homeostasis by supporting the colonization of beneficial species and preventing pathogens attachment. This study reinforces the concept of EVs as valid postbiotics and opens the perspective of developing postbiotics from vaginal strains to maintain microbiota homeostasis and promote women’s health.

Complete Genome Sequence of Lactobacillus salivarius AR809, a Probiotic Strain with Oropharyngeal Tract Resistance and Adhesion to the Oral Epithelial Cells

Lactobacillus salivarius AR809 was isolated from a healthy adult oral cavity with multiple probiotic properties, such as high antimicrobial activity, adhesion to the oral epithelium, resistance to acidic pH, bile, lysozyme, and H₂O₂. In this study, to investigate the genetic basis on probiotic potential and identify the functional genes in the strain, the complete genome of strain AR809 was sequenced by Illumina and PacBio platforms. Then comparative genome analysis on 11 strains of Lactobacillus salivarius was performed. The complete genome of AR809 consisted of a circular 1,747,224 bp chromosome with 33.00% GC content and four circular plasmids [pA (247,948 bp), pB (27,292 bp), pC (3349 bp), and pD (2898 bp), respectively]. From among the 1866 protein-coding genes, 130 carbohydrate metabolism-related genes, 18 bacteriocin biosynthesis-related genes, 74 environmental stress-related genes, and a series of adhesion-related genes were identified via clusters of orthologous genes, Koyto Encyclopedia of Genes and Genomes, and carbohydrate-active enzymes annotation. The comparative genome analysis indicated that genomic homology between AR809 and CICC23174 was the highest. In conclusion, the present work provided valuable insights into the gene's function prediction and understanding the genetic basis on adapting to host oropharyngeal-gastrointestinal tract in strain AR809.

Mechanism of gastrointestinal adaptability and antioxidant function of infant-derived Lactobacillus plantarum BF_15 through genomics

Lactobacillus plantarum is an essential probiotic in the human gastrointestinal tract. L. plantarum BF_15, a functional probiotic isolated from the feces of breast-fed infants, has been reported in many in vitro and in vivo studies with strong gastrointestinal adaptability and outstanding anti-oxidative activities. Therefore, the whole genome of L. plantarum BF_15 was sequenced. Several genes, encoding the gastrointestinal adaptability-related proteins, were identified, including genes related to gastrointestinal environment-induced stress resistance, adhesive performance, and ability to transport and metabolize resistant starch and oligosaccharides. Genes related to alleviating oxidative stress were also found. Further functional verification was carried out by RT-qPCR on the 10 and 12 key adhesion and antioxidant genes. Overall, this study might provide a critical basis for L. plantarum BF_15 as a potential candidate for probiotics.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01132-w.

Genomic Insight Into Lacticaseibacillus paracasei SP5, Reveals Genes and Gene Clusters of Probiotic Interest and Biotechnological Potential

The Lacticaseibacillus paracasei species is comprised by nomadic bacteria inhabiting a wide variety of ecological niches, from fermented foodstuffs to host-associated microenvironments. Lc. paracasei SP5 is a novel strain, originally isolated from kefir grains that presents desirable probiotic and biotechnological attributes. In this study, we applied genomic tools to further characterize the probiotic and biotechnological potential of the strain. Firstly, whole genome sequencing and assembly, were performed to construct the chromosome map of the strain and determine its genomic stability. Lc. paracasei SP5 carriers several insertion sequences, however, no plasmids or mobile elements were detected. Furthermore, phylogenomic and comparative genomic analyses were utilized to study the nomadic attributes of the strain, and more specifically, its metabolic capacity and ability to withstand environmental stresses imposed during food processing and passage through the gastrointestinal (GI) tract. More specifically, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Carbohydrate-active enzyme (CAZymes) analyses provided evidence for the ability of the stain to utilize an array of carbohydrates as growth substrates. Consequently, genes for heat, cold, osmotic shock, acidic pH, and bile salt tolerance were annotated. Importantly bioinformatic analysis showed that the novel strain does not harbor acquired antimicrobial resistance genes nor virulence factors, in agreement with previous experimental data. Putative bacteriocin biosynthesis clusters were identified using BAGEL4, suggesting its potential antimicrobial activity. Concerning microbe-host interactions, adhesins, moonlighting proteins, exopolysaccharide (EPS) biosynthesis genes and pilins mediating the adhesive phenotype were, also, pinpointed in the genome of Lc. paracasei SP5. Validation of this phenotype was performed by employing a microbiological method and confocal microscopy. Conclusively, Lc. paracasei SP5 harbors genes necessary for the manifestation of the probiotic character and application in the food industry. Upcoming studies will focus on the mechanisms of action of the novel strain at multiple levels.

Production and in vitro evaluation of prebiotic manno-oligosaccharides prepared with a recombinant Aspergillus niger endo-mannanase, Man26A

In this study, a GH26 endo-mannanase (Man26A) from an Aspergillus niger ATCC 10864 strain, with a molecular mass of 47.8 kDa, was cloned in a yBBH1 vector and expressed in Saccharomyces cerevisiae Y294 strain cells. Upon fractionation by ultra-filtration, the substrate specificity and substrate degradation pattern of the endo-mannanase (Man26A) were investigated using ivory nut linear mannan and two galactomannan substrates with varying amounts of galactosyl substitutions, guar gum and locust bean gum. Man26A exhibited substrate specificity in the order: locust bean gum ≥ ivory nut mannan > guar gum; however, the enzyme generated more manno-oligosaccharides (MOS) from the galactomannans than from linear mannan during extended periods of mannan hydrolysis. MOS with a DP of 2-4 were the major products from mannan substrate hydrolysis, while guar gum also generated higher DP length MOS. All the Man26A generated MOS significantly improved the growth (approximately 3-fold) of the probiotic bacterial strains Streptococcus thermophilus and Bacillus subtilis in M9 minimal medium. Ivory nut mannan and locust bean gum derived MOS did not influence the auto-aggregation ability of the bacteria, while the guar gum derived MOS led to a 50 % reduction in bacterial auto-aggregation. On the other hand, all the MOS significantly improved bacterial biofilm formation (approximately 3-fold). This study suggests that the prebiotic characteristics exhibited by MOS may be dependent on their primary structure, i.e. galactose substitution and DP. Furthermore, the data suggests that the enzyme-generated MOS may be useful as potent additives to dietary foods.

Adhesion Characteristics and Dual Transcriptomic and Proteomic Analysis of Lactobacillus reuteri SH23 upon Gastrointestinal Fluid Stress

The ability to survive in the harsh gastrointestinal tract (GIT) environment is essential for Lactobacillus reuteri (L. reuteri) exhibiting beneficial effects. In this study, we found that the hydrophobicity and auto-aggregation of L. reuteri SH23 were significantly decreased and biofilm production was also significantly decreased when L. reuteri SH23 passes through the simulated GIT. Furthermore, according to the comparative transcriptome analysis, gene expression involved in the cell envelope, metabolic processes, common stress response, regulatory systems, and transporters were also affected. Meanwhile, label-free quantitative proteomics was used to identify the differential expression of surface proteins of L. reuteri in response to simulated gastrointestinal fluid. Proteins related to the ABC transporters (Lreu_0517, Lreu_0098, and Lreu_0296) and LPxTG anchor domain proteins were upregulated in the cell surface after gastrointestinal fluid treatment, which is useful for adherence and colonization of L. reuteri in the GIT. Additionally, the recombinant Mub protein could also enhance the survival ability of L. reuteri SH23 in GIT stress environment. This study provides a comprehensive understanding of the adaptation and adhesion mechanisms of L. reuteri SH23 under the gastrointestinal tract by the transcriptomics and proteomics analysis, and mucus-binding proteins were involved in the adhesion and GIT tolerance process.

Antipathogenic and probiotic potential of Lactobacillus brevis strains newly isolated from Algerian artisanal cheeses

From 98 Lactobacillus strains, isolated from Algerian homemade cheeses, 14 (B1-B14) were selected based on their anti-Escherichia coli and anti-Staphylococcus aureus activities. These strains were also tested towards Listeria monocytogenes 161 and Salmonella Typhimurium LT2 and further investigated for their resistance to simulated gastrointestinal digestion, cell surface properties, ability to adhere to HT-29 cells, cholesterol lowering, antioxidant activity, and technological traits. Five isolates (B9, B13, B18, B19, and B38) were active against L. monocytogenes and Salmonella. From them, three isolates, identified as Lactobacillus brevis (B9, B13, and B38) by MALDI-TOF spectrometry and 16S rDNA sequencing, exhibited high tolerance to pancreatic juice, bile salts and acidic juices, high percentages of hydrophobicity (87, 92, and 81%, respectively), auto-aggregation (61, 68, and 72%, respectively), and adherence to HT-29 cells (79, 84, and 74%, respectively), which testify on their potential of colonization of the human intestine. On the other way, the strains B9 and B13 manifested the most relevant antioxidant activity and cholesterol-lowering ability, respectively. L. brevis strains showed low acidifying and good proteolytic activities with noticeable heat tolerance. The results gathered in this study highlighted the richness of Algerian artisanal cheeses on new lactobacilli strains with an excellent probiotic potential and demonstrated that L. brevis, largely used as nonstarter in cheese manufacture, could be exploited also as a probiotic for human use.

The Russian Doll Model: How Bacteria Shape Successful and Sustainable Inter-Kingdom Relationships

Successful inter-kingdom relationships are based upon a dynamic balance between defense and cooperation. A certain degree of competition is necessary to guarantee life spread and development. On the other hand, cooperation is a powerful tool to ensure a long lasting adaptation to changing environmental conditions and to support evolution to a higher level of complexity. Bacteria can interact with their (true or potential) parasites (i.e., phages) and with their multicellular hosts. In these model interactions, bacteria learnt how to cope with their inner and outer host, transforming dangerous signals into opportunities and modulating responses in order to achieve an agreement that is beneficial for the overall participants, thus giving rise to a more complex "organism" or ecosystem. In this review, particular attention will be addressed to underline the minimal energy expenditure required for these successful interactions [e.g., moonlighting proteins, post-translational modifications (PTMs), and multitasking signals] and the systemic vision of these processes and ways of life in which the system proves to be more than the sum of the single components. Using an inside-out perspective, I will examine the possibility of multilevel interactions, in which viruses help bacteria to cope with the animal host and bacteria support the human immune system to counteract viral infection in a circular vision. In this sophisticated network, bacteria represent the precious link that insures system stability with relative low energy expenditure.

Paraprobiotics and Postbiotics of Probiotic Lactobacilli, Their Positive Effects on the Host and Action Mechanisms: A Review

Lactobacilli comprise an important group of probiotics for both human and animals. The emerging concern regarding safety problems associated with live microbial cells is enhancing the interest in using cell components and metabolites derived from probiotic strains. Here, we define cell structural components and metabolites of probiotic bacteria as paraprobiotics and postbiotics, respectively. Paraprobiotics and postbiotics produced from Lactobacilli consist of a wide range of molecules including peptidoglycans, surface proteins, cell wall polysaccharides, secreted proteins, bacteriocins, and organic acids, which mediate positive effect on the host, such as immunomodulatory, anti-tumor, antimicrobial, and barrier-preservation effects. In this review, we systematically summarize the paraprobiotics and postbiotics derived from Lactobacilli and their beneficial functions. We also discuss the mechanisms underlying their beneficial effects on the host, and their interaction with the host cells. This review may boost our understanding on the benefits and molecular mechanisms associated with paraprobiotics and probiotics from Lactobacilli, which may promote their applications in humans and animals.

Identification of the key physiological characteristics of Lactobacillus plantarum strains for ulcerative colitis alleviation

Lactobacillus plantarum is a probiotic that is widely used to prevent ulcerative colitis (UC). However, the effects of this species are strain-specific. We believe that the physiological characteristics of L. plantarum strains may affect their UC-alleviating function. Therefore, this study investigated the relationship between the alleviating effect of L. plantarum strains on UC and their physiological characteristics in vitro. The physiological characteristics of 14 L. plantarum strains were assayed in vitro, including gastrointestinal transit tolerance, oligosaccharide fermentation, HT-29 cell adhesion, generation time, exopolysaccharide production, acetic acid production, and conjugated linoleic acid (CLA) synthesis. To create animal models, colitis was established in C57BL/6 mice by adding 3.5% dextran sulfate sodium to drinking water for 7 days. L. plantarum strains with significantly different physiological characteristics were orally administered to the mice at a dose of 3 × 109 CFU. The results indicated that among the tested L. plantarum strains, L. plantarum N13 and L. plantarum CCFM8610 significantly alleviated colitis in the mice, as observed from the restoration of the body weight and disease activity index (DAI) score, recovery of the gut microbiota composition, reduced expression of pro-inflammatory cytokines, and significantly inhibited expression of p65. Correlation analysis indicated that four of the measured physiological characteristics (gastrointestinal transit tolerance, HT-29 cell adhesion, generation time, and CLA synthesis) were related to the UC-alleviating effects to different degrees. The strongest correlation was observed between the CLA synthesis ability and UC-alleviating effects (with Pearson correlation coefficients for IL-1β, IL-6, IL-17F, TNF-α, myeloperoxidase, and the DAI all below -0.95). The ability to synthesize CLA may be the key physiological characteristic of L. plantarum in UC alleviation. Our findings may contribute to the rapid screening of lactic acid bacterial strains with UC-alleviating effects.

Enterococcus faecium NCIMB10415 responds to norepinephrine by altering protein profiles and phenotypic characters

The long-term established symbiosis between gut microbiota and humans is based upon a dynamic equilibrium that, if unbalanced, could lead to the development of diseases. Despite the huge amount of data concerning the microbiota-gut-brain-axis, little information is available on what happens at the molecular level in bacteria, when exposed to human signals. In the present study, the physiological effects exerted by norepinephrine (NE), a human hormone present in significant amounts in the host gut, were analyzed using the commensal/probiotic strain Enterococcus faecium NCIMB10415 as a target. The aim was to compare the protein profiles of treated and untreated bacteria and relating these proteome patterns to some phenotypic modifications important for bacteria-host interaction. Actually, to date, only pathogens have been considered. Combining a gel-free/label-free proteomic analysis with the evaluation of bile salts resistance, biofilm formation and autoaggregation ability (as well as with the bacterial growth kinetics), allowed to detect changes induced by NE treatment on all the tested probiotic properties. Furthermore, exposure to the bioactive molecule increased the abundance of proteins related to stress response and to host-microbe interaction, such as moonlight proteins involved in adhesion and immune stimulation. The results of this investigation demonstrated that, not only pathogens, but also commensal gut bacteria are affected by host-derived hormones, underlining the importance of a correct cross-signalling in the maintenance of gut homeostasis. SIGNIFICANCE: The crucial role played by the human gut microbiota in ensuring host homeostasis and health is definitively ascertained as suggested by the holobiome concept. The present research was intended to shed light on the endocrinological perturbations possibly affecting microbiota. The microbial model used in this study belongs to Enterococcus faecium species, whose controversial role as gut commensal and opportunistic pathogen in the gut ecosystem is well recognized. The results obtained in the present investigation clearly demonstrate that E. faecium NCIMB10415 can sense and respond to norepinephrine, a human hormone abundant at the gut level, by changing protein profiles and physiology, inducing changes that could favor survival and colonization of the host tissues. To our knowledge, this is the first proteomic report concerning the impact of a human hormone on a commensal/probiotic bacterium, since previous research has focused on exploring the effects of neuroendocrine molecules on growth and virulence of pathogenic species.

Living the Sweet Life: How Liquorilactobacillus hordei TMW 1.1822 Changes Its Behavior in the Presence of Sucrose in Comparison to Glucose

Liquorilactobacillus (L.) hordei (formerly Lactobacillus hordei) is one of the dominating lactic acid bacteria within the water kefir consortium, being highly adapted to survive in this environment, while producing high molecular weight dextrans from sucrose. In this work, we extensively studied the physiological response of L. hordei TMW 1.1822 to sucrose compared to glucose, applying label-free, quantitative proteomics of cell lysates and exoproteomes. This revealed the differential expression of 53 proteins within cellular proteomes, mostly associated with carbohydrate uptake and metabolism. Supported by growth experiments, this suggests that L. hordei TMW 1.1822 favors fructose over other sugars. The dextransucrase was expressed irrespectively of the present carbon source, while it was significantly more released in the presence of sucrose (log₂FC = 3.09), being among the most abundant proteins within exoproteomes of sucrose-treated cells. Still, L. hordei TMW 1.1822 expressed other sucrose active enzymes, predictively competing with the dextransucrase reaction. While osmolysis appeared to be unlikely, sucrose led to increased release of a multitude of cytoplasmic proteins, suggesting that biofilm formation in L. hordei is not only composed of a polysaccharide matrix but is also of proteinaceous nature. Therefore, our study highlights the intrinsic adaptation of water kefir-borne L. hordei to sucrose-rich habitats and provides fundamental knowledge for its use as a starter culture in plant-based food fermentations with in situ dextran formation.

Binding activity to intestinal cells and transient colonization in mice of two Lactobacillus paracasei subsp. paracasei strains with high aggregation potential

Surface properties like hydrophobicity, aggregation ability, adhesion to mucosal surfaces and epithelial cells and transit time are key features for the characterization of probiotic strains. In this study, we used two Lactobacillus paracasei subsp. paracasei strains (BGNJ1-64 and BGSJ2-8) strains which were previously described with very strong aggregation capacity. The aggregation promoting factor (AggLb) expressed in these strains showed high level of binding to collagen and fibronectin, components of extracellular matrix. The working hypothesis was that strains able to aggregate have an advantage to resist in intestinal tract. So, we assessed whether these strains and their derivatives (without aggLb gene) are able to bind or not to intestinal components and we compared the transit time of each strains in mice. In that purpose parental strains (BGNJ1-64 and BGSJ2-8) and their aggregation negative derivatives (BGNJ1-641 and BGSJ2-83) were marked with double antibiotic resistance in order to be tracked in in vivo experiments in mice. Comparative analysis of binding ability of WT and aggregation negative strains to different human intestinal cell lines and mucin revealed no significant difference among them, excluding involvement of AggLb in interaction with surface of intestinal cells and mucin. In vivo experiments showed that surviving and transit time of marked strains in mice did not drastically depend on the presence of the AggLb aggregation factor.

Dietary Nutrients, Proteomes, and Adhesion of Probiotic Lactobacilli to Mucin and Host Epithelial Cells

The key role of diet and environment in human health receives increasing attention. Thus functional foods, probiotics, prebiotics, and synbiotics with beneficial effects on health and ability to prevent diseases are in focus. The efficacy of probiotic bacteria has been connected with their adherence to the host epithelium and residence in the gut. Several in vitro techniques are available for analyzing bacterial interactions with mucin and intestinal cells, simulating adhesion to the host in vivo. Proteomics has monitored and identified proteins of probiotic bacteria showing differential abundance elicited in vitro by exposure to food components, including potential prebiotics (e.g., certain carbohydrates, and plant polyphenols). While adhesion of probiotic bacteria influenced by various environmental factors relevant to the gastrointestinal tract has been measured previously, this was rarely correlated with changes in the bacterial proteome induced by dietary nutrients. The present mini-review deals with effects of selected emerging prebiotics, food components and ingredients on the adhesion of probiotic lactobacilli to mucin and gut epithelial cells and concomitant abundancy changes of specific bacterial proteins. Applying this in vitro synbiotics-like approach enabled identification of moonlighting and other surface-located proteins of Lactobacillus acidophilus NCFM that are possibly associated with the adhesive mechanism.

Extractable Bacterial Surface Proteins in Probiotic-Host Interaction

Some Gram-positive bacteria, including probiotic ones, are covered with an external proteinaceous layer called a surface-layer. Described as a paracrystalline layer and formed by the self-assembly of a surface-layer-protein (Slp), this optional structure is peculiar. The surface layer per se is conserved and encountered in many prokaryotes. However, the sequence of the corresponding Slp protein is highly variable among bacterial species, or even among strains of the same species. Other proteins, including surface layer associated proteins (SLAPs), and other non-covalently surface-bound proteins may also be extracted with this surface structure. They can be involved a various functions. In probiotic Gram-positives, they were shown by different authors and experimental approaches to play a role in key interactions with the host. Depending on the species, and sometime on the strain, they can be involved in stress tolerance, in survival within the host digestive tract, in adhesion to host cells or mucus, or in the modulation of intestinal inflammation. Future trends include the valorization of their properties in the formation of nanoparticles, coating and encapsulation, and in the development of new vaccines.

Biofilm formation and adhesion to bovine udder epithelium of potentially probiotic lactic acid bacteria

Mastitis is one of the most important diseases threatening modern dairy herds. The idea of fighting the disease through colonising the udder with lactic acid bacteria (LAB), thereby building a beneficial biofilm, is the base for a probiotic approach towards mastitis control. The purpose of this study was to screen 13 LAB strains (eleven wild strains, two ATCC strains) inhibitory to the growth of mastitis-causing pathogens for their in vitro ability to form a biofilm and to adhere to bovine glandular mammary epithelium in order to assess their probiotic potential. Furthermore, we aimed to gain knowledge about the chemical nature of the adhesins involved by subjecting the bacteria to various chemical and enzymatical pre-treatments. The biofilms were grown on hydrophilic glass and on hydrophobic polypropylene in de Man, Rogosa and Sharpe (MRS) broth and afterwards quantified with a crystal violet assay. Biofilm formation was observed in all strains. However, the extent strongly depended on the strain, surface charge and medium. The adhesion assay also revealed a strong strain dependency, but this trait was also present in all of the investigated LAB isolates. Depending on the strain, chemical or enzymatical pre-treatment revealed carbohydrate molecules as well as proteins and lipids to be crucial for the adhesion of LAB to epithelial cells. The seven strains showing the strongest biofilm formation and/or adhesion represent promising candidates for further investigation in order to develop a probiotic remedy for the treatment of mastitis. Still, their safety for consumers and patients as well as their capability to colonise the udder remain to be investigated in in vivo studies.

Exo- and surface proteomes of the probiotic bacterium Lactobacillus acidophilus NCFM

Lactobacillus acidophilus NCFM is a well-known probiotic bacterium extensively studied for its beneficial health effects. Exoproteome (proteins exported into culture medium) and surface proteome (proteins attached to S-layer) of this probiotic were identified by using 2DE followed by MALDI TOF MS to find proteins potentially involved in bacteria-host interactions. The exo- and surface proteomes included 43 and 39 different proteins from 72 and 49 successfully identified spots, respectively. Twenty-two proteins were shared between the two proteomes; both contained the major surface layer protein that participates in host interaction as well as several well-known and putative moonlighting proteins. The exoproteome contained nine classically-secreted (containing a signal sequence) and ten nonclassically-secreted proteins, while the surface proteome contained four classically-secreted and eight nonclassically secreted proteins. Identification of exo- and surface proteomes contributes describing potential protein-mediated probiotic-host interactions.

Complete genome sequence of bacteriocin-producing Lactobacillus plantarum KLDS1.0391, a probiotic strain with gastrointestinal tract resistance and adhesion to the intestinal epithelial cells

Lactobacillus plantarum KLDS1.0391 is a probiotic strain isolated from the traditional fermented dairy products and identified to produce bacteriocin against Gram-positive and Gram-negative bacteria. Previous studies showed that the strain has a high resistance to gastrointestinal stress and has a high adhesion ability to the intestinal epithelial cells (Caco-2). We reported the entire genome sequence of this strain, which contains a circular 2,886,607-bp chromosome and three circular plasmids. Genes, which are related to the biosynthesis of bacteriocins, the stress resistance to gastrointestinal tract environment and adhesive performance, were identified. Whole genome sequence of Lactobacillus plantarum KLDS1.0391 will be helpful for its applications in food industry.

Brucella central carbon metabolism: an update

The brucellae are facultative intracellular pathogens causing brucellosis, an important zoonosis. Here, we review the nutritional, genetic, proteomic and transcriptomic studies on Brucella carbon uptake and central metabolism, information that is needed for a better understanding of Brucella virulence. There is no uniform picture across species but the studies suggest primary and/or secondary transporters for unknown carbohydrates, lactate, glycerol phosphate, erythritol, xylose, ribose, glucose and glucose/galactose, and routes for their incorporation to central metabolism, including an erythritol pathway feeding the pentose phosphate cycle. Significantly, all brucellae lack phosphoenolpyruvate synthase and phosphofructokinase genes, which confirms previous evidence on glycolysis absence, but carry all Entner-Doudoroff (ED) pathway and Krebs cycle (and glyoxylate pathway) genes. However, glucose catabolism proceeds through the pentose phosphate cycle in the classical species, and the ED pathway operates in some rodent-associated brucellae, suggesting an ancestral character for this pathway in this group. Gluconeogenesis is functional but does not rely exclusively on classical fructose bisphosphatases. Evidence obtained using infection models is fragmentary but suggests the combined or sequential use of hexoses/pentoses, amino acids and gluconeogenic substrates. We also discuss the role of the phosphotransferase system, stringent reponse, quorum sensing, BvrR/S and sRNAs in metabolism control, an essential aspect of the life style of facultative intracellular parasites.

Functional proteomics within the genus Lactobacillus

Lactobacillus are mainly used for the manufacture of fermented dairy, sourdough, meat, and vegetable foods or used as probiotics. Under optimal processing conditions, Lactobacillus strains contribute to food functionality through their enzyme portfolio and the release of metabolites. An extensive genomic diversity analysis was conducted to elucidate the core features of the genus Lactobacillus, and to provide a better comprehension of niche adaptation of the strains. However, proteomics is an indispensable "omics" science to elucidate the proteome diversity, and the mechanisms of regulation and adaptation of Lactobacillus strains. This review focuses on the novel and comprehensive knowledge of functional proteomics and metaproteomics of Lactobacillus species. A large list of proteomic case studies of different Lactobacillus species is provided to illustrate the adaptability of the main metabolic pathways (e.g., carbohydrate transport and metabolism, pyruvate metabolism, proteolytic system, amino acid metabolism, and protein synthesis) to various life conditions. These investigations have highlighted that lactobacilli modulate the level of a complex panel of proteins to growth/survive in different ecological niches. In addition to the general regulation and stress response, specific metabolic pathways can be switched on and off, modifying the behavior of the strains.

Shortening of the Lactobacillus paracasei subsp. paracasei BGNJ1-64 AggLb Protein Switches Its Activity from Auto-aggregation to Biofilm Formation

AggLb is the largest (318.6 kDa) aggregation-promoting protein of Lactobacillus paracasei subsp. paracasei BGNJ1-64 responsible for forming large cell aggregates, which causes auto-aggregation, collagen binding and pathogen exclusion in vitro. It contains an N-terminus leader peptide, followed by six successive collagen binding domains, 20 successive repeats (CnaB-like domains) and an LPXTG sorting signal at the C-terminus for cell wall anchoring. Experimental information about the roles of the domains of AggLb is currently unknown. To define the domain that confers cell aggregation and the key domains for interactions of specific affinity between AggLb and components of the extracellular matrix, we constructed a series of variants of the aggLb gene and expressed them in Lactococcus lactis subsp. lactis BGKP1-20 using a lactococcal promoter. All of the variants contained a leader peptide, an inter collagen binding-CnaB domain region (used to raise an anti-AggLb antibody), an anchor domain and a different number of collagen binding and CnaB-like domains. The role of the collagen binding repeats of the N-terminus in auto-aggregation and binding to collagen and fibronectin was confirmed. Deletion of the collagen binding repeats II, III, and IV resulted in a loss of the strong auto-aggregation, collagen and fibronectin binding abilities whereas the biofilm formation capability was increased. The strong auto-aggregation, collagen and fibronectin binding abilities of AggLb were negatively correlated to biofilm formation.

Differential proteome and cellular adhesion analyses of the probiotic bacterium Lactobacillus acidophilus NCFM grown on raffinose - an emerging prebiotic

Whole cell and surface proteomes were analyzed together with adhesive properties of the probiotic bacterium Lactobacillus acidophilus NCFM (NCFM) grown on the emerging prebiotic raffinose, exemplifying a synbiotic. Adhesion of NCFM to mucin and intestinal HT-29 cells increased three-fold after culture with raffinose versus glucose, as also visualized by scanning electron microscopy. Comparative proteomics using 2D-DIGE showed 43 unique proteins to change in relative abundance in whole cell lysates from NCFM grown on raffinose compared to glucose. Furthermore, 14 unique proteins in 18 spots of the surface subproteome underwent changes identified by differential 2DE, including elongation factor G, thermostable pullulanase, and phosphate starvation inducible stress-related protein increasing in a range of +2.1 - +4.7 fold. By contrast five known moonlighting proteins decreased in relative abundance by up to -2.4 fold. Enzymes involved in raffinose catabolism were elevated in the whole cell proteome; α-galactosidase (+13.9 fold); sucrose phosphorylase (+5.4 fold) together with metabolic enzymes from the Leloir pathway for galactose utilization and the glycolysis; β-galactosidase (+5.7 fold); galactose (+2.9/+3.1 fold) and fructose (+2.8 fold) kinases. The insights at the molecular and cellular levels contributed to the understanding of the interplay of a synbiotic composed of NCFM and raffinose with the host.

AggLb Is the Largest Cell-Aggregation Factor from Lactobacillus paracasei Subsp. paracasei BGNJ1-64, Functions in Collagen Adhesion, and Pathogen Exclusion In Vitro

Eleven Lactobacillus strains with strong aggregation abilities were selected from a laboratory collection. In two of the strains, genes associated with aggregation capability were plasmid located and found to strongly correlate with collagen binding. The gene encoding the auto-aggregation-promoting protein (AggLb) of Lactobacillus paracasei subsp. paracasei BGNJ1-64 was cloned using a novel, wide-range-host shuttle cloning vector, pAZILSJ. The clone pALb35, containing a 11377-bp DNA fragment, was selected from the SacI plasmid library for its ability to provide carriers with the aggregation phenotype. The complete fragment was sequenced and four potential ORFs were detected, including the aggLb gene and three surrounding transposase genes. AggLb is the largest known cell-surface protein in lactobacilli, consisting of 2998 aa (318,611 Da). AggLb belongs to the collagen-binding superfamily and its C-terminal region contains 20 successive repeats that are identical even at the nucleotide level. Deletion of aggLb causes a loss of the capacity to form cell aggregates, whereas overexpression increases cellular aggregation, hydrophobicity and collagen-binding potential. PCR screening performed with three sets of primers based on the aggLb gene of BGNJ1-64 enabled detection of the same type of aggLb gene in five of eleven selected aggregation-positive Lactobacillus strains. Heterologous expression of aggLb confirmed the crucial role of the AggLb protein in cell aggregation and specific collagen binding, indicating that AggLb has a useful probiotic function in effective colonization of host tissue and prevention of pathogen colonization.