Identification and characterization of novel surface proteins in Lactobacillus johnsonii and Lactobacillus gasseri

Lactobacillus crispatus S-layer proteins modulate innate immune response and inflammation in the lower female reproductive tract

Lactobacillus species dominance of the vaginal microbiome is a hallmark of vaginal health. Pathogen displacement of vaginal lactobacilli drives innate immune activation and mucosal barrier disruption, increasing the risks of STI acquisition and, in pregnancy, of preterm birth. We describe differential TLR mediated activation of the proinflammatory transcription factor NF-κB by vaginal pathogens and commensals. Vaginal Lactobacillus strains associated with optimal health selectively interact with anti-inflammatory innate immune receptors whereas species associated with suboptimal health including L. iners and Gardnerella vaginalis interact with both pro- and anti-inflammatory receptors. Anti-inflammatory action of L. crispatus is regulated by surface layer protein (SLPs)-mediated shielding of TLR ligands and selective interaction with the anti-inflammatory receptor DC-SIGN. Detection of SLPs within cervicovaginal fluid samples is associated with decreased concentrations of pro-inflammatory cytokines in Lactobacillus crispatus-dominated samples. These data offer mechanistic insights into how vaginal microbiota modulate host immune response and thus reproductive health and disease states.

Development of a Limosilactobacillus reuteri therapeutic delivery platform with reduced colonization potential

Bacterial biotherapeutic delivery vehicles have the potential to treat a variety of diseases. This approach obviates the need to purify the recombinant effector molecule, allows delivery of therapeutics in situ via oral or intranasal administration, and protects the effector molecule during gastrointestinal transit. Lactic acid bacteria have been broadly developed as therapeutic delivery vehicles though risks associated with the colonization of a genetically modified microorganism have so-far not been addressed. Here, we present an engineered Limosilactobacillus reuteri strain with reduced colonization potential. We applied a dual-recombineering scheme for efficient barcoding and generated mutants in genes encoding five previously characterized and four uncharacterized putative adhesins. Compared with the wild type, none of the mutants were reduced in their ability to survive gastrointestinal transit in mice. CmbA was identified as a key protein in L. reuteri adhesion to HT-29 and enteroid cells. The nonuple mutant, a single strain with all nine genes encoding adhesins inactivated, had reduced capacity to adhere to enteroid monolayers. The nonuple mutant producing murine IFN-β was equally effective as its wild-type counterpart in mitigating radiation toxicity in mice. Thus, this work established a novel therapeutic delivery platform that lays a foundation for its application in other microbial therapeutic delivery candidates and furthers the progress of the L. reuteri delivery system towards human use.IMPORTANCEOne major advantage to leverage gut microbes that have co-evolved with the vertebrate host is that evolution already has taken care of the difficult task to optimize survival within a complex ecosystem. The availability of the ecological niche will support colonization. However, long-term colonization of a recombinant microbe may not be desirable. Therefore, strategies need to be developed to overcome this potential safety concern. In this work, we developed a single strain in which we inactivated the encoding sortase, and eight genes encoding characterized/putative adhesins. Each individual mutant was characterized for growth and adhesion to epithelial cells. On enteroid cells, the nonuple mutant has a reduced adhesion potential compared with the wild-type strain. In a model of total-body irradiation, the nonuple strain engineered to release murine interferon-β performed comparable to a derivative of the wild-type strain that releases interferon-β. This work is an important step toward the application of recombinant L. reuteri in humans.

Modulation of Mouse Dendritic Cells In Vitro by Lactobacillus gasseri Postbiotic Proteins

Different lactobacilli are probiotics for their beneficial effects that confer to the host. Recently, some of these effects were associated with released metabolic products/constituents (postbiotics). In the present study, the potential immunomodulatory capacity of the probiotic Lactobacillus gasseri OLL2809 cell-free supernatant (sup) was investigated in murine bone marrow-derived dendritic cells (DCs). Bacteria induced significantly higher expression of all examined cytokines than those induced by the stimulatory lipopolysaccharide (LPS) itself. On the contrary, sup only induced the anti-inflammatory IL-10 similarly to LPS, whereas IL-12 and IL-6 secretions were stimulated at a lower level. Moreover, sup reduced the surface expression of the analyzed co-stimulatory markers CD40, CD80, and CD86. Treatments of sup with different digestive enzymes indicated the proteinaceous nature of these immunomodulatory metabolites. Western blot and immunoadsorption analyzes revealed cross-reactivity of sup with the surface-layer proteins (SLPs) isolated from OLL2809. Therefore, we directly tested the ability of OLL2809 SLPs to stimulate specifically cytokine expression in iDCs. Interestingly, we found that all tested cytokines were induced by SLPs and in a dose-dependent manner. In conclusion, our results highlighted distinct immune properties between L. gasseri OLL2809 and its metabolites, supporting the concept that bacterial viability is not an essential prerequisite to exert immunomodulatory effects.

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.

A New Method of Myostatin Inhibition in Mice via Oral Administration of Lactobacillus casei Expressing Modified Myostatin Protein, BLS-M22

Myostatin is a member of the transforming growth factor-beta superfamily and is an endogenous negative regulator of muscle growth. This study aimed to determine whether an oral administration of Lactobacillus casei expressing modified human myostatin (BLS-M22) could elicit sufficient levels of myostatin-specific antibody and improve the dystrophic features of an animal model of Duchenne muscular dystrophy (DMD; mdx mouse). BLS-M22 is a recombinant L. casei engineered to harbor the pKV vector and poly-gamma-glutamic acid gene linked to a modified human myostatin gene. Serological analysis showed that anti-myostatin IgG titers were significantly increased, and serum creatine kinase was significantly reduced in the BLS-M22-treated mdx mice compared to the control mice. In addition, treatment of BLS-M22 resulted in a significant increase in body weight and motor function (Rotarod behavior test). Histological analysis showed an improvement in the dystrophic features (fibrosis and muscle hypertrophy) of the mdx mice with the administration of BLS-M22. The circulating antibodies generated after BLS-M22 oral administration successfully lowered serum myostatin concentration. Myostatin blockade resulted in serological, histological, and functional improvements in mdx mice. Overall, the findings suggest the potential of BLS-M22 to treat DMD; however, further clinical trials are essential to ascertain its efficacy and safety in humans.

Investigating the effects of peptide-based, MOS and protease feed additives on the growth performance and fecal microbial composition of weaned pigs

Background

Digestive disorders in weaning pigs remain a major challenge for swine producers. Different types of commercial feed additives have been developed to promote gut health and development in young pigs, but their effects on resident gut microbial communities remain largely unexplored. The aim of this study was to investigate the impact of a peptide-based product (Peptiva) in combination with mannose oligosaccharides (MOS) and an exogenous protease on the performance and fecal microbiome of nursery pigs.

Methods

A total of 1097 weaned pigs were divided into 44 pens (24–26 pigs/pen) with each pen randomly assigned to one of four experimental diets as part of Phase II and Phase III of a standard nursery phase feeding program. Fecal samples collected from representative control and treatment pigs were used to investigate bacterial composition profiles by high throughput sequencing of PCR-generated amplicons targeting the V1-V3 region of the 16S rRNA gene.

Results

Higher gain:feed was observed for pigs fed Peptiva and MOS compared to Controls during the period when experimental diets were fed, but the benefits of supplementation were not maintained after pigs were transitioned to a non-supplemented diet. Three candidate bacterial species, identified as Operational Taxonomic Units (OTUs), were found to have significantly different abundances between control samples and treatment samples during the same phase. In Phase III samples, SD_Ssd-00039, predicted to be a strain of Streptococcus alactolyticus based on nucleotide sequence identity, was the most highly represented of these OTUs with an average abundance in pigs fed Peptiva, MOS and protease that was 3.9 times higher than in Controls. The report also presents evidence of microbial succession that occurred during the trial, with 16 of the 32 most abundant OTUs found to vary between Phase II and Phase III samples for the same dietary treatment.

Conclusions

Dietary supplementation with a combination of a peptide-based product, MOS, and protease increased the growth performance of weaned pigs compared to control animals during the nursery phase, but these benefits were no longer observed within 2 weeks after all animals were transitioned to a non-supplemented diet. Supplementation with these feed additives was found to modulate the composition of the swine gut microbiome during this period.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00681-8.

Genome Sequence and Assessment of Safety and Potential Probiotic Traits of Lactobacillus johnsonii CNCM I-4884

The probiotic strain Lactobacillus johnsonii CNCM I-4884 exhibits anti-Giardia activity in vitro and in vivo in a murine model of giardiasis. The aim of this study was the identification and characterization of the probiotic potential of L. johnsonii CNCM I-4884, as well as its safety assessment. This strain was originally classified as Lactobacillus gasseri based on 16S gene sequence analysis. Whole genome sequencing led to a reclassification as L. johnsonii. A genome-wide search for biosynthetic pathways revealed a high degree of auxotrophy, balanced by large transport and catabolic systems. The strain also exhibits tolerance to low pH and bile salts and shows strong bile salt hydrolase (BSH) activity. Sequencing results revealed the absence of antimicrobial resistance genes and other virulence factors. Phenotypic tests confirm that the strain is susceptible to a panel of 8 antibiotics of both human and animal relevance. Altogether, the in silico and in vitro results confirm that L. johnsonii CNCM I-4884 is well adapted to the gastrointestinal environment and could be safely used in probiotic formulations.

Polymicrobial interaction between Lactobacillus and Saccharomyces cerevisiae: coexistence-relevant mechanisms

The coordination of single or multiple microorganisms are required for the manufacture of traditional fermented foods, improving the flavour and nutrition of the food materials. However, both the additional economic benefits and safety concerns have been raised by microbiotas in fermented products. Among the fermented products, Lactobacillus and Saccharomyces cerevisiae are one of the stable microbiotas, suggesting their interaction is mediated by coexistence-relevant mechanisms and prevent to be excluded by other microbial species. Thus, aiming to guide the manufacture of fermented foods, this review will focus on interactions of coexistence-relevant mechanisms between Lactobacillus and S. cerevisiae, including metabolites communications, aggregation, and polymicrobial biofilm. Also, the molecular regulatory network of the coexistence-relevant mechanisms is discussed according to omics researches.

Comparative analysis of the ileal bacterial composition of post-weaned pigs fed different high-quality protein sources

To further understand the contribution of feedstuff ingredients to gut health in swine, gut histology and intestinal bacterial profiles associated with the use of two high-quality protein sources, microbially enhanced soybean meal (MSBM) and Menhaden fishmeal (FM) were assessed. Weaned pigs were fed one of three experimental diets: (1) basic diet containing corn and soybean meal (Negative Control (NEG)), (2) basic diet + fishmeal (FM; Positive Control (POS)) and (3) basic diet + MSBM (MSBM). Phase I POS and MSBM diets (d 0 to d 7 post-wean) included FM or MSBM at 7.5%, while Phase II POS and MSBM diets (d 8 to d 21) included FM or MSBM at 5.0%. Gastrointestinal tissue and ileal digesta were collected from euthanised pigs at d 21 (eight pigs/diet) to assess gut histology and intestinal bacterial profiles, respectively. Data were analysed using Proc Mixed in SAS, with pig as the experimental unit and pig (treatment) as the random effect. Histological and immunohistochemical analyses of stomach and small intestinal tissue using haematoxylin-eosin, Periodic Acid Schiff/Alcian blue and inflammatory cell staining did not reveal detectable differences in host response to dietary treatment. Ileal bacterial composition profiles were obtained from next-generation sequencing of PCR generated amplicons targeting the V1 to V3 regions of the 16S rRNA gene. Lactobacillus-affiliated sequences were found to be the most highly represented across treatments, with an average relative abundance of 64.0%, 59.9% and 41.80% in samples from pigs fed the NEG, POS and MSBM diets, respectively. Accordingly, the three most abundant Operational Taxonomic Units (OTUs) were affiliated to Lactobacillus, showing a distinct abundance pattern relative to dietary treatment. One OTU (SD_Ssd_00001), most closely related to Lactobacillus amylovorus, was found to be more abundant in NEG and POS samples compared to MSBM (23.5% and 35.0% v. 9.2%). Another OTU (SD_Ssd_00002), closely related to Lactobacillus johnsonii, was more highly represented in POS and MSBM samples compared to NEG (14.0% and 15.8% v. 0.1%). Finally, OTU Sd_Ssd-00011, highest sequence identity to Lactobacillus delbrueckii, was found in highest abundance in ileal samples from MSBM-fed pigs (1.9% and 3.3% v. 11.3, in POS, NEG and MSBM, respectively). There was no effect of protein source on bacterial taxa to the genus level or diversity based on principal component analysis. Dietary protein source may provide opportunity to enhance presence of specific members of Lactobacillus genus that are associated with immune-modulating properties without altering overall intestinal bacterial diversity.

Identification of putative adhesins and carbohydrate ligands of Lactobacillus paracasei using a combinatorial in silico and glycomics microarray profiling approach

Commensal bacteria must colonize host mucosal surfaces to exert health-promoting properties, and bind to gastrointestinal tract (GIT) mucins via their cell surface adhesins. Considerable effort has been directed towards discovery of pathogen adhesins and their ligands to develop anti-infective strategies; however, little is known about the lectin-like adhesins and associated carbohydrate ligands in commensals. In this study, an in silico approach was used to detect surface exposed adhesins in the human commensal Lactobacillus paracasei subsp. paracasei, a promising probiotic commonly used in dairy product fermentation that presents anti-microbial activity. Of the 13 adhesin candidates, 3 sortase-dependent pili clusters were identified in this strain and expression of the adhesin candidate genes was confirmed in vitro. Mass spectrometry analysis confirmed the presence of surface adhesin elongation factor Tu and the chaperonin GroEL, but not pili expression. Whole cells were subsequently incubated on microarrays featuring a panel of GIT mucins from nine different mammalian species and two human-derived cell lines and a library of carbohydrate structures. Binding profiles were compared to those of two known pili-producing lactobacilli, L. johnsonii and L. rhamnosus and all Lactobacillus species displayed overlapping but distinct signatures, which may indicate different abilities for regiospecific GIT colonization. In addition, L. paracasei whole cells favoured binding to α-(2 → 3)-linked sialic acid and α-(1 → 2)-linked fucose-containing carbohydrate structures including blood groups A, B and O and Lewis antigens x, y and b. This study furthers our understanding of host-commensal cross-talk by identifying potential adhesins and specific GIT mucin and carbohydrate ligands and provides insight into the selection of colonization sites by commensals in the GIT.

Deletion of S-Layer Associated Ig-Like Domain Protein Disrupts the Lactobacillus acidophilus Cell Surface

Bacterial surface-layers (S-layers) are crystalline arrays of repeating proteinaceous subunits that coat the exterior of many cell envelopes. S-layers have demonstrated diverse functions in growth and survival, maintenance of cell integrity, and mediation of host interactions. Additionally, S-layers can act as scaffolds for the outward display of auxiliary proteins and glycoproteins. These non-covalently bound S-layer associated proteins (SLAPs) have characterized roles in cell division, adherence to intestinal cells, and modulation of the host immune response. Recently, IgdA (LBA0695), a Lactobacillus acidophilus SLAP that possesses a Group 3 immunoglobulin (Ig)-like domain and GW (Gly-Tryp) dipeptide surface anchor, was recognized for its high conservation among S-layer-forming lactobacilli, constitutive expression, and surface localization. These findings prompted its selection for examination within the present study. Although IgdA and corresponding orthologs were shown to be unique to host-adapted lactobacilli, the Ig domain itself was specific to vertebrate-adapted species suggesting a role in vertebrate adaptation. Using a counterselective gene replacement system, igdA was deleted from the L. acidophilus NCFM chromosome. The resultant mutant, NCK2532, exhibited a visibly disrupted cell surface which likely contributed to its higher salt sensitivity, severely reduced adhesive capacity, and altered immunogenicity profile. Transcriptomic analyses revealed the induction of several stress response genes and secondary surface proteins. Due to the broad impact of IgdA on the cellular physiology and probiotic attributes of L. acidophilus, identification of similar proteins in alternative bacterial species may help pinpoint next-generation host-adapted probiotic candidates.

Galacto-Oligosaccharides Modulate the Juvenile Gut Microbiome and Innate Immunity To Improve Broiler Chicken Performance

Improvements in growth performance and health are key goals in broiler chicken production. Inclusion of prebiotic galacto-oligosaccharides (GOS) in broiler feed enhanced the growth rate and feed conversion of chickens relative to those obtained with a calorie-matched control diet. Comparison of the cecal microbiota identified key differences in abundances of Lactobacillus spp. Increased levels of Lactobacillus johnsonii in GOS-fed juvenile birds at the expense of Lactobacillus crispatus were linked to improved performance (growth rate and market weight). Investigation of the innate immune responses highlighted increases of ileal and cecal interleukin-17A (IL-17A) gene expression counterposed to a decrease in IL-10. Quantification of the autochthonous Lactobacillus spp. revealed a correlation between bird performance and L. johnsonii abundance. Shifts in the cecal populations of key Lactobacillus spp. of juvenile birds primed intestinal innate immunity without harmful pathogen challenge.IMPORTANCE Improvements in the growth rate of broiler chickens can be achieved through dietary manipulation of the naturally occurring bacterial populations while mitigating the withdrawal of antibiotic growth promoters. Prebiotic galacto-oligosaccharides (GOS) are manufactured as a by-product of dairy cheese production and can be incorporated into the diets of juvenile chickens to improve their health and performance. This study investigated the key mechanisms behind this progression and pinpointed L. johnsonii as a key species that facilitates the enhancements in growth rate and gut health. The study identified the relationships between the GOS diet, L. johnsonii intestinal populations, and cytokine immune effectors to improve growth.

Effect of Fermented Medicinal Plants as Dietary Additives on Food Preference and Fecal Microbial Quality in Dogs

Simple Summary

Dog foods are becoming more equivalent to human foods, and functional additives are being included in their diets to promote health. In this study, turmeric, glasswort, and Ganghwa mugwort were used as medicinal plants and were subjected to fermentation by autochthonous Enterococcus faecium. Fermentation significantly improved the in vitro antioxidant activities of these plants. Food preference tests of dog foods containing these fermented medicinal plants were conducted in beagles.

Abstract

This research determined the antioxidant activities of medicinal plants fermented by Enterococcus faecium and their subsequent applications as dog food additives. Turmeric (5%, w/v), glasswort (2.5%, w/v), Ganghwa mugwort (2.5%, w/v), and their mixture (5%, w/v) were fermented by autochthonous E. faecium (1%, v/v) for 72 h. Bacterial cell counts and pH were monitored during fermentation. Total polyphenol content (TPC), total flavonoid content (TFC), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, and intracellular superoxide scavenging activity in bovine mammary alveolar epithelial (MAC-T) cells were measured with the fermented and non-fermented samples. Only the antioxidant capacity of the mixture was increased after fermentation. However, intracellular superoxide level in MAC-T cells was significantly reduced after treatment with fermented plant samples (p < 0.001) as compared with that in non-fermented plants. Fermented plants were then sprayed at 1% (v/w) onto dog foods. TPC, TFC, ABTS radical scavenging activity, and DPPH radical scavenging activity of dog foods were significantly enhanced after the addition of fermented plants. Food preference testing was conducted using a two-pan method—control diet vs. four treatment diets—for 4 days for each additive diet, a total 16 days in 9 beagles. Feces were collected to enumerate bacterial counts. Preferences for glasswort and Ganghwa mugwort were higher than those of the control (p < 0.05). Furthermore, fecal microbiota enumeration displayed a higher number of beneficial microorganisms in treated groups. These results suggest that fermented plants with enhanced antioxidant abilities might be useful as potential additives for dog foods.

Patulin removal from synbiotic apple juice using Lactobacillus plantarum ATCC 8014

AIMS

The aim of this study was to evaluate the elimination of patulin (PAT) by Lactobacillus plantarum ATCC 8014 from artificially contaminated apple juice and its dependence on prebiotic, citric acid and ascorbic acid content.

METHODS AND RESULTS

A central composite design was used for studying each of the three factors at five levels to find the optimum concentrations. The results showed that inserting 2·3% (w/v) fructooligosaccharide, 213 mg l^-1 ascorbic acid and 1·4 g l^-1 citric acid to apple juice with inoculating 3·6 × 10¹¹ CFU per ml, L. plantarum improved the efficiency of PAT removal to 95·91% during 6 weeks cold storage. SDS-PAGE of cell surface proteins of probiotics revealed that surface layer proteins have an important role in PAT removal from apple juice. No significant difference was observed in the flavour and colour of the optimized synbiotic apple juice and in the control sample until 3 weeks of cold storage.

CONCLUSION

Lactobacillus plantarum ATCC 8014 is capable of PAT removal from artificially contaminated synbiotic apple juice.

SIGNIFICANCE AND IMPACT OF THE STUDY

Synbiotic apple juice artificially contaminated with PAT will be safe for consumers after the first day of probiotic inoculation; and surface layer proteins of probiotic cells are responsible for PAT removal.

A Surface Protein From Lactobacillus plantarum Increases the Adhesion of Lactobacillus Strains to Human Epithelial Cells

Adhesion to epithelial cells is considered important for Lactobacillus to exert probiotic effects. In this study, we found that trypsin treatment decreased the adhesion ability of Lactobacillus plantarum AR326 and AR269, which exhibit good adhesion ability, and surface proteins extracts increased the adhesion of the strains with poor adhesion ability. By SDS–polyacrylamide gel electrophoresis and mass spectrometry analysis, the main component of the surface proteins was detected and identified as a protein of approximately 37 kDa. It was 100% homologous with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from L. plantarum WCFS1. The adhesion of AR326 and AR269 was decreased significantly by blocking with the anti-GAPDH antibody, and GAPDH restored the adhesion of AR326 and AR269 treated with trypsin. In addition, purified GAPDH significantly increased the adhesion of the strains with poor adhesion ability. These results indicated that GAPDH mediates the adhesion of these highly adhesive lactobacilli to epithelial cells and can be used to improve the adhesion ability of probiotics or other bacteria of interest.

A Cell Surface Aggregation-Promoting Factor from Lactobacillus gasseri Contributes to Inhibition of Trichomonas vaginalis Adhesion to Human Vaginal Ectocervical Cells

Trichomoniasis, a prevalent sexually transmitted infection, is commonly symptomatic in women. The causative agent is Trichomonas vaginalis, an extracellular protozoan parasite. The host-protective mechanisms and molecules of vaginal lactobacilli that counteract this pathogen are largely unknown. This study examines the inhibition promoted by Lactobacillus gasseri against the adhesion of T. vaginalis to host cells, a critical virulence aspect of this pathogen. We observed that the vaginal strain L. gasseri ATCC 9857 is highly inhibitory by various contact-dependent mechanisms and that surface proteins are largely responsible for this inhibitory phenotype. We found that the aggregation-promoting factor APF-2 from these bacteria significantly contributes to inhibition of the adhesion of T. vaginalis to human vaginal ectocervical cells. Understanding the molecules and mechanisms used by lactobacilli to protect the host against T. vaginalis might help in the development of novel and specific therapeutic strategies that take advantage of the natural microbiota.

The aggregation-promoting factor in Lactobacillus delbrueckii ssp. bulgaricus: confirmation of the presence and expression of the apf gene and in silico analysis of the corresponding protein

In lactobacilli the aggregation phenotype is linked to their ability to colonize the intestinal and urogenital tracts and to counteract pathogenic bacteria. In all available complete genome sequences of Lactobacillus delbrueckii ssp. bulgaricus there are at least two genes putatively related to aggregation, one of which is annotated as aggregation-promoting factor (apf). Here we report the results from the in silico analysis of this gene and its product. The apf gene was present in the genome of all 70 tested L. delbr. ssp. bulgaricus strains. Its expression was confirmed for a selection of five strains with aggregation phenotype and two aggregation-negative strains. The mature Apf protein had a length of 257-284 amino acids with predicted molecular weight in the range of 28.64-30.36 kDa and isoelectric point of 10.6 ± 0.1, showing some similarity to Apf1 and Apf2 from L. johnsonii NCC533 and Apf1 and Apf2 from L. gasseri which are similar in size (28-35 kDa) and share a similar high isoelectric point (pI > 9). Predictive analyzes have indicated that Apf is a secretory protein. The 30 amino acid signal peptide and the predicted cleavage site in the pre-protein suggested that it was processed by Type I Signal protease. In the mature Apf protein a glutamine-rich N-terminal region was followed by an unusual lysine/alanine-rich region with variable length, supposed to be positively charged under physiological conditions, interacting with bacterial teichoic acids. The alignment of the C-termini of the Apf proteins showed similarity to conserved C-terminal domains in aggregation-related proteins in other lactobacilli such as Apf1 of Lactobacillus johnsonii ATCC 11506 and the secretory protein Sep of L. fermentum BR11, that may be involved in non-covalent binding to carbohydrates. The C-terminal anchor and the cationic domain in Apf may serve as mediators of physical cell-to-cell interaction in L. delbr. ssp. bulgaricus.

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.

Adhesion of Lactobacilli and their anti-infectivity potential

The probiotic potential of lactic acid bacteria primarily point toward colonizing ability of Lactobacilli as the most important attribute for endowing all the known beneficial effects in a host. Lactobacillus species exert health-promoting function in the gastrointestinal tract through various mechanisms such as pathogen exclusion, maintenance of microbial balance, immunomodulation, and other crucial functions. It has been seen that many surface layer proteins are involved in host adhesion, and play significant role in the modification of some signaling pathways within the host cells. Interaction between different bacterial cell surface proteins and host receptor has been imperative for a better understanding of the mechanism through which Lactobacilli exert their health-promoting functions.

Proteomic and genetics insights on the response of the bacteriocinogenic Lactobacillus sakei CRL1862 during biofilm formation on stainless steel surface at 10°C

Some lactic acid bacteria have the ability to form biofilms on food-industry surfaces and this property could be used to control food pathogens colonization. Lactobacillus sakei CR1862 was selected considering its bacteriocinogenic nature and ability to adhere to abiotic surfaces at low temperatures. In this study, the proteome of L. sakei CRL1862 grown either under biofilm on stainless steel surface and planktonic modes of growth at 10°C, was investigated. Using two-dimensional gel electrophoresis, 29 out of 43 statistically significant spots were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Ten proteins resulted up-regulated whereas 16 were down-regulated during biofilm formation. Differentially expressed proteins were found to belong to carbohydrate, nucleotide, aminoacid and lipid metabolisms as well as translation, peptide hydrolysis, cell envelope/cell wall biosynthesis, adaption to atypical conditions and protein secretion. Some proteins related to carbohydrate and nucleotide metabolisms, translation and peptide degradation were overexpressed whereas those associated to stress conditions were synthesized in lower amounts. It seems that conditions for biofilm development would not imply a stressful environment for L. sakei CRL1862 cells, directing its growth strategy towards glycolytic flux regulation and reinforcing protein synthesis. In addition, L. sakei CRL1862 showed to harbor nine out of ten assayed genes involved in biofilm formation and protein anchoring. By applying qRT-PCR analysis, four of these genes showed to be up regulated, srtA2 being the most remarkable. The results of this study contribute to the knowledge of the physiology of L. sakei CRL1862 growing in biofilm on a characteristic food contact surface. The use of this strain as green biocide preventing L. monocytogenes post-processing contamination on industrial surfaces may be considered.

Effect of probiotics on patulin removal from synbiotic apple juice

BACKGROUND

Studies have reported the occurrence of the mycotoxin patulin in apple products. The aim of this study was to produce synbiotic apple juice and investigate the detoxification of patulin by Lactobacillus acidophilus and Lactobacillus plantarum as probiotic strains. The impact of seven process variables on efficiency of toxin removal was investigated using Plackett-Burman design and presence of the surface-layer proteins as binding site of probiotics to patulin was confirmed during 6 weeks of cold storage.

RESULTS

Results showed that the removal of patulin by probiotic bacteria from apple juice depends significantly (P < 0.05) on the fructooligosaccharide content (as a prebiotic), concentration of patulin and the addition of ascorbic acid. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of cell surface proteins of probiotic strains revealed that surface layer proteins have an important role in patulin removal from apple juice. In the best conditions, 91.23% of initial patulin concentration was removed from juice during 6 weeks refrigerated storage. No significant difference was observed in organoleptic properties of the synbiotic apple juice and raw sample.

CONCLUSION

In the best condition reported in this study, contaminated synbiotic apple juice by patulin will be safe for consumers after the first day of probiotic inoculation. © 2016 Society of Chemical Industry.

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.

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.

Characteristics of surface layer proteins from two new and native strains of Lactobacillus brevis

In this work, some important characteristics of surface layer (S-layer) proteins extracted from two new and native Lactobacillus strains, L.brevis KM3 and L.brevis KM7, were investigated. The presence of S-layer on the external surface of L.brevis KM3 was displayed by thin sectioning and negative staining. SDS-PAGE analysis were shown same dominant protein bands approximately around 48kDa for both S-layer proteins. Moreover, the S-layer reappeared when LiCl treated cells were allowed to grow again. Protein secondary structure and thermal behavior were evaluated by using circular dichroism (CD) and differential scanning calorimetry (DSC), respectively. Both S-layer proteins had high content of β-sheet and low amount of α-helix. The thermograms of lyophilized S-layer proteins of L.brevis KM3 and L.brevis KM7 showed one transition peak at 67.9°C and 59.14°C, respectively. To determine monodispersity of extracted S-layer proteins, dynamic light scattering (DLS) was used. The results indicated that the main population of S-layer molecules in two tested lactobacillus strains were composed of monomer with an expected diameter close to 10nm. Furthermore, Zeta potential measurements were showed positive potential for both S-layer proteins, as expected. Our results could be used as the basis for biotechnological applications of these two new S-layer proteins.

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.

Discovering probiotic microorganisms: in vitro, in vivo, genetic and omics approaches

Over the past decades the food industry has been revolutionized toward the production of functional foods due to an increasing awareness of the consumers on the positive role of food in wellbeing and health. By definition probiotic foods must contain live microorganisms in adequate amounts so as to be beneficial for the consumer’s health. There are numerous probiotic foods marketed today and many probiotic strains are commercially available. However, the question that arises is how to determine the real probiotic potential of microorganisms. This is becoming increasingly important, as even a superficial search of the relevant literature reveals that the number of proclaimed probiotics is growing fast. While the vast majority of probiotic microorganisms are food-related or commensal bacteria that are often regarded as safe, probiotics from other sources are increasingly being reported raising possible regulatory and safety issues. Potential probiotics are selected after in vitro or in vivo assays by evaluating simple traits such as resistance to the acidic conditions of the stomach or bile resistance, or by assessing their impact on complicated host functions such as immune development, metabolic function or gut–brain interaction. While final human clinical trials are considered mandatory for communicating health benefits, rather few strains with positive studies have been able to convince legal authorities with these health claims. Consequently, concern has been raised about the validity of the workflows currently used to characterize probiotics. In this review we will present an overview of the most common assays employed in screening for probiotics, highlighting the potential strengths and limitations of these approaches. Furthermore, we will focus on how the advent of omics technologies has reshaped our understanding of the biology of probiotics, allowing the exploration of novel routes for screening and studying such microorganisms.

Role of S-layer proteins in the biosorption capacity of lead by Lactobacillus kefir

The role of S-layer proteins (SLP) on the Pb(2+) sequestrant capacity by Lactobacillus kefir CIDCA 8348 and JCM 5818 was investigated. Cultures in the stationary phase were treated with proteinase K. A dot blot assay was carried out to assess the removal of SLP. Strains with and without SLP were exposed to 0-0.5 mM Pb(NO3)2. The maximum binding capacity (q max ) and the affinity coefficient (b) were calculated using the Langmuir equation. The structural effect of Pb(2+) on microorganisms with and without SLP was determined using Raman spectroscopy. The bacterial interaction with Pb(2+) led to a broadening in the phosphate bands (1,300-1,200 cm(-1) region) and strong alterations on amide and carboxylate-related bands (νCOO(-) as and νCOO(-) s). Microorganisms without SLP removed higher percentages of Pb(2+) and had higher q max than those bearing SLP. Isolated SLP had much lower q max and also removed lower percentages of Pb(2+) than the corresponding whole microorganisms. The hydrofobicity of both strains dramatically dropped when removing SLP. When bearing SLP, strains do not expose a large amount of charged groups on their surfaces, thus making less efficient the Pb(2+) removal. On the contrary, the extremely low hydrofobicity of microorganisms without SLP (and consequently, their higher capacity to remove Pb(2+)) can be explained on the basis of a greater exposure of charged chemical groups for the interaction with Pb(2+). The viability of bacteria without SLP was not significantly lower than that of bacteria bearing SLP. However, microorganisms without SLP were more prone to the detrimental effect of Pb(2+), thus suggesting that SLP acts as a protective rather than as a sequestrant layer.

Impact of the exopolysaccharide layer on biofilms, adhesion and resistance to stress in Lactobacillus johnsonii FI9785

BACKGROUND

The bacterial cell surface is a crucial factor in cell-cell and cell-host interactions. Lactobacillus johnsonii FI9785 produces an exopolysaccharide (EPS) layer whose quantity and composition is altered in mutants that harbour genetic changes in their eps gene clusters. We have assessed the effect of changes in EPS production on cell surface characteristics that may affect the ability of L. johnsonii to colonise the poultry host and exclude pathogens.

RESULTS

Analysis of physicochemical cell surface characteristics reflected by Zeta potential and adhesion to hexadecane showed that an increase in EPS gave a less negative, more hydrophilic surface and reduced autoaggregation. Autoaggregation was significantly higher in mutants that have reduced EPS, indicating that EPS can mask surface structures responsible for cell-cell interactions. EPS also affected biofilm formation, but here the quantity of EPS produced was not the only determinant. A reduction in EPS production increased bacterial adhesion to chicken gut explants, but made the bacteria less able to survive some stresses.

CONCLUSIONS

This study showed that manipulation of EPS production in L. johnsonii FI9785 can affect properties which may improve its performance as a competitive exclusion agent, but that positive changes in adhesion may be compromised by a reduction in the ability to survive stress.

Comparison of five methods for direct extraction of surface proteins from Listeria monocytogenes for proteomic analysis by orbitrap mass spectrometry

Extracts of surface proteins, with minimal artifacts from contaminating cytosolic components, are highly desirable for investigating surface factors involved in the attachment and formation of biofilms by bacteria that are problematic in commercial food processing facilities. In this study, we compared the protein profiles of the food pathogen, Listeria monocytogenes, recovered after applying different surface protein extraction methods compiled from the literature: trypsin-enzymatic shaving with BICAM/sucrose or Tris/sucrose buffers (Tryp B+S, Tryp T+S), Tris-buffered urea (UB), lithium chloride (LiCl) and Tris-buffered urea applied with hypotonic-stressed cells (UB-Ghost), and subjected them to liquid chromatography tandem mass spectrometry and protein identification. The data indicate that the UB-Ghost extraction method provides a cleaner extract of surface proteins including the predicted (this study and the literature) or validated members (literature) from L. monocytogenes. This was determined by an accumulative lower unique peptide number exhibited by mass spectrometry for total cytoplasmic proteins among different surface extracts, with a majority of proteins demonstrating hydrophilic properties. The extracted proteins were from different functional categories and have associations with the cell surface, intermediary metabolism, information pathways, or functionally unknown proteins as suggested by in silico analyses performed by other groups (Leger and ListiList). The utilization of an optimized method for surface protein extraction should greatly facilitate identification by LC-MS/MS that could be useful to anyone working on molecular proteomics of bacterial surfaces.

Aggregation factor as an inhibitor of bacterial binding to gut mucosa

Modern research in the area of probiotics is largely devoted to discovering factors that promote the adherence of probiotic candidates to host mucosal surfaces. The aim of the present study was to test the role of aggregation factor (AggL) and mucin-binding protein (MbpL) from Lactococcus sp. in adhesion to gastrointestinal mucosa. In vitro, ex vivo, and in vivo experiments in rats were used to assess the adhesive potential of these two proteins expressed in heterologous host Lactobacillus salivarius BGHO1. Although there was no influence of MbpL protein expression on BGHO1 adhesion to gut mucosa, expression of AggL had a negative effect on BGHO1 binding to ileal and colonic rat mucosa, as well as to human HT29-MTX cells and porcine gastric mucin in vitro. Because AggL did not decrease the adhesion of bacteria to intestinal fragments in ex vivo tests, where peristaltic simulation conditions were missing, we propose that intestinal motility could be a crucial force for eliminating aggregation-factor-bearing bacteria. Bacterial strains expressing aggregation factor could facilitate the removal of pathogens through the coaggregation mechanism, thus balancing gut microbial ecosystems in people affected by intestinal bacteria overgrowth.

Lactobacillus gasseri SBT2055 reduces infection by and colonization of Campylobacter jejuni

Campylobacter is a normal inhabitant of the chicken gut. Pathogenic infection with this organism in humans is accompanied by severe inflammation of the intestinal mucosal surface. The aim of this study was to evaluate the ability of Lactobacillus gasseri SBT2055 (LG2055) to inhibit the adhesion and invasion of Campylobacter jejuni in vitro and to suppress C. jejuni colonization of chicks in vivo. Pretreatment with LG2055 significantly reduced adhesion to and invasion of a human epithelial cell line, Intestine 407, by C. jejuni 81-176. Methanol (MeOH)-fixed LG2055 also reduced infection by C. jejuni 81-176. However, proteinase K (ProK)-treated LG2055 eliminated the inhibitory effects. Moreover, LG2055 co-aggregated with C. jejuni 81-176. ProK treatment prevented this co-aggregation, indicating that the co-aggregation phenotype mediated by the proteinaceous cell-surface components of LG2055 is important for reducing C. jejuni 81-176 adhesion and invasion. In an in vivo assay, oral doses of LG2055 were administered to chicks daily for 14 days after oral inoculation with C. jejuni 81-176. At 14 days post-inoculation, chicks treated with LG2055 had significantly reduced cecum colonization by C. jejuni. Reduction in the number of C. jejuni 81-176 cells adhering to and internalized by human epithelial cells demonstrated that LG2055 is an organism that effectively and competitively excludes C. jejuni 81-176. In addition, the results of the chick colonization assay suggest that treatment with LG2055 could be useful in suppressing C. jejuni colonization of the chicks at early growth stages.

Adhesion of indigenous Lactobacillus plantarum to gut extracellular matrix and its physicochemical characterization

Adhesion to the human intestinal epithelial cell is considered as one of the important selection criteria of lactobacilli for probiotic attributes. Sixteen Lactobacillus plantarum strains from human origins were subjected for adhesion to extracellular matrix (ECM) components, and their physiochemical characterization, incubation time course and effect of different pH on bacterial adhesion in vitro were studied. Four strains showed significant binding to both fibronectin and mucin. After pretreatment with pepsin and trypsin, the bacterial adhesion to ECM reduced to the level of 50 % and with lysozyme significantly decreased by 65-70 %. Treatment with LiCl also strongly inhibited (90 %) the bacterial adhesion to ECM. Tested strains showed highest binding efficacy at time course of 120 and 180 min. Additionally, the binding of Lp91 to ECM was highest at pH 6 (155 ± 2.90 CFU/well). This study proved that surface layer components are proteinaceous in nature, which contributed in adhesion of lactobacillus strains. Further, the study can provide a better platform for introduction of new indigenous probiotic strains having strong adhesion potential for future use.

Generation of food-grade recombinant Lactobacillus casei delivering Myxococcus xanthus prolyl endopeptidase

Prolyl endopeptidases (PEP) (EC 3.4.21.26), a family of serine proteases with the ability to hydrolyze the peptide bond on the carboxyl side of an internal proline residue, are able to degrade immunotoxic peptides responsible for celiac disease (CD), such as a 33-residue gluten peptide (33-mer). Oral administration of PEP has been suggested as a potential therapeutic approach for CD, although delivery of the enzyme to the small intestine requires intrinsic gastric stability or advanced formulation technologies. We have engineered two food-grade Lactobacillus casei strains to deliver PEP in an in vitro model of small intestine environment. One strain secretes PEP into the extracellular medium, whereas the other retains PEP in the intracellular environment. The strain that secretes PEP into the extracellular medium is the most effective to degrade the 33-mer and is resistant to simulated gastrointestinal stress. Our results suggest that in the future, after more studies and clinical trials, an engineered food-grade Lactobacillus strain may be useful as a vector for in situ production of PEP in the upper small intestine of CD patients.

Variability of S-layer proteins in Lactobacillus helveticus strains

The presence of S-layer proteins in the cell envelope of Lactobacillus helveticus may be technologically important. S-layer proteins are the adhesion site for cell envelope proteinase, which forms the proteolytic pathway in bacteria. Eleven strains of L. helveticus were examined for the presence of S-layer proteins and slpH genes. S-layer proteins from six strains were identified and sequenced. Multiple alignments of the deduced amino acid sequences demonstrated a strong sequence conservation of all Slp studied. Transmission Electron Microscopy analysis of the cells revealed the typical cell wall architecture of the S-layer. This is the first report on characterisation of glycosylated S-layer proteins from different strains of L. helveticus. The amino acid composition, the secondary structure, and the physical properties of these proteins were found to be quite similar to those of S-layer proteins from other lactobacilli. However, PCR analysis revealed that five of the examined strains of L. helveticus did not have slpH genes. This finding suggests that S-layer protein genes cannot be considered as housekeeping genes and cannot be used as molecular markers for L. helveticus.

An extracellular Serine/Threonine-rich protein from Lactobacillus plantarum NCIMB 8826 is a novel aggregation-promoting factor with affinity to mucin

Autoaggregation in lactic acid bacteria is directly related to the production of certain extracellular proteins, notably, aggregation-promoting factors (APFs). Production of aggregation-promoting factors confers beneficial traits to probiotic-producing strains, contributing to their fitness for the intestinal environment. Furthermore, coaggregation with pathogens has been proposed to be a beneficial mechanism in probiotic lactic acid bacteria. This mechanism would limit attachment of the pathogen to the gut mucosa, favoring its removal by the human immune system. In the present paper, we have characterized a novel aggregation-promoting factor in Lactobacillus plantarum. A mutant with a knockout of the D1 gene showed loss of its autoaggregative phenotype and a decreased ability to bind to mucin, indicating an adhesion role of this protein. In addition, heterologous production of the D1 protein or an internal fragment of the protein, characterized by its abundance in serine/threonine, strongly induced autoaggregation in Lactococcus lactis. This result strongly suggested that this internal fragment is responsible for the bioactivity of D1 as an APF. To our knowledge, this is the first report on a gene coding for an aggregation-promoting factor in Lb. plantarum.

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.

Genomic and phenotypic evidence for probiotic influences of Lactobacillus gasseri on human health

Certain lactic acid bacteria (LAB) have the capacity to occupy mucosal niches of humans, including the oral cavity, gastrointestinal tract, and vagina. Among commensal, LAB are species of the acidophilus complex, which have proven to be a substantial reservoir for microorganisms with probiotic attributes. Specifically, Lactobacillus gasseri is an autochthonous microorganism which has been evaluated for probiotic activity based on the availability of genome sequence and species-specific adaptation to the human mucosa. Niche-related characteristics of L. gasseri contributing to indigenous colonization include tolerance of low pH environments, resistance to bile salts, and adhesion to the host epithelium. In humans, L. gasseri elicits various health benefits through its antimicrobial activity, bacteriocin production, and immunomodulation of the innate and adaptive systems. The genomic and empirical evidence supporting use of L. gasseri in probiotic applications is substantiated by clinical trial data displaying maintenance of vaginal homeostasis, mitigation of Helicobacter pylori infection, and amelioration of diarrhea.

Spontaneous mutation reveals influence of exopolysaccharide on Lactobacillus johnsonii surface characteristics

As a competitive exclusion agent, Lactobacillus johnsonii FI9785 has been shown to prevent the colonization of selected pathogenic bacteria from the chicken gastrointestinal tract. During growth of the bacterium a rare but consistent emergence of an altered phenotype was noted, generating smooth colonies in contrast to the wild type rough form. A smooth colony variant was isolated and two-dimensional gel analysis of both strains revealed a protein spot with different migration properties in the two phenotypes. The spot in both gels was identified as a putative tyrosine kinase (EpsC), associated with a predicted exopolysaccharide gene cluster. Sequencing of the epsC gene from the smooth mutant revealed a single substitution (G to A) in the coding strand, resulting in the amino acid change D88N in the corresponding gene product. A native plasmid of L. johnsonii was engineered to produce a novel vector for constitutive expression and this was used to demonstrate that expression of the wild type epsC gene in the smooth mutant produced a reversion to the rough colony phenotype. Both the mutant and epsC complemented strains had increased levels of exopolysaccharides compared to the wild type strain, indicating that the rough phenotype is not solely associated with the quantity of exopolysaccharide. Another gene in the cluster, epsE, that encoded a putative undecaprenyl-phosphate galactosephosphotransferase, was deleted in order to investigate its role in exopolysaccharide biosynthesis. The ΔepsE strain exhibited a large increase in cell aggregation and a reduction in exopolysaccharide content, while plasmid complementation of epsE restored the wild type phenotype. Flow cytometry showed that the wild type and derivative strains exhibited clear differences in their adhesive ability to HT29 monolayers in tissue culture, demonstrating an impact of EPS on surface properties and bacteria-host interactions.

Studying the Stability of S-Layer Protein of Lactobacillus Acidophilus ATCC 4356 in Simulated Gastrointestinal Fluids Using SDS-PAGE and Circular Dichroism

Crystalline arrays of proteinaceous subunits forming surface layers (S-layers) are now recognized as one of the most common outermost cell envelope components of prokaryotic organisms. The surface layer protein of Lactobacillus acidophilus ATCC4356 is composed of a single species of protein of apparent molecular weight of 43-46 KDa. Considering the Lactobacillus acidophilus ATCC4356 having the S-layer is stable in harsh gastrointestinal (GI) conditions, a protective role against destructive GI factors which has been proposed for these nanostructures. It opens interesting perspectives in the using and development of this S-layer as a protective coat for oral administration of unstable drug nanocarriers. To achieve this goal, it is necessary to study the in-vitro stability of the S-layers in the simulated gastrointestinal fluids (SGIF). This study was planned to evaluate the in-vitro stability of the extracted S-layer protein of Lactobacillus acidophilus ATCC4356 in SGIF using it as a protective coat in oral drug delivery. Sodium dodecyl sulfate gel electrophoresis (SDS-PAGE) and circular dichroism (CD) spectroscopy were used to study the stability of the S-layer protein incubated in SGIF. Both the SDS-PAGE and CD spectra results showed that Lactobacillus acidophilus ATCC4356 S-layer protein is stable in simulated gastric fluid (SGF) with pH = 2 up to 5 min. It is stable in SGF pH = 3.2 and above it, with and without pepsin. It is also stable in all the simulated intestinal fluids. This S-layer is also stable in all of the simulated intestinal fluids.

Inhibition of Staphylococcus aureus by lysostaphin-expressing Lactobacillus plantarum WCFS1 in a modified genital tract secretion medium

Lactobacillus species are a predominant member of the vaginal microflora and are critical in maintaining an acidic vaginal environment thought to contribute to the prevention of a number of urogenital diseases. However, during menstruation the pH of the vaginal environment increases to neutrality, a pH conducive for Staphylococcus aureus proliferation and the production of toxic shock syndrome toxin 1 (TSST-1) in susceptible women. In order to generate Lactobacillus species capable of expressing lysostaphin (an endopeptidase that cleaves the cell wall of S. aureus) in a modified genital tract secretion medium (mGTS) under neutral-pH conditions, six prominent proteins from Lactobacillus plantarum WCFS1 spent medium were identified by mass spectrometry. Sequences for promoters, signal peptides, and mature lysostaphin were used to construct plasmids that were subsequently transformed into L. plantarum WCFS1. The promoter and signal sequences of Lp_3014 (putatively identified as a transglycosylase) or the promoter sequence of Lp_0789 (putatively identified as glyceraldehyde 3-phosphate dehydrogenase) with the signal sequence of Lp_3014 exhibited lysostaphin activity on buffered medium containing heat-killed S. aureus. The cassettes were integrated into the chromosome of L. plantarum WCFS1, but only the cassette containing the promoter and signal sequence from Lp_3014 had integrated into the appropriate site. Coculture assays using buffered mGTS showed that lysostaphin expressed from L. plantarum WCFS1 reduced the growth of TSST-1-producing strains of S. aureus under neutral-pH conditions. This study provides the basis for determining whether lysostaphin-producing Lactobacillus strains could potentially be used as a means to inhibit the growth of S. aureus during menstruation.

Lactobacilli at the front line of defense against vaginally acquired infections

Probiotics are microorganisms that provide a health benefit to the host and are promoted as alternatives for the treatment and prevention of infectious diseases and other conditions. One of the most rapidly developing areas of probiotic research is in the management of vaginally acquired infections. Several Lactobacillus species produce compounds that kill or inhibit the growth of vaginally acquired pathogens. Other lactobacilli reduce the adherence of pathogens to urogenital epithelial cells in culture. This article discusses the mechanisms by which vaginal lactobacilli prevent pathogen colonization of the urogenital tract, and potential mechanisms that warrant investigation. Animal models and clinical studies, while limited, are discussed with the idea that these are the next critical steps to advance the study of probiotics for the treatment and prevention of vaginally acquired infections.

Integrative expression system for delivery of antibody fragments by lactobacilli

A series of expression cassettes which mediate secretion or surface display of antibody fragments was stably integrated in the chromosome of Lactobacillus paracasei. L. paracasei producing surface-anchored variable domain of llama heavy chain (VHH) (ARP1) directed against rotavirus showed efficient binding to rotavirus and protection in the mouse model of rotavirus infection.

LAB-Secretome: a genome-scale comparative analysis of the predicted extracellular and surface-associated proteins of Lactic Acid Bacteria

Background

In Lactic Acid Bacteria (LAB), the extracellular and surface-associated proteins can be involved in processes such as cell wall metabolism, degradation and uptake of nutrients, communication and binding to substrates or hosts. A genome-scale comparative study of these proteins (secretomes) can provide vast information towards the understanding of the molecular evolution, diversity, function and adaptation of LAB to their specific environmental niches.

Results

We have performed an extensive prediction and comparison of the secretomes from 26 sequenced LAB genomes. A new approach to detect homolog clusters of secretome proteins (LaCOGs) was designed by integrating protein subcellular location prediction and homology clustering methods. The initial clusters were further adjusted semi-manually based on multiple sequence alignments, domain compositions, pseudogene analysis and biological function of the proteins. Ubiquitous protein families were identified, as well as species-specific, strain-specific, and niche-specific LaCOGs. Comparative analysis of protein subfamilies has shown that the distribution and functional specificity of LaCOGs could be used to explain many niche-specific phenotypes.

A comprehensive and user-friendly database LAB-Secretome was constructed to store, visualize and update the extracellular proteins and LaCOGs http://www.cmbi.ru.nl/lab_secretome/. This database will be updated regularly when new bacterial genomes become available.

Conclusions

The LAB-Secretome database could be used to understand the evolution and adaptation of lactic acid bacteria to their environmental niches, to improve protein functional annotation and to serve as basis for targeted experimental studies.