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    Lipopolysaccharide structure impacts the entry kinetics of bacterial outer membrane vesicles into host cells. O'Donoghue Eloise J,Sirisaengtaksin Natalie,Browning Douglas F,Bielska Ewa,Hadis Mohammed,Fernandez-Trillo Francisco,Alderwick Luke,Jabbari Sara,Krachler Anne Marie PLoS pathogens Outer membrane vesicles are nano-sized microvesicles shed from the outer membrane of Gram-negative bacteria and play important roles in immune priming and disease pathogenesis. However, our current mechanistic understanding of vesicle-host cell interactions is limited by a lack of methods to study the rapid kinetics of vesicle entry and cargo delivery to host cells. Here, we describe a highly sensitive method to study the kinetics of vesicle entry into host cells in real-time using a genetically encoded, vesicle-targeted probe. We found that the route of vesicular uptake, and thus entry kinetics and efficiency, are shaped by bacterial cell wall composition. The presence of lipopolysaccharide O antigen enables vesicles to bypass clathrin-mediated endocytosis, which enhances both their entry rate and efficiency into host cells. Collectively, our findings highlight the composition of the bacterial cell wall as a major determinant of secretion-independent delivery of virulence factors during Gram-negative infections. 10.1371/journal.ppat.1006760
    Biological functions and biogenesis of secreted bacterial outer membrane vesicles. Kulp Adam,Kuehn Meta J Annual review of microbiology Gram-negative bacteria produce outer membrane vesicles (OMVs) that contain biologically active proteins and perform diverse biological processes. Unlike other secretion mechanisms, OMVs enable bacteria to secrete insoluble molecules in addition to and in complex with soluble material. OMVs allow enzymes to reach distant targets in a concentrated, protected, and targeted form. OMVs also play roles in bacterial survival: Their production is a bacterial stress response and important for nutrient acquisition, biofilm development, and pathogenesis. Key characteristics of OMV biogenesis include outward bulging of areas lacking membrane-peptidoglycan bonds, the capacity to upregulate vesicle production without also losing outer membrane integrity, enrichment or exclusion of certain proteins and lipids, and membrane fission without direct energy from ATP/GTP hydrolysis. Comparisons of similar budding mechanisms from diverse biological domains have provided new insight into evaluating mechanisms for outer membrane vesiculation. 10.1146/annurev.micro.091208.073413
    Outer-membrane vesicles from Gram-negative bacteria: biogenesis and functions. Schwechheimer Carmen,Kuehn Meta J Nature reviews. Microbiology Outer-membrane vesicles (OMVs) are spherical buds of the outer membrane filled with periplasmic content and are commonly produced by Gram-negative bacteria. The production of OMVs allows bacteria to interact with their environment, and OMVs have been found to mediate diverse functions, including promoting pathogenesis, enabling bacterial survival during stress conditions and regulating microbial interactions within bacterial communities. Additionally, because of this functional versatility, researchers have begun to explore OMVs as a platform for bioengineering applications. In this Review, we discuss recent advances in the study of OMVs, focusing on new insights into the mechanisms of biogenesis and the functions of these vesicles. 10.1038/nrmicro3525
    Explosive cell lysis as a mechanism for the biogenesis of bacterial membrane vesicles and biofilms. Turnbull Lynne,Toyofuku Masanori,Hynen Amelia L,Kurosawa Masaharu,Pessi Gabriella,Petty Nicola K,Osvath Sarah R,Cárcamo-Oyarce Gerardo,Gloag Erin S,Shimoni Raz,Omasits Ulrich,Ito Satoshi,Yap Xinhui,Monahan Leigh G,Cavaliere Rosalia,Ahrens Christian H,Charles Ian G,Nomura Nobuhiko,Eberl Leo,Whitchurch Cynthia B Nature communications Many bacteria produce extracellular and surface-associated components such as membrane vesicles (MVs), extracellular DNA and moonlighting cytosolic proteins for which the biogenesis and export pathways are not fully understood. Here we show that the explosive cell lysis of a sub-population of cells accounts for the liberation of cytosolic content in Pseudomonas aeruginosa biofilms. Super-resolution microscopy reveals that explosive cell lysis also produces shattered membrane fragments that rapidly form MVs. A prophage endolysin encoded within the R- and F-pyocin gene cluster is essential for explosive cell lysis. Endolysin-deficient mutants are defective in MV production and biofilm development, consistent with a crucial role in the biogenesis of MVs and liberation of extracellular DNA and other biofilm matrix components. Our findings reveal that explosive cell lysis, mediated through the activity of a cryptic prophage endolysin, acts as a mechanism for the production of bacterial MVs. 10.1038/ncomms11220
    Enzyme-Responsive Polymeric Vesicles for Bacterial-Strain-Selective Delivery of Antimicrobial Agents. Li Yamin,Liu Guhuan,Wang Xiaorui,Hu Jinming,Liu Shiyong Angewandte Chemie (International ed. in English) Antimicrobial resistance poses serious public health concerns and antibiotic misuse/abuse further complicates the situation; thus, it remains a considerable challenge to optimize/improve the usage of currently available drugs. We report a general strategy to construct a bacterial strain-selective delivery system for antibiotics based on responsive polymeric vesicles. In response to enzymes including penicillin G amidase (PGA) and β-lactamase (Bla), which are closely associated with drug-resistant bacterial strains, antibiotic-loaded polymeric vesicles undergo self-immolative structural rearrangement and morphological transitions, leading to sustained release of antibiotics. Enhanced stability, reduced side effects, and bacterial strain-selective drug release were achieved. Considering that Bla is the main cause of bacterial resistance to β-lactam antibiotic drugs, as a further validation, we demonstrate methicillin-resistant S. aureus (MRSA)-triggered release of antibiotics from Bla-degradable polymeric vesicles, in vitro inhibition of MRSA growth, and enhanced wound healing in an in vivo murine model. 10.1002/anie.201509401
    Virulence and immunomodulatory roles of bacterial outer membrane vesicles. Ellis Terri N,Kuehn Meta J Microbiology and molecular biology reviews : MMBR Outer membrane (OM) vesicles are ubiquitously produced by Gram-negative bacteria during all stages of bacterial growth. OM vesicles are naturally secreted by both pathogenic and nonpathogenic bacteria. Strong experimental evidence exists to categorize OM vesicle production as a type of Gram-negative bacterial virulence factor. A growing body of data demonstrates an association of active virulence factors and toxins with vesicles, suggesting that they play a role in pathogenesis. One of the most popular and best-studied pathogenic functions for membrane vesicles is to serve as natural vehicles for the intercellular transport of virulence factors and other materials directly into host cells. The production of OM vesicles has been identified as an independent bacterial stress response pathway that is activated when bacteria encounter environmental stress, such as what might be experienced during the colonization of host tissues. Their detection in infected human tissues reinforces this theory. Various other virulence factors are also associated with OM vesicles, including adhesins and degradative enzymes. As a result, OM vesicles are heavily laden with pathogen-associated molecular patterns (PAMPs), virulence factors, and other OM components that can impact the course of infection by having toxigenic effects or by the activation of the innate immune response. However, infected hosts can also benefit from OM vesicle production by stimulating their ability to mount an effective defense. Vesicles display antigens and can elicit potent inflammatory and immune responses. In sum, OM vesicles are likely to play a significant role in the virulence of Gram-negative bacterial pathogens. 10.1128/MMBR.00031-09