Lactobacillus surface layers and their applications

Therapeutic potential of Parabacteroides distasonis in gastrointestinal and hepatic disease

Increasing evidences indicate that the gut microbiota is involved in the development and therapy of gastrointestinal and hepatic disease. Imbalance of gut microbiota occurs in the early stages of diseases, and maintaining the balance of the gut microbiota provides a new strategy for the treatment of diseases. It has been reported that Parabacteroides distasonis is associated with multiple diseases. As the next-generation probiotics, several studies have demonstrated its positive regulation on the gastrointestinal and hepatic disease, including inflammatory bowel disease, colorectal cancer, hepatic fibrosis, and fatty liver. The function of P. distasonis and its metabolites mainly affect host immune system, intestinal barrier function, and metabolic networks. Manipulation of P. distasonis with natural components lead to the protective effect on enterohepatic disease. In this review, the metabolic pathways regulated by P. distasonis are summarized to illustrate its active metabolites and their impact on host metabolism, the role and action mechanism in gastrointestinal and hepatic disease are discussed. More importantly, the natural components can be used to manipulate P. distasonis as treatment strategies, and the challenges and perspectives of P. distasonis in clinical applications are discussed.

Specific gut microbiome signatures predict the risk of acute ischemic stroke

Introduction

Numerous studies have reported alterations in the composition of gut microbiota in patients with acute ischemic stroke (AIS), with changes becoming more pronounced as the disease progresses. However, the association between the progression of transient ischemic attack (TIA) and AIS remains unclear. This study aims to elucidate the microbial differences among TIA, AIS, and healthy controls (HC) while exploring the associations between disease progression and gut microbiota.

Methods

Fecal samples were collected from acute TIA patients (n = 28), AIS patients (n = 235), and healthy controls (n = 75) and analyzed using 16 s rRNA gene sequencing. We determined characteristic microbiota through linear discriminant analysis effect size and used the receiver operating characteristic (ROC) curve to assess their predictive value as diagnostic biomarkers.

Results

Our results showed significant gut microbial differences among the TIA, AIS, and HC groups. Patients with AIS exhibited higher abundances of Lactobacillus and Streptococcus, along with lower abundances of Butyricicoccaceae and Lachnospiraceae_UCG-004. Further analysis revealed that the abundance of characteristic bacteria, such as Lactobacillus and Streptococcus, was negatively correlated with HDL levels, while Lactobacillus was positively correlated with risk factors such as homocysteine (Hcy). In contrast, the abundance of Lachnospiraceae_UCG-004 was negatively correlated with both Hcy and D-dimer levels. ROC models based on the characteristic bacteria Streptococcus and Lactobacillus effectively distinguished TIA from AIS, yielding areas under the curve of 0.699 and 0.626, respectively.

Conclusion

We identified distinct changes in gut bacteria associated with the progression from TIA to AIS and highlighted specific characteristic bacteria as predictive biomarkers. Overall, our findings may promote the development of microbiome-oriented diagnostic methods for the early detection of AIS.

Alginate Oligosaccharides Enhance Gut Microbiota and Intestinal Barrier Function, Alleviating Host Damage Induced by Deoxynivalenol in Mice

BACKGROUND

Alginate oligosaccharides (AOS) exhibits notable effects in terms of anti-inflammatory, antibacterial, and antioxidant properties. Deoxynivalenol (DON) has the potential to trigger intestinal inflammation by upregulating pro-inflammatory cytokines and apoptosis, thereby compromising the integrity of the intestinal barrier function and perturbing the balance of the gut microbiota.

OBJECTIVES

We assessed the impact of AOS on mitigating DON-induced intestinal damage and systemic inflammation in mice.

METHODS

After a 1-wk acclimatization period, the mice were divided into 4 groups. For 3 wk, the AOS and AOS + DON groups were gavaged daily with 200 μL of AOS [200 mg/kg body weight (BW)], whereas the CON and DON groups received an equivalent volume of sterile Phosphate-Buffered Saline (PBS). Subsequently, for 1 wk, the DON and AOS + DON groups received 100 μL of DON (4.8 mg/kg BW) daily, whereas the control (CON) and AOS groups continued receiving PBS.

RESULTS

After administering DON via gavage to mice, there was a significant decrease (P < 0.05) in body weights compared with the CON group. Interestingly, AOS exhibited a tendency to mitigate this weight loss in the AOS + DON group. In the feces of mice treated with both AOS and DON, the concentration of DON significantly increased (P < 0.05) compared with the DON group alone. Histological analysis revealed that DON exposure caused increased intestinal damage, including shortened villi and eroded epithelial cells, which was ameliorated by presupplementation with AOS, alleviating harm to the intestinal barrier function. In both jejunum and colon tissues, DON exposure significantly reduced (P < 0.05) the expression of tight junction proteins (claudin and occludin in the colon) and the mucin protein mucin 2, compared with the CON group. Prophylactic administration of AOS alleviated these reductions, thereby improving the expression levels of these key proteins. Additionally, AOS supplementation protected DON-exposed mice by increasing the abundance of probiotics such as Bifidobacterium, Faecalibaculum, and Romboutsia. These gut microbes are known to enhance (P < 0.05) anti-inflammatory responses and the production of short-chain fatty acids (SCFAs), including total SCFAs, acetate, and valerate, compared with the DON group.

CONCLUSIONS

This study unveils that AOS not only enhances gut microbiota and intestinal barrier function but also significantly mitigates DON-induced intestinal damage.

Lactobacillus gasseri and Gardnerella vaginalis produce extracellular vesicles that contribute to the function of the vaginal microbiome and modulate host-Trichomonas vaginalis interactions

Trichomonas vaginalis is an extracellular protozoan parasite of the human urogenital tract, responsible for a prevalent sexually transmitted infection. Trichomoniasis is accompanied by a dysbiotic microbiome that is characterised by the depletion of host-protective commensals such as Lactobacillus gasseri, and the flourishing of a bacterial consortium that is comparable to the one seen for bacterial vaginosis, including the founder species Gardnerella vaginalis. These two vaginal bacteria are known to have opposite effects on T. vaginalis pathogenicity. Studies on extracellular vesicles (EVs) have been focused on the direction of a microbial producer (commensal or pathogen) to a host recipient, and largely in the context of the gut microbiome. Here, taking advantage of the simplicity of the human cervicovaginal microbiome, we determined the molecular cargo of EVs produced by L. gasseri and G. vaginalis and examined how these vesicles modulate the interaction of T. vaginalis and host cells. We show that these EVs carry a specific cargo of proteins, which functions can be attributed to the opposite roles that these bacteria play in the vaginal biome. Furthermore, these bacterial EVs are delivered to host and protozoan cells, modulating host-pathogen interactions in a way that mimics the opposite effects that these bacteria have on T. vaginalis pathogenicity. This is the first study to describe side-by-side the protein composition of EVs produced by two bacteria belonging to the opposite spectrum of a microbiome and to demonstrate that these vesicles modulate the pathogenicity of a protozoan parasite. Such as in trichomoniasis, infections and dysbiosis co-occur frequently resulting in significant co-morbidities. Therefore, studies like this provide the knowledge for the development of antimicrobial therapies that aim to clear the infection while restoring a healthy microbiome.

The complex world of kefir: Structural insights and symbiotic relationships

Kefir milk, known for its high nutritional value and health benefits, is traditionally produced by fermenting milk with kefir grains. These grains are a complex symbiotic community of lactic acid bacteria, acetic acid bacteria, yeasts, and other microorganisms. However, the intricate coexistence mechanisms within these microbial colonies remain a mystery, posing challenges in predicting their biological and functional traits. This uncertainty often leads to variability in kefir milk's quality and safety. This review delves into the unique structural characteristics of kefir grains, particularly their distinctive hollow structure. We propose hypotheses on their formation, which appears to be influenced by the aggregation behaviors of the community members and their alliances. In kefir milk, a systematic colonization process is driven by metabolite release, orchestrating the spatiotemporal rearrangement of ecological niches. We place special emphasis on the dynamic spatiotemporal changes within the kefir microbial community. Spatially, we observe variations in species morphology and distribution across different locations within the grain structure. Temporally, the review highlights the succession patterns of the microbial community, shedding light on their evolving interactions.Furthermore, we explore the ecological mechanisms underpinning the formation of a stable community composition. The interplay of cooperative and competitive species within these microorganisms ensures a dynamic balance, contributing to the community's richness and stability. In kefir community, competitive species foster diversity and stability, whereas cooperative species bolster mutualistic symbiosis. By deepening our understanding of the behaviors of these complex microbial communities, we can pave the way for future advancements in the development and diversification of starter cultures for food fermentation processes.

The molecular architecture of Lactobacillus S-layer: Assembly and attachment to teichoic acids

S-layers are crystalline arrays found on bacterial and archaeal cells. Lactobacillus is a diverse family of bacteria known especially for potential gut health benefits. This study focuses on the S-layer proteins from Lactobacillus acidophilus and Lactobacillus amylovorus common in the mammalian gut. Atomic resolution structures of Lactobacillus S-layer proteins SlpA and SlpX exhibit domain swapping, and the obtained assembly model of the main S-layer protein SlpA aligns well with prior electron microscopy and mutagenesis data. The S-layer's pore size suggests a protective role, with charged areas aiding adhesion. A highly similar domain organization and interaction network are observed across the Lactobacillus genus. Interaction studies revealed conserved binding areas specific for attachment to teichoic acids. The structure of the SlpA S-layer and the suggested incorporation of SlpX as well as its interaction with teichoic acids lay the foundation for deciphering its role in immune responses and for developing effective treatments for a variety of infectious and bacteria-mediated inflammation processes, opening opportunities for targeted engineering of the S-layer or lactobacilli bacteria in general.

Formulation of food grade Limosilactobacillus fermentum for antifungal properties isolated from home-made curd

Food spoilage has become a worldwide problem. Limosilactobacillus fermentum LAB212, isolated from home-made curd produces some potent antifungal compounds which can combat a wide range of spoilage and pathogenic fungi by disrupting their cell wall. Dual culture overlay assay and co-culture assay have confirmedly shown the potentiality of the strain. DOWEX50H + extraction and chemical characterization by high performance liquid chromatography show that lactic acid and acetic acid are playing the key roles in executing the antifungal activity. DPPH scavenging assay proves that the strain also exhibits a good antioxidant activity. After observing all the beneficial features and social need of the chemical preservative free food it is becoming highly prospective to exploite the strain commercially. In an experiment conducted for 180 days it was standardized that LAB212 supplemented with MRS and inulin is found most effective combination when challenged against the spoilage fungal species of Aspergillus flavus VBAH14, Penicillium rubens VBCA11, thus can be used as a very effective preservative agent. Using this strain as bio-preservative agent will also minimize the food borne diseases.

Promising application of probiotic microorganisms as Pickering emulsions stabilizers

The purpose of this work was to study the ability of nineteen food-grade microorganisms as Pickering emulsion (PE) stabilizers. Medium-chain triacylglycerol (MCT) oil-in-water (50:50) PEs were fabricated by 10 wt% or 15 wt% of thermally-inactivated yeast, cocci, Bacillus spp. and lactobacilli cells. The characteristics of microorganisms related to "Pickering stabilization" including morphology, surface charge, interfacial tension, and "contact angle" were firstly studied. After that, the cells-stabilized PEs were characterized from both kinetic and thermodynamic viewpoints, microstructure and rheological properties. The interfacial tension and "contact angle" values of various microorganisms ranged from 16.33 to 38.31 mN/m, and from 15° to 106°, respectively. The mean droplet size of PEs ranged from 11.51 to 57.69 µm. Generally, the physical stability of cell-stabilized PEs followed this order: lactobacilli > Bacillus spp. > cocci > yeast. These variations were attributed to the morphology and cell wall composition. Increasing the microorganism concentration significantly increased the physical stability of PEs from a maximum of 12 days at 10 wt% to 35 days at 15 wt% as a result of better interface coverage. Shear-thinning and dominant elastic behaviors were observed in PEs. Physical stability was affected by the free energy of detachment. Therefore, food-grade microorganisms are suggested for stabilizing PEs.

Application of two glycosylated Lactobacillus surface layer proteins in coating cationic liposomes

The ability of isolated surface layer proteins (SLPs) to reassemble on suitable surfaces enables the application of SLPs in various fields of nanotechnology. In this work, SLPs from Lactobacillus buchneri BNCC 187,964 and L. kefir BNCC 190,565 were extracted and verified as glycosylated proteins. They were applied to coat on the surface of cationic liposomes. The absorption of the two SLPs on liposomes induced the zeta potential reduction and particle size increase. The two kinds of SLP-coated liposomes demonstrated better thermal, light and pH stability than the control liposomes. And the L. kefir SLP showed better protective effects than the L. buchneri SLP. Moreover, both of the SLPs could endow liposomes with the function of binding ferritin as observed by transmission electron microscope. Fourier transform infrared spectroscopy illustrated that the interaction between the two SLPs and liposomes was similar. The recrystallization of the two SLPs on the liposomes might drive the lipid into a higher order state and hydrogen bonds were formed between the two SLPs and the liposomes. All the findings demonstrated that L. kefir SLP and L. buchneri SLP had great potential to be explored as effective coating agents to improve the stability and function of cationic liposomes.Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary.Yes, all have been checked.

Characterization of keystone taxa and microbial metabolic potentials in copper tailing soils

Copper mining has caused serious soil contamination and threaten the balance of underground ecosystem. Effects of metal contamination on the soil microbial community assembly and their multifunctionality are still unclear. In this study, the keystone taxa and microbial metabolic potential of soil microorganisms surrounding a typical copper tailing were investigated. Results showed that pH and metal contents of adjacent soil in copper tailing increased, which largely reduced soil microbial communities' diversity. Metal contaminated soils enriched a group of keystone taxa with metal-tolerance such as Bacteroidota (20-54%) and Firmicutes (24-48%), which were distinct from the uncontaminated background soils that dominated by Proteobacteria (19-24%) and Actinobacteria (13-24%). In the contaminated soils, these keystone taxa were identified as Alistipes, Bacteroides, and Faecalibacterium, suggesting their adaptation to the metal-rich environment. Co-occurrence network analysis showed that the microbial community was loosely connected in the metal contaminated soils with a lower number of nodes and links. Co-occurrence networks further revealed that the dynamics of keystone taxa significantly correlated with copper content. Functional gene analysis of soil microorganisms indicated that metal contamination might inhibit important microbial metabolic potentials, such as secondary metabolites biosynthesis, carbon fixation, and nitrogen fixation. Results also found the flexible adaptation strategies of soil microbial communities to metal-rich environments with metal-resistance or bio-transformation, such as efflux (CusB/CusF/CzsB and pcoB/copB) and oxidation (aoxAB). These findings provide insight into the interaction between keystone taxa and soil environment, which is helpful to reveal the microbial metabolic potential and physiological characteristics in tailing contaminated soils.

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.

Protective effect of surface-layer proteins from four Lactobacillus strains on tumor necrosis factor-α-induced intestinal barrier dysfunction

BACKGROUND

The intestinal epithelium is considered the first defense protection against exogenous harmful substances, playing an indispensable role in regulating intestinal health. The protection offered by surface-layer proteins (Slps) from different Lactobacillus strains on an impaired intestinal barrier was investigated in this study.

RESULTS

Four Slps pre-incubated for 6 h significantly prevented the reduced transepithelial electrical resistance value and increased paracellular permeability in tumor necrosis factor (TNF)-α-induced Caco-2 monolayers. TNF-α induced lower protein expression of occludin and zonula occludens-1, and abnormal distributions of occludin and zonula occludens-1 were ameliorated by four Slps as well. Additionally, four Slps weakened TNF-α-evoked interleukin-8 secretion and nuclear factor-κB activation.

CONCLUSION

Four Slps from different strains prevent the intestinal barrier from TNF-α-induced dysfunction through blocking the nuclear factor-κB signaling pathway. © 2022 Society of Chemical Industry.

Dynamic Profile of S-Layer Proteins Controls Surface Properties of Emetic Bacillus cereus AH187 Strain

Many prokaryotes are covered by a two-dimensional array of proteinaceous subunits. This surface layers (S-layer) is incompletely characterized for many microorganisms. Here, we studied Bacillus cereus AH187. A genome analysis identified two genes encoding the S-layer proteins SL2 and EA1, which we experimentally confirmed to encode the two protein components of the S-layer covering the surface of B. cereus. Shotgun proteomics analysis indicated that SL2 is the major component of the B. cereus S-layer at the beginning of exponential growth, whereas EA1 becomes more abundant than SL2 during later stages of stationary growth. Microscopy analysis revealed the spatial organization of SL2 and EA1 at the surface of B. cereus to depend on their temporal-dynamics during growth. Our results also show that a mutant strain lacking functional SL2 and EA1 proteins has distinct surface properties compared to its parental strain, in terms of stiffness and hydrophilicity during the stationary growth phase. Surface properties, self-aggregation capacity, and bacterial adhesion were observed to correlate. We conclude that the dynamics of SL2 and EA1 expression is a key determinant of the surface properties of B. cereus AH187, and that the S-layer could contribute to B. cereus survival in starvation conditions.

Genetic Elements Orchestrating Lactobacillus crispatus Glycogen Metabolism in the Vagina

Glycogen in the female lower reproductive tract is a major carbon source for colonization and acidification by common vaginal Lactobacillus species, such as Lactobacillus crispatus. Previously, we identified the amylopullulanase encoding gene pulA of Lactobacillus crispatus to correlate with the ability to autonomously utilize glycogen for growth. Here, we further characterize genetic variation and differential regulation of pulA affecting the presence of its gene product on the outer surface layer. We show that alpha-glucan degrading activity dissipates when Lactobacillus crispatus is grown on glucose, maltose and maltotriose, in agreement with carbon catabolite repression elements flanking the pulA gene. Proteome analysis of the S-layer confirmed that the amylopullulanase protein is highly abundant in an S-layer enriched fraction, but not in a strain with a defective amylopullulanase variant or in an amylopullulanase-sufficient strain grown on glucose. In addition, we provide evidence that Lactobacillus crispatus pulA mutants are relevant in vivo, as they are commonly observed in metagenome datasets of human vaginal microbial communities. Analysis of the largest publicly available dataset of 1507 human vaginal metagenomes indicates that among the 270 samples that contain a Lactobacillus crispatuspulA gene, 62 samples (23%) had a defective variant of this gene. Taken together, these results demonstrate that both environmental, as well as genetic factors explain the variation of Lactobacillus crispatus alpha-glucosidases in the vaginal environment.

Anti-inflammation and adhesion enhancement properties of the multifunctional LPxTG-motif surface protein derived from the Lactobacillus reuteri DSM 8533

LPxTG-motif protein (LMP) is one kind of a precursor protein that contains a conserved LPxTG-motif at the C-terminus, which can be recognized by sortase A (SrtA) and covalently bind to the bacterial peptidoglycan. In this study, LMP derived from Lactobacillus reuteri (L. reuteri) was heterologous expressed and the tolerance and intestinal colonization ability of the LMP on L. reuteri were analyzed in simulated gastrointestinal fluid. Meanwhile, the anti-inflammatory activity of LMP was also evaluated in the LPS-stimulated RAW 264.7 cell model. The results indicated that LMP can promote the intestinal survival rate and adhesion characteristics of L. reuteri and enhanced the autoinducer-2 (AI-2) signaling molecule of the Lactobacillus strains in quorum sensing. Furthermore, LMP can inhibit the expressions of inflammatory cytokine TNF-α and IL-1β via ERK-JNK related MAPK signaling cascades. These findings provide a better understanding of the multifunctional LPxTG-motif surface protein derived from L. reuteri in the gastrointestinal tract environment.

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.

Nanoarchitectonics for enhanced antibacterial activity with Lactobacillus buchneri S-layer proteins-coated silver nanoparticles

Various multi-drug-resistant microorganisms have appeared while a single antibacterial agent is increasingly no longer adequate for dealing with these resistant microorganisms. Herein, commercially purchased 50 nm-average-diameter silver nanoparticles (AgNPs) and Lactobacillus buchneri-isolated surface-layer proteins (SLPs) as a capping agent were used to fabricate a hybrid antibacterial agent (SLP-AgNPs) with enhanced antibacterial activity, and the possible synergistic antibacterial mechanism was explored. Characterization results revealed that SLP-AgNPs were uniformly surrounded by protein corona provided from SLP, and the formulations were mainly mediated by the electrostatic interactions and hydrogen bonding, which was evidenced by the results of Fourier transform infrared spectroscopy. According to the antibacterial tests, the minimum inhibitory concentration of SLP-AgNPs against Salmonella enterica (0.010 mg/mL) and Staphylococcus aureus (0.005 mg/mL) was 5-10 times lower than that of bare AgNPs, and while SLP-AgNPs showed a higher antibiofilm activity. Furthermore, bacterial cells exposed to SLP-AgNPs exhibited higher cell membrane permeability and stronger inhibition of respiratory-chain dehydrogenase activity, resulting in more severe cell death compared with bare AgNPs. The synergistic effect of SLP on AgNPs was probably carried out by enhanced function of adhesion to bacteria and antibacterial ability of SLP and SLP's supramolecular lattice structure on the sustained release of silver ion.

Microbial cell surface engineering for high-level synthesis of bio-products

Microbial cell surface layers, which mainly include the cell membrane, cell wall, periplasmic space, outer membrane, capsules, S-layers, pili, and flagella, control material exchange between the cell and the extracellular environment, and have great impact on production titers and yields of various bio-products synthesized by microbes. Recent research work has made exciting achievements in metabolic engineering using microbial cell surface components as novel regulation targets without direct modifications of the metabolic pathways of the desired products. This review article will summarize the accomplishments obtained in this emerging field, and will describe various engineering strategies that have been adopted in bacteria and yeasts for the enhancement of mass transfer across the cell surface, improvement of protein expression and folding, modulation of cell size and shape, and re-direction of cellular resources, all of which contribute to the construction of more efficient microbial cell factories toward the synthesis of a variety of bio-products. The existing problems and possible future directions will also be discussed.

Characteristics of surface layer protein from Lactobacillus kefiri HBA20 and the role in mediating interactions with Saccharomyces cerevisiae Y8

In this study, the surface layer protein (SLP) from Lactobacillus kefiri HBA20 was characterized. The SLP was extracted by 5 M LiCl. The molecular mass of the SLP was approximately 64 kDa as analyzed via SDS-PAGE. The surface morphology and the adhesion potential of L. kefiri HBA20 in the absence and presence of SLP were measured by AFM. Moreover, the protein secondary structure was evaluated by using circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR), respectively. SLP had high β-sheet contents and low content of α-helix. Thermal analysis of SLP of Lactobacillus kefiri HBA20 exhibited one transition peak at 129.64 °C. Furthermore, SEM measurements were showed that after the SLP were removed from the cell surface, the coaggregation ability with Saccharomyces cerevisiae Y8 of the strain was significantly reduced. In conclusion, the SLP of Lactobacillus kefiri HBA20 has a stable structure and the ability of adhesion to yeast. Molecular docking study revealed that mannan bind with the hydrophobic residues of SLP. Our results will help further understanding of the new surface layer protein and the interaction between L. kefiri and S. cerevisiae.

The Polygonal Cell Shape and Surface Protein Layer of Anaerobic Methane-Oxidizing Methylomirabilis lanthanidiphila Bacteria

Methylomirabilis bacteria perform anaerobic methane oxidation coupled to nitrite reduction via an intra-aerobic pathway, producing carbon dioxide and dinitrogen gas. These diderm bacteria possess an unusual polygonal cell shape with sharp ridges that run along the cell body. Previously, a putative surface protein layer (S-layer) was observed as the outermost cell layer of these bacteria. We hypothesized that this S-layer is the determining factor for their polygonal cell shape. Therefore, we enriched the S-layer from M. lanthanidiphila cells and through LC-MS/MS identified a 31 kDa candidate S-layer protein, mela_00855, which had no homology to any other known protein. Antibodies were generated against a synthesized peptide derived from the mela_00855 protein sequence and used in immunogold localization to verify its identity and location. Both on thin sections of M. lanthanidiphila cells and in negative-stained enriched S-layer patches, the immunogold localization identified mela_00855 as the S-layer protein. Using electron cryo-tomography and sub-tomogram averaging of S-layer patches, we observed that the S-layer has a hexagonal symmetry. Cryo-tomography of whole cells showed that the S-layer and the outer membrane, but not the peptidoglycan layer and the cytoplasmic membrane, exhibited the polygonal shape. Moreover, the S-layer consisted of multiple rigid sheets that partially overlapped, most likely giving rise to the unique polygonal cell shape. These characteristics make the S-layer of M. lanthanidiphila a distinctive and intriguing case to study.

Use of encapsulated lactic acid bacteria as bioprotective cultures in fresh Brazilian cheese

There is great interest for biopreservation of food products, and encapsulation may be a good strategy to extend the viability of protective cultures. In this study, Lactobacillus paraplantarum FT-259 and Lactococcus lactis QMF 11 were separately encapsulated in casein/pectin (C/P) microparticles, which were tested for antilisterial and anti-staphylococcal activity in fresh Minas cheese (FMC) stored at 8 °C. The encapsulation efficiency for both lactic acid bacteria (LAB) was 82.5%, with viability over 6.2 log CFU/g after storage of C/P microparticles for 90 days under refrigeration. Interestingly, free Lb. paraplantarum and free Lc. lactis grew significantly in refrigerated FMC, both in the presence and absence of pathogens, but only the first significatively grew when encapsulated. Encapsulation increased the antilisterial activity of Lb. paraplantarum in FMC. Moreover, Lc. lactis significantly inhibited listerial growth in FMC in both its free and encapsulated forms, whereas Staphylococcus aureus counts were only significantly reduced in the presence of free Lc. lactis. In conclusion, these results indicate that C/P microparticles are effective carriers of LAB in FMC, which can contribute for the assurance of the safety of this product.

Exoproteome Analysis of Antagonistic Interactions between the Probiotic Bacteria Limosilactobacillus reuteri LR1 and Lacticaseibacillus rhamnosus F and Multidrug Resistant Strain of Klebsiella pneumonia

The expansion of multiple drug resistant (MDR) strains of Klebsiella pneumoniae presents an immense threat for public health. Annually, this microorganism causes thousands of lethal nosocomial infections worldwide. Currently, it has been shown that certain strains of lactic acid bacteria (LAB) can efficiently inhibit growth of K. pneumoniae and the formation of its biofilms; however, the active principle of such action remains unknown. In the current article, the growth inhibition of MDR K. pneumoniae by two LAB—Limosilactobacillus reuteri LR1 and Lacticaseibacillus rhamnosus F—is demonstrated, and the nature of this inhibition studied at the level of exoproteome. This article shows that the exoproteomes of studied LAB contains both classically and non-classically secreted proteins. While for L. reuteri LR1 the substantial portion of classically secreted proteins was presented by cell-wall-degrading enzymes, for L. rhamnosus F only one out of four classically secreted proteins was presented by cell-wall hydrolase. Non-classically secreted proteins of both LAB were primarily metabolic enzymes, for some of which a possible moonlighting functioning was proposed. These results contribute to knowledge regarding antagonistic interaction between LAB and pathogenic and opportunistic microorganisms and set new perspectives for the use of LAB to control the spread of these microorganisms.

Probiotic Properties and Potentiality of Lactiplantibacillus plantarum Strains for the Biological Control of Chalkbrood Disease

Ascosphaera apis is an entomopathogenic fungus that affects honeybees. In stressful conditions, this fungus (due not only to its presence, but also to the combination of other biotic and abiotic stressors) can cause chalkbrood disease. In recent years, there has been increasing attention paid towards the use of lactic acid bacteria (LAB) in the honeybees' diets to improve their health, productivity and ability to resist infections by pathogenic microorganisms. The screening of 22 strains of Lactiplantibacillus plantarum, isolated from the gastrointestinal tracts of honeybees and beebread, led to the selection of five strains possessing high antagonistic activity against A. apis. This study focused on the antifungal activity of these five strains against A. apis DSM 3116 and DSM 3117 using different matrices: cell lysate, broth culture, cell-free supernatant and cell pellet. In addition, some functional properties and the antioxidant activity of the five L. plantarum strains were evaluated. All five strains exhibited high antagonistic activity against A. apis, good surface cellular properties (extracellular polysaccharide (EPS) production and biofilm formation) and antioxidant activity. Although preliminary, these results are encouraging, and in future investigations, the effectiveness of these bacteria as probiotics in honeybee nutrition will be tested in vivo in the context of an eco-friendly strategy for the biological control of chalkbrood disease.

Molecular Logic of Prokaryotic Surface Layer Structures

Most prokaryotic cells are encased in a surface layer (S-layer) consisting of a paracrystalline array of repeating lattice-forming proteins. S-layer proteins populate a vast and diverse sequence space, performing disparate functions in prokaryotic cells, including cellular defense, cell-shape maintenance, and regulation of import and export of materials. This article highlights recent advances in the understanding of S-layer structure and assembly, made possible by rapidly evolving structural and cell biology methods. We underscore shared assembly principles revealed by recent work and discuss a common molecular framework that may be used to understand the structural organization of S-layer proteins across bacteria and archaea.

Coating function and stabilizing effects of surface layer protein from Lactobacillus acidophilus ATCC 4356 on liposomes

Surface layer proteins (SLPs) are crystalline arrays in the outermost layer of cell envelope in many archaea and bacteria. SLPs subunits have the ability to reassemble on the surface of lipid layers. In this work, the SLP from Lactobacillus acidophilus ATCC 4356 was extracted and reassembled on the surface of positively charged liposomes composed of dipalmitoyl phosphatidylcholine, cholesterol and octadecylamine. Zeta potentials and particle size were determined to describe the adsorption process of SLP on liposomes. The liposomes completely coated with SLP were observed by transmission electron microscope. To investigate the stabilizing effects of SLP on liposomes, carboxyfluorescein (CF) was encapsulated and its leakage was determined as an evaluation index. The results showed that the L. acidophilus ATCC 4356 SLP significantly (P < 0.05) increased the stability of the liposomes in the course of thermal challenge. Furthermore, SLP was able to reduce the aggregation of liposomes in serum. Storage stability of liposomes was performed at 25 °C, 4 °C and -20 °C for 90 days. And the SLP-coated liposomes released less CF than the control liposomes during storage at the three evaluated temperatures. Our findings extended the application field of Lactobacillus SLPs and introduced a novel nanocarrier system with good chemical stability.

Characterization of Lactobacillus species proposed as probiotics

An isolated Lactobacillus from several various sources were identified depending on morphological, microscopically and biochemical tests in vitro analysis of probiotic properties that included: an ability to tolerate in different concentration of bile salt, survival in acidic conditions, their antimicrobial activity, and S-layer characterizations were carried out. It was noticed that isolates of Lactobacillus rhamnosus and L. delbrueckii have a broad activity of antimicrobial and found the isolate L. rhamnosus represented with a survival percentage 6.9% at pH 4.5 and 5.1% at pH 2.0) also L. rhamnosus (5.7% at pH 4.5 and 4.9% at pH 2.0) tolerated acidic media, Lactobacillus spp. has antimicrobial activity against all gram-positive and negative tested isolates. 70 kDa of S-layer protein bands were detected with whole-cell SDS-PAGE analysis, and it's predominant in cells of isolates which grown in MRS broth anaerobically. It was noticed that the collected Lactobacillus isolates could be used as probiotic.

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.

Protein denature extracts of Lactobacillus crispatus KT-11 strain promote interleukin 12p40 production via Toll-like receptor 2 in J774.1 cell culture

The objective of the present study is to investigate the mechanism and the cell components of Lactobacillus crispatus KT-11 strain (KT-11) that induce interleukin (IL)-12p40 production. IL-12p40 production induced by KT-11 was decreased in the presence of inhibitors of extracellular signal-regulated kinase or nuclear factor kappa B. Guanidine hydrochloride, urea or lithium chloride extract of KT-11 induced IL-12p40 production, but production was suppressed in the presence of Toll-like receptor 2-specific neutralizing antibody. These findings suggest that the protein denature extracts of KT-11 promote IL-12p40 production via Toll-like receptor 2 in J774.1 cells. PRACTICAL APPLICATIONS: Heat-treated lactic acid bacteria are added to some foods because it is easier to store and transport, and have less interference with other food ingredients compared with living lactic acid bacteria. Heat-treated Lactobacillus crispatus KT-11 strain (KT-11) is included in some foods because of good handling characteristics and good dispersibility in the food product. We have previously reported that the administration of KT-11 led to beneficial health effects through the regulation of the immune system in mice, but the mechanism is not clear. We found that protein denature extracts, which may include proteins such as SLP and SLAPs, of KT-11 cells promoted IL-12p40 production via TLR2 in the J774.1 cell culture. This result will contribute to providing more effective lactic acid bacteria functional food.

How to outwit nature: Omics insight into butanol tolerance

The energy crisis, depletion of oil reserves, and global climate changes are pressing problems of developed societies. One possibility to counteract that is microbial production of butanol, a promising new fuel and alternative to many petrochemical reagents. However, the high butanol toxicity to all known microbial species is the main obstacle to its industrial implementation. The present state of the art review aims to expound the recent advances in modern omics approaches to resolving this insurmountable to date problem of low butanol tolerance. Genomics, transcriptomics, and proteomics show that butanol tolerance is a complex phenomenon affecting multiple genes and their expression. Efflux pumps, stress and multidrug response, membrane transport, and redox-related genes are indicated as being most important during butanol challenge, in addition to fine-tuning of global regulators of transcription (Spo0A, GntR), which may further improve tolerance. Lipidomics shows that the alterations in membrane composition (saturated lipids and plasmalogen increase) are very much species-specific and butanol-related. Glycomics discloses the pleiotropic effect of CcpA, the role of alternative sugar transport, and the production of exopolysaccharides as alternative routes to overcoming butanol stress. Unfortunately, the strain that simultaneously syntheses and tolerates butanol in concentrations that allow its commercialization has not yet been discovered or produced. Omics insight will allow the purposeful increase of butanol tolerance in natural and engineered producers and the effective heterologous expression of synthetic butanol pathways in strains hereditary butanol-resistant up to 3.2 - 4.9% (w/v). Future breakthrough can be achieved by a detailed study of the membrane proteome, of which 21% are proteins with unknown functions.

Surface-layer protein produced by Lactobacillus crispatus JCM 2009 ameliorates lipopolysaccharide-induced inflammation through autophagy cross-talk with the NF-κB signaling pathway

In recent years, studies on immunomodulation by surface-layer proteins (Slps) have mainly focused on Lactobacillus acidophilus, there is little information on Slp from L. crispatus and its intestinal immunomodulatory mechanisms in macrophages. In our study, the anti-inflammatory actions of Slp derived from L. crispatus JCM 2009 and its related molecular mechanisms were investigated. We initially found that incubation with Slp (5-10 μg/mL) for 4 h significantly inhibited nitric oxide (NO) and prostaglandin E₂ (PGE₂) production in LPS-stimulated RAW264.7 cells (P < 0.001). We then found that Slp inhibited the inflammatory response by regulating the PI3K/AKT/mTOR signaling pathway and activating autophagy in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Furthermore, ELISA and Western blotting results demonstrated that the NF-κB signaling pathway positively regulated autophagic activity to inhibit the productions of PGE₂ and NO during this inflammatory response. And p65 was identified as a potentially important NF-κB signaling pathway molecule mediating the effects of Slp on the LPS-induced inflammatory response in RAW264.7 cells. Our findings provide the novel perspective that Slp exerts its anti-inflammatory effects through the activation of autophagy, making it a promising bioactive ingredient for the development of functional foods.

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

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

Enhancement of Versatile Extracellular Cellulolytic and Hemicellulolytic Enzyme Productions by Lactobacillus plantarum RI 11 Isolated from Malaysian Food Using Renewable Natural Polymers

Lactobacillus plantarum RI 11 was reported recently to be a potential lignocellulosic biomass degrader since it has the capability of producing versatile extracellular cellulolytic and hemicellulolytic enzymes. Thus, this study was conducted to evaluate further the effects of various renewable natural polymers on the growth and production of extracellular cellulolytic and hemicellulolytic enzymes by this novel isolate. Basal medium supplemented with molasses and yeast extract produced the highest cell biomass (log 10.51 CFU/mL) and extracellular endoglucanase (11.70 µg/min/mg), exoglucanase (9.99 µg/min/mg), β-glucosidase (10.43 nmol/min/mg), and mannanase (8.03 µg/min/mg), respectively. Subsequently, a statistical optimization approach was employed for the enhancement of cell biomass, and cellulolytic and hemicellulolytic enzyme productions. Basal medium that supplemented with glucose, molasses and soybean pulp (F5 medium) or with rice straw, yeast extract and soybean pulp (F6 medium) produced the highest cell population of log 11.76 CFU/mL, respectively. However, formulated F12 medium supplemented with glucose, molasses and palm kernel cake enhanced extracellular endoglucanase (4 folds), exoglucanase (2.6 folds) and mannanase (2.6 folds) specific activities significantly, indicating that the F12 medium could induce the highest production of extracellular cellulolytic and hemicellulolytic enzymes concomitantly. In conclusion, L. plantarum RI 11 is a promising and versatile bio-transformation agent for lignocellulolytic biomass.

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.

Antagonistic Activity against Ascosphaera apis and Functional Properties of Lactobacillus kunkeei Strains

: Lactic acid bacteria (LAB) are an important group of honeybee gut microbiota. These bacteria are involved in food digestion, stimulate the immune system, and may antagonize undesirable microorganisms in the gastrointestinal tract. Lactobacillus kunkeei is a fructophilic lactic acid bacterium (FLAB) most frequently found in the gastrointestinal tracts of honeybees. Ascosphaera apis is an important pathogenic fungus of honeybee larvae; it can colonize the intestine, especially in conditions of nutritional or environmental stress that cause microbial dysbiosis. In this work, some functional properties of nine selected L. kunkeei strains were evaluated. The study focused on the antifungal activity of these strains against A. apis DSM 3116, using different matrices: cell lysate, broth culture, cell-free supernatant, and cell pellet. The cell lysate showed the highest antifungal activity. Moreover, the strains were shown to possess good cell-surface properties (hydrophobicity, auto-aggregation, and biofilm production) and a good resistance to high sugar concentrations. These L. kunkeei strains were demonstrated to be functional for use in "probiotic syrup", useful to restore the symbiotic communities of the intestine in case of dysbiosis and to exert a prophylactic action against A. apis.

Constitutive expression and cell-surface display of a bacterial β-mannanase in Lactobacillus plantarum

BACKGROUND

Lactic acid bacteria (LAB) are important microorganisms in the food and beverage industry. Due to their food-grade status and probiotic characteristics, several LAB are considered as safe and effective cell-factories for food-application purposes. In this present study, we aimed at constitutive expression of a mannanase from Bacillus licheniformis DSM13, which was subsequently displayed on the cell surface of Lactobacillus plantarum WCFS1, for use as whole-cell biocatalyst in oligosaccharide production.

RESULTS

Two strong constitutive promoters, Pgm and SlpA, from L. acidophilus NCFM and L. acidophilus ATCC4356, respectively, were used to replace the inducible promoter in the lactobacillal pSIP expression system for the construction of constitutive pSIP vectors. The mannanase-encoding gene (manB) was fused to the N-terminal lipoprotein anchor (Lp_1261) from L. plantarum and the resulting fusion protein was cloned into constitutive pSIP vectors and expressed in L. plantarum WCFS1. The localization of the protein on the bacterial cell surface was confirmed by flow cytometry and immunofluorescence microscopy. The mannanase activity and the reusability of the constructed L. plantarum displaying cells were evaluated. The highest mannanase activities on the surface of L. plantarum cells obtained under the control of the Pgm and SlpA promoters were 1200 and 3500 U/g dry cell weight, respectively, which were 2.6- and 7.8-fold higher compared to the activity obtained from inducible pSIP anchoring vectors. Surface-displayed mannanase was shown to be able to degrade galactomannan into manno-oligosaccharides (MOS).

CONCLUSION

This work demonstrated successful displaying of ManB on the cell surface of L. plantarum WCFS1 using constitutive promoter-based anchoring vectors for use in the production of manno-oligosaccharides, which are potentially prebiotic compounds with health-promoting effects. Our approach, where the enzyme of interest is displayed on the cell surface of a food-grade organism with the use of strong constitutive promoters, which continuously drive synthesis of the recombinant protein without the need to add an inducer or change the growth conditions of the host strain, should result in the availability of safe, stable food-grade biocatalysts.

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.

Low cell surface hydrophobicity is one of the key factors for high butanol tolerance of Lactic acid bacteria

Highly butanol-tolerant strains have always been attractive because of their potential as microbial hosts for butanol production. However, due to the amphiphilic nature of 1-butanol as a solvent, the relationship between the cell surface hydrophobicity and butanol resistance remained ambiguous to date. In this work, the quantitatively estimated cell surface hydrophobicity of 74 Lactic acid bacteria strains were juxtaposed to their tolerance to various butanol concentrations. The obtained results revealed that the strains' hydrophobicity was inversely proportional to their butanol tolerance. All highly butanol-resistant strains were hydrophilic (cell surface hydrophobicity<1%), whereas the more hydrophobic the strains were, the more sensitive to butanol they were. Furthermore, cultivation at increasing butanol concentrations showed a clear tendency to decrease the level of hydrophobicity in all tested organisms, thus suggesting possible adaptation mechanisms. Purposeful reduction of cell surface hydrophobicity (by removal of S-layer proteins from the cell envelope) also led to an increase of butanol resistance. Since the results covered 23 different Lactic acid bacteria species of seven genera, it could be concluded that regardless of the species, the lower degree of cells' hydrophobicity clearly correlates with the higher level of butanol tolerance.

Caloric restriction promotes functional changes involving short-chain fatty acid biosynthesis in the rat gut microbiota

Caloric restriction (CR) is known to promote health and longevity, likely via modification of the gut microbiota (GM). However, functional and metabolic changes induced in the GM during CR are still unidentified. Here, we investigated the short- and long-term effects of CR on the rat GM using a metaproteogenomic approach. We show that a switch from ad libitum (AL) low fat diet to CR in young rats is able to induce rapid and deep changes in their GM metaproteomic profile, related to a reduction of the Firmicutes/Bacteroidetes ratio and an expansion of lactobacilli. Specifically, we observed a significant change in the expression of the microbial enzymes responsible for short-chain fatty acid biosynthesis, with CR boosting propionogenesis and limiting butyrogenesis and acetogenesis. Furthermore, these CR-induced effects were maintained up to adulthood and started to be reversed after a short-term diet change. We also found that CR alters the abundance of an array of host proteins released in stool, mainly related to epithelial barrier integrity and inflammation. Hence, our results provide thorough information about CR-induced modifications to GM and host functional activity, and might constitute the basis for novel GM-based approaches aimed at monitoring the effectiveness of dietary interventions.

Engineering Components of the Lactobacillus S-Layer for Biotherapeutic Applications

Lactic acid bacteria (LAB) are frequently harnessed for the delivery of biomolecules to mucosal tissues. Several species of Lactobacillus are commonly employed for this task, of which a subset are known to possess surface-layers (S-layers). S-layers are two-dimensional crystalline arrays of repeating proteinaceous subunits that form the outermost coating of many prokaryotic cell envelopes. Their periodicity and abundance have made them a target for numerous biotechnological applications. In the following review, we examine the multi-faceted S-layer protein (Slp), and its use in both heterologous protein expression systems and mucosal vaccine delivery frameworks, through its diverse genetic components: the strong native promoter, capable of synthesizing as many as 500 Slp subunits per second; the signal peptide that stimulates robust secretion of recombinant proteins; and the structural domains, which can be harnessed for both cell surface display of foreign peptides or adhesion enhancement of a host bacterium. Although numerous studies have established vaccine platforms based on one or more components of the Lactobacillus S-layer, this area of research still remains largely in its infancy, thus this review is meant to not only highlight past works, but also advocate for the future usage of Slps in biotherapeutic research.

Surface-Layer Protein from Lactobacillus acidophilus NCFM Inhibits Lipopolysaccharide-Induced Inflammation through MAPK and NF-κB Signaling Pathways in RAW264.7 Cells

The objective of our research was to evaluate the molecular mechanism of the anti-inflammatory effects of surface-layer protein (Slp) derived from Lactobacillus acidophilus NCFM in lipopolysaccharide-induced RAW264.7 cells. Our results presented that Slp, with an apparent size of 46 kDa, attenuated the production of TNF-α, IL-1β, and reactive oxygen species (ROS), by inhibiting the MAPK and NF-κB signaling pathways. In addition, 10 μg mL^-1 of Slp significantly inhibited NO and PGE₂ production ( P < 0.001) through downregulating the expression levels of iNOS and COX-2 protein. Furthermore, Slp was found to inhibit NF-κB p65 translocation into the nucleus to activate inflammatory gene transcription. These findings suggest that Slp is a potential immune-modulating bioactive protein derived from probiotics and holds promise for use as an additive in functional foods.

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.