Yields and Immunomodulatory Effects of Pneumococcal Membrane Vesicles Differ with the Bacterial Growth Phase

Synergistic strategies in tissue engineering: The role of exosomes and decellularized extracellular matrix hydrogels

Tissue engineering aims to mimic the natural microenvironment of biological structures by utilizing the distinctive characteristics of extracellular matrix (ECM) scaffolds. The combination of decellularized extracellular matrix hydrogels (dECMHs) with exosomes (EXs) represents an innovative therapeutic approach for tissue regeneration. These dECMHs, sourced from diverse tissues, provide biocompatible scaffolds that conform to irregular defect geometries, thereby addressing the limitations of conventional ECM scaffolds. EXs, which are nanovesicles secreted by virtually all cells, play crucial role in cell communication and tissue regeneration. However, their short half-life presents challenges for systemic administration. The incorporation of EXs into dECMHs enables localized and prolonged release, thereby enhancing their therapeutic merits. This review thoroughly explains the techniques for decellularization, the characteristics of dECM, as well as the preparation and applications of dECMHs in tissue engineering. It also explores the synergistic effects of EX-dECMH systems on cellular activities essential for tissue repair, including proliferation, differentiation, and neovascularization. The mechanisms of EX release from dECMHs and their applications in the regeneration of skin, intervertebral disc, cartilage, and nerve tissues are elucidated, highlighting the considerable potential of this integrated strategy to improve tissue engineering techniques. Furthermore, the synergistic effect of EX-dECMH systems in tissue healing is investigated. Finally, the limitations associated with the clinical application of EX, dECM, and dECMH as well as the future prospect are included.

Microbial DNA Profiles of Bacterial Extracellular Vesicles from 3D Salivary Polymicrobial Biofilms - A Pilot Study

With the advent of multi-layered and 3D scaffolds, the understanding of microbiome composition and pathogenic mechanisms within polymicrobial biofilms is continuously evolving. A fundamental component in mediating the microenvironment and bacterial-host communication within the biofilm are bilayered nanoparticles secreted by bacteria, known as bacterial extracellular vesicles (BEVs), which transport key biomolecules including proteins, nucleic acids, and metabolites. Their characteristics and microbiome profiles are yet to be explored in the context of in vitro salivary polymicrobial biofilm. This pilot study aimed to compare the profiles of BEVs from salivary biofilm cultured on a 2D tissue culture plate and 3D melt electrowritten medical-grade polycaprolactone (MEW mPCL) scaffold. BEVs derived from MEW mPCL biofilm exhibited enhanced purity and yield without altered EV morphology and lipopolysaccharide (LPS) content, with enriched BEVs-associated DNA from Capnocytophaga, porphyromonas, and veillonella genus. Moreover, compared to saliva controls, MEW mPCL BEVs showed comparable DNA expression of Tannerella forsythia, and Treponema denticola and significantly higher expression in Porphyromonas gingivalis, Eikenella corrodens and Lactobacillus acidophilus. Together, these findings highlight a more detailed microbial profile with BEVs derived from salivary biofilms cultured on 3D MEW PCL scaffolds, which facilitates an effective in vitro model with a greater resemblance to naturally occurring biofilms.

Characterization and Anti-Inflammatory Effects of Akkermansia muciniphila-Derived Extracellular Vesicles

Bacterial extracellular vesicles (EVs) play a pivotal role in host-microbe communication. Akkermansia muciniphila, a symbiotic bacterium essential for intestinal health, is hypothesized to exert its effects via EVs. Here, we successfully isolated and characterized EVs derived from A. muciniphila (Am-EVs) using ultracentrifugation. Am-EVs exhibited a double-membrane structure, with an average diameter of 92.48 ± 0.28 nm and a proteomic profile comprising 850 proteins. In an in vitro model of lipopolysaccharide (LPS)-induced inflammation in human colorectal adenocarcinoma cells (Caco-2), treatment with both 25 and 50 μg/mL Am-EVs significantly reduced oxidative stress markers, including reactive oxygen species (ROS), nitric oxide (NO), and malondialdehyde (MDA), while restoring catalase activity (CAT). Am-EVs also suppressed the expression of pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6). Subsequent transcriptomic sequencing and Western blot experiments revealed that Am-EVs attenuate the MAPK signaling pathway by downregulating TRIF, MyD88, p38 MAPK, and FOS while upregulating TGFBR2. These findings suggest that Am-EVs mediate anti-inflammatory effects through modulation of MAPK signaling, highlighting their potential as therapeutic agents in intestinal inflammation.

Consistency in bacterial extracellular vesicle production: key to their application in human health

Bacterial extracellular vesicles (BEVs) are naturally occurring functional structures that play critical roles in bacterial life processes. These vesicles, commonly known as outer membrane vesicles (OMVs), were first found to be released by Gram-negative bacteria; however, it has since been confirmed that Gram-positive bacteria also secrete BEVs. As research advances, BEVs are increasingly utilized in diverse applications, including vaccine development and drug delivery. Nevertheless, the effective employment of BEVs in these contexts requires the acquisition of vesicles with consistent properties and functions through appropriate culture, isolation, and purification methods. This review examines the advantages and disadvantages of various purification techniques alongside the heterogeneity they may introduce. We utilize the heterogeneity of BEVs as a framework to critically analyze the barriers to their application and the factors influencing their characteristics. Additionally, we constructively propose solutions to enhance the consistency of BEVs, thereby facilitating their further development and application.

Growth phase matters: Boosting immunity via Lacticasebacillus-derived membrane vesicles and their interactions with TLR2 pathways

Lipid bi-layered particles known as membrane vesicles (MVs), produced by Gram-positive bacteria are a communication tool throughout the entire bacterial growth. However, the MVs characteristics may vary across all stages of maternal culture growth, leading to inconsistencies in MVs research. This, in turn, hinders their employment as nanocarriers, vaccines and other medical applications. In this study, we aimed to comprehensively characterize MVs derived from Lacticaseibacillus rhamnosus CCM7091 isolated at different growth stages: early exponential (6 h, MV6), late exponential (12 h, MV12) and late stationary phase (48 h, MV48). We observed significant differences in protein content between MV6 and MV48 (data are available via ProteomeXchange with identifier PXD041580), likely contributing to their different immunomodulatory capacities. In vitro analysis demonstrated that MV48 uptake rate by epithelial Caco-2 cells is significantly higher and they stimulate an immune response in murine macrophages RAW 264.7 (elevated production of TNFα, IL-6, IL-10, NO). This correlated with increased expression of lipoteichoic acid (LTA) and enhanced TLR2 signalling in MV48, suggesting that LTA contributes to the immunomodulation. In conclusion, we showed that Lacticaseibacillus rhamnosus CCM7091-derived MVs from the late stationary phase boost the immune response the most effectively, which pre-destines them for therapeutical application as nanocarriers.

Hydrogel-exosome system in tissue engineering: A promising therapeutic strategy

Characterized by their pivotal roles in cell-to-cell communication, cell proliferation, and immune regulation during tissue repair, exosomes have emerged as a promising avenue for "cell-free therapy" in clinical applications. Hydrogels, possessing commendable biocompatibility, degradability, adjustability, and physical properties akin to biological tissues, have also found extensive utility in tissue engineering and regenerative repair. The synergistic combination of exosomes and hydrogels holds the potential not only to enhance the efficiency of exosomes but also to collaboratively advance the tissue repair process. This review has summarized the advancements made over the past decade in the research of hydrogel-exosome systems for regenerating various tissues including skin, bone, cartilage, nerves and tendons, with a focus on the methods for encapsulating and releasing exosomes within the hydrogels. It has also critically examined the gaps and limitations in current research, whilst proposed future directions and potential applications of this innovative approach.

Interactions of Gram-Positive Bacterial Membrane Vesicles and Hosts: Updates and Future Directions

Extracellular vesicles (EVs) are lipid bilayers derived from cell membranes, released by both eukaryotic cells and bacteria into the extracellular environment. During production, EVs carry proteins, nucleic acids, and various compounds, which are then released. While Gram-positive bacteria were traditionally thought incapable of producing EVs due to their thick peptidoglycan cell walls, recent studies on membrane vesicles (MVs) in Gram-positive bacteria have revealed their significant role in bacterial physiology and disease progression. This review explores the current understanding of MVs in Gram-positive bacteria, including the characterization of their content and functions, as well as their interactions with host and bacterial cells. It offers a fresh perspective to enhance our comprehension of Gram-positive bacterial EVs.

Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches

Extracellular vesicles (EVs), through their complex cargo, can reflect the state of their cell of origin and change the functions and phenotypes of other cells. These features indicate strong biomarker and therapeutic potential and have generated broad interest, as evidenced by the steady year-on-year increase in the numbers of scientific publications about EVs. Important advances have been made in EV metrology and in understanding and applying EV biology. However, hurdles remain to realising the potential of EVs in domains ranging from basic biology to clinical applications due to challenges in EV nomenclature, separation from non-vesicular extracellular particles, characterisation and functional studies. To address the challenges and opportunities in this rapidly evolving field, the International Society for Extracellular Vesicles (ISEV) updates its 'Minimal Information for Studies of Extracellular Vesicles', which was first published in 2014 and then in 2018 as MISEV2014 and MISEV2018, respectively. The goal of the current document, MISEV2023, is to provide researchers with an updated snapshot of available approaches and their advantages and limitations for production, separation and characterisation of EVs from multiple sources, including cell culture, body fluids and solid tissues. In addition to presenting the latest state of the art in basic principles of EV research, this document also covers advanced techniques and approaches that are currently expanding the boundaries of the field. MISEV2023 also includes new sections on EV release and uptake and a brief discussion of in vivo approaches to study EVs. Compiling feedback from ISEV expert task forces and more than 1000 researchers, this document conveys the current state of EV research to facilitate robust scientific discoveries and move the field forward even more rapidly.

Spray Drying of Bacterial Membrane Vesicles for Vaccine Delivery

Extracellular vesicles are nanosized lipid-bilayered spheres secreted from every living cell and they serve physiological and pathophysiological functions. Bacterial membrane vesicles are shed from both Gram-negative and Gram-positive bacteria and harbor many virulence factors, nuclear material, polysaccharides, proteins, and antigenic determinants, which are essential for immune recognition and evasion. Hence, bacterial membrane vesicles are very promising vaccine candidates. Spray drying is a well-established pharmaceutical technique to produce inhalable dry powders with enhanced stability for formulations of vaccines. In this chapter, we illustrate general guidelines for spray drying of bacterial extracellular vesicles to improve their stability without compromising their immunogenic protective effect. We discuss some of the most important experiments to characterize the generated spray-dried bacterial membrane vesicle powder vaccine.

Lactic acid bacteria derived extracellular vesicles: emerging bioactive nanoparticles in modulating host health

Lactic acid bacteria derived extracellular vesicles (LAB-EVs) are nano-sized and carry a variety of biological cargoes. LAB-EVs have proven to be potential mediators of intercellular communication, serving not only the parental bacteria but also the host cell in both physiology and pathology. LAB-EVs are therapeutically beneficial in various diseases through a cell-free strategy. Particularly, EVs secreted from probiotics can exert health-promoting effects on humans. Additionally, the excitement around LAB-EVs has extended to their use as nano-sized drug carriers, since they can traverse biological barriers. Nevertheless, significant challenges in terms of isolation, characterization, and safety must be addressed to ensure the clinical application of LAB-EVs. Therefore, this review emphasizes the isolation and purification methods of LAB-EVs. We also introduce the biogenesis, cargo sorting, and functions of LAB-EVs. The biological regulatory factors of LAB-EVs are summarized and discussed. Special attention is given to the interaction between LAB-EVs and the host, their ability to maintain intestinal homeostasis, and the immunity and inflammation they induce in diverse diseases. Furthermore, we summarize the characterization of LAB-EV cargoes by advanced analytical methods such as proteomics. Finally, we discuss the challenges and opportunities of LAB-EVs as a means of diagnosis and treatment in clinical translation. In conclusion, this review scrutinizes current knowledge and provides guidelines for proposing new perspectives for future research in the field of LAB-EVs.

Augmenting Immunotherapy via Bioinspired MOF-Based ROS Homeostasis Disruptor with Nanozyme-Cascade Reaction

Despite its remarkable clinical breakthroughs, immune checkpoint blockade (ICB) therapy remains limited by the insufficient immune response in the "cold" tumor. Nanozyme-based antitumor catalysis is associated with precise immune activation in the tumor microenvironment (TME). In this study, a cascade-augmented nanoimmunomodulator (CMZM) with multienzyme-like activities, which includes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione oxidase (GSHOx), that dissociates under an acidic and abundant GSH TME, is proposed for multimodal imaging-guided chemodynamic therapy (CDT)/photodynamic therapy (PDT) enhanced immunotherapy. Vigorous multienzyme-like activities can not only produce O2 to alleviate hypoxia and promote the polarization of M2 to M1 macrophages, but also generate ROS (•OH and 1 O2 ) and deplete GSH in the TME to expose necrotic cell fragments and reverse immunosuppressive TME by eliciting the maturation of dendritic cells and infiltration of cytotoxic T lymphocytes (CTLs) in tumors. Therefore, inhibitory effects on both primary and distant tumors are achieved through synergy with an α-PD-L1 blocking antibody. This cascade multienzyme-based nanoplatform provides a smart strategy for highly efficient ICB immunotherapy against "cold" tumors by revising immunosuppressive TME.

An update on our understanding of Gram-positive bacterial membrane vesicles: discovery, functions, and applications

Extracellular vesicles (EVs) are nano-sized particles released from cells into the extracellular environment, and are separated from eukaryotic cells, bacteria, and other organisms with cellular structures. EVs alter cell communication by delivering their contents and performing various functions depending on their cargo and release into certain environments or other cells. The cell walls of Gram-positive bacteria have a thick peptidoglycan layer and were previously thought to be unable to produce EVs. However, recent studies have demonstrated that Gram-positive bacterial EVs are crucial for health and disease. In this review, we have summarized the formation, composition, and characteristics of the contents, resistance to external stress, participation in immune regulation, and other functions of Gram-positive bacterial EVs, as well as their application in clinical diagnosis and treatment, to provide a new perspective to further our understanding of Gram-positive bacterial EVs.

The role of pneumococcal extracellular vesicles on the pathophysiology of the kidney disease hemolytic uremic syndrome

Streptococcus pneumoniae-induced hemolytic uremic syndrome (Sp-HUS) is a kidney disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. This disease is frequently underdiagnosed and its pathophysiology is poorly understood. In this work, we compared clinical strains, isolated from infant Sp-HUS patients, with a reference pathogenic strain D39, for host cytotoxicity and further explored the role of Sp-derived extracellular vesicles (EVs) in the pathogenesis of an HUS infection. In comparison with the wild-type strain, pneumococcal HUS strains caused significant lysis of human erythrocytes and increased the release of hydrogen peroxide. Isolated Sp-HUS EVs were characterized by performing dynamic light-scattering microscopy and proteomic analysis. Sp-HUS strain released EVs at a constant concentration during growth, yet the size of the EVs varied and several subpopulations emerged at later time points. The cargo of the Sp-HUS EVs included several virulence factors at high abundance, i.e., the ribosomal subunit assembly factor BipA, the pneumococcal surface protein A, the lytic enzyme LytC, several sugar utilization, and fatty acid synthesis proteins. Sp-HUS EVs strongly downregulated the expression of the endothelial surface marker platelet endothelial cell adhesion molecule-1 and were internalized by human endothelial cells. Sp-HUS EVs elicited the release of pro-inflammatory cytokines (interleukin [IL]-1β, IL-6) and chemokines (CCL2, CCL3, CXCL1) by human monocytes. These findings shed new light on the overall function of Sp-EVs, in the scope of infection-mediated HUS, and suggest new avenues of research for exploring the usefulness of Sp-EVs as therapeutic and diagnostic targets. IMPORTANCE Streptococcus pneumoniae-associated hemolytic uremic syndrome (Sp-HUS) is a serious and underdiagnosed deadly complication of invasive pneumococcal disease. Despite the introduction of the pneumococcal vaccine, cases of Sp-HUS continue to emerge, especially in children under the age of 2. While a lot has been studied regarding pneumococcal proteins and their role on Sp-HUS pathophysiology, little is known about the role of extracellular vesicles (EVs). In our work, we isolate and initially characterize EVs from a reference pathogenic strain (D39) and a strain isolated from a 2-year-old patient suffering from Sp-HUS. We demonstrate that despite lacking cytotoxicity toward human cells, Sp-HUS EVs are highly internalized by endothelial cells and can trigger cytokine and chemokine production in monocytes. In addition, this work specifically highlights the distinct morphological characteristics of Sp-HUS EVs and their unique cargo. Overall, this work sheds new light into potentially relevant players contained in EVs that might elucidate about pneumococcal EVs biogenesis or pose as interesting candidates for vaccine design.

Systematic Assessment of Small RNA Profiling in Human Extracellular Vesicles

MOTIVATION

Extracellular vesicles (EVs) are produced and released by most cells and are now recognized to play a role in intercellular communication through the delivery of molecular cargo, including proteins, lipids, and RNA. Small RNA sequencing (small RNA-seq) has been widely used to characterize the small RNA content in EVs. However, there is a lack of a systematic assessment of the quality, technical biases, RNA composition, and RNA biotypes enrichment for small RNA profiling of EVs across cell types, biofluids, and conditions.

METHODS

We collected and reanalyzed small RNA-seq datasets for 2756 samples from 83 studies involving 55 with EVs only and 28 with both EVs and matched donor cells. We assessed their quality by the total number of reads after adapter trimming, the overall alignment rate to the host and non-host genomes, and the proportional abundance of total small RNA and specific biotypes, such as miRNA, tRNA, rRNA, and Y RNA.

RESULTS

We found that EV extraction methods varied in their reproducibility in isolating small RNAs, with effects on small RNA composition. Comparing proportional abundances of RNA biotypes between EVs and matched donor cells, we discovered that rRNA and tRNA fragments were relatively enriched, but miRNAs and snoRNA were depleted in EVs. Except for the export of eight miRNAs being context-independent, the selective release of most miRNAs into EVs was study-specific.

CONCLUSION

This work guides quality control and the selection of EV isolation methods and enhances the interpretation of small RNA contents and preferential loading in EVs.

Different culture media and purification methods unveil the core proteome of Propionibacterium freudenreichii-derived extracellular vesicles

Bacterial extracellular vesicles (EVs) are natural lipidic nanoparticles implicated in intercellular communication. Although EV research focused mainly on pathogens, the interest in probiotic-derived EVs is now rising. One example is Propionibacterium freudenreichii, which produces EVs with anti-inflammatory effects on human epithelial cells. Our previous study with P. freudenreichii showed that EVs purified by size exclusion chromatography (SEC) displayed variations in protein content according to bacterial growth conditions. Considering these content variations, we hypothesized that a comparative proteomic analysis of EVs recovered in different conditions would elucidate whether a representative vesicular proteome existed, possibly providing a robust proteome dataset for further analysis. Therefore, P. freudenreichii was grown in two culture media, and EVs were purified by sucrose density gradient ultracentrifugation (UC). Microscopic and size characterization confirmed EV purification, while shotgun proteomics unveiled that they carried a diverse set of proteins. A comparative analysis of the protein content of UC- and SEC-derived EVs, isolated from cultures either in UF (cow milk ultrafiltrate medium) or YEL (laboratory yeast extract lactate medium), showed that EVs from all these conditions shared 308 proteins. This EV core proteome was notably enriched in proteins related to immunomodulation. Moreover, it showed distinctive features, including highly interacting proteins, compositional biases for some specific amino acids, and other biochemical parameters. Overall, this work broadens the toolset for the purification of P. freudenreichii-derived EVs, identifies a representative vesicular proteome, and enumerates conserved features in vesicular proteins. These results hold the potential for providing candidate biomarkers of purification quality, and insights into the mechanisms of EV biogenesis and cargo sorting.

Computational analysis and expression profiling of potassium transport-related gene families in mango (Mangifera indica) indicate their role in stress response and fruit development

Mango (Mangifera indica) fruit is known for its taste, health benefits, and drought tolerance. Potassium (K⁺) is one of the most abundant ions in a plant cell. It is important for various biological functions related to plant growth, development, and flowering/fruiting. It significantly contributes to fruit yield, quality, and drought tolerance in plants. However, molecular mechanisms comprising K⁺ transport in mango are least known. In the present study, 37 members of K⁺ transport-related genes (PTGs) were identified in mango, which include 22 K⁺ transporters (16 HAKs, 1 HKT, and 6 KEAs) and 15 K⁺ channels (6 TPKs and 8 Shakers). All PTGs were predicted to be expressed at the plasma membrane and possess characteristic motifs and domains. Phylogenetic analysis identified a strong kinship of PTGs among Oryza sativa, Arabidopsis thaliana, Cicer arietinum, Malus domestica, and M. indica. The promoter analysis identified 60 types of cis-elements related to various biological processes. RNA-seq-based expression profiling identified that MiTPK1.2, MiHAK1, MiHAK2.1, HAK6.1, and MiAKT1.1 were most upregulated in roots and that MiKEA2, MiAKT2, and MiAKT1 were upregulated in leaves. Moreover, MiAKT6, MiHAK1.1, MiKAT2, MiKAT2.1, MiHKT1, MiTPK1.1, MiHAK7, and MiHAK12 were highly expressed during the five growth stages of mango fruit. The current study is the first comprehensive report on K⁺ transport system in tropical fruits. Therefore, it will provide the foundation knowledge for the functional characterization of K⁺ genes in mango and related plants.

Rhodococcus equi-Derived Extracellular Vesicles Promoting Inflammatory Response in Macrophage through TLR2-NF-κB/MAPK Pathways

Rhodococcus equi (R. equi) is a Gram-positive coccobacillus that causes pneumonia in foals of less than 3 months, which have the ability of replication in macrophages. The ability of R. equi persist in macrophages is dependent on the virulence plasmid pVAPA. Gram-positive extracellular vesicles (EVs) carry a variety of virulence factors and play an important role in pathogenic infection. There are few studies on R. equi-derived EVs (R. equi-EVs), and little knowledge regarding the mechanisms of how R. equi-EVs communicate with the host cell. In this study, we examine the properties of EVs produced by the virulence strain R. equi 103+ (103+-EVs) and avirulenct strain R. equi 103− (103−-EVs). We observed that 103+-EVs and 103−-EVs are similar to other Gram-positive extracellular vesicles, which range from 40 to 260 nm in diameter. The 103+-EVs or 103−-EVs could be taken up by mouse macrophage J774A.1 and cause macrophage cytotoxicity. Incubation of 103+-EVs or 103−-EVs with J774A.1 cells would result in increased expression levels of IL-1β, IL-6, and TNF-α. Moreover, the expression of TLR2, p-NF-κB, p-p38, and p-ERK were significantly increased in J774A.1 cells stimulated with R. equi-EVs. In addition, we presented that the level of inflammatory factors and expression of TLR2, p-NF-κB, p-p38, and p-ERK in J774A.1 cells showed a significant decreased when incubation with proteinase K pretreated-R. equi-EVs. Overall, our data indicate that R. equi-derived EVs are capable of mediating inflammatory responses in macrophages via TLR2-NF-κB/MAPK pathways, and R. equi-EVs proteins were responsible for TLR2-NF-κB/MAPK mediated inflammatory responses in macrophage. Our study is the first to reveal potential roles for R. equi-EVs in immune response in R. equi-host interactions and to compare the differences in macrophage inflammatory responses mediated by EVs derived from virulent strain R. equi and avirulent strain R. equi. The results of this study have improved our knowledge of the pathogenicity of R. equi.

Effect of Iron Limitation, Elevated Temperature, and Florfenicol on the Proteome and Vesiculation of the Fish Pathogen Aeromonas salmonicida

We analyzed the proteomic response of the Gram-negative fish pathogen A. salmonicida to iron limitation, an elevated incubation temperature, and the antibiotic florfenicol. Proteins from different subcellular fractions (cytosol, inner membrane, outer membrane, extracellular and outer membrane vesicles) were enriched and analyzed. We identified several iron-regulated proteins that were not reported in the literature for A. salmonicida before. We could also show that hemolysin, an oxidative-stress-resistance chaperone, a putative hemin receptor, an M36 peptidase, and an uncharacterized protein were significantly higher in abundance not only under iron limitation but also with an elevated incubation temperature. This may indicate that these proteins involved in the infection process of A. salmonicida are induced by both factors. The analysis of the outer membrane vesicles (OMVs) with and without applied stresses revealed significant differences in the proteomes. OMVs were smaller and contained more cytoplasmic proteins after antibiotic treatment. After cultivation with low iron availability, several iron-regulated proteins were found in the OMVs, indicating that A. salmonicida OMVs potentially have a function in iron acquisition, as reported for other bacteria. The presence of iron-regulated transporters further indicates that OMVs obtained from ‘stressed’ bacteria might be suitable vaccine candidates that induce a protective anti-virulence immune response.

Spray-dried Pneumococcal Membrane Vesicles are Promising Candidates for Pulmonary Immunization

Pneumococcal infections represent a global health threat, which requires novel vaccine developments. Extracellular vesicles are secreted from most cells, including prokaryotes, and harbor virulence factors and antigens. Hence, bacterial membrane vesicles (MVs) may induce a protective immune response. For the first time, we formulate spray-dried gram-positive pneumococcal MVs-loaded vaccine microparticles using lactose/leucine as inert carriers to enhance their stability and delivery for pulmonary immunization. The optimized vaccine microparticles showed a mean particle size of 1-2µm, corrugated surface, and nanocrystalline nature. Their aerodynamic diameter of 2.34µm, average percentage emitted dose of 88.8%, and fine powder fraction 79.7%, demonstrated optimal flow properties for deep alveolar delivery using a next-generation impactor. Furthermore, confocal microscopy confirmed the successful encapsulation of pneumococcal MVs within the prepared microparticles. Human macrophage-like THP-1 cells displayed excellent viability, negligible cytotoxicity, and a rapid uptake around 60% of fluorescently labeled MVs after incubation with vaccine microparticles. Moreover, vaccine microparticles increased the release of pro-inflammatory cytokines tumor necrosis factor and interleukin-6 from primary human peripheral blood mononuclear cells. Vaccine microparticles exhibited excellent properties as promising vaccine candidates for pulmonary immunization and are optimal for further animal testing, scale-up and clinical translation.

Proteome analysis of the Gram-positive fish pathogen Renibacterium salmoninarum reveals putative role of membrane vesicles in virulence

Bacterial kidney disease (BKD) is a chronic bacterial disease affecting both wild and farmed salmonids. The causative agent for BKD is the Gram-positive fish pathogen Renibacterium salmoninarum. As treatment and prevention of BKD have proven to be difficult, it is important to know and identify the key bacterial proteins that interact with the host. We used subcellular fractionation to report semi-quantitative data for the cytosolic, membrane, extracellular, and membrane vesicle (MV) proteome of R. salmoninarum. These data can aid as a backbone for more targeted experiments regarding the development of new drugs for the treatment of BKD. Further analysis was focused on the MV proteome, where both major immunosuppressive proteins P57/Msa and P22 and proteins involved in bacterial adhesion were found in high abundance. Interestingly, the P22 protein was relatively enriched only in the extracellular and MV fraction, implicating that MVs may play a role in host–pathogen interaction. Compared to the other subcellular fractions, the MVs were also relatively enriched in lipoproteins and all four cell wall hydrolases belonging to the New Lipoprotein C/Protein of 60 kDa (NlpC/P60) family were detected, suggesting an involvement in the formation of the MVs.