A Universal Strategy to Promote Secretion of G+/G- Bacterial Extracellular Vesicles and Its Application in Host Innate Immune Responses

Beta-Lactam Antibiotics Promote Extracellular Vesicle Production of Staphylococcus aureus Through ROS-Mediated Lipid Metabolic Reprogramming

Bacterial extracellular vesicles (EVs) are natural reservoirs of biological active substances. They exhibit promising application in developing bioproducts such as vaccine, drug-delivery system and anticancer agent. However, the low yield of naturally secreted EVs during bacterial growth is a bottleneck factor that restricts EV applications. In this study, we showed that sub-minimum inhibitory concentration (MIC) of β-lactams boosted EV production in various Staphylococcus aureus strains. The expression of penicillin-binding protein (PBP) genes increased after β-lactam treatment, and the inactivation of alternative PBPs promoted EV secretion of S. aureus. We also demonstrated that sub-MIC β-lactams promoted EV production via a reactive oxygen species (ROS)-dependent pathway. Deletion of redundant pbp genes enhanced oxacillin (OXA)-stimulated ROS levels. Transcriptomic and lipidomic analyses revealed that OXA-induced ROS triggered lipid metabolic reprogramming in S. aureus. Particularly, ROS promoted lipid peroxidation (LPO) and increased the biosynthesis of phosphatidic acid (PA) and lipoteichoic acid (LTA) that contributed to EV generation. Furthermore, OXA treatment altered the diversity of EV-loaded proteins. OXA-treated ∆ agr /OXAEVs induced stronger Dengue EDIII-specific antibodies in BALB/c mice than did ∆ agrEVs. Overall, this study provided mechanic insights into β-lactam-promoted EV production in S. aureus, and highlighted the potential strategies to prepare EVs for various applications.

Engineered Therapeutic Bacteria with High-Yield Membrane Vesicle Production Inspired by Eukaryotic Membrane Curvature for Treating Inflammatory Bowel Disease

Bacterial membrane vesicles (BMVs) are emerging as powerful natural nanoparticles with transformative potential in medicine and industry. Despite their promise, scaling up BMV production and ensuring stable isolation and storage remain formidable challenges that limit their broader application. Inspired by eukaryotic mechanisms of membrane curvature, we engineered Escherichia coli DH5α to serve as a high-efficiency BMV factory. By fusing the ethanolamine utilization microcompartment shell protein EutS with the outer membrane via the ompA signal peptide, we induced dramatic membrane curvatures that drove enhanced vesiculation. Simultaneously, overexpression of fatty acyl reductase led to the production of amphiphilic fatty alcohols, further amplifying the BMV yield. Dynamic modulation of peptidoglycan hydrolase (PGase) expression facilitated efficient BMV release, resulting in a striking 149.11-fold increase in vesicle production. Notably, the high-yield BMVs from our engineered strain, without the need for purification, significantly bolstered innate immune responses and demonstrated therapeutic efficacy in treating inflammatory bowel disease (IBD). This study presents a strategy to overcome BMV production barriers, showcasing the therapeutic potential of engineered bacteria and BMVs for IBD treatment, while highlighting their potential applications in diverse biomedical fields.

Deciphering the role of host-gut microbiota crosstalk via diverse sources of extracellular vesicles in colorectal cancer

Colorectal cancer is the most common type of cancer in the digestive system and poses a major threat to human health. The gut microbiota has been found to be a key factor influencing the development of colorectal cancer. Extracellular vesicles are important mediators of intercellular communication. Not only do they regulate life activities within the same individual, but they have also been found in recent years to be important mediators of communication between different species, such as the gut microbiota and the host. Their preventive, diagnostic, and therapeutic value in colorectal cancer is being explored. The aim of this review is to provide insights into the complex interactions between host and gut microbiota, particularly those mediated through extracellular vesicles, and how these interactions affect colorectal cancer development. In addition, the potential of extracellular vesicles from various body fluids as biomarkers was evaluated. Finally, we discuss the potential, challenges, and future research directions of extracellular vesicles in their application to colorectal cancer. Overall, extracellular vesicles have great potential for application in medical processes related to colorectal cancer, but their isolation and characterization techniques, intercellular communication mechanisms, and the effectiveness of their clinical application require further research and exploration.

Bile promotes Lactobacillus johnsonii N6.2 extracellular vesicle production with conserved immunomodulatory properties

Recently, Lactobacillus johnsonii N6.2-derived extracellular vesicles (EVs) were shown to reduce apoptosis in human beta cell lines and stimulate insulin secretion in human islets. Our goal was to identify a physiologically relevant environmental condition that induces a hypervesiculation phenotype in L. johnsonii N6.2 and to evaluate if transcriptional changes are involved in this process. Culturing this strain in the presence of 0.2% bovine bile, which mimics a stressor encountered by the bacterium in the small intestine, resulted in approximately a 100-fold increase in EVs relative to cells grown in media without bile. Whole transcriptome analysis of cells grown with bile revealed upregulation of several peptidoglycan hydrolases as well as several genes involved in fatty acid utilization. These results suggest that the hypervesiculation phenotype may be the result of increased cell wall turnover combined with increased accumulation of phospholipids, in agreement with our previous proteomic and lipidomics results. Additionally, EVs isolated from L. johnsonii N6.2 grown in presence of bile maintained their immunomodulatory properties in host-derived βlox5 pancreatic and THP-1 macrophage cell lines. Our findings suggest that in L. johnsonii N6.2 vesiculogenesis is significantly impacted by the expression of cell wall modifying enzymes and proteins utilized for exogenous fatty acid uptake that are regulated at the transcriptional level. Furthermore, this data suggests that vesiculogenesis could be stimulated in vivo using small molecules thereby maximizing the beneficial interactions between bacteria and their hosts.

Microorganism-derived extracellular vesicles: emerging contributors to female reproductive health

Extracellular vesicles (EVs) are cell-derived nanoparticles that carry small molecules, nucleic acids, and proteins long distances in the body facilitating cell-cell communication. Microorganism-derived EVs mediate communication between parent cells and host cells, with recent evidence supporting their role in biofilm formation, horizontal gene transfer, and suppression of the host immune system. As lipid-bound bacterial byproducts, EVs demonstrate improved cellular uptake and distribution in vivo compared to cell-free nucleic acids, proteins, or small molecules, allowing these biological nanoparticles to recapitulate the effects of parent cells and contribute to a range of human health outcomes. Here, we focus on how EVs derived from vaginal microorganisms contribute to gynecologic and obstetric outcomes. As the composition of the vaginal microbiome significantly impacts women's health, we discuss bacterial EVs from both healthy and dysbiotic vaginal microbiota. We also examine recent work done to evaluate the role of EVs from common vaginal bacterial, fungal, and parasitic pathogens in pathogenesis of female reproductive tract disease. We highlight evidence for the role of EVs in women's health, gaps in current knowledge, and opportunities for future work. Finally, we discuss how leveraging the innate interactions between microorganisms and mammalian cells may establish EVs as a novel therapeutic modality for gynecologic and obstetric indications.

Bacterial extracellular vesicles: Modulation of biofilm and virulence properties

Microbial pathogens cause persistent infections by forming biofilms and producing numerous virulence factors. Bacterial extracellular vesicles (BEVs) are nanostructures produced by various bacterial species vital for molecular transport. BEVs include various components, including lipids (glycolipids, LPS, and phospholipids), nucleic acids (genomic DNA, plasmids, and short RNA), proteins (membrane proteins, enzymes, and toxins), and quorum-sensing signaling molecules. BEVs play a major role in forming extracellular polymeric substances (EPS) in biofilms by transporting EPS components such as extracellular polysaccharides, proteins, and extracellular DNA. BEVs have been observed to carry various secretory virulence factors. Thus, BEVs play critical roles in cell-to-cell communication, biofilm formation, virulence, disease progression, and resistance to antimicrobial treatment. In contrast, BEVs have been shown to impede early-stage biofilm formation, disseminate mature biofilms, and reduce virulence. This review summarizes the current status in the literature regarding the composition and role of BEVs in microbial infections. Furthermore, the dual functions of BEVs in eliciting and suppressing biofilm formation and virulence in various microbial pathogens are thoroughly discussed. This review is expected to improve our understanding of the use of BEVs in determining the mechanism of biofilm development in pathogenic bacteria and in developing drugs to inhibit biofilm formation by microbial pathogens. STATEMENT OF SIGNIFICANCE: Bacterial extracellular vesicles (BEVs) are nanostructures formed by membrane blebbing and explosive cell lysis. It is essential for transporting lipids, nucleic acids, proteins, and quorum-sensing signaling molecules. BEVs play an important role in the formation of the biofilm's extracellular polymeric substances (EPS) by transporting its components, such as extracellular polysaccharides, proteins, and extracellular DNA. Furthermore, BEVs shield genetic material from nucleases and thermodegradation by packaging it during horizontal gene transfer, contributing to the transmission of bacterial adaptation determinants like antibiotic resistance. Thus, BEVs play a critical role in cell-to-cell communication, biofilm formation, virulence enhancement, disease progression, and drug resistance. In contrast, BEVs have been shown to prevent early-stage biofilm, disperse mature biofilm, and reduce virulence characteristics.

BACTERIAL EXTRACELLULAR VESICLES IN THE REGULATION OF INFLAMMATORY RESPONSE AND HOST-MICROBE INTERACTIONS

ABSTRACT

Extracellular vesicles (EVs) are a new revelation in cross-kingdom communication, with increasing evidence showing the diverse roles of bacterial EVs (BEVs) in mammalian cells and host-microbe interactions. Bacterial EVs include outer membrane vesicles released by gram-negative bacteria and membrane vesicles generated from gram-positive bacteria. Recently, BEVs have drawn attention for their potential as biomarkers and therapeutic tools because they are nano-sized and can deliver bacterial cargo into host cells. Importantly, exposure to BEVs significantly affects various physiological and pathological responses in mammalian cells. Herein, we provide a comprehensive overview of the various effects of BEVs on host cells (i.e., immune cells, endothelial cells, and epithelial cells) and inflammatory/infectious diseases. First, the biogenesis and purification methods of BEVs are summarized. Next, the mechanisms and pathways identified by BEVs that stimulate either proinflammatory or anti-inflammatory responses are highlighted. In addition, we discuss the mechanisms by which BEVs regulate host-microbe interactions and their effects on the immune system. Finally, this review focuses on the contribution of BEVs to the pathogenesis of sepsis/septic shock and their therapeutic potential for the treatment of sepsis.

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.

Preventing Production Escape Using an Engineered Glucose-Inducible Genetic Circuit

A proper balance of metabolic pathways is crucial for engineering microbial strains that can efficiently produce biochemicals on an industrial scale while maintaining cell fitness. High production loads can negatively impact cell fitness and hinder industrial-scale production. To address this, fine-tuning gene expression using engineered promoters and genetic circuits can promote control over multiple targets in pathways and reduce the burden. We took advantage of the robust carbon catabolite repression system of Bacillus subtilis to engineer a glucose-inducible genetic circuit that supports growth and production. The circuit is resilient, enabling a quick switch in the production status when exposed to the correct carbon source. By performing serial cultivations for 61 generations under repressive conditions, we preserved the production capacity of the cells, which could be fully accessed by switching to glucose in the next cultivation step. Switching to glucose after 61 generations resulted in 34-fold activation and generated 70% higher production in comparison to standard cultivation in glucose. Conversely, serial cultivation under permanent induction resulted in 62% production loss after 67 generations alongside an increase in the culture growth rate. As a pathway-independent circuit activated by the preferred carbon source, our engineered glucose-inducible genetic circuit is broadly useful and imposes no additional cost to traditional production processes.

Engineering Escherichia coli Nissle 1917 as a microbial chassis for therapeutic and industrial applications

Genetically engineered microbes, especially Escherichia coli, have been widely used in the biosynthesis of proteins and metabolites for medical and industrial applications. As a traditional probiotic with a well-established safety record, E. coli Nissle 1917 (EcN) has recently emerged as a microbial chassis for generating living therapeutics, drug delivery vehicles, and microbial platforms for industrial production. Despite the availability of genetic tools for engineering laboratory E. coli K-12 and B strains, new genetic engineering systems are still greatly needed to expand the application range of EcN. In this review, we have summarized the latest progress in the development of genetic engineering systems in EcN, as well as their applications in the biosynthesis and delivery of valuable small molecules and biomacromolecules of medical and/or industrial interest, followed by a glimpse of how this rapidly growing field will evolve in the future.