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Bacterial Membrane (bacterial + membrane)
Kinds of Bacterial Membrane Selected AbstractsCoexistence of Domains with Distinct Order and Polarity in Fluid Bacterial Membranes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2002Sharon Vanounou ABSTRACT In this study we sought the detection and characterization of bacterial membrane domains. Fluorescence generalized polarization (GP) spectra of laurdan-labeled Escherichia coli and temperature dependencies of both laurdan's GP and fluorescence anisotropy of 1,3-diphenyl-1,3,5-hexatriene (DPH) (rDPH) affirmed that at physiological temperatures, the E. coli membrane is in a liquid-crystalline phase. However, the strong excitation wavelength dependence of rlaurdan at 37°C reflects membrane heterogeneity. Time-resolved fluorescence emission spectra, which display distinct biphasic redshift kinetics, verified the coexistence of two subpopulations of laurdan. In the initial phase, <50 ps, the redshift in the spectral mass center is much faster for laurdan excited at the blue edge (350 nm), whereas at longer time intervals, similar kinetics is observed upon excitation at either blue or red edge (400 nm). Excitation in the blue region selects laurdan molecules presumably located in a lipid domain in which fast intramolecular relaxation and low anisotropy characterize laurdan's emission. In the proteo-lipid domain, laurdan motion and conformation are restricted as exhibited by a slower relaxation rate, higher anisotropy and a lower GP value. Triple-Gaussian decomposition of laurdan emission spectra showed a sharp phase transition in the temperature dependence of individual components when excited in the blue but not in the red region. At least two kinds of domains of distinct polarity and order are suggested to coexist in the liquid-crystalline bacterial membrane: a lipid-enriched and a proteo-lipid domain. In bacteria with chloramphenicol (Cam),inhibited protein synthesis, laurdan showed reduced polarity and restoration of an isoemissive point in the temperature-dependent spectra. These results suggest a decrease in membrane heterogeneity caused by Cam-induced domain dissipation. [source] Volume recovery, surface properties and membrane integrity of Lactobacillus delbrueckii subsp. bulgaricus dehydrated in the presence of trehalose or sucroseJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2007E.E. Tymczyszyn Abstract Aims:, Although the practical importance of adding sugars before drying is well known, the mechanism of protection of bacteria by sugars is not clear. The response of the dehydrated micro-organisms to rehydration is analysed in terms of structural and functional changes, and correlated with their potentiality to grow in rich media. These aspects are related with the membrane integrity and the metabolic state of the rehydrated bacteria, measured by means of surface properties and permeability. To attain this objective, Lactobacillus delbrueckii subsp. bulgaricus was dehydrated in the presence and in the absence of sucrose and trehalose. The bacterial response upon rehydration was investigated by determining: (i) the lag time of the bacterial growing in rich media, (ii) the restoration of the surface properties and the cellular volume and (iii) the membrane integrity. Methods and Results:,Lactobacillus delbrueckii subsp. bulgaricus was grown in MRS at 37°C overnight [De Man et al. (1960)J Appl Bacteriol 23, 130] and then dehydrated for 10, 20 and 30 min at 70°C in a vacuum centrifuge. The lag time of micro-organisms was determined by optical density changes after rehydration. The surface properties were determined by measuring the zeta potential of the bacteria suspended in aqueous solution. The cellular volume recovery was measured, after stabilization in saline solution, by light scattering and by the haematocrit method [Alemohammad and Knowles (1974)J Gen Microbiol 82, 125]. Finally, the membrane integrity has been determined by using specific fluorescent probes [SYTO 9 and propidium iodide, (PI)] that bind differentially depending on the integrity of the bacterial membrane. The lag time of Lact. delbrueckii subsp bulgaricus, dehydrated by heat in the presence of sucrose or trehalose and after that rehydrated, was significantly shortened, when compared with that obtained for bacteria dried in the absence of sugars. In these conditions, trehalose and sucrose maintained the zeta potential and the cell volume close to the control (nondried) cells. However, the membrane integrity, measured with fluorescent probes, was maintained only when cells were dehydrated for 10 min in the presence of sugars. For larger times of dehydration, the membrane integrity was not preserved, even in the presence of sugars. Conclusions:, When the micro-organisms are dehydrated in the absence of protectants, the membrane damage occurs with a decrease in the absolute value of the zeta potential and a decrease in the cellular volume recovered after rehydration. In contrast, when the zeta potential and the cellular volume are restored after rehydration to that corresponding to nondried cells, the micro-organisms are able to recover and grow with a reduced lag time. This can only be achieved when the dehydration is carried out in the presence of sugars. At short dehydration times, the response is associated with the preservation of the membrane integrity. However, for longer times of dehydration the zeta potential and volume recovery occurs in the presence of sugars in spite of a severe damage at membrane level. In this condition, cells are also recovered. In conclusion, to predict the ability of growing after dehydration, other bacterial structural parameters besides membrane integrity, such as zeta potential and cellular volume, should be taken into account. Significance and Impact of the Study:, The correlation of the lag time with the surface and permeability properties is of practical importance because the correlation of these two parameters with cell viability, allow to determine the potential bacterial capacity to grow in a rich medium after the preservation procedure, without necessity of performing a kinetic curve of growth, which is certainly time-consuming. [source] Atomic force microscopy study of the role of LPS O-antigen on adhesion of E. coliJOURNAL OF MOLECULAR RECOGNITION, Issue 5 2009Joshua Strauss Abstract The O-antigen is a highly variable component of the lipopolysaccharide (LPS) among Escherichia coli strains and is useful for strain identification and assessing virulence. While the O-antigen has been chemically well characterized in terms of sugar composition, physical properties such as O-antigen length of E. coli LPS have not been well studied, even though LPS length is important for determining binding of bacteria to biomolecules and epithelial cells. Atomic force microscopy (AFM) was used to characterize the physicochemical properties of the LPS of eight E. coli strains. Steric repulsion between the AFM tip (silicon nitride) and the E. coli cells was measured and modeled, to determine LPS lengths for three O157 and two O113 E. coli strains, and three control (K12) strains that do not express the O-antigen. For strains with an O-antigen, the LPS lengths ranged from 17,±,10 to 37,±,9,nm, and LPS length was positively correlated with the force of adhesion (Fadh). Longer lengths of LPS may have allowed for more hydrogen bonding between the O-antigen and silanol groups of the AFM silicon nitride tip, which controlled the magnitude of Fadh. For control strains, LPS lengths ranged from 3,±,2 to 5,±,3,nm, and there was no relationship between LPS length and adhesion force between the bacterium and the silicon nitride tip. In the absence of the O-antigen, we attributed Fadh to electrostatic interactions with lipids in the bacterial membrane. Copyright © 2009 John Wiley & Sons, Ltd. [source] Hydrophobic peptides: novel regulators within bacterial membraneMOLECULAR MICROBIOLOGY, Issue 1 2009Eric Alix Summary Identification of short coding sequences is challenging, both experimentally and in silico, and functional natural peptides (< 50 amino acids) have to a large extent been overlooked in Gram-negative bacteria. Recent results have converged to highlight the role of hydrophobic peptides that form a novel class of active molecules in Escherichia coli and Salmonella enterica serovar Typhimurium. These peptides can play a regulatory role by interacting with protein partners at the inner membrane and by modulating protein partner activity or stability. Genome-wide analyses in both bacterial species have identified several conserved short open reading frames encoding a single transmembrane segment. We discuss the known and predicted membrane-associated peptides and the tools for their identification. Besides the identification of novel regulatory networks, characterization of peptides with a single transmembrane helix segment and proteins that interact with them provides a powerful opportunity to study interactions between alpha helices within biological membranes. In addition, some bioactive membrane peptides could provide a basis for engineering membrane protein antagonists. [source] Coexistence of Domains with Distinct Order and Polarity in Fluid Bacterial Membranes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2002Sharon Vanounou ABSTRACT In this study we sought the detection and characterization of bacterial membrane domains. Fluorescence generalized polarization (GP) spectra of laurdan-labeled Escherichia coli and temperature dependencies of both laurdan's GP and fluorescence anisotropy of 1,3-diphenyl-1,3,5-hexatriene (DPH) (rDPH) affirmed that at physiological temperatures, the E. coli membrane is in a liquid-crystalline phase. However, the strong excitation wavelength dependence of rlaurdan at 37°C reflects membrane heterogeneity. Time-resolved fluorescence emission spectra, which display distinct biphasic redshift kinetics, verified the coexistence of two subpopulations of laurdan. In the initial phase, <50 ps, the redshift in the spectral mass center is much faster for laurdan excited at the blue edge (350 nm), whereas at longer time intervals, similar kinetics is observed upon excitation at either blue or red edge (400 nm). Excitation in the blue region selects laurdan molecules presumably located in a lipid domain in which fast intramolecular relaxation and low anisotropy characterize laurdan's emission. In the proteo-lipid domain, laurdan motion and conformation are restricted as exhibited by a slower relaxation rate, higher anisotropy and a lower GP value. Triple-Gaussian decomposition of laurdan emission spectra showed a sharp phase transition in the temperature dependence of individual components when excited in the blue but not in the red region. At least two kinds of domains of distinct polarity and order are suggested to coexist in the liquid-crystalline bacterial membrane: a lipid-enriched and a proteo-lipid domain. In bacteria with chloramphenicol (Cam),inhibited protein synthesis, laurdan showed reduced polarity and restoration of an isoemissive point in the temperature-dependent spectra. These results suggest a decrease in membrane heterogeneity caused by Cam-induced domain dissipation. [source] Rapid Control of Wound Infections by Targeted Photodynamic Therapy Monitored by In Vivo Bioluminescence Imaging,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2002Michael R. Hamblin ABSTRACT The worldwide rise in antibiotic resistance necessitates the development of novel antimicrobial strategies. In this study we report on the first use of a photochemical approach to destroy bacteria infecting a wound in an animal model. Following topical application, a targeted polycationic photosensitizer conjugate between poly- l -lysine and chlorine6 penetrated the Gram (,) outer bacterial membrane, and subsequent activation with 660 nm laser light rapidly killed Escherichia coli infecting excisional wounds in mice. To facilitate real-time monitoring of infection, we used bacteria that expressed the lux operon from Photorhabdus luminescens; these cells emitted a bioluminescent signal that allowed the infection to be rapidly quantified, using a low-light imaging system. There was a light-dose dependent loss of luminescence in the wound treated with conjugate and light, not seen in untreated wounds. Treated wounds healed as well as control wounds, showing that the photodynamic treatment did not damage the host tissue. Our study points to the possible use of this methodology in the rapid control of wounds and other localized infections. [source] Crystallization and preliminary crystallographic characterization of the iron-regulated outer membrane lipoprotein FrpD from Neisseria meningitidisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2010Ekaterina Sviridova Fe-regulated protein D (FrpD) is a Neisseria meningitidis outer membrane lipoprotein that may be involved in the anchoring of the secreted repeat in toxins (RTX) protein FrpC to the outer bacterial membrane. However, the function and biological roles of the FrpD and FrpC proteins remain unknown. Native and selenomethionine-substituted variants of recombinant FrpD43,271 protein were crystallized using the sitting-drop vapour-diffusion method. Diffraction data were collected to a resolution of 2.25,Å for native FrpD43,271 protein and to a resolution of 2.00,Å for selenomethionine-substituted FrpD43,271 (SeMet FrpD43,271) protein. The crystals of native FrpD43,271 protein belonged to the hexagonal space group P62 or P64, while the crystals of SeMet FrpD43,271 protein belonged to the primitive orthorhombic space group P212121. [source] Molecular structure of the outer bacterial membrane of Pseudomonas aeruginosa via classical simulationBIOPOLYMERS, Issue 6 2002Robert M. Shroll Abstract A detailed structural analysis has been performed of the outer bacterial membrane of Pseudomonas aeruginosa using a parameterized classical simulation model (R. D. Lins and T. P. Straatsma, Biophysical Journal, 2001, Vol. 81, pp. 1037,1046) with modest modifications. The structural analysis of the membrane is presented and newly discovered characteristics of the membrane are discussed. Simulations indicate that the relative contribution of different ligands to calcium ion coordination varies across the membrane, while maintaining a constant average coordination number of 6.1. Water penetrates the surface of the membrane to a depth of about 30 Å. The hydration of ions and phosphate groups is shown to depend on location within the membrane. A measure of saccharide residue orientation is defined and average orientations are presented. Saccharide residues possess varying degrees of motion with a trend of greater mobility at the membrane surface. However, their motion is limited and even in the membrane outer core region the average structure appears fairly rigid over a period of 1 ns. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 395,407, 2002 [source] Disperse distribution of cationic amino acids on hydrophilic surface of helical wheel enhances antimicrobial peptide activityBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010Young Soo Kim Abstract The antimicrobial action of amphipathic antimicrobial peptides (AMPs) generally depends on perturbation of the bacterial membrane via electrostatic interactions promoting initial binding to the surface and hydrophobic interactions for pore formation into the membrane. Several studies have focused on the structure,activity relationship (SAR) of AMPs by modulation of structural parameters. However, modulation of one parameter commonly induces simultaneous changes in other parameters, making it difficult to investigate the specific influence of a single variable. In the present work, we investigated the distribution effect of cationic amino acids on the hydrophilic surface of the helical wheel using model AMPs composed of only lysine (K) and leucine (L) as representative cationic and hydrophobic residues, respectively, under conditions in which other parameters are fixed. Based on SAR analyses of ,-helical KL model AMPs displaying different cationic distributions, we propose that the dispersity of cationic amino acids on the hydrophilic surface is a factor that contributes to the antimicrobial activity of AMP. Moreover, antimicrobial activity is enhanced by rearrangement of cationic amino acids to promote dispersed distribution. We confirmed the cationic distribution effect using natural AMP-derived ,-helical CRAMP18 and its analogs. Our data show that accumulation of lysine shifts in the CRAMP18 analog leads to higher dispersion, and subsequently to improved antimicrobial activity. Therefore, we propose that the cationic distribution effect can be applied for the rational redesign of amino acid sequences to improve the antimicrobial activities of natural ,-helical AMPs, in combination with regulation of other known structural parameters. Biotechnol. Bioeng. 2010;107: 216,223. © 2010 Wiley Periodicals, Inc. [source] Structure of the catalytic domain of Streptococcus pneumoniae sialidase NanAACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2008Guogang Xu Streptococcus pneumoniae genomes encode three sialidases, NanA, NanB and NanC, which are key virulence factors that remove sialic acids from various glycoconjugates. The enzymes have potential as drug targets and also as vaccine candidates. The 115,kDa NanA is the largest of the three sialidases and is anchored to the bacterial membrane. Although recombinantly expressed full-length NanA was soluble, it failed to crystallize; therefore, a 56.5,kDa domain that retained full enzyme activity was subcloned. The purified enzyme was crystallized in 0.1,M MES pH 6.5, 30%(w/v) PEG 4000 using the sitting-drop vapour-diffusion method. Data were collected at 100,K to 2.5,Å resolution from a crystal grown in the presence of the inhibitor 2-deoxy-2,3-dehydro- N -acetyl neuraminic acid. The crystal belongs to space group P212121, with unit-cell parameters a = 49.2, b = 95.6, c = 226.6,Å. The structure was solved by molecular replacement and refined to final R and Rfree factors of 0.246 and 0.298, respectively. [source] Shuffling genes around in hot environments: the unique DNA transporter of Thermus thermophilusFEMS MICROBIOLOGY REVIEWS, Issue 3 2009Beate Averhoff Abstract Natural transformation permits the transport of DNA through bacterial membranes and represents a dominant mode for the transfer of genetic information between bacteria and between microorganisms of distant evolutionary lineages and even between members of different domains. This phenomenon, known as horizontal, or lateral, gene transfer, has been a major force for genome plasticity over evolutionary history, and is largely responsible for the spread of fitness-enhancing traits, including antibiotic resistance and virulence factors. In particular, for adaptation of prokaryotes to extreme environments, lateral gene transfer seems to have played a crucial role. Here, we present a survey of the natural transformation machinery of the thermophile Thermus thermophilus HB27. A tentative model of the transformation machinery comprising of components similar to proteins of type IV pili and type II secretion systems is presented. A comparative discussion of the subunits and the structure of the DNA translocator and the underlying mechanism of transfer of free DNA in T. thermophilus highlights conserved and unique features of the DNA translocator in T. thermophilus. We hypothesize that the extraordinary broad substrate specificity and the high efficiency of the T. thermophilus DNA uptake system is of major importance for thermoadaptation and interdomain DNA transfer in hot environments. [source] Supported Lipid Bilayer on Nanocrystalline Diamond: Dual Optical and Field-Effect Sensor for Membrane DisruptionADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Priscilla Kailian Ang Abstract It is demonstrated that a good biomimetic model lipid membrane with dynamic fluidity can be established on optically transparent nanocrystalline diamond (OTND) with surface roughness below 10,nm. Maigainin II, an antimicrobial peptide, is chosen to investigate the permeation of artificial bacterial membranes constructed on OTND. Due to the unique combination of optical transparency and highly sensitive surface conducting channel, intrinsic OTND affords the possibility of dual-mode sensing based on optical and field effect properties. This opens up new possibilities for making integrated biomolecule,semiconductor microdevices, or sensors where the binding of biomolecules can be tracked using confocal microscopy whilst the associated changes in charge density during membrane perforation can be tracked using the space charge effect in the semiconductor. Such a synergistic approach may provide a powerful methodology for the screening of specific bactericidal activity on biomimetic membrane systems. [source] Antibacterial peptides: basic facts and emerging conceptsJOURNAL OF INTERNAL MEDICINE, Issue 3 2003H. G. Boman Abstract., Boman HG (Microbiology and Tumor Biology Center, Karolinska Institutet, Stockholm, Sweden). Antibacterial peptides: basic facts and emerging concepts (Review). J Intern Med 2003; 254: 197,215. Antibacterial peptides are the effector molecules of innate immunity. Generally they contain 15,45 amino acid residues and the net charge is positive. The cecropin type of linear peptides without cysteine were found first in insects, whilst the defensin type with three disulphide bridges were found in rabbit granulocytes. Now a database stores more than 800 sequences of antibacterial peptides and proteins from the animal and plant kingdoms. Generally, each species has 15,40 peptides made from genes, which code for only one precursor. The dominating targets are bacterial membranes and the killing reaction must be faster than the growth rate of the bacteria. Some antibacterial peptides are clearly multifunctional and an attempt to predict this property from the hydrophobicity of all amino acid side chains are given. Gene structures and biosynthesis are known both in the fruit fly Drosophila and several mammals. Humans need two classes of defensins and the cathelicidin-derived linear peptide LL-37. Clinical cases show that deficiencies in these peptides give severe symptoms. Examples given are morbus Kostmann and atopic allergy. Several antibacterial peptides are being developed as drugs. [source] Different mechanisms of action of antimicrobial peptides: insights from fluorescence spectroscopy experiments and molecular dynamics simulations,JOURNAL OF PEPTIDE SCIENCE, Issue 9 2009Gianfranco Bocchinfuso Abstract Most antimicrobial peptides exert their activity by interacting with bacterial membranes, thus perturbing their permeability. They are investigated as a possible solution to the insurgence of bacteria resistant to the presently available antibiotic drugs. However, several different models have been proposed for their mechanism of membrane perturbation, and the molecular details of this process are still debated. Here, we compare fluorescence spectroscopy experiments and molecular dynamics (MD) simulations regarding the association with lipid bilayers and lipid perturbation for two different amphiphilic helical antimicrobial peptides, PMAP-23 and trichogin GA IV. PMAP-23, a cationic peptide member of the cathelicidin family, is considered to induce membrane permeability according to the Shai-Matsuzaki-Huang "carpet" model, while trichogin GA IV is a neutral peptide, member of the peptaibol family. Although several lines of evidence suggest a "barrel-stave" mechanism of pore formation for the latter peptide, its length is only half the normal thickness of a lipid bilayer. Both fluorescence spectroscopy experiments and MD simulations indicated that PMAP-23 associates with membranes close to their surface and parallel to it, and in this arrangement it causes a severe perturbation to the bilayer, both regarding its surface tension and lipid order. By contrast, trichogin GA IV can undergo a transition from a surface-bound state to a transmembrane orientation. In the first arrangement, it does not cause any strong membrane perturbation, while in the second orientation it might be able to span the bilayer from one side to the other, despite its relatively short length, by causing a significant thinning of the membrane. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [source] The MprF protein is required for lysinylation of phospholipids in listerial membranes and confers resistance to cationic antimicrobial peptides (CAMPs) on Listeria monocytogenesMOLECULAR MICROBIOLOGY, Issue 5 2006Kathrin Thedieck Summary Pathogenic bacteria have to cope with defence mechanisms mediated by adaptive and innate immunity of the host cells. Cationic antimicrobial peptides (CAMPs) represent one of the most effective components of the host innate immune response. Here we establish the function of Lmo1695, a member of the VirR-dependent virulence regulon, recently identified in Listeria monocytogenes. Lmo1695 encodes a membrane protein of 98 kDa with strong homology to the multiple peptide resistance factor (MprF) of Staphylococcus aureus. Like staphylococcal MprF, we found that Lmo1695 is involved in the synthesis of the membrane phospholipid lysylphosphatidylglycerol (L-PG). In addition, Lmo1695 is also essential for lysinylation of diphosphatidylglycerol (DPG), another phospholipid widely distributed in bacterial membranes. A ,lmo1695 mutant lacking the lysinylated phospholipids was particularly susceptible to CAMPs of human and bacterial origin. The mutant strain infected both epithelial cells and macrophages only poorly and was attenuated for virulence when tested in a mouse model of infection. Lmo1695 is a member of a growing list of survival factors which enable growth of L. monocytogenes in different environments. [source] Isolation and characterisation of crocosin, an antibacterial compound from crocodile (Crocodylus siamensis) plasmaANIMAL SCIENCE JOURNAL, Issue 3 2010Sutthidech PREECHARRAM ABSTRACT An antibacterial compound from crocodile blood was partially purified and functionally characterised. The freshwater crocodile (Crocodylus siamensis) plasma with antibacterial activity was partially purified by using a centrifugal concentrator and reverse phase high powered liquid chromatography, and designated as crocosin. Crocosin exhibits antibacterial activity toward Salmonella typhi and Staphylococcus aureus. Crocosin is thermostable and resistant to pronase digestion. The structure of crocosin analyzed by mass spectrometry contains repeating units of 94 and 136 m/z. Scanning electron microscopy indicates that crocosin probably penetrates progressively into cytoplasm space, perturbing and damaging bacterial membranes. Crocosin may provide an early defense mechanism toward bacterial infection in freshwater. [source] | |||||||||||||