Characterization of a S-layer protein from Lactobacillus crispatus K313 and the domains responsible for binding to cell wall and adherence to collagen

Probiotics and Postbiotics as an Alternative to Antibiotics: An Emphasis on Pigs

Probiotics are being used as feed/food supplements as an alternative to antibiotics. It has been demonstrated that probiotics provide several health benefits, including preventing diarrhea, irritable bowel syndrome, and immunomodulation. Alongside probiotic bacteria-fermented foods, the different structural components, such as lipoteichoic acids, teichoic acids, peptidoglycans, and surface-layer proteins, offer several advantages. Probiotics can produce different antimicrobial components, enzymes, peptides, vitamins, and exopolysaccharides. Besides live probiotics, there has been growing interest in consuming inactivated probiotics in farm animals, including pigs. Several reports have shown that live and killed probiotics can boost immunity, modulate intestinal microbiota, improve feed efficiency and growth performance, and decrease the incidence of diarrhea, positioning them as an interesting strategy as a potential feed supplement for pigs. Therefore, effective selection and approach to the use of probiotics might provide essential features of using probiotics as an important functional feed for pigs. This review aimed to systematically investigate the potential effects of lactic acid bacteria in their live and inactivated forms on pigs.

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.

Potential oral probiotic Lactobacillus pentosus MJM60383 inhibits Streptococcus mutans biofilm formation by inhibiting sucrose decomposition

Streptococcus mutans is known as a contributor to dental caries. In this work, Lactobacillus pentosus MJM60383 was selected for its strong antagonistic activity against S. mutans and was characterized by good oral probiotic properties including lysozyme tolerance, adhesive ability to oral cells, good aggregation (auto-aggregation, co-aggregation) ability, hydrogen peroxide production and inhibition of biofilm formation of S. mutans. L. pentosus MJM60383 also exhibited safety as a probiotic characterized by no hemolytic activity, no D-lactate production, no biogenic amine production, and susceptibility to antibiotics. Furthermore, the biofilm formation of S. mutans was also significantly inhibited by the supernatant of L. pentosus MJM60383. An anti-biofilm mechanism study revealed that sucrose decomposition and the production of water-insoluble exopolysaccharides by S. mutans were inhibited by the treatment with L. pentosus MJM60383 supernatant. Real-time PCR analysis indicated that the supernatant of L. pentosus MJM60383 significantly inhibited the mRNA expression of S. mutans glycosyltransferases, which synthesize glucan to construct biofilm architecture and mediate bacterial adherence. Our study demonstrated L. pentosus MJM60383 as a potential oral probiotic and revealed its anti-biofilm mechanism.

Identification and Characterization of Domains Responsible for Cell Wall Binding, Self-Assembly, and Adhesion of S-layer Protein from Lactobacillus acidophilus CICC 6074

Lactobacillus S-layer protein (SLP) is a biologically active protein on the cell surface. To further elucidate the structures and functions of SLP in Lactobacillus acidophilus CICC 6074, this study was conducted to identify the functional domains of SLP which is responsible for cell wall anchoring, self-assembly, and adhesion. The gene (slpA) of L. acidophilus CICC 6074 SLP was amplified by polymerase chain reaction and speculated functional domains. Fusion proteins of C-terminal truncations from SLP were exogenously expressed in Escherichia coli BL21 (DE3). FITC-labeling N-terminal truncations of SLP were synthesized. The C-terminal domain was more likely to be the binding region, and the cell wall-anchored receptor of SLP was teichoic acid. Furthermore, N-terminal truncations could self-assemble to milk fat globule membrane polar lipid liposomes observed using a fluorescence microscope. Notably, SAN1 (region 32-55) of N-terminal truncations was mainly responsible for the adhesion of SLP to HT-29 cells. These results showed that SLP played a crucial role in the functions of L. acidophilus CICC 6074, which might be of significant reference value for future studies.

Lactobacillus, glycans and drivers of health in the vaginal microbiome

A microbiome consists of microbes and their genomes, encompassing bacteria, viruses, fungi, protozoa, archaea, and eukaryotes. These elements interact dynamically in the specific environment in which they reside and evolve. In the past decade, studies of various microbiomes have been prevalent in the scientific literature, accounting for the shift from culture-dependent to culture-independent identification of microbes using new high-throughput sequencing technologies that decipher their composition and sometimes provide insights into their functions. Despite tremendous advances in understanding the gut microbiome, relatively little attention has been devoted to the vaginal environment, notably regarding the ubiquity and diversity of glycans which denote the significant role they play in the maintenance of homeostasis. Hopefully, emerging technologies will aid in the determination of what is a healthy vaginal microbiome, and provide insights into the roles of Lactobacillus, glycans and microbiome-related drivers of health and disease.

Lactobacillus crispatus Strain KT-11 S-Layer Protein Inhibits Rotavirus Infection

S-layer proteins (SLPs), which are present in the external layer of certain strains of lactic acid bacteria isolated from the intestinal tract, are known to recognize and bind to specific proteins and glycan structures and contribute to adsorption to the host intestinal mucosa. The binding properties of certain SLPs are considered to exert a competitive inhibitory effect on infection because similar properties are involved in the infection mechanisms of several viruses. However, little is known regarding whether SLPs directly inhibit viral infection. In the present study, we investigated the effect of an SLP of the Lactobacillus crispatus KT-11 strain, a probiotic strain isolated from a healthy human infant, on human rotavirus infection. The impact of KT-11 lithium chloride extract (KT-11 LE), which contains SLP, on the infection of the P[4] genotype human rotavirus strain DS-1 was evaluated by monitoring the amplification of viral protein 6 (VP6) expression in human intestinal epithelial Caco-2 cells by quantitative reverse transcription-polymerase chain reaction assay after infection. KT-11 LE showed a significant suppressive effect on DS-1 infection in a dose-dependent manner with pre-infection treatment, whereas post-infection treatment was not effective. A 45 KDa protein isolated from KT-11 LE was investigated for homology using the BLAST database and was found to be a novel SLP. KT-11 SLP concentrate (KT-11 SLP) significantly inhibited the proliferative process of the DS-1 strain but not that of the P[8] genotype human rotavirus strain Wa. KT-11 SLP exerted significant inhibitory effect on DS-1 infection by pre-infection treatment even after digestion with gastric juice up to 2 h. Our results provided crucial evidence that SLPs from certain Lactobacillus strains can inhibit human rotavirus infection of intestinal epithelial cells.

Protective function of surface layer protein from Lactobacillus casei fb05 against intestinal pathogens in vitro

Escherichia coli and Salmonella are common pathogenic bacteria in human intestine, which can infect epithelial cells and cause diseases. Adhesion to intestinal tissue is the first step of pathogen infection. This work was to investigate the protective function of surface layer protein (SLP) from Lactobacillus casei fb05 against the harmful effects of E. coli and Salmonella on intestinal tissue (collagen and HT-29 cells). The SLP of L. casei fb05 was identified by transmission electron microscopy and SDS-PAGE. The purified SLP could reduce the adhesion of E. coli and Salmonella to collagen and HT-29 cells as observed by light microscope. The flow cytometry results showed that the L. casei fb05 SLP decreased the two pathogens-induced apoptosis of HT-29 cells by about 45%-49%. In addition, the activation of caspase-9 and caspase-3 caused by the two pathogens was significantly declined by the interference of the L. casei fb05 SLP. All the findings demonstrated that the L. casei fb05 SLP could decrease the deleterious effects of E. coli and Salmonella on intestinal tract in two ways: reducing pathogen adhesion and inhibiting pathogen-induced apoptosis. The potential of L. casei fb05 SLP in the treatment of intestinal diseases might be explored in this work.

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.

A surface-layer protein from Lactobacillus acidophilus NCFM induces autophagic death in HCT116 cells requiring ROS-mediated modulation of mTOR and JNK signaling pathways

A surface-layer protein (Slp) derived from Lactobacillus acidophilus NCFM has been reported to possess multiple biological properties, including anti-inflammatory, inhibition of apoptosis in pathogen-invaded HT-29 cells and oxidative stress relief. However, its anti-tumor ability and underlying molecular mechanism are unknown. Here, we report that Slp suppresses cell proliferation and induces autophagic cell death in HCT116 cells. Accumulation of Beclin-1 and microtubule-associated protein 1 light chain 3 from II (LC3-II), and the degradation of p62 were observed when cells were treated with various concentrations of Slp (25, 50, 100 μg mL-1) for 24 h. We also found that the mammalian targets of rapamycin (mTOR) and c-Jun N-terminal kinase (JNK) signaling pathways were crucial mediators regulating Slp-induced autophagic cell death. Additionally, treatment with Slp resulted in the obvious formation of reactive oxygen species (ROS). SP600125, a JNK inhibitor, and N-acetylcysteine (NAC), a ROS inhibitor, attenuated Slp-induced autophagic cell death in HCT116 cells. Furthermore, NAC was found to prevent Slp-induced p70 and JNK phosphorylation. Taken together, our results suggest a novel mechanism of action of Slp induced autophagy, acting simultaneously through the ROS-mediated mTOR and JNK signaling pathways in HCT116 colon cancer cells.

Surface Layer of Lactobacillus helveticus MIMLh5 Promotes Endocytosis by Dendritic Cells

Surface layers (S-layers) are proteinaceous arrays covering the cell walls of numerous bacteria. Their suggested properties, such as interactions with the host immune system, have been only poorly described. Here, we aimed to elucidate the role of the S-layer from the probiotic bacterial strain Lactobacillus helveticus MIMLh5 in the stimulation of murine bone-marrow-derived dendritic cells (DCs). MIMLh5 induced greater production of interferon beta (IFN-β), interleukin 10 (IL-10), and IL-12p70, compared to S-layer-depleted MIMLh5 (naked MIMLh5 [n-MIMLh5]), whereas the isolated S-layer was a poor immunostimulator. No differences in the production of tumor necrosis factor alpha (TNF-α) or IL-1β were found. Inhibition of the mitogen-activated protein kinases JNK1/2, p38, and ERK1/2 modified IL-12p70 production similarly in MIMLh5 and n-MIMLh5, suggesting the induction of the same signaling pathways by the two bacterial preparations. Treatment of DCs with cytochalasin D to inhibit endocytosis before the addition of fluorescently labeled MIMLh5 cells led to a dramatic reduction in the proportion of fluorescence-positive DCs and decreased IL-12 production. Endocytosis and IL-12 production were only marginally affected by cytochalasin D pretreatment when fluorescently labeled n-MIMLh5 was used. Treatment of DCs with fluorescently labeled S-layer-coated polystyrene beads (Sl-beads) resulted in much greater uptake of beads, compared to noncoated beads. Prestimulation of DCs with cytochalasin D reduced the uptake of Sl-beads more than plain beads. These findings indicate that the S-layer plays a role in the endocytosis of MIMLh5 by DCs. In conclusion, this study provides evidence that the S-layer of L. helveticus MIMLh5 is involved in endocytosis of the bacterium, which is important for strong Th1-inducing cytokine production.IMPORTANCE Beneficial microbes may positively affect host physiology at various levels, e.g., by participating in immune system maturation and modulation, boosting defenses and dampening reactions, thus affecting the whole homeostasis. As a consequence, the use of probiotics is increasingly regarded as suitable for more extended applications for health maintenance, not only microbiota balancing. This implies a deep knowledge of the mechanisms and molecules involved in host-microbe interactions, for the final purpose of fine tuning the choice of a probiotic strain for a specific outcome. With this aim, studies targeted to the description of strain-related immunomodulatory effects and the identification of bacterial molecules responsible for specific responses are indispensable. This study provides new insights in the characterization of the food-origin probiotic bacterium L. helveticus MIMLh5 and its S-layer protein as a driver for the cross-talk with DCs.

Comparative analysis of immunological properties of S-layer proteins isolated from Lactobacillus strains

Previous studies have suggested that some Lactobacillus S-layer proteins could modulate immune responses. Primary structures of the S-layer proteins are variable, and their immunological differences are poorly understood. In this study, we evaluated the immunological properties of eight distinct S-layer proteins from different Lactobacillus species. We found that removal of the S-layer proteins from the cell surface reduced the immunological activities of Lactobacillus cells in THP-1 cells. Furthermore, the purified S-layer proteins induced the production of IL-12 p40, although their immunological activities varied between the different S-layer proteins. The production of IL-12 p40 was notably induced by the S-layer protein SLP(aly) from Lactobacillus amylolyticus NRIC 0558^T. Multiple sequence alignment revealed that the percent identity of the S-layer proteins of the eight strains vary from 10 to 90 %. In particular, N-terminal regions showed high levels of diversity. To obtain more information about their structure and the immunogenicity, truncated and chimeric S-layer proteins were constructed in recombinant E. coli. Profiling of cytokine production in THP-1 cells by truncated and chimeric S-layer proteins suggested that the intact conformation of the N-terminal region of SLP(aly) contributes to high immunogenicity.

Class III bacteriocin Helveticin-M causes sublethal damage on target cells through impairment of cell wall and membrane

Helveticin-M, a novel Class III bacteriocin produced by Lactobacillus crispatus exhibited an antimicrobial activity against Staphylococcus aureus, S. saprophyticus, and Enterobacter cloacae. To understand how Helveticin-M injured target cells, Helveticin-M was cloned and heterologously expressed in Escherichia coli. Subsequently, the cell wall organization and cell membrane integrity of target cells were determined. The mechanism of cellular damage differed according to bacterial species. Based on morphology analysis, Helveticin-M disrupted the cell wall of Gram-positive bacteria and disorganized the outer membrane of Gram-negative bacteria, therefore, altering surface structure. Helveticin-M also disrupted the inner membrane, as confirmed by leakage of intracellular ATP from cells and depolarization of membrane potential of target bacteria. Based on cell population analysis, Helveticin-M treatment caused the increase of cell membrane permeability, but the cytosolic enzymes were not influenced, indicating that it was the sublethal injury. Therefore, the mode of Helveticin-M action is bacteriostatic rather than bactericidal.

Inhibition of Shigella sonnei-induced epithelial barrier disruption by surface-layer associated proteins of lactobacilli from Chinese fermented food

Surface-layer associated proteins (SLAP) of Lactobacillus paracasei ssp. paracasei M5-L and Lactobacillus casei Q8-L were examined to identify the functional basis for their protection within intestinal epithelial cells. The results showed that SLAP of M5-L and Q8-L remained active in a trypsin solution and retained a 45-kDa protein band, similar to that observed in controls. In contrast, under conditions of simulated gastric juice, the SLAP were partially degraded. Inhibitory effects of SLAP on adherence of Shigella sonnei to HT-29 cells were assessed with use of exclusion, competition, and replacement assays. In response to M5-L at 50 μg/mL SLAP, an inhibition ratio of 33% was obtained, while for Q8-L at 400 μg/mL SLAP, the inhibition ratio was 48%. Hoechst 33258 test results showed that cells infected with S. sonnei and co-incubated with SLAP of M5-L and Q8-L were only partially apoptotic, with apoptosis rates of 37.67 and 43.67%, respectively. These levels of apoptosis were substantially lower than that observed with cells infected with S. sonnei alone. In addition, the SLAP of Q8-L and M5-L reduced downstream caspase-1 activity and further modified apoptotic cell damage. Finally, SLAP of M5-L and Q8-L were also able to prevent S. sonnei-induced membrane damage by inhibiting delocalization of zonula occludens (ZO)-1 and reducing the amount of occludin produced by S. sonnei.

Synergistic antibacterial mechanism of the Lactobacillus crispatus surface layer protein and nisin on Staphylococcus saprophyticus

SlpB, a surface layer protein isolated from Lactobacillus crispatus, has the potential to enhance the antimicrobial activity of nisin. Previous research indicated that, when combined with nisin, SlpB acted synergistically to inhibit Staphylococcus saprophyticus growth, thus extending the shelf life of chicken meat. In order to understand how SlpB enhances the antibacterial activity of nisin, electron microscopy, confocal laser scanning microscopy, flow cytometry and transmembrane electrical potential analysis were used to study cell wall organization and cell membrane integrity. No remarkable bacteriolytic effects were observed, indicating that cell death could not be attributed to cell lysis, although SlpB caused dramatic modifications of cell wall, thereby altering cell shape. The combination of SlpB and nisin also induced the release of ATP or UV-absorbing materials, as well as sudden dissipation of the transmembrane electrical potential by compromising membrane integrity. Considering that SlpB led to structural disorganization of the cell wall, and nisin access is enhanced to form a stable pore, cell death is a predictable outcome. SlpB significantly enhanced the effect of nisin at half of the minimum inhibitory concentration, which resulted in cell death by destroying the cell wall and cell membrane, therefore providing a new, feasible approach in food preservation.

The Adhesion of Lactobacillus salivarius REN to a Human Intestinal Epithelial Cell Line Requires S-layer Proteins

Lactobacillus salivarius REN, a novel probiotic isolated from Chinese centenarians, can adhere to intestinal epithelial cells and subsequently colonize the host. We show here that the surface-layer protein choline-binding protein A (CbpA) of L. salivarius REN was involved in adherence to the human colorectal adenocarcinoma cell line HT-29. Adhesion of a cbpA deletion mutant was significantly reduced compared with that of wild-type, suggesting that CbpA acts as an adhesin that mediates the interaction between the bacterium and its host. To identify the molecular mechanism of adhesion, we determined the crystal structure of a truncated form of CbpA that is likely involved in binding to its cell-surface receptor. The crystal structure identified CbpA as a peptidase of the M23 family whose members harbor a zinc-dependent catalytic site. Therefore, we propose that CbpA acts as a multifunctional surface protein that cleaves the host extracellular matrix and participates in adherence. Moreover, we identified enolase as the CbpA receptor on the surface of HT-29 cells. The present study reveals a new class of surface-layer proteins as well as the molecular mechanism that may contribute to the ability of L. salivarius REN to colonize the human gut.

Lactobacillus kefiri shows inter-strain variations in the amino acid sequence of the S-layer proteins

The S-layer is a proteinaceous envelope constituted by subunits that self-assemble to form a two-dimensional lattice that covers the surface of different species of Bacteria and Archaea, and it could be involved in cell recognition of microbes among other several distinct functions. In this work, both proteomic and genomic approaches were used to gain knowledge about the sequences of the S-layer protein (SLPs) encoding genes expressed by six aggregative and sixteen non-aggregative strains of potentially probiotic Lactobacillus kefiri. Peptide mass fingerprint (PMF) analysis confirmed the identity of SLPs extracted from L. kefiri, and based on the homology with phylogenetically related species, primers located outside and inside the SLP-genes were employed to amplify genomic DNA. The O-glycosylation site SASSAS was found in all L. kefiri SLPs. Ten strains were selected for sequencing of the complete genes. The total length of the mature proteins varies from 492 to 576 amino acids, and all SLPs have a calculated pI between 9.37 and 9.60. The N-terminal region is relatively conserved and shows a high percentage of positively charged amino acids. Major differences among strains are found in the C-terminal region. Different groups could be distinguished regarding the mature SLPs and the similarities observed in the PMF spectra. Interestingly, SLPs of the aggregative strains are 100% homologous, although these strains were isolated from different kefir grains. This knowledge provides relevant data for better understanding of the mechanisms involved in SLPs functionality and could contribute to the development of products of biotechnological interest from potentially probiotic bacteria.

FACTORS OF ADHESION OF BIFIDOBACTERIA

Data on fimbrial and afimbrial adhesion factors of bifidobacteria are presented. Pili-like structures, their composition and conditions of formation in various species of bifidobacteria are described. Several sugar-lytic enzymes serve as afimbrial adhesins in bifidobacteria. Transaldolase and enolase are detected in bifidobacteria on cells’ surface. Transaldolase ensures binding of bifidobacteria with mucin and their auto-aggregation. Surface enolase has an affinity to plasminogen, thus bifidobacteria obtain a surface-bound protein with proteolytic activity. Molecular structures giving bifidobacteria hydrophobic properties are described - surface lipoprotein Bop A and lipoteichoic acids.

Diversity in S-layers

Surface layers, referred simply as S-layers, are the two-dimensional crystalline arrays of protein or glycoprotein subunits on cell surface. They are one of the most common outermost envelope components observed in prokaryotic organisms (Archaea and Bacteria). Over the past decades, S-layers have become an issue of increasing interest due to their ubiquitousness, special features and functions. Substantial work in this field provides evidences of an enormous diversity in S-layers. This paper reviews and illustrates the diversity from several different aspects, involving the S-layer-carrying strains, the structure of S-layers, the S-layer proteins and genes, as well as the functions of S-layers.

A food-grade fimbrial adhesin FaeG expression system inLactococcus lactisandLactobacillus casei

Enterotoxigenic Escherichia coli (ETEC) infection is the major cause of diarrhea in neonatal piglets. The fimbriae as colonizing factor in the pathogenesis of ETEC constitute a primary target for vaccination against ETEC. Lactic acid bacteria (LAB) are attractive tools to deliver antigens at the mucosal level. With the safety of genetically modified LAB in mind, a food-grade secretion vector (pALRc or pALRb) was constructed with DNA entirely from LAB, including the replicon, promoter, signal peptide, and selection marker alanine racemase gene (alr). To evaluate the feasibility of the system, the nuclease gene (nuc) from Staphylococcus aureus was used as a reporter to be expressed in both Lactococcus lactis and Lactobacillus casei. Subsequently, the extracellular secretion of the fimbrial adhesin FaeG of ETEC was confirmed by Western blot analysis. These results showed that this food-grade expression system has potential as the delivery vehicle for the safe use of genetically modified LAB for the development of vaccines against ETEC infection.

Multidomain, Surface Layer-associated Glycoside Hydrolases Contribute to Plant Polysaccharide Degradation by Caldicellulosiruptor Species

The genome of the extremely thermophilic bacterium Caldicellulosiruptor kronotskyensisencodes 19 surface layer (S-layer) homology (SLH) domain-containing proteins, the most in any Caldicellulosiruptorspecies genome sequenced to date. These SLH proteins include five glycoside hydrolases (GHs) and one polysaccharide lyase, the genes for which were transcribed at high levels during growth on plant biomass. The largest GH identified so far in this genus, Calkro_0111 (2,435 amino acids), is completely unique toC. kronotskyensisand contains SLH domains. Calkro_0111 was produced recombinantly inEscherichia colias two pieces, containing the GH16 and GH55 domains, respectively, as well as putative binding and spacer domains. These displayed endo- and exoglucanase activity on the β-1,3-1,6-glucan laminarin. A series of additional truncation mutants of Calkro_0111 revealed the essential architectural features required for catalytic function. Calkro_0402, another of the SLH domain GHs inC. kronotskyensis, when produced inE. coli, was active on a variety of xylans and β-glucans. Unlike Calkro_0111, Calkro_0402 is highly conserved in the genus Caldicellulosiruptorand among other biomass-degrading Firmicutes but missing from Caldicellulosiruptor bescii As such, the gene encoding Calkro_0402 was inserted into the C. besciigenome, creating a mutant strain with its S-layer extensively decorated with Calkro_0402. This strain consequently degraded xylans more extensively than wild-typeC. bescii The results here provide new insights into the architecture and role of SLH domain GHs and demonstrate that hemicellulose degradation can be enhanced through non-native SLH domain GHs engineered into the genomes of Caldicellulosiruptorspecies.

Conserved S-Layer-Associated Proteins Revealed by Exoproteomic Survey of S-Layer-Forming Lactobacilli

The Lactobacillus acidophilus homology group comprises Gram-positive species that include L. acidophilus, L. helveticus, L. crispatus, L. amylovorus, L. gallinarum, L. delbrueckii subsp. bulgaricus, L. gasseri, and L. johnsonii. While these bacteria are closely related, they have varied ecological lifestyles as dairy and food fermenters, allochthonous probiotics, or autochthonous commensals of the host gastrointestinal tract. Bacterial cell surface components play a critical role in the molecular dialogue between bacteria and interaction signaling with the intestinal mucosa. Notably, the L. acidophilus complex is distinguished in two clades by the presence or absence of S-layers, which are semiporous crystalline arrays of self-assembling proteinaceous subunits found as the outermost layer of the bacterial cell wall. In this study, S-layer-associated proteins (SLAPs) in the exoproteomes of various S-layer-forming Lactobacillus species were proteomically identified, genomically compared, and transcriptionally analyzed. Four gene regions encoding six putative SLAPs were conserved in the S-layer-forming Lactobacillus species but not identified in the extracts of the closely related progenitor, L. delbrueckii subsp. bulgaricus, which does not produce an S-layer. Therefore, the presence or absence of an S-layer has a clear impact on the exoproteomic composition of Lactobacillus species. This proteomic complexity and differences in the cell surface properties between S-layer- and non-S-layer-forming lactobacilli reveal the potential for SLAPs to mediate intimate probiotic interactions and signaling with the host intestinal mucosa.

Screening of Probiotic Candidates in Human Oral Bacteria for the Prevention of Dental Disease

The oral cavity in healthy subjects has a well-balanced microbiota that consists of more than 700 species. However, a disturbance of this balance, with an increase of harmful microbes and a decrease of beneficial microbes, causes oral disorders such as periodontal disease or dental caries. Nowadays, probiotics are expected to confer oral health benefits by modulating the oral microbiota. This study screened new probiotic candidates with potential oral health benefits and no harmful effects on the oral cavity. We screened 14 lactobacillus strains and 36 streptococcus strains out of 896 oral isolates derived from healthy subjects. These bacteria did not produce volatile sulfur compounds or water-insoluble glucan, had higher antibacterial activity against periodontal bacteria, and had higher adherence activity to oral epithelial cells or salivary-coated hydroxyapatite in vitro. We then evaluated the risk of primary cariogenicity and infective endocarditis of the selected oral isolates. As a result, Lactobacillus crispatus YIT 12319, Lactobacillus fermentum YIT 12320, Lactobacillus gasseri YIT 12321, and Streptococcus mitis YIT 12322 were selected because they showed no cariogenic potential in an artificial mouth system and a lower risk of experimental infective endocarditis in a rat model. These candidates are expected as new probiotics with potential oral health benefits and no adverse effects on general health.

Extensive intra-phylotype diversity in lactobacilli and bifidobacteria from the honeybee gut

Background

In the honeybee Apis mellifera, the bacterial gut community is consistently colonized by eight distinct phylotypes of bacteria. Managed bee colonies are of considerable economic interest and it is therefore important to elucidate the diversity and role of this microbiota in the honeybee. In this study, we have sequenced the genomes of eleven strains of lactobacilli and bifidobacteria isolated from the honey crop of the honeybee A. mellifera.

Results

Single gene phylogenies confirmed that the isolated strains represent the diversity of lactobacilli and bifidobacteria in the gut, as previously identified by 16S rRNA gene sequencing. Core genome phylogenies of the lactobacilli and bifidobacteria further indicated extensive divergence between strains classified as the same phylotype. Phylotype-specific protein families included unique surface proteins. Within phylotypes, we found a remarkably high level of gene content diversity. Carbohydrate metabolism and transport functions contributed up to 45% of the accessory genes, with some genomes having a higher content of genes encoding phosphotransferase systems for the uptake of carbohydrates than any previously sequenced genome. These genes were often located in highly variable genomic segments that also contained genes for enzymes involved in the degradation and modification of sugar residues. Strain-specific gene clusters for the biosynthesis of exopolysaccharides were identified in two phylotypes. The dynamics of these segments contrasted with low recombination frequencies and conserved gene order structures for the core genes. Hits for CRISPR spacers were almost exclusively found within phylotypes, suggesting that the phylotypes are associated with distinct phage populations.

Conclusions

The honeybee gut microbiota has been described as consisting of a modest number of phylotypes; however, the genomes sequenced in the current study demonstrated a very high level of gene content diversity within all three described phylotypes of lactobacilli and bifidobacteria, particularly in terms of metabolic functions and surface structures, where many features were strain-specific. Together, these results indicate niche differentiation within phylotypes, suggesting that the honeybee gut microbiota is more complex than previously thought.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1476-6) contains supplementary material, which is available to authorized users.

Identification and characterization of enolase as a collagen-binding protein in Lactobacillus plantarum

Collagen is a target of pathogens for adhesion, colonization, and invasion of host tissue. Probiotic bacteria can mimic the same mechanism as used by the pathogens in the colonization process, expressing cell surface proteins that specifically interact with extracellular matrix component proteins. The capability to bind collagen is expressed by several Lactobacillus isolates, including some Lactobacillus plantarum strains. In this study we report the involvement of the L. plantarum EnoA1 alfa-enolase in type I collagen (CnI) binding. By adhesion assays, we show that the mutant strain LM3-CC1, carrying a null mutation in the enoA1 gene, binds to immobilized collagen less efficiently than wild type strain. CnI overlay assay and Elisa tests, performed on the purified EnoA1, show that this protein can bind collagen both under denaturing and native conditions. By using truncated recombinant enolase proteins, we also show that the region spanning from 73rd to the 140th amino acid residues is involved in CnI binding.

Comparative genomics of Lactobacillus crispatus suggests novel mechanisms for the competitive exclusion of Gardnerella vaginalis

BACKGROUND

Lactobacillus crispatus is a ubiquitous micro-organism encountered in a wide range of host-associated habitats. It can be recovered from the gastrointestinal tract of animals and it is a common constituent of the vaginal microbiota of humans. Moreover, L. crispatus can contribute to the urogenital health of the host through competitive exclusion and the production of antimicrobial agents. In order to investigate the genetic diversity of this important urogenital species, we performed a comparative genomic analysis of L. crispatus.

RESULTS

Utilizing the completed genome sequence of a strain ST1 and the draft genome sequences of nine other L. crispatus isolates, we defined the scale and scope of the pan- and core genomic potential of L. crispatus. Our comparative analysis identified 1,224 and 2,705 ortholog groups present in all or only some of the ten strains, respectively. Based on mathematical modeling, sequencing of additional L. crispatus isolates would result in the identification of new genes and functions, whereas the conserved core of the ten strains was a good representation of the final L. crispatus core genome, estimated to level at about 1,116 ortholog groups. Importantly, the current core was observed to encode bacterial components potentially promoting urogenital health. Using antibody fragments specific for one of the conserved L. crispatus adhesins, we demonstrated that the L. crispatus core proteins have a potential to reduce the ability of Gardnerella vaginalis to adhere to epithelial cells. These findings thereby suggest that L. crispatus core proteins could protect the vagina from G. vaginalis and bacterial vaginosis.

CONCLUSIONS

Our pan-genome analysis provides insights into the intraspecific genome variability and the collective molecular mechanisms of the species L. crispatus. Using this approach, we described the differences and similarities between the genomes and identified features likely to be important for urogenital health. Notably, the conserved genetic backbone of L. crispatus accounted for close to 60% of the ortholog groups of an average L. crispatus strain and included factors for the competitive exclusion of G. vaginalis, providing an explanation on how this urogenital species could improve vaginal health.

Heterologous expression of carcinoembryonic antigen in Lactococcus lactis via LcsB-mediated surface displaying system for oral vaccine development

BACKGROUND/PURPOSE

Carcinoembryonic antigen (CEA) is an attractive target for immunotherapy because it is expressed minimally in normal tissue, but is overexpressed in a wide variety of malignant epithelial tissues. Lactic acid bacteria (LABs), widely used in food processes, are attractive candidates for oral vaccination. Thus, we examined whether LABs could be used as a live vaccine vector to deliver CEA antigen.

METHODS

CEA was cloned into an Escherichia coli/Lactococcus lactis shuttle vector pSEC:LEISS under the control of a nisin promoter. For displaying the CEA on the cell surface of the L. lactis strain, the anchor motif LcsB from the S-layer protein of Lactobacillus crispatus was fused with CEA. Intracellular and cell surface expression of the CEA-LcsB fusion was confirmed by western blot analysis.

RESULTS

Significantly higher levels of CEA-specific secretory immunoglobulin A in the sera of mice were observed upon oral administration of strain cultures containing the CEA-LcsB fused protein. In addition, the CEA-LcsB antigen group showed a higher spleen index compared to the CEA antigen alone or negative control, demonstrating that surface-displayed CEA antigen could induce a higher immune response.

CONCLUSION

These results provided the first evidence for displaying CEA antigen on the cell surfaces of LABs as oral vaccines against cancer or infectious diseases.

Functional characterization of probiotic surface layer protein-carrying Lactobacillus amylovorus strains

BACKGROUND

Adhesiveness to intestinal epithelium, beneficial immunomodulating effects and the production of pathogen-inhibitory compounds are generally considered as beneficial characteristics of probiotic organisms. We showed the potential health-promoting properties and the mechanisms of probiotic action of seven swine intestinal Lactobacillus amylovorus isolates plus the type strain (DSM 20531T) by investigating their adherence to porcine intestinal epithelial cells (IPEC-1) and mucus as well as the capacities of the strains to i) inhibit the adherence of Escherichia coli to IPEC-1 cells, ii) to produce soluble inhibitors against intestinal pathogens and iii) to induce immune signaling in dendritic cells (DCs). Moreover, the role of the L. amylovorus surface (S) -layers - symmetric, porous arrays of identical protein subunits present as the outermost layer of the cell envelope - in adherence to IPEC-1 cells was assessed using a novel approach which utilized purified cell wall fragments of the strains as carriers for the recombinantly produced S-layer proteins.

RESULTS

Three of the L. amylovorus strains studied adhered to IPEC-1 cells, while four strains inhibited the adherence of E. coli, indicating additional mechanisms other than competition for binding sites being involved in the inhibition. None of the strains bound to porcine mucus. The culture supernatants of all of the strains exerted inhibitory effects on the growth of E. coli, Salmonella, Listeria and Yersinia, and a variable, strain-dependent induction was observed of both pro- and anti-inflammatory cytokines in human DCs. L. amylovorus DSM 16698 was shown to carry two S-layer-like proteins on its surface in addition to the major S-layer protein SlpA. In contrast to expectations, none of the major S-layer proteins of the IPEC-1 -adhering strains mediated bacterial adherence.

CONCLUSIONS

We demonstrated adhesive and significant pathogen inhibitory efficacies among the swine intestinal L. amylovorus strains studied, pointing to their potential use as probiotic feed supplements, but no independent role could be demonstrated for the major S-layer proteins in adherence to epithelial cells. The results indicate that many intestinal bacteria may coexist with and confer benefits to the host by mechanisms not attributable to adhesion to epithelial cells or mucus.

Biogenesis and functions of bacterial S-layers

The outer surface of many archaea and bacteria is coated with a proteinaceous surface layer (known as an S-layer), which is formed by the self-assembly of monomeric proteins into a regularly spaced, two-dimensional array. Bacteria possess dedicated pathways for the secretion and anchoring of the S-layer to the cell wall, and some Gram-positive species have large S-layer-associated gene families. S-layers have important roles in growth and survival, and their many functions include the maintenance of cell integrity, enzyme display and, in pathogens and commensals, interaction with the host and its immune system. In this Review, we discuss our current knowledge of S-layer and related proteins, including their structures, mechanisms of secretion and anchoring and their diverse functions.

A new addition to the cell plan of anammox bacteria: "Candidatus Kuenenia stuttgartiensis" has a protein surface layer as the outermost layer of the cell

Anammox bacteria perform anaerobic ammonium oxidation (anammox) and have a unique compartmentalized cell consisting of three membrane-bound compartments (from inside outwards): the anammoxosome, riboplasm, and paryphoplasm. The cell envelope of anammox bacteria has been proposed to deviate from typical bacterial cell envelopes by lacking both peptidoglycan and a typical outer membrane. However, the composition of the anammox cell envelope is presently unknown. Here, we investigated the outermost layer of the anammox cell and identified a proteinaceous surface layer (S-layer) (a crystalline array of protein subunits) as the outermost component of the cell envelope of the anammox bacterium "Candidatus Kuenenia stuttgartiensis." This is the first description of an S-layer in the phylum of the Planctomycetes and a new addition to the cell plan of anammox bacteria. This S-layer showed hexagonal symmetry with a unit cell consisting of six protein subunits. The enrichment of the S-layer from the cell led to a 160-kDa candidate protein, Kustd1514, which has no homology to any known protein. This protein is present in a glycosylated form. Antibodies were generated against the glycoprotein and used for immunogold localization. The antiserum localized Kustd1514 to the S-layer and thus verified that this protein forms the "Ca. Kuenenia stuttgartiensis" S-layer.

Understanding and modulating mammalian-microbial communication for improved human health

The fact that the bacteria in the human gastrointestinal (GI) tract play a symbiotic role was noted as early as 1885, well before we began to manage microbial infections using antibiotics. However, even with the first antimicrobial compounds used in humans, the sulfa drugs, microbes were recognized to be critically involved in the biotransformation of these therapeutics. Thus, the roles played by the microbiota in physiology and in the management of human health have long been appreciated. Detailed examinations of GI symbiotic bacteria that started in the early 2000s and the first phases of the Human Microbiome Project that were completed in 2012 have ushered in an exciting period of granularity with respect to the ecology, genetics, and chemistry of the mammalian-microbial axes of communication. Here we review aspects of the biochemical pathways at play between commensal GI bacteria and several mammalian systems, including both local-epithelia and nonlocal responses impacting inflammation, immunology, metabolism, and neurobiology. Finally, we discuss how the microbial biotransformation of therapeutic compounds, such as anticancer or nonsteroidal anti-inflammatory drugs, can be modulated to reduce toxicity and potentially improve therapeutic efficacy.

Understanding and modulating mammalian-microbial communication for improved human health

The molecular basis for the regulation of the intestinal barrier is a very fertile research area. A growing body of knowledge supports the targeting of various components of intestinal barrier function as means to treat a variety of diseases, including the inflammatory bowel diseases. Herein, we will summarize the current state of knowledge of key xenobiotic receptor regulators of barrier function, highlighting recent advances, such that the field and its future are succinctly reviewed. We posit that these receptors confer an additional dimension of host-microbe interaction in the gut, by sensing and responding to metabolites released from the symbiotic microbiota, in innate immunity and also in host drug metabolism. The scientific evidence for involvement of the receptors and its molecular basis for the control of barrier function and innate immunity regulation would serve as a rationale towards development of non-toxic probes and ligands as drugs.

Lactobacillus surface layer proteins: structure, function and applications

Bacterial surface (S) layers are the outermost proteinaceous cell envelope structures found on members of nearly all taxonomic groups of bacteria and Archaea. They are composed of numerous identical subunits forming a symmetric, porous, lattice-like layer that completely covers the cell surface. The subunits are held together and attached to cell wall carbohydrates by non-covalent interactions, and they spontaneously reassemble in vitro by an entropy-driven process. Due to the low amino acid sequence similarity among S-layer proteins in general, verification of the presence of an S-layer on the bacterial cell surface usually requires electron microscopy. In lactobacilli, S-layer proteins have been detected on many but not all species. Lactobacillus S-layer proteins differ from those of other bacteria in their smaller size and high predicted pI. The positive charge in Lactobacillus S-layer proteins is concentrated in the more conserved cell wall binding domain, which can be either N- or C-terminal depending on the species. The more variable domain is responsible for the self-assembly of the monomers to a periodic structure. The biological functions of Lactobacillus S-layer proteins are poorly understood, but in some species S-layer proteins mediate bacterial adherence to host cells or extracellular matrix proteins or have protective or enzymatic functions. Lactobacillus S-layer proteins show potential for use as antigen carriers in live oral vaccine design because of their adhesive and immunomodulatory properties and the general non-pathogenicity of the species.

Characterization of pro-inflammatory flagellin proteins produced by Lactobacillus ruminis and related motile Lactobacilli

Lactobacillus ruminis is one of at least twelve motile but poorly characterized species found in the genus Lactobacillus. Of these, only L. ruminis has been isolated from mammals, and this species may be considered as an autochthonous member of the gastrointestinal microbiota of humans, pigs and cows. Nine L. ruminis strains were investigated here to elucidate the biochemistry and genetics of Lactobacillus motility. Six strains isolated from humans were non-motile while three bovine isolates were motile. A complete set of flagellum biogenesis genes was annotated in the sequenced genomes of two strains, ATCC25644 (human isolate) and ATCC27782 (bovine isolate), but only the latter strain produced flagella. Comparison of the L. ruminis and L. mali DSM20444(T) motility loci showed that their genetic content and gene-order were broadly similar, although the L. mali motility locus was interrupted by an 11.8 Kb region encoding rhamnose utilization genes that is absent from the L. ruminis motility locus. Phylogenetic analysis of 39 motile bacteria indicated that Lactobacillus motility genes were most closely related to those of motile carnobacteria and enterococci. Transcriptome analysis revealed that motility genes were transcribed at a significantly higher level in motile L. ruminis ATCC27782 than in non-motile ATCC25644. Flagellin proteins were isolated from L. ruminis ATCC27782 and from three other Lactobacillus species, while recombinant flagellin of aflagellate L. ruminis ATCC25644 was expressed and purified from E. coli. These native and recombinant Lactobacillus flagellins, and also flagellate L. ruminis cells, triggered interleukin-8 production in cultured human intestinal epithelial cells in a manner suppressed by short interfering RNA directed against Toll-Like Receptor 5. This study provides genetic, transcriptomic, phylogenetic and immunological insights into the trait of flagellum-mediated motility in the lactobacilli.