Adsorptive removal of Safranine T dye from aqueous solutions using sodium alginate-Festuca arundinacea seeds bio-composite microbeads.

In this study, composite microbeads were prepared using Festuca arundinacea seeds and sodium alginate biopolymer at different ratios and utilized as sorbents for the sorption of Safranine T from wastewater. The sorbents were characterized by FTIR, SEM, XRD, and BET analysis. According to BET analysis, the specific surface area of the adsorbents was calculated to be 10.99 m2/g and the surface was found to be mesoporous. The optimum conditions for adsorption studies including initial pH (2-12), concentration (10-50 mg/L), contact time (0-150 min), and adsorbent mass (0.05 g/50 mL-0.25 g/50 mL) were determined at 25 °C. The raw data obtained from sorption tests were applied to Freundlich, Langmuir-1, Langmuir-2, Langmuir-3, Langmuir-4, Temkin, Toth, and Koble-Corrigan isotherm models. The best results were obtained from the Langmuir-2 and accordingly the qm values were calculated as 454.54, 833.33, and 625.00 mg/g for FA, FA-SA-20, and FA-SA-30 at 25 °C, respectively. Adsorption kinetic data illustrated that the process followed the PSO model. Reusability and desorption studies were performed for composite microbeads. Additionally, the thermodynamic studies were performed at 25, 35 and 45 °C. Considering all these results, it was seen that the FA-SA-20 composite had the highest adsorption capacity and the best desorption efficiency.

Thermodynamic Characterization of Polyetherimide/Single-Walled Carbon Nanotube Composites.

The aim of this study is to examine the interactions of composite materials obtained by adding single-walled carbon nanotubes (SWCNT) to polyetherimide (ULTEM) in different weight ratios with various organic solvents, and to evaluate the solubility of composites in these organic solvents. The characterization of prepared composites was performed with SEM analysis. Thermodynamic properties of ULTEM/SWCNT composites were determined by the inverse gas chromatography (IGC) method at 260-285°C in infinite dilution. According to the IGC method, the retention behaviors were examined by passing different organic solvent vapors over the composites used as stationary phase, and retention diagrams were drawn using the obtained retention data. Thermodynamic parameters including Flory-Huggins interaction parameters (${\chi}_{12}^{\infty }$), equation of state interaction parameters (${\chi}_{12}^{\ast }$), weight fraction activity coefficients in infinite dilution (${\Omega}_1^{\infty }$), effective exchange energy parameters (${\chi}_{\mathrm{eff}}$), partial molar sorption enthalpies ($\Delta{\overline{H}}_1^S$), partial molar dissolution enthalpies in infinite dilution ($\Delta{\overline{H}}_1^{\infty }$) and molar evaporation enthalpies ($\Delta{\overline{H}}_v$) were calculated using the linear retention diagrams. According to ${\chi}_{12}^{\infty }$, ${\chi}_{12}^{\ast }$, ${\Omega}_1^{\infty }$ and ${\chi}_{\mathrm{eff}}$ values, organic solvents were found to be poor solvents for composites at all temperatures. Besides, the solubility parameters of composites were determined by IGC method at infinite dilution.

Small RNAs Activate Salmonella Pathogenicity Island 1 by Modulating mRNA Stability through the hilD mRNA 3' Untranslated Region.

Salmonella enterica serovar Typhimurium is an enteric pathogen associated with foodborne disease. Salmonella invades the intestinal epithelium using a type three secretion system encoded on Salmonella pathogenicity island 1 (SPI-1). SPI-1 genes are tightly regulated by a complex feed-forward loop to ensure proper spatial and temporal expression. Most regulatory input is integrated at HilD, through control of hilD mRNA translation or HilD protein activity. The hilD mRNA possesses a 310-nucleotide 3' untranslated region (UTR) that influences HilD and SPI-1 expression, and this regulation is dependent on Hfq and RNase E, cofactors known to mediate small RNA (sRNA) activities. Thus, we hypothesized that the hilD mRNA 3' UTR is a target for sRNAs. Here, we show that two sRNAs, SdsR and Spot 42, regulate SPI-1 by targeting different regions of the hilD mRNA 3' UTR. Regulatory activities of these sRNAs depended on Hfq and RNase E, in agreement with previous roles found for both at the hilD 3' UTR. Salmonella mutants lacking SdsR and Spot 42 had decreased virulence in a mouse model of infection. Collectively, this work suggests that these sRNAs targeting the hilD mRNA 3' UTR increase hilD mRNA levels by interfering with RNase E-dependent mRNA degradation and that this regulatory effect is required for Salmonella invasiveness. Our work provides novel insights into mechanisms of sRNA regulation at bacterial mRNA 3' UTRs and adds to our knowledge of post-transcriptional regulation of the SPI-1 complex feed-forward loop. IMPORTANCE Salmonella enterica serovar Typhimurium is a prominent foodborne pathogen, infecting millions of people a year. To express virulence genes at the correct time and place in the host, Salmonella uses a complex regulatory network that senses environmental conditions. Known for their role in allowing quick responses to stress and virulence conditions, we investigated the role of small RNAs in facilitating precise expression of virulence genes. We found that the 3' untranslated region of the hilD mRNA, encoding a key virulence regulator, is a target for small RNAs and RNase E. The small RNAs stabilize hilD mRNA to allow proper expression of Salmonella virulence genes in the host.

Adsorptive removal of hazardous dye (crystal violet) using bay leaves (Laurus nobilis L.): surface characterization, batch adsorption studies, and statistical analysis.

In this study, the surface properties of Laurus nobilis L. were determined by inverse gas chromatography. From this, the surface of Laurus nobilis L. was found to be an acidic ([Formula: see text]). Then, the adsorption of hazardous crystal violet dye on Laurus nobilis L. was examined. For the adsorption process, the optimum conditions were determined as contact time (60 min), adsorbent dosage (1.0 g/L), agitation rate (200 rpm), and initial pH (≅ 7). The efficiencies of initial concentration, contact time, temperature, and their binary combinations on the improvement of adsorption percentage were statistically investigated via three different two-way ANOVA analyses. Adsorption data were applied to different isotherms, and it was determined that the Langmuir isotherm (r2 = 0.9998) was the most suitable isotherm for the adsorption process. The [Formula: see text] value was calculated as 400.0 mg/g at 25 °C from the Langmuir isotherm. According to kinetic models, it was observed that the adsorption occurred in three steps. According to enthalpy (+ 7.52 kJ/mol), activation energy (+ 8.91 kJ/mol), and Gibbs free energy (- 30.0 kJ/mol) values, it was determined that the adsorption occurred endothermically and spontaneously. As a result of reusability studies, it was determined that the adsorbent could be used repeatedly.

Adsorptive removal of crystal violet from wastewater using sodium alginate-gelatin-montmorillonite ternary composite microbeads.

In this study, the performance of the montmorillonite-filled sodium alginate/gelatin (SA-GEL-MMT) ternary biocomposite microbeads on the adsorptive removal of crystal violet (CV) dye was investigated. Firstly, the composites containing different weight ratios of MMT such as 10 %, 15 %, and 20 % were prepared. The composite beads were cross-linked using a calcium chloride (3%wt/v) solution. To determine the optimum sorption conditions the studies were performed at different parameters namely temperature, pH, contact time, sorbent dose, and dye concentration. From the sorption studies, the maximum capacity of the microbeads was found as 1000.0 mg/g whereas the maximum removal of the dye was 92.1 % at pH = 7 and a temperature of 25 °C. Additionally, the kinetic studies showed that the sorption of the dye followed the pseudo-second-order kinetics. Moreover, the adsorptive removal of the dye occurs spontaneously. This study suggests that the use of SA-GEL-MMT can be highly effective and reusable for the treatment of wastewater.

A comparative study of surface properties of Urtica dioica (nettle) leaves, roots, and seeds and examination of their ability to separate xylene isomers.

INTRODUCTION: Urtica dioica (nettle) is a plant species of the Urticaceae family that grows in various parts of the world and exerts antioxidant, antibacterial, antiulcer, antiviral, and anti-inflammatory effects. Their leaves, roots, and seeds are used in various fields such as food, medicine, and cosmetics. OBJECTIVES: Inverse gas chromatography (IGC) was used to evaluate the surface characteristics and separation ability of U. dioica leaves, roots, and seeds. Characterization of these biomasses was performed by Fourier transform infrared spectroscopy (FTIR) analyses. METHODOLOGY: The surface properties of the biomasses including dispersive surface energy, adsorption enthalpy, Gibbs free energy, and acidity-basicity constants were determined at infinite dilution using various organic solvents. These properties were compared with each other. Dispersive surface energies were calculated using the Dorris-Gray, Donnet-Park, and Schultz methods. The accuracy of these methods and their applicability were evaluated. In the last stage of this study, the separation of xylene isomers was investigated by using U. dioica biomasses as stationary phases. RESULTS: The surface functional groups were determined by FTIR analysis. As a result of the IGC studies, it was found that the adsorption of polar solvents on biomasses occurred exothermically and spontaneously. Besides, it was found that the surfaces of biomasses were basic. From the retention diagrams and selectivity coefficients, it was determined that xylene isomers were effectively separated. CONCLUSION: IGC is a promising, low-cost, easy-to-apply, and high-accuracy technique for the investigation of the surface properties of biomasses and their ability to separate isomers.

Investigation of the Surface Properties of Hexagonal Boron Nitride and Boron Phosphate by Inverse Gas Chromatography at Infinite Dilution.

The boron-based ceramics namely hexagonal boron nitride (h-BN) and boron phosphate (BPO4) were synthesized and characterized by Fourier transform infrared spectroscopy and X-ray diffraction analysis. The surface properties of h-BN and BPO4 were examined by inverse gas chromatography method. The dispersive surface energy and the acidic-basic character of h-BN, and BPO4 surfaces were estimated by the retention time with probes such as n-hexane, n-heptane, n-octane, n-nonane, n-decane, acetone, ethyl acetate, dichloromethane, chloroform and tetrahydrofuran at infinite dilution region. The dispersive surface free energies calculated using both Schultz and Dorris-Gray methods, decreased linearly with increasing temperature. The specific adsorption free energy and the specific adsorption enthalpy corresponding to acid-base surface interactions were determined. By correlating with the donor and acceptor numbers of the probes, the acidic and the basic parameters of the h-BN and BPO4 were calculated. The values obtained for and parameters indicated that h-BN has a basic character, whereas BPO4 has an acidic character.

The Small RNA MicC Downregulates hilD Translation To Control the Salmonella Pathogenicity Island 1 Type III Secretion System in Salmonella enterica Serovar Typhimurium.

Salmonella enterica serovar Typhimurium invades the intestinal epithelium and induces inflammatory diarrhea using the Salmonella pathogenicity island 1 (SPI1) type III secretion system (T3SS). Expression of the SPI1 T3SS is controlled by three AraC-like regulators, HilD, HilC, and RtsA, which form a feed-forward regulatory loop that leads to activation of hilA, encoding the main transcriptional regulator of the T3SS structural genes. This complex system is affected by numerous regulatory proteins and environmental signals, many of which act at the level of hilD mRNA translation or HilD protein function. Here, we show that the sRNA MicC blocks translation of the hilD mRNA by base pairing near the ribosome binding site. MicC does not induce degradation of the hilD message. Our data indicate that micC is transcriptionally activated by SlyA, and SlyA feeds into the SPI1 regulatory network solely through MicC. Transcription of micC is negatively regulated by the OmpR/EnvZ two-component system, but this regulation is dependent on SlyA. OmpR/EnvZ control SPI1 expression partially through MicC but also affect expression through other pathways, including an EnvZ-dependent, OmpR-independent mechanism. MicC-mediated regulation plays a role during infection, as evidenced by an SPI1 T3SS-dependent increase in Salmonella fitness in the intestine in the micC deletion mutant. These results further elucidate the complex regulatory network controlling SPI1 expression and add to the list of sRNAs that control this primary virulence factor. IMPORTANCE The Salmonella pathogenicity island 1 (SPI1) type III secretion system (T3SS) is the primary virulence factor required for causing intestinal disease and initiating systemic infection. The system is regulated in response to a large variety of environmental and physiological factors such that the T3SS is expressed at only the appropriate time and place in the host during infection. Here, we show how the sRNA MicC affects expression of the system. This work adds to our detailed mechanistic studies aimed at a complete understanding of the regulatory circuit.

Application of inverse gas chromatography in the surface characterization of diethanol amine modified polystyrene based polymer.

In the present work, diethanol amine modified polystyrene based polymer (PVBC-Diethanol amine) was synthesized and characterized, then surface properties of the polymer were examined by inverse gas chromatography method at infinite dilution. The retention diagrams obtained based on the interaction of polar and nonpolar probes with the polymer were drawn over a temperature range from 30 to 55 °C. Through the diagrams, the dispersive component of the surface free energy, g S D of the polymer surface, and the specific enthalpy of adsorption, DH A S , of probes on the polymer were also calculated. Lewis acid, K A , and Lewis base, K D , parameters of PVBC-Diethanol amine surface were determined. The values of K A and K D indicated that PVBC-Diethanol amine surface exhibited a basic behavior.

Evaluation of the surface properties of 4-(Decyloxy) benzoic acid liquid crystal and its use in structural isomer separation.

The selectivity of 4-(Decyloxy) benzoic acid (DBA) liquid crystal in surface adsorption region (303.2-328.2 K) and thermodynamic region (423.2 - 433.2 K) was investigated by inverse gas chromatography at infinite dilution (IGC-ID). The selectivity parameters of the structural isomer series named butyl acetate, butyl alcohol, and amyl alcohol series were calculated for the DBA using IGC-ID technique. Additionally, the surface properties including dispersive surface energy (gS D), free energy (DGA S), enthalpy (DHA S), and acidity-basicity constants were calculated with net retention volumes obtained from IGC-ID experiment results. When the DHA S and DGA S are constants, DBA surface was found to be an acidic character (KD/KA @ 0.89).

Synthesis and characterization of novel 4-benzyloxyphenyl 4-[4-(n-dodecyloxy)benzoyloxy]benzoate liquid crystal.

Liquid crystal (LC) compound 4-Benzyloxyphenyl 4-[4-( n -dodecyloxy)benzoyloxy]benzoate (BDBB) was prepared and characterized. Inverse gas chromatography (IGC) was to be a beneficial analysis method for the research of thermodynamic characteristics of the new LC. Acetate and alcohol isomers were used to examine LC selectivity via the IGC technique at temperatures between 333.2 K and 483.2 K. The retention diagrams of n -heptane, n -octane, n -nonane, n -decane, undecane, dodecane, tridecane, n -butyl acetate, isobutyl acetate, ethyl acetate, n -propylbenzene, isopropylbenzene, ethylbenzene, chlorobenzene, and toluene on BDBB were plotted with temperatures of 483.2-493.2 K. Flory-Huggins interaction parameter and weight fraction activity coefficient at infinite dilution were researched for BDBB.

Outer Membrane Vesiculation Facilitates Surface Exchange and In Vivo Adaptation of Vibrio cholerae.

Gram-negative bacteria release outer membrane vesicles into the external milieu to deliver effector molecules that alter the host and facilitate virulence. Vesicle formation is driven by phospholipid accumulation in the outer membrane and regulated by the phospholipid transporter VacJ/Yrb. We use the facultative human pathogen Vibrio cholerae to show that VacJ/Yrb is silenced early during mammalian infection, which stimulates vesiculation that expedites bacterial surface exchange and adaptation to the host environment. Hypervesiculating strains rapidly alter their bacterial membrane composition and exhibit enhanced intestinal colonization fitness. This adaptation is exemplified by faster accumulation of glycine-modified lipopolysaccharide (LPS) and depletion of outer membrane porin OmpT, which confers resistance to host-derived antimicrobial peptides and bile, respectively. The competitive advantage of hypervesiculation is lost upon pre-adaptation to bile and antimicrobial peptides, indicating the importance of these adaptive processes. Thus, bacteria use outer membrane vesiculation to exchange cell surface components, thereby increasing survival during mammalian infection.

Synthesis and liquid crystalline properties of new triazine-based π-conjugated macromolecules with chiral side groups.

In this study, we reported the synthesis of a new tribranched macromolecule liquid crystal with triazine in the centre. The central triazine core is bonded via sequences of Sonigashira coupling to 3 triazine unites through acetylenic bridges. The triazines at the periphery are substituted with 2 chiral citronellyloxy side groups. The salt of the resulting star-shaped macromolecule, which was oily at room temperature, with 4-dodecyloxybenzoic acid at 1:1 ratio exhibited a Smectic C (SmC) mesophase. The liquid crystalline properties of organic salt were investigated using DSC (differential scanning calorimetry) and POM (polarizing optical microscopy).

Silence is golden: gene silencing of V. cholerae during intestinal colonization delivers new aspects to the acid tolerance response.

Bacterial pathogens of the gastrointestinal tract alter their expression profile upon ingestion by the host and activate a variety of factors enhancing colonization and virulence. However, gene silencing during infection might be as important as gene activation to achieve full colonization fitness. Thus, we developed and successfully applied a reporter technology to identify 101 in vivo repressed (ivr) genes of the bacterial pathogen Vibrio cholerae. In depth analysis of the in vivo repressed H+/Cl- transporter ClcA revealed an inverse requirement along gastrointestinal colonization. ClcA could be linked to acid tolerance response required during stomach passage, but ClcA expression is detrimental during subsequent colonization of the lower intestinal tract as it exploits the proton-motive force in alkaline environments. The study summarized in this addendum demonstrates that constitutive expression of ivr genes can reduce intestinal colonization fitness of V. cholerae, highlighting the necessity to downregulate these genes in vivo.

Comparative analyses of biofilm formation among different Cutibacterium acnes isolates.

The Gram-positive anaerobic bacterium Cutibacterium acnes is a commensal of the human skin, but also an opportunistic pathogen that contributes to the pathophysiology of the skin disease acne vulgaris. Moreover, C. acnes, in addition to other skin-colonizing bacteria such as S. epidermidis and S. aureus, is an emerging pathogen of implant-associated infections. Notably, C. acnes isolates exhibit marked heterogeneity and can be divided into at least 6 phylotypes by multilocus sequence typing. It is becoming increasingly evident that biofilm formation is a relevant factor for C. acnes virulence, but information on biofilm formation by diverse C. acnes isolates is limited. In this study we performed a first comparative analysis of 58 diverse skin- or implant-isolates covering all six C. acnes phylotypes to investigate biofilm formation dynamics, biofilm morphology and attachment properties to abiotic surfaces. The results presented herein suggest that biofilm formation correlates with the phylotype, rather than the anatomical isolation site. IA1 isolates, particularly SLST sub-types A1 and A2, showed highest biofilm amounts in the microtiter plate assays, followed by isolates of the IC, IA2 and II phylotypes. Microscopic evaluation revealed well-structured three-dimensional biofilms and relatively high adhesive properties to abiotic surfaces for phylotypes IA1, IA2 and IC. Representatives of phylotype III formed biofilms with comparable biomass, but with less defined structures, whereas IB as well as II isolates showed the least complex three-dimensional morphology. Proteinase K- and DNase I-treatment reduced attachment rates of all phylotypes, therefore, indicating that extracellular DNA and proteins are critical for adhesion to abiotic surfaces. Moreover, proteins seem to be pivotal structural biofilm components as mature biofilms of all phylotypes were proteinase K-sensitive, whereas the sensitivity to DNase I-treatment varied depending on the phylotype.

Genes Activated by Vibrio cholerae upon Exposure to Caenorhabditis elegans Reveal the Mannose-Sensitive Hemagglutinin To Be Essential for Colonization.

During its life cycle, the facultative human pathogen Vibrio cholerae, which is the causative agent of the diarrheal disease cholera, needs to adapt to a variety of different conditions, such as the human host or the aquatic environment. Importantly, cholera infections originate from the aquatic reservoir where V. cholerae persists between the outbreaks. In the aquatic environment, bacteria are constantly threatened by predatory protozoa and nematodes, but our knowledge of the response pathways and adaptation strategies of V. cholerae to such stressors is limited. Using a temporally controlled reporter system of transcription, we identified more than 100 genes of V. cholerae induced upon exposure to the nematode Caenorhabditis elegans, which emerged recently as a valuable model for environmental predation during the aquatic lifestyle of V. cholerae Besides others, we identified and validated the genes encoding the mannose-sensitive hemagglutinin (MSHA) type IV pilus to be significantly induced upon exposure to the nematode. Subsequent analyses demonstrated that the mannose-sensitive hemagglutinin is crucial for attachment of V. cholerae in the pharynx of the worm and initiation of colonization, which results in growth retardation and developmental delay of C. elegans Thus, the surface adhesion factor MSHA could be linked to a fitness advantage of V. cholerae upon contact with bacterium-grazing nematodes.IMPORTANCE The waterborne diarrheal disease cholera is caused by the bacterium Vibrio cholerae The facultative human pathogen persists as a natural inhabitant in the aquatic ecosystem between outbreaks. In contrast to the human host, V. cholerae requires a different set of genes to survive in this hostile environment. For example, predatory micrograzers are commonly found in the aquatic environment and use bacteria as a nutrient source, but knowledge of the interaction between bacterivorous grazers and V. cholerae is limited. In this study, we successfully adapted a genetic reporter technology and identified more than 100 genes activated by V. cholerae upon exposure to the bacterium-grazing nematode Caenorhabditis elegans This screen provides a first glimpse into responses and adaptational strategies of the bacterial pathogen against such natural predators. Subsequent phenotypic characterization revealed the mannose-sensitive hemagglutinin to be crucial for colonization of the worm, which causes developmental delay and growth retardation.

In vivo repressed genes of Vibrio cholerae reveal inverse requirements of an H+/Cl- transporter along the gastrointestinal passage.

The facultative human pathogen Vibrio cholerae changes its transcriptional profile upon oral ingestion by the host to facilitate survival and colonization fitness. Here, we used a modified version of recombination-based in vivo expression technology to investigate gene silencing during the in vivo passage, which has been understudied. Using a murine model of cholera, we screened a V. cholerae transposon library composed of 10,000 randomly generated reporter fusions and identified 101 in vivo repressed (ivr) genes. Our data indicate that constitutive expression of ivr genes reduces colonization fitness, highlighting the necessity to down-regulate these genes in vivo. For example, the ivr gene clcA, encoding an H+/Cl- transporter, could be linked to the acid tolerance response against hydrochloric acid. In a chloride-dependent manner, ClcA facilitates survival under low pH (e.g., the stomach), but its presence becomes detrimental under alkaline conditions (e.g., lower gastrointestinal tract). This pH-dependent clcA expression is controlled by the LysR-type activator AphB, which acts in concert with AphA to initiate the virulence cascade in V. cholerae after oral ingestion. Thus, transcriptional networks dictating induction of virulence factors and the repression of ivr genes overlap to regulate in vivo colonization dynamics. Overall, the results presented herein highlight the impact of spatiotemporal gene silencing in vivo. The molecular characterization of the underlying mechanisms can provide important insights into in vivo physiology and virulence network regulation.

AAA+ proteases and their role in distinct stages along the Vibrio cholerae lifecycle.

The facultative human pathogen Vibrio cholerae has to adapt to different environmental conditions along its lifecycle by means of transcriptional, translational and post-translational regulation. This study provides a first comprehensive analysis regarding the contribution of the cytoplasmic AAA+ proteases Lon, ClpP and HslV to distinct features of V. cholerae behaviour, including biofilm formation, motility, cholera toxin expression and colonization fitness in the mouse model. While absence of HslV did not yield to any altered phenotype compared to wildtype, absence of Lon or ClpP resulted in significantly reduced colonization in vivo. In addition, a Δlon deletion mutant showed altered biofilm formation and increased motility, which could be correlated with higher expression of V. cholerae flagella gene class IV. Concordantly, we could show by immunoblot analysis, that Lon is the main protease responsible for proteolytic control of FliA, which is required for class IV flagella gene transcription, but also downregulates virulence gene expression. FliA becomes highly sensitive to proteolytic degradation in absence of its anti-sigma factor FlgM, a scenario reported to occur during mucosal penetration due to FlgM secretion through the broken flagellum. Our results confirm that the high stability of FliA in the absence of Lon results in less cholera toxin and toxin corgulated pilus production under virulence gene inducing conditions and in the presence of a damaged flagellum. Thus, the data presented herein provide a molecular explanation on how V. cholerae can achieve full expression of virulence genes during early stages of colonization, despite FliA getting liberated from the anti-sigma factor FlgM.

A novel mechanism for the biogenesis of outer membrane vesicles in Gram-negative bacteria.

Bacterial outer membrane vesicles (OMVs) have important biological roles in pathogenesis and intercellular interactions, but a general mechanism of OMV formation is lacking. Here we show that the VacJ/Yrb ABC (ATP-binding cassette) transport system, a proposed phospholipid transporter, is involved in OMV formation. Deletion or repression of VacJ/Yrb increases OMV production in two distantly related Gram-negative bacteria, Haemophilus influenzae and Vibrio cholerae. Lipidome analyses demonstrate that OMVs from VacJ/Yrb-defective mutants in H. influenzae are enriched in phospholipids and certain fatty acids. Furthermore, we demonstrate that OMV production and regulation of the VacJ/Yrb ABC transport system respond to iron starvation. Our results suggest a new general mechanism of OMV biogenesis based on phospholipid accumulation in the outer leaflet of the outer membrane. This mechanism is highly conserved among Gram-negative bacteria, provides a means for regulation, can account for OMV formation under all growth conditions, and might have important pathophysiological roles in vivo.

Bacterial outer membrane vesicle biogenesis: a new mechanism and its implications.

Outer membrane vesicle (OMV) release by Gram-negative bacteria has been observed and studied for decades. First considered as a by-product of cell lysis, it soon became evident that OMVs are actively secreted from the outer membrane (OM) of Gram-negative bacteria. Accordingly, these small particles (~ 10-300 nm in diameter) consist mainly of OM components like phospholipids (PLs), OM proteins, and lipopolysaccharides or lipooligosaccharides. However, OMVs may also comprise periplasmic, inner membrane, or cytoplasmic components. Since the shedding of substantial amounts of OM material represents a significant energy cost to the bacterial cell, OMV production must have some vital biological functions for Gram-negative bacteria. Indeed, intense research on that topic revealed that OMVs play important roles in bacterial physiology and pathogenesis, ranging from secretion and delivery of biomolecules (for example, toxins, DNA, or quorum sensing molecules) over stress response and biofilm formation to immunomodulation and adherence to host cells. Only recently researchers have begun to elucidate the mechanistic aspects of OMV formation, but a general mechanism for the biogenesis of these vesicles is still lacking. Here we review the findings and implications of our recent study published in Nature Communications (Roier S, et al. (2016) Nat. Commun. 7:10515), where we propose a novel and highly conserved bacterial OMV biogenesis mechanism based on PL accumulation in the outer leaflet of the OM. This mechanism might not only have important pathophysiological roles in vivo, but also represents the first general mechanism of OMV formation applicable to all Gram-negative bacteria.