S-layer proteins of Lactobacillus acidophilus inhibits JUNV infection

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.

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

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

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.

Uptake of Levilactobacillus brevis JCM 1059 by THP-1 Cells via Interaction between SlpB and CAP-1 Promotes Cytokine Production

Several probiotic lactic acid bacteria (LAB) exert immunomodulatory effects on the host. However, the reasons for the different effects of LAB have not been fully elucidated. To understand the different immunomodulatory effects of LAB, we evaluated the levels of critical molecules in differentiated monocytic THP-1 and dendritic cells (DCs) following the uptake of various LAB strains. Lactobacillus helveticus JCM 1120, Lactobacillus acidophilus JCM 1132, Levilactobacillus brevis JCM 1059, and Lentilactobacillus kefiri JCM 5818 showed significantly higher uptake among the 12 LAB species tested. The uptake of microbeads by THP-1 DC increased when coupled with the surface layer proteins (Slps) from the tested strains. SlpB was mainly observed in the L. brevis JCM 1059 Slps extract. The expected cell surface receptor for SlpB on THP-1 DC was purified using SlpB-coupled affinity resin and identified as adenylyl cyclase-associated protein 1 (CAP-1). SlpB binding to THP-1 DC decreased after the addition of anti-CAP-1 and anti-DC-SIGN antibodies but not after the addition of anti-macrophage-inducible C-type lectin (Mincle) antibody. These results suggest that SlpB on L. brevis JCM 1059 plays preferentially binds to CAP-1 on THP-1 DC and plays a crucial role in bacterial uptake by THP-1 cells as well as in subsequent interleukin-12 (IL-12) production.

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

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

The potential role of adherence factors in probiotic function in the gastrointestinal tract of adults and pediatrics: a narrative review of experimental and human studies

Numerous studies point to the important role of probiotic bacteria in gastrointestinal health. Probiotics act through mechanisms affecting enteric pathogens, epithelial barrier function, immune signaling, and conditioning of indigenous microbiota. Once administered, probiotics reach the gastrointestinal tract and interact with the host through bacterial surface molecules, here called adhesion factors, which are either strain- or specie-specific. Probiotic adhesion, through structural adhesion factors, is a mechanism that facilitates persistence within the gastrointestinal tract and triggers the initial host responses. Thus, an understanding of specific probiotic adhesion mechanisms could predict how specific probiotic strains elicit benefits and the potential of adherence factors as a proxy to predict probiotic function. This review summarizes the present understanding of probiotic adherence in the gastrointestinal tract. It highlights the bacterial adhesion structure types, their molecular communication with the host and the consequent impact on intestinal diseases in both adult and pediatric populations. Finally, we discuss knockout/isolation studies as direct evidence for adhesion factors conferring anti-inflammatory and pathogen inhibition properties to a probiotic.What is known: Probiotics can be used to treat clinical conditions.Probiotics improve dysbiosis and symptoms.Clinical trials may not confirm in vitro and animal studies.What is new: Adhesion structures may be important for probiotic function.Need to systematically determine physical characteristics of probiotics before selecting for clinical trials.Probiotics may be genetically engineered to add to clinical efficacy.

Recent Advances in Sensing Applications of Molecularly Imprinted Photonic Crystals

Photonic crystals (PhCs) with a brightly colored structure are novel materials and are widely used in chemical and biological sensing. Combining PhCs with molecular imprinting technology (MIT), the molecularly imprinted PhC (MIPC) sensors are fabricated, which can specifically recognize the target molecules. Aside from high sensitivity and selectivity, the MIPC sensors could recognize the naked eye detection because of its optical properties. In this review, an overview of recent advances in sensing applications of MIPC sensors including the responsive mechanisms, application in environmental monitoring, and the application to human health were illustrated. The MIPC sensors all responded to the analytes specifically and also showed high sensitivity in real samples, which provided a method to realize the rapid, convenient, naked eye, and real-time detection. Furthermore, the current limitations and potential future directions of MIPC sensors were also discussed.

Respiratory syndrome coronavirus-2 response: Microbiota as lactobacilli could make the difference

Coronavirus disease 2019 (COVID-19) is caused by respiratory syndrome coronavirus qualified as SARS-CoV-2. Viral penetration requires binding of the viral spike (S) protein to a specific cellular receptor (ACE2) highly expressed in a nasal goblet and ciliated cells. In several countries, the COVID-19 evolution was relatively benign compared to others and despite noncompliance with health recommendations on several occasions. In this overview, we attempt to define the criteria that could explain such a difference. Among these criteria, the specificity of Lactobacillus genus strains, as a part of nasal microbiota, could play a role of a barrier against viral penetration and could strengthen the host's immune system in some populations rather than others. In fact, several studies have shown the role of lactic acid bacteria, including lactobacilli, in the prevention of viral respiratory infections. This could provide important information on a possible mechanism of the virus spreading.

Chikungunya and Zika Viruses: Co-Circulation and the Interplay between Viral Proteins and Host Factors

Chikungunya and Zika viruses, both transmitted by mosquito vectors, have globally re-emerged over for the last 60 years and resulted in crucial social and economic concerns. Presently, there is no specific antiviral agent or vaccine against these debilitating viruses. Understanding viral-host interactions is needed to develop targeted therapeutics. However, there is presently limited information in this area. In this review, we start with the updated virology and replication cycle of each virus. Transmission by similar mosquito vectors, frequent co-circulation, and occurrence of co-infection are summarized. Finally, the targeted host proteins/factors used by the viruses are discussed. There is an urgent need to better understand the virus-host interactions that will facilitate antiviral drug development and thus reduce the global burden of infections caused by arboviruses.

S-layers: The Proteinaceous Multifunctional Armors of Gram-Positive Pathogens

S-layers are self-assembled crystalline 2D lattices enclosing the cell envelopes of several bacteria and archaea. Despite their abundance, the landscape of S-layer structure and function remains a land of wonder. By virtue of their location, bacterial S-layers have been hypothesized to add structural stability to the cell envelope. In addition, S-layers are implicated in mediating cell-environment and cell-host interactions playing a key role in adhesion, cell growth, and division. Significant strides in the understanding of these bacterial cell envelope components were made possible by recent studies that have provided structural and functional insights on the critical S-layer and S-layer-associated proteins (SLPs and SLAPs), highlighting their roles in pathogenicity and their potential as therapeutic or vaccine targets. In this mini-review, we revisit the sequence-structure-function relationships of S-layers, SLPs, and SLAPs in Gram-positive pathogens, focusing on the best-studied classes, Bacilli (Bacillus anthracis) and Clostridia (Clostridioides difficile). We delineate the domains and their architectures in archetypal S-layer proteins across Gram-positive genera and reconcile them with experimental findings. Similarly, we highlight a few key "flavors" of SLPs displayed by Gram-positive pathogens to assemble and support the bacterial S-layers. Together, these findings indicate that S-layers are excellent candidates for translational research (developing diagnostics, antibacterial therapeutics, and vaccines) since they display the three crucial characteristics: accessible location at the cell surface, abundance, and unique lineage-specific signatures.

Development of an Antigen Delivery Platform Using Lactobacillus acidophilus Decorated With Heterologous Proteins: A Sheep in Wolf's Clothing Story

S-layers are bacterial structures present on the surface of several Gram-positive and Gram-negative bacteria that play a role in bacterial protection. In Lactobacillus acidophilus (L. acidophilus ATCC 4356), the S-layer is mainly composed of the protein SlpA. A tandem of two copies of the protein domain SLP-A (pfam: 03217) was identified at the C-terminal of SlpA, being this double SLP-A protein domain (in short dSLP-A) necessary and sufficient for the association of the protein to the L. acidophilus cell wall. A variety of proteins fused to the dSLP-A domain were able to spontaneously associate with high affinity to the cell wall of L. acidophilus and Bacillus subtilis var. natto, in a process that we termed decoration. Binding of dSLP-A-containing-proteins to L. acidophilus was stable at conditions that mimic the gastrointestinal transit in terms of pH, proteases, and bile salts. To evaluate if protein decoration of L. acidophilus can be adapted to generate an oral vaccine platform, a chimeric antigen derived from the bacterial pathogen Shiga-toxin-producing Escherichia coli (STEC) was constructed by fusing the sequences encoding the polypeptides EspA^36–192, Intimin^653–953, Tir^240–378, and H7 flagellin^352–374 (EITH7) to the dSLP-A domain (EITH7-dSLP-A). Recombinantly expressed EITH7-dSLP-A protein was affinity purified and combined with L. acidophilus cultures to allow the association of the chimeric antigen to the bacterial surface. EITH7-decorated L. acidophilus was orally administered to BALB/c mice and the induction of anti-EITH7 specific antibodies in sera and feces determined by ELISA. Mice presenting significantly higher anti-EITH7 antibodies titers were able to control more efficiently an experimental STEC infection than mice that received the non-decorated L. acidophilus carrier, indicating that antigen-decorated L. acidophilus can be adapted as a mucosal immunization delivery platform to elicit a protective immune response for vaccine purposes.

Bacillus subtilis, an ideal probiotic bacterium to shrimp and fish aquaculture that increase feed digestibility, prevent microbial diseases, and avoid water pollution

Beneficial microorganisms maintain the ecosystems, plants, animals and humans working in healthy conditions. In nature, around 95% of all microorganisms produce beneficial effects by increasing nutrients digestion and assimilation, preventing pathogens development and by improving environmental parameters. However, increase in human population and indiscriminate uses of antibiotics have been exerting a great pressure on agriculture, livestock, aquaculture, and also to the environment. This pressure has induced the decomposition of environmental parameters and the development of pathogenic strains resistant to most antibiotics. Therefore, all antibiotics have been restricted by corresponding authorities; hence, new and healthy alternatives to prevent or eliminate these pathogens need to be identified. Thus, probiotic bacteria utilization in aquaculture systems has emerged as a solution to prevent pathogens development, to enhance nutrients assimilation and to improve environmental parameters. In this sense, B. subtilis is an ideal multifunctional probiotic bacterium, with the capacity to solve these problems and also to increase aquaculture profitability.

Selective, sensitive, and fast determination of S-layer proteins by a molecularly imprinted photonic polymer coated film and a fiber-optic spectrometer

A newly developed molecularly imprinted photonic polymer (MIPP) film, which was prepared by colloidal crystal templating and surface molecular imprinting, was used for selective capture of S-layer protein (SLP) from a complex Lactobacillus acidophilus sample. The colloidal crystal templates were formed by a dipping process followed by chemical binding of the imprinted template SLP molecules. A sandwich structure consisting of two glass slides was formed after the SLP-silica layer had been covered with a poly(methyl methacrylate) glass slide. After polymerization of the SLP-silica layer with the preprepared polymerization solution, hydrofluoric acid and acetic phosphate buffer solutions removed the silica particles and SLP molecules, respectively. The MIPP film obtained exhibited a three-dimensional, highly ordered and interconnected macroporous structure (pore size greater than 200 nm), which is specifically accessible to SLP molecules. The adsorbed SLP molecules were simply and straightforwardly detected by a fiber-optic spectrometer. The redshift of the Bragg diffraction peak of the MIPP film was linearly related to the number of SLP molecules that had been harvested in the film. The detection limit of the SLP-MMIP-fiber-optic spectrometer method for SLP was 1 ng mL^-1. The MIPP sensor was successfully applied to detect SLP molecules in a crudely extracted Lactobacillus acidophilus sample. Our results prove the applicability of the SLP-MIPP film for fast and real-time measurement of SLP. Graphical abstract.

S-Layer Protein of Lactobacillus helveticus SBT2171 Promotes Human β-Defensin 2 Expression via TLR2-JNK Signaling

Antimicrobial peptides that contribute to innate immunity are among the most important protective measures against infection in many organisms. Several substances are known to regulate the expression of antimicrobial peptides. In this study, we investigated the factors in lactic acid bacteria (LAB) that induce antimicrobial peptide expression in the host. We found that Lactobacillus helveticus SBT2171 (LH2171) induced the expression of human β-defensin (hBD)2 in Caco-2 human colonic epithelial cells. Specifically, surface layer protein (SLP) of LH2171 stimulated hBD2 expression by activating c-Jun N-terminal kinase (JNK) signaling via Toll-like receptor (TLR)2 in Caco-2 cells. SLPs extracted from other lactobacilli similarly increased hBD2 expression, suggesting that this stimulatory effect is common feature of Lactobacillus SLPs. Interestingly, Lactobacillus strains that strongly induced hBD2 expression also potently activated JNK signaling. Thus, upregulation of hBD2 induced by TLR2–JNK signaling contributes to protection of the host against infection.

Health Benefits of Heat-Killed (Tyndallized) Probiotics: An Overview

Nowadays, the oral use of probiotics is widespread. However, the safety profile with the use of live probiotics is still a matter of debate. Main risks include: Cases of systemic infections due to translocation, particularly in vulnerable patients and pediatric populations; acquisition of antibiotic resistance genes; or interference with gut colonization in neonates. To avoid these risks, there is an increasing interest in non-viable microorganisms or microbial cell extracts to be used as probiotics, mainly heat-killed (including tyndallized) probiotic bacteria (lactic acid bacteria and bifidobacteria). Heat-treated probiotic cells, cell-free supernatants, and purified key components are able to confer beneficial effects, mainly immunomodulatory effects, protection against enteropathogens, and maintenance of intestinal barrier integrity. At the clinical level, products containing tyndallized probiotic strains have had a role in gastrointestinal diseases, including bloating and infantile coli-in combination with mucosal protectors-and diarrhea. Heat-inactivated probiotics could also have a role in the management of dermatological or respiratory allergic diseases. The reviewed data indicate that heat-killed bacteria or their fractions or purified components have key probiotic effects, with advantages versus live probiotics (mainly their safety profile), positioning them as interesting strategies for the management of common prevalent conditions in a wide variety of patients´ characteristics.

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

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

Surface (S) Layer Proteins of Lactobacillus acidophilus Block Virus Infection via DC-SIGN Interaction

Alphaviruses and flaviviruses are important human pathogens that include Chikungunya virus (CHIKV), Dengue virus (DENV), and Zika virus (ZIKV), which can cause diseases in humans ranging from arthralgia to hemorrhagic fevers and microcephaly. It was previously shown that treatment with surface layer (S-layer) protein, present on the bacterial cell-envelope of Lactobacillus acidophilus, is able to inhibit viral and bacterial infections by blocking the pathogen’s interaction with DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN), a trans-membrane protein that is a C-type calcium-dependent lectin. DC-SIGN is known to act as an attachment factor for several viruses including alphaviruses and flaviviruses. In the present study, we used alphaviruses as a model system to dissect the mechanism of S-layer inhibition. We first evaluated the protective effect of S-layer using 3T3 cells, either wild type or stably expressing DC-SIGN, and infecting with the alphaviruses Semliki Forest virus (SFV) and CHIKV and the flaviviruses ZIKV and DENV. DC-SIGN expression significantly enhanced infection by all four viruses. Treatment of the cells with S-layer prior to infection decreased infectivity of all viruses only in cells expressing DC-SIGN. In vitro ELISA experiments showed a direct interaction between S-layer and DC-SIGN; however, confocal microscopy and flow cytometry demonstrated that S-layer binding to the cells was independent of DC-SIGN expression. S-layer protein prevented SFV binding and internalization in DC-SIGN-expressing cells but had no effect on virus binding to DC-SIGN-negative cells. Inhibition of virus binding occurred in a time-dependent manner, with a significant reduction of infection requiring at least a 30-min pre-incubation of S-layer with DC-SIGN-expressing cells. These results suggest that S-layer has a different mechanism of action compared to mannan, a common DC-SIGN-binding compound that has an immediate effect in blocking viral infection. This difference could reflect slower kinetics of S-layer binding to the DC-SIGN present at the plasma membrane (PM). Alternatively, the S-layer/DC-SIGN interaction may trigger the activation of signaling pathways that are required for the inhibition of viral infection. Together our results add important information relevant to the potential use of L. acidophilus S-layer protein as an antiviral therapy.

An Acid Up-Regulated Surface Protein of Lactobacillus paracasei Strain GCRL 46 is Phylogenetically Related to the Secreted Glucan- (GpbB) and Immunoglobulin-Binding (SibA) Protein of Pathogenic Streptococci

Bacterial cell wall hydrolases, including amidases and peptidases, play a critical role in peptidoglycan turnover during growth, impacting daughter cell separation, and cell death, through autolysis. When exploring the regulation of protein expression across the growth cycle of an acid-resistant strain of Lactobacillus paracasei, GCRL 46, we observed temporal up-regulation of proteins in the 40⁻45 kDa molecular weight range for whole-cell extracts when culturing in fermenters at a controlled pH of 4.0 versus optimum growth pH of 6.3. Up-regulation of proteins in this size range was not detected in SDS-PAGE gels of the cytosolic fraction, but was routinely detected following growth at low pH in whole cells and cell debris obtained after bead beating and centrifugation, indicating a cell surface location. N-terminal sequencing and in silico analyses showed sequence similarity with proteins in the L. casei group (L. casei, L. paracasei and L. rhamnosus) which were variously annotated as uncharacterized proteins, surface antigens, possible TrsG proteins, CHAP (cysteine, histidine-dependent amidohydrolases/peptidases)-domain proteins or putative peptidoglycan d,l-endopeptidase due to the presence of a CwlO domain. This protein is a homologue of the p40 (Msp2) secreted protein of L. rhamnosus LGG, which is linked to probiotic functionality in this species, and is phylogenetically related to structurally-similar proteins found in Enterococcus, Streptococcus and Bifidobacterium species, including the glucan-binding (GbpB), surface antigen (SagA) proteins detected in pathogenic group A streptococci species as secreted, immunoglobulin-binding (SibA) proteins (also named PcsB). Three-dimensional (3D) modelling predicted structural similarities in the CHAP proteins from the L. casei group and streptococcal species, indicating retention of overall architecture despite sequence divergence, and an implied retention of function during evolution. A phylogenetically-related hydrolase also contained the CwlO domain with a NLPC_P60 domain, and showed similar overall but distinct architecture to the CHAP proteins. We concluded that the surface-located, CHAP protein in L. casei is up-regulated during long-term exposure to acidic conditions during growth but not during acid shock.

Probiotics, mechanisms of action, and clinical perspectives for diarrhea management in children

Infectious diarrhea is the second most common cause of morbidity and mortality in children under 5 years of age in the underdeveloped areas of the world. Conventional treatment consists of rehydration, which may be coupled with antimicrobial agents in more severe bacterial infections or with antiprotozoal agents. In the last few decades, research on the use of probiotic strains, such as Lactobacillus rhamnosus GG ATCC 53013 (LGG), Lactobacillus reuteri DSM 17938 and Saccharomyces boulardii, has gained much attention to prevent and treat diarrheal diseases. However, they are rarely used in the clinical routine, perhaps because there are still gaps in the knowledge about the effective benefit to the patient in terms of the reduction of the duration of diarrhea and its prevention. Furthermore, only a few probiotic strains are safely indicated for usage in pediatric practice. This review summarizes the current knowledge on the antimicrobial mechanisms of probiotics on distinct enteropathogens and their role in stimulating host defense mechanisms against intestinal infections. In addition, we highlight the potential of probiotics for the treatment and prevention of diarrhea in children. We conclude that the use of probiotics is beneficial for both the treatment and prevention of diarrhea in children and that the identification of other candidate probiotics might represent an important advance to a greater reduction in hospital stays and to prevent infectious diarrhea in a larger portion of this population.

Lactobacillus acidophilus S-layer protein-mediated inhibition of PEDV-induced apoptosis of Vero cells

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Lactobacillus S-layer protein plays an inhibitory role during PEDV infection.

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In Vero cells infected with PEDV, apoptosis was mediated by caspase-8/3 activation.

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Lactobacillus S-layer protein inhibited PEDV-induced apoptosis in Vero cells.

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S-layer protein reduced caspase-8/3 activation against PEDV-induced apoptosis.

To gain insight into the mechanism of Lactobacillus acidophilus (L. acidophilus) S-layer protein antiviral activity, we examined how S-layer protein impacts porcine epidemic diarrhea virus (PEDV) infection and PEDV-induced apoptosis of Vero cells. Pretreatment (exclusion assay), coincubation (competition assay), and post-treatment (displacement assay) of PEDV-infected Vero cells with the S-layer protein was examined. Interestingly, significant inhibition of PEDV by S-layer protein was only observed in the exclusion assay. In Vero cells infected with PEDV, we found that apoptosis was mediated by activation of caspase-8 and caspase-3 in the late stage of infection. When PEDV-infected Vero cells were pretreated with S-layer protein, rates of Vero cell apoptosis were markedly decreased and cell damage was significantly reduced, as evaluated by flow cytometry and microscopy. Detailed analyses showed that the S-layer protein inhibited caspase-8 and caspase-3 activity. Taken together, our results suggest that L. acidophilus S-layer protein plays an inhibitory role during PEDV infection of Vero cells, and that the antagonistic activity of the protein is not via competition with PEDV for binding sites. In addition, the findings suggest that L. acidophilus S-layer protein protects against PEDV-induced apoptosis through reduced caspase-8 and caspase-3 activation in the later stages of infection. This mechanism may represent a novel approach for antagonizing PEDV and other viruses.

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

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

Functional Characterization of c-di-GMP Signaling-Related Genes in the Probiotic Lactobacillus acidophilus

The bacterial second messenger cyclic diguanylate monophosphate (c-di-GMP) regulates a series of cellular functions, including biofilm formation, motility, virulence, and other processes. In this study, we confirmed the presence of several c-di-GMP related genes and evaluated their activities and functions in Lactobacillus species. Bioinformatic and biochemical analyses revealed that Lactobacillus acidophilus La-14 have an active c-di-GMP phosphodiesterase (PdeA) that may act in the metabolic cycle of c-di-GMP. A GGDEF protein (DgcA) induced two c-di-GMP-dependent phenotypes (low motility and high production of curli fimbriae) in Escherichia coli by heterologously expressed in vivo but showed no diguanylate cyclases activity in vitro while in the expression without the N-terminal transmembrane domain. The degenerated EAL-domain protein (PdeB), encoded by the last gene in the gts operon, serve as a c-di-GMP receptor which may be associated with exopolysaccharide (EPS) synthesis in L. acidophilus. Heterologously expressed GtsA and GtsB, encoded by the gts operon, stimulated EPS and biofilm formation in E. coli BL21. Constitutive expression in L. acidophilus revealed that a high concentration of intracellular DgcA levels increased EPS production in L. acidophilus and enhanced the co-aggregation ability with E. coli MG1655, which may be beneficial to the probiotic properties of Lactobacillus species. Our study imply that the c-di-GMP metabolism-related genes, in L. acidophilus, work jointly to regulate its functions in EPS formation and co-aggregation.

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.

Lactobacillus reuteri Surface Mucus Adhesins Upregulate Inflammatory Responses Through Interactions With Innate C-Type Lectin Receptors

The vertebrate gut symbiont Lactobacillus reuteri exhibits strain-specific adhesion and health-promoting properties. Here, we investigated the role of the mucus adhesins, CmbA and MUB, upon interaction of L. reuteri ATCC PTA 6475 and ATCC 53608 strains with human monocyte-derived dendritic cells (moDCs). We showed that mucus adhesins increased the capacity of L. reuteri strains to interact with moDCs and promoted phagocytosis. Our data also indicated that mucus adhesins mediate anti- and pro-inflammatory effects by the induction of interleukin-10 (IL-10), tumor necrosis factor alpha (TNF-α), IL-1β, IL-6, and IL-12 cytokines. L. reuteri ATCC PTA 6475 and ATCC 53608 were exclusively able to induce moDC-mediated Th1 and Th17 immune responses. We further showed that purified MUB activates moDCs and induces Th1 polarized immune responses associated with increased IFNγ production. MUB appeared to mediate these effects via binding to C-type lectin receptors (CLRs), as shown using cell reporter assays. Blocking moDCs with antibodies against DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) or Dectin-2 did not affect the uptake of the MUB-expressing strain, but reduced the production of TNF-α and IL-6 by moDCs significantly, in line with the Th1 polarizing capacity of moDCs. The direct interaction between MUB and CLRs was further confirmed by atomic force spectroscopy. Taken together these data suggest that mucus adhesins expressed at the cell surface of L. reuteri strains may exert immunoregulatory effects in the gut through modulating the Th1-promoting capacity of DCs upon interaction with C-type lectins.

Inhibition of H9N2 Virus Invasion into Dendritic Cells by the S-Layer Protein from L. acidophilus ATCC 4356

Probiotics are essential for the prevention of virus invasion and the maintenance of the immune balance. However, the mechanism of competition between probiotics and virus are unknown. The objectives of this study were to isolate the surface layer (S-layer) protein from L. acidophilus ATCC 4356 as a new antiviral material, to evaluate the stimulatory effects of the S-layer protein on mouse dendritic cells (DCs) and to verify its ability to inhibit the invasion of H9N2 avian influenza virus (AIV) in DCs. We found that the S-layer protein induced DCs activation and up-regulated the IL-10 secretion. The invasion and replication of the H9N2 virus in mouse DCs was successfully demonstrated. However, the invasion of H9N2 virus into DCs could be inhibited by treatment with the S-layer protein prior to infection, which was verified by the reduced hemagglutinin (HA) and neuraminidase (NA) mRNA expression, and nucleoprotein (NP) protein expression in the DCs. Furthermore, treatment with the S-layer protein increases the Mx1, Isg15, and Ddx58 mRNA expressions, and remits the inflammatory process to inhibit H9N2 AIV infection. In conclusion, the S-layer protein stimulates the activation of mouse DCs, inhibits H9N2 virus invasion of DCs, and stimulates the IFN-I signaling pathway. Thus, the S-layer protein from Lactobacillus is a promising biological antiviral material for AIV prevention.

S-layer proteins from Lactobacillus sp. inhibit bacterial infection by blockage of DC-SIGN cell receptor

Many species of Lactobacillus sp. possess Surface(s) layer proteins in their envelope. Among other important characteristics S-layer from Lactobacillus acidophilus binds to the cellular receptor DC-SIGN (Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin; CD209), which is involved in adhesion and infection of several families of bacteria. In this report we investigate the activity of new S-layer proteins from the Lactobacillus family (Lactobacillus acidophilus, Lactobacillus brevis, Lactobacillus helveticus and Lactobacillus kefiri) over the infection of representative microorganisms important to human health. After the treatment of DC-SIGN expressing cells with these proteins, we were able to diminish bacterial infection by up to 79% in both gram negative and mycobacterial models. We discovered that pre-treatment of the bacteria with S-layers from Lactobacillus acidophilus and Lactobacillus brevis reduced bacteria viability but also prevent infection by the pathogenic bacteria. We also proved the importance of the glycosylation of the S-layer from Lactobacillus kefiri in the binding to the receptor and thus inhibition of infection. This novel characteristic of the S-layers proteins may contribute to the already reported pathogen exclusion activity for these Lactobacillus probiotic strains; and might be also considered as a novel enzymatic antimicrobial agents to inhibit bacterial infection and entry to host cells.

Influence of osmotic stress on the profile and gene expression of surface layer proteins in Lactobacillus acidophilus ATCC 4356

In this work, we studied the role of surface layer (S-layer) proteins in the adaptation of Lactobacillus acidophilus ATCC 4356 to the osmotic stress generated by high salt. The amounts of the predominant and the auxiliary S-layer proteins SlpA and SlpX were strongly influenced by the growth phase and high-salt conditions (0.6 M NaCl). Changes in gene expression were also observed as the mRNAs of the slpA and slpX genes increased related to the growth phase and presence of high salt. A growth stage-dependent modification on the S-layer protein profile in response to NaCl was observed: while in control conditions, the auxiliary SlpX protein represented less than 10 % of the total S-layer protein, in high-salt conditions, it increased to almost 40 % in the stationary phase. The increase in S-layer protein synthesis in the stress condition could be a consequence of or a way to counteract the fragility of the cell wall, since a decrease in the cell wall thickness and envelope components (peptidoglycan layer and lipoteichoic acid content) was observed in L. acidophilus when compared to a non-S-layer-producing species such as Lactobacillus casei. Also, the stationary phase and growth in high-salt medium resulted in increased release of S-layer proteins to the supernatant medium. Overall, these findings suggest that pre-growth in high-salt conditions would result in an advantage for the probiotic nature of L. acidophilus ATCC 4356 as the increased amount and release of the S-layer might be appropriate for its antimicrobial capacity.

Identification of Lactobacillus proteins with different recognition patterns between immune rabbit sera and nonimmune mice or human sera

Background

The genus Lactobacillus belongs to a large heterogeneous group of low G + C Gram-positive anaerobic bacteria, which are frequently used as probiotics. The health-beneficial effects, in particular the immunomodulation effect, of probiotics depend on the strain and dose used. Strain variations may be related to diversity of the cell surface architecture of bacteria and the ability to express specific antigens or secrete compounds. The use of Lactobacillus as probiotic requires a comprehensive understanding of its effect on host immune system. To evaluate the potential immunoreactive properties of proteins isolated from four Lactobacillus strains: L. johnsonii 142 and L. johnsonii 151, L. rhamnosus LOCK 0900 and L. casei LOCK 0919, the polyclonal sera obtained from mouse and human have been tested as well as with sera from rabbits immunized with whole lactobacilli cells.

Results

The reactivity of isolated proteins detected by SDS-PAGE and Western blotting was heterogeneous and varied between different serum samples. The proteins with the highest immunoreactivity were isolated, purified and sequenced, in particular the fractions were identified as phosphoglycerate kinase (L. johnsonii 142), glyceraldehyde 3-phosphate dehydrogenase (L. johnosnii 142, L. rhamnosus LOCK 0900), hypothetic protein JDM1_1307 (L. johnsonii 151) and fructose/tagatose-bisphosphate-aldolase (L. casei LOCK 0919).

Conclusion

The different prevalence of reactions against tested antigens in rabbit, mouse and human sera may indicate significant differences in immune system and commensal cross-talk in these groups. The identification of immunoreactive lactobacilli proteins opens the possibility to use them as an antigens for development of vaccines.

Draft Genome Sequence of the Probiotic Strain Lactobacillus acidophilus ATCC 4356

We present the 1,956,699-bp draft genome sequence of Lactobacillus acidophilus strain ATCC 4356. Comparative genomic analysis revealed 99.96% similarity with L. acidophilus NCFM NC_006814.3 and 99.97% with La-14 NC_021181.2 genomes.

S-layers: principles and applications

Monomolecular arrays of protein or glycoprotein subunits forming surface layers (S-layers) are one of the most commonly observed prokaryotic cell envelope components. S-layers are generally the most abundantly expressed proteins, have been observed in species of nearly every taxonomical group of walled bacteria, and represent an almost universal feature of archaeal envelopes. The isoporous lattices completely covering the cell surface provide organisms with various selection advantages including functioning as protective coats, molecular sieves and ion traps, as structures involved in surface recognition and cell adhesion, and as antifouling layers. S-layers are also identified to contribute to virulence when present as a structural component of pathogens. In Archaea, most of which possess S-layers as exclusive wall component, they are involved in determining cell shape and cell division. Studies on structure, chemistry, genetics, assembly, function, and evolutionary relationship of S-layers revealed considerable application potential in (nano)biotechnology, biomimetics, biomedicine, and synthetic biology.

Vaginal microbiota and its role in HIV transmission and infection

The urogenital tract appears to be the only niche of the human body that shows clear differences in microbiota between men and women. The female reproductive tract has special features in terms of immunological organization, an epithelial barrier, microbiota, and influence by sex hormones such as estrogen. While the upper genital tract is regarded as free of microorganisms, the vagina is colonized by bacteria dominated by Lactobacillus species, although their numbers vary considerably during life. Bacterial vaginosis is a common pathology characterized by dysbiosis, which increases the susceptibility for HIV infection and transmission. On the other hand, HIV infections are often characterized by a disturbed vaginal microbiota. The endogenous vaginal microbiota may protect against HIV by direct production of antiviral compounds, through blocking of adhesion and transmission by ligands such as lectins, and/or by stimulation of immune responses. The potential role of probiotics in the prevention of HIV infections and associated symptoms, by introducing them to the vaginal and gastrointestinal tract (GIT), is also discussed. Of note, the GIT is a site of considerable HIV replication and CD4(+) T-cell destruction, resulting in both local and systemic inflammation. Finally, genetically engineered lactobacilli show promise as new microbicidal agents against HIV.

Multistrain probiotic modulation of intestinal epithelial cells' immune response to a double-stranded RNA ligand, poly(i·c)

A commercially available product containing three probiotic bacterial strains (Lactobacillus helveticus R0052, Bifidobacterium longum subsp. infantis R0033, and Bifidobacterium bifidum R0071) was previously shown in animal trials to modulate both TH1 and TH2 immune responses. Clinical studies on this combination of bacteria have also shown positive health effects against seasonal winter diseases and rotavirus infection. The goal of this study was to use a well-established in vitro intestinal epithelial (HT-29) cell model that has been shown to constitutively express double-stranded RNA (dsRNA) sensors (Toll-like receptor 3 [TLR3], retinoic acid-inducible gene I, melanoma differentiation-associated gene 5, and dsRNA-activated protein kinase). By using the HT-29 cell model, we wanted to evaluate whether or not this combination of three bacteria had the capacity to immune modulate the host cell response to a dsRNA ligand, poly(I·C). Using a custom-designed, two-color expression microarray targeting genes of the human immune system, we investigated the response of HT-29 cells challenged with poly(I·C) both in the presence and in the absence of the three probiotic bacteria. We observed that the combination of the three bacteria had a major impact on attenuating the expression of genes connected to proinflammatory TH1 and antiviral innate immune responses compared to that obtained by the poly(I·C)-only challenge. Major pathways through which the multistrain combination may be eliciting its immune-modulatory effect include the TLR3 domain-containing adapter-inducing beta interferon (TRIF), mitogen-activated protein kinase, and NF-κB signaling pathways. Such a model may be useful for selecting potential biomarkers for the design of future clinical trials.

Using phage display selected antibodies to dissect microbiomes for complete de novo genome sequencing of low abundance microbes

BACKGROUND

Single cell genomics has revolutionized microbial sequencing, but complete coverage of genomes in complex microbiomes is imperfect due to enormous variation in organismal abundance and amplification bias. Empirical methods that complement rapidly improving bioinformatic tools will improve characterization of microbiomes and facilitate better genome coverage for low abundance microbes.

METHODS

We describe a new approach to sequencing individual species from microbiomes that combines antibody phage display against intact bacteria with fluorescence activated cell sorting (FACS). Single chain (scFv) antibodies are selected using phage display against a bacteria or microbial community, resulting in species-specific antibodies that can be used in FACS for relative quantification of an organism in a community, as well as enrichment or depletion prior to genome sequencing.

RESULTS

We selected antibodies against Lactobacillus acidophilus and demonstrate a FACS-based approach for identification and enrichment of the organism from both laboratory-cultured and commercially derived bacterial mixtures. The ability to selectively enrich for L. acidophilus when it is present at a very low abundance (<0.2%) leads to complete (>99.8%) de novo genome coverage whereas the standard single-cell sequencing approach is incomplete (<68%). We show that specific antibodies can be selected against L. acidophilus when the monoculture is used as antigen as well as when a community of 10 closely related species is used demonstrating that in principal antibodies can be generated against individual organisms within microbial communities.

CONCLUSIONS

The approach presented here demonstrates that phage-selected antibodies against bacteria enable identification, enrichment of rare species, and depletion of abundant organisms making it tractable to virtually any microbe or microbial community. Combining antibody specificity with FACS provides a new approach for characterizing and manipulating microbial communities prior to genome sequencing.

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.

Utilization of human DC-SIGN and L-SIGN for entry and infection of host cells by the New World arenavirus, Junín virus

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The C-type lectins hDC-SIGN and hL-SIGN are important for entry of Junín arenavirus.

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hDC-SIGN and hL-SIGN substantially augment the use of transferrin receptor.

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hL-SIGN may act as a co-receptor for Junín arenavirus.

The target cell tropism of enveloped viruses is regulated by interactions between viral proteins and cellular receptors determining susceptibility at a host cell, tissue or species level. However, a number of additional cell-surface moieties can also bind viral envelope glycoproteins and could act as capture receptors, serving as attachment factors to concentrate virus particles on the cell surface, or to disseminate the virus infection to target organs or susceptible cells within the host. Here, we used Junín virus (JUNV) or JUNV glycoprotein complex (GPC)-pseudotyped particles to study their ability to be internalized by the human C-type lectins hDC- or hL-SIGN. Our results provide evidence that hDC- and hL-SIGN can mediate the entry of Junín virus into cells, and may play an important role in virus infection and dissemination in the host.

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.

Anti-influenza virus effects of both live and non-live Lactobacillus acidophilus L-92 accompanied by the activation of innate immunity

The antiviral effects of both a live and non-live Lactobacillus acidophilus strain L-92 (L-92) were investigated by oral administration (10 mg/mouse per d) daily for 21 d in a mouse model infected intranasally with influenza virus (H1N1). Virus titres in the lung of mice administered either live or non-live L-92 cells daily for 15 d were repressed 6 d after virus infection compared with the control group. Natural killer (NK) activity in the orally administered non-live L-92 group was higher compared with that of the control group before virus infection and on day 6. In contrast, NK activity in the live L-92 group compared with the control group was not significantly changed on both days, but was significantly higher on day 1. In contrast, live L-92 showed a greater repression of virus proliferation compared with non-live L-92, 6 d after the infection. Live L-92 decreased the number of neutrophils in the lung and suppressed lung weight, leading to the consequent deterioration of consolidation scores of the lung. These results indicated that pretreatment of live or non-live L-92 cells had protective effects against influenza virus infection. Among the measured cytokines and chemokines, eotaxin, macrophage colony-stimulating factor, IL-1b, RANTES (regulated on activation, normal T cell expressed and secreted) and interferon-a were significantly increased in the lung: IL-17 was significantly increased in Peyer’s patch of the live L-92 group compared with the control group. A mechanistic study suggested that the enhancement of NK activity in the lung caused by stimulating various antiviral cytokines and chemokines after the oral administration of L-92 cells might be important in protecting against virus infection.

A systems biology starter kit for arenaviruses

Systems biology approaches in virology aim to integrate viral and host biological networks, and thus model the infection process. The growing availability of high-throughput “-omics” techniques and datasets, as well as the ever-increasing sophistication of in silico modeling tools, has resulted in a corresponding rise in the complexity of the analyses that can be performed. The present study seeks to review and organize published evidence regarding virus-host interactions for the arenaviruses, from alterations in the host proteome during infection, to reported protein-protein interactions. In this way, we hope to provide an overview of the interplay between arenaviruses and the host cell, and lay the foundations for complementing current arenavirus research with a systems-level approach.