Isolation and characterization of outer and inner membranes from Pseudomonas aeruginosa and effect of EDTA on the membranes

Structural, mechanistic and physiological insights into phospholipase A-mediated membrane phospholipid degradation in Pseudomonas aeruginosa

Cells steadily adapt their membrane glycerophospholipid (GPL) composition to changing environmental and developmental conditions. While the regulation of membrane homeostasis via GPL synthesis in bacteria has been studied in detail, the mechanisms underlying the controlled degradation of endogenous GPLs remain unknown. Thus far, the function of intracellular phospholipases A (PLAs) in GPL remodeling (Lands cycle) in bacteria is not clearly established. Here, we identified the first cytoplasmic membrane-bound phospholipase A₁ (PlaF) from Pseudomonas aeruginosa, which might be involved in the Lands cycle. PlaF is an important virulence factor, as the P. aeruginosa ΔplaF mutant showed strongly attenuated virulence in Galleria mellonella and macrophages. We present a 2.0-Å-resolution crystal structure of PlaF, the first structure that reveals homodimerization of a single-pass transmembrane (TM) full-length protein. PlaF dimerization, mediated solely through the intermolecular interactions of TM and juxtamembrane regions, inhibits its activity. The dimerization site and the catalytic sites are linked by an intricate ligand-mediated interaction network, which might explain the product (fatty acid) feedback inhibition observed with the purified PlaF protein. We used molecular dynamics simulations and configurational free energy computations to suggest a model of PlaF activation through a coupled monomerization and tilting of the monomer in the membrane, which constrains the active site cavity into contact with the GPL substrates. Thus, these data show the importance of the PlaF-mediated GPL remodeling pathway for virulence and could pave the way for the development of novel therapeutics targeting PlaF.

AB569, a Novel, Topical Bactericidal Gel Formulation, Kills Pseudomonas aeruginosa and Promotes Wound Healing in a Murine Model of Burn Wound Infection

Cutaneous thermal injuries from burns/explosives are a major cause of morbidity and mortality and represent a monumental burden on our current health care system. Injury severity is predominantly due to potentially lethal sepsis caused by multidrug-resistant (MDR) bacteria such as Pseudomonas aeruginosa (MDR-PA). Thus, there is a critical need to develop novel and effective antimicrobials for the (i) prevention, (ii) treatment, and (iii) healing of such wounds that are complicated by MDR-P. aeruginosa and other bacterial infections. AB569 is a novel bactericidal tandem consisting of acidified NaNO₂ (A-NO_2-) and Na₂-EDTA. Here, we first show that AB569 acts synergistically to kill all human burn wound strains of P. aeruginosa in vitro. This was found to be due, in part, to the generation of A-NO_2--mediated nitric oxide (NO) formation coupled with the metal chelating properties of Na₂-EDTA. Using a murine scald burn wound model of P. aeruginosa infection, an AB569-Solosite gel formulation eradicated all bacteria. Futher, we also demonstrate enhanced AB569-mediated wound healing by not only accelerating wound contraction, but also by reducing levels of the proinflammatory cytokines interleukin-6 (IL-6) and IL-1β while increasing the levels of anti-inflammatory cytokine, IL-10, and granulocyte-colony-stimulating factor (G-CSF). We also observed better epidermal restoration in AB569-treated wounds. Taken together, we conclude that this study provides solid foundational evidence that AB569 can be used topically to treat highly problematic dermal insults, including wound, burn, blast, and likely, diabetic infections in civilian and military populations, and help relieve the economical burden that MDR organisms have on the global health care system.

Membrane Vesicle Production as a Bacterial Defense Against Stress

Membrane vesicles are the nano-sized vesicles originating from membranes. The production of membrane vesicles is a common feature among bacteria. Depending on the bacterial growth phase and environmental conditions, membrane vesicles show diverse characteristics. Various physiological and ecological roles have been attributed to membrane vesicles under both homeostatic and stressful conditions. Pathogens encounter several stressors during colonization in the hostile environment of host tissues. Nutrient deficiency, the presence of antibiotics as well as elements of the host’s immune system are examples of stressors threatening pathogens inside their host. To combat stressors and survive, pathogens have established various defensive mechanisms, one of them is production of membrane vesicles. Pathogens produce membrane vesicles to alleviate the destructive effects of antibiotics or other types of antibacterial treatments. Additionally, membrane vesicles can also provide benefits for the wider bacterial community during infections, through the transfer of resistance or virulence factors. Hence, given that membrane vesicle production may affect the activities of antibacterial agents, their production should be considered when administering antibacterial treatments. Besides, regarding that membrane vesicles play vital roles in bacteria, disrupting their production may suggest an alternative strategy for battling against pathogens. Here, we aim to review the stressors encountered by pathogens and shed light on the roles of membrane vesicles in increasing pathogen adaptabilities in the presence of stress-inducing factors.

A Novel Bactericidal Drug Effective Against Gram-Positive and Gram-Negative Pathogenic Bacteria: Easy as AB569

Global antibiotic resistance, driven by intensive antibiotic exposure/abuse, constitutes a serious challenge to all health care, particularly in an era when new antimicrobial development has slowed to a trickle. Recently, we published work demonstrating the discovery and partial mechanism of action of a novel bactericidal agent that is effective against both gram-positive and gram-negative multidrug-resistant bacteria. This drug, called AB569, consists of acidified nitrite (A-NO₂^-) and EDTA, of which there is no mechanism of resistance. Using both chemistry-, genetic-, and bioinformatics-based techniques, we first discovered that AB569 was able to generate bactericidal levels of nitric oxide (NO), while the EDTA component stabilized S-nitrosyl thiols, thereby furthering NO and downstream reactive nitrogen species production. This elegant chemistry triggered a paralytic downregulation of vital genes using RNA-seq involved in the synthesis of DNA, RNA, ATP, and protein in the representative ESKAPE pathogen, Pseudomonas aeruginosa.

On the Antibacterial Activity of Azacarboxylate Ligands: Lowered Metal Ion Affinities for Bis-amide Derivatives of EDTA do not mean Reduced Activity

EDTA is widely used as an inhibitor of bacterial growth, affecting the uptake and control of metal ions by microorganisms. We describe the synthesis and characterisation of two symmetrical bis-amide derivatives of EDTA, featuring glycyl or pyridyl substituents: AmGly₂ and AmPy₂ . Metal ion affinities (logK) have been evaluated for a range of metals (Mg²⁺ , Ca²⁺ , Fe³⁺ , Mn²⁺ , Zn²⁺ ), revealing less avid binding compared to EDTA. The solid-state structures of AmGly₂ and of its Mg²⁺ complex have been determined crystallographically. The latter shows an unusual 7-coordinate, capped octahedral Mg²⁺ centre. The antibacterial activities of the two ligands and of EDTA have been evaluated against a range of health-relevant bacterial species, three Gram negative (Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae) and a Gram positive (Staphylococcus aureus). The AmPy₂ ligand is the only one that displays a significant inhibitory effect against K. pneumoniae, but is less effective against the other organisms. AmGly₂ exhibits a more powerful inhibitory effect against E. coli at lower concentrations than EDTA (<3 mm) or AmPy₂ , but loses its efficacy at higher concentrations. The growth inhibition of EDTA and AmGly₂ on mutant E. coli strains with defects in outer-membrane lipopolysaccharide (LPS) structures has been assessed to provide insight into the unexpected behaviour. Taken together, the results contradict the assumption of a simple link between metal ion affinity and antimicrobial efficacy.

A Putative ABC Transporter Permease Is Necessary for Resistance to Acidified Nitrite and EDTA in Pseudomonas aeruginosa under Aerobic and Anaerobic Planktonic and Biofilm Conditions

Pseudomonas aeruginosa (PA) is an important airway pathogen of cystic fibrosis and chronic obstructive disease patients. Multiply drug resistant PA is becoming increasing prevalent and new strategies are needed to combat such insidious organisms. We have previously shown that a mucoid, mucA22 mutant PA is exquisitely sensitive to acidified nitrite (A-NO2−, pH 6.5) at concentrations that are well tolerated in humans. Here, we used a transposon mutagenesis approach to identify PA mutants that are hypersensitive to A-NO2−. Among greater than 10,000 mutants screened, we focused on PA4455, in which the transposon was found to disrupt the production of a putative cytoplasmic membrane-spanning ABC transporter permease. The PA4455 mutant was not only highly sensitive to A-NO2−, but also the membrane perturbing agent, EDTA and the antibiotics doxycycline, tigecycline, colistin, and chloramphenicol, respectively. Treatment of bacteria with A-NO2− plus EDTA, however, had the most dramatic and synergistic effect, with virtually all bacteria killed by 10 mM A-NO2−, and EDTA (1 mM, aerobic, anaerobic). Most importantly, the PA4455 mutant was also sensitive to A-NO2− in biofilms. A-NO2− sensitivity and an anaerobic growth defect was also noted in two mutants (rmlC and wbpM) that are defective in B-band LPS synthesis, potentially indicating a membrane defect in the PA4455 mutant. Finally, this study describes a gene, PA4455, that when mutated, allows for dramatic sensitivity to the potential therapeutic agent, A-NO2− as well as EDTA. Furthermore, the synergy between the two compounds could offer future benefits against antibiotic resistant PA strains.

MexCD-OprJ multidrug efflux system of Pseudomonas aeruginosa: involvement in chlorhexidine resistance and induction by membrane-damaging agents dependent upon the AlgU stress response sigma factor

The biocide chlorhexidine (CHX) as well as additional membrane-active agents were shown to induce expression of the mexCD-oprJ multidrug efflux operon, dependent upon the AlgU stress response sigma factor. Hyperexpression of this efflux system in nfxB mutants was also substantially AlgU dependent. CHX resistance correlated with efflux gene expression in various mutants, consistent with MexCD-OprJ being a determinant of CHX resistance.

Chitosan-EDTA conjugate: a novel polymer for topical gels

A recently developed chitosan-EDTA conjugate, neutralized with sodium hydroxide (NaChito-EDTA), has been tested for possible topical use. The technical properties and microbial stability of NaChito-EDTA have been compared with those of carmellose sodium (NaCMC), hydroxypropylmethylcellulose (HPMC), sodium polycarbophil (NaPCP) and sodium carbopol 980 (NaC980), well established gelatinizing agents. NaChito-EDTA forms stable, colourless, completely transparent hydrogels at a polymer concentration of 0.5%. Of the polymers tested the novel polymer had the lowest incompatibility with multivalent cations and with ethanol, and much the best swelling properties. After 28 days of incubation at room temperature the rates of growth of the complete bacterial spectrum occurring in demineralized water and of Escherichia coli, serving as model strain representative of gram-negative bacteria, were at least 2 log and 5.7 log, respectively, lower in NaChito-EDTA gels than in the other hydrogels. This antimicrobial activity of NaChito-EDTA can be explained by its highest binding affinity towards magnesium, which stabilizes the outer membrane of gram-negative bacteria. However, this antimicrobial effect is insufficient to guarantee microbial stability. Further results showed that the antimicrobially acting polypeptide nisin can be recommended as an alternative novel preservative for NaChito-EDTA gels, because its antimicrobial spectrum could also be increased towards gram-negative bacteria in combination with chelating excipients. NaChito-EDTA seems, therefore, to be a promising novel polymer for topically-used gels, with advantages over well established gelatinizing agents.

Immunoblot and ultrastructural analysis of antigens extracted from Dichelobacter nodosus with potassium thiocyanate

The antigens extracted from Dichelobacter nodosus with potassium thiocyanate were analyzed by western blotting with sera from footrot-free sheep and from sheep infected with D. nodosus to identify components specific for infection. Several components with molecular mass < 33 kD were associated with infection, particularly bands of 32.5 kD, 30.5 kD, and 28 kD. Components with molecular mass > 56 kD may be responsible for false-positive reactions observed when sera of footrot-free sheep react with the potassium thiocyanate extract in solid phase enzyme-linked immunosorbent assays (ELISAs). Bands of 62.5 kD, 56 kD, 40 kD, and 19 kD were recognized for most sheep regardless of their disease status or ELISA reactivity and therefore do not appear to be detected by the ELISA. No components of the potassium thiocyanate extract were completely specific for infection. Antigens in the extract were identified primarily on the cell envelope by immunogold electron microscopy. Labeling was concentrated in the periplasm, with minor labeling of the cell surface. The extract consisted of tangled strands of particles with electron-dense cores, and few vesicular structures were observed.

Extraction, purification, and characterization of major outer membrane proteins from Wolinella recta ATCC 33238

The outer membrane of Wolinella recta ATCC 33238 was isolated by French pressure cell disruption and differential centrifugation. Outer membrane proteins (OMPs) were solubilized by Zwittergent 3.14 extraction and separated by DEAE-Sephacel ion-exchange chromatography. The major OMPs that were found in W. recta ATCC 33238 and in several other Wolinella spp. consisted of proteins with apparent molecular masses of 51, 45, and 43 kDa. These three conserved proteins were purified to essential homogeneity by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and characterized chemically. Heating at between 75 and 100 degrees C revealed both the 43- and 51-kDa proteins to be heat modified from apparent molecular masses of 32 and 38 kDa, respectively. The 45-kDa protein was unmodified at all temperatures tested. Two-dimensional isoelectric focusing-SDS-PAGE revealed the 51-kDa protein to be composed of multiple pIs between a pH of 5.0 and greater than 8.0 while the 43- and 45-kDa proteins had a pI of approximately 6.0. N'-terminal amino acid sequence analysis of the first 30 to 40 amino acids and search of the Protein Identification Resource data base for similar proteins only revealed the 43-kDa protein to be similar to the P.69 OMP of Bordetella pertussis; however, the homology was weak (33%). Amino acid analysis revealed the 43-kDa protein to be noncharged and the 45- and 51-kDa proteins to be hydrophilic, containing between 38 to 42% polar residues but no cysteine. This study reports the purification and partial characterization of three conserved proteins in W. recta ATCC 33238.

Polysaccharide antigens of Pseudomonas aeruginosa

The major polysaccharide antigens of P. aeruginosa are the cell-wall lipopolysaccharides many of which have an acidic polysaccharide chain (O-antigen) rich in unusual amino sugars. The D-rhamnose-rich polysaccharide antigen common to many serologically distinct strains is also associated with the lipopolysaccharide. The high-molecular-weight polysaccharides with O-specificity are present in extracellular slime produced by strains isolated from the environmental and from the immunocompromised hosts. The extracellular antigenic polysaccharide of another type (bacterial alginate) is expressed by mucoid strains isolated from patients with cystic fibrosis. Serotype-specific immune responses after infection are directed at the lipopolysaccharides and these heat-stable antigens serve as the basis for differentiation of P. aeruginosa strains. Both the cell-wall antigens including conjugates of the O-polysaccharides with different proteins and the extracellular antigens have been used to prepare specific antibodies tested for protection against infections due to P. aeruginosa.

Cloning and expression of a type 1 fimbrial subunit of Actinomyces viscosus T14V

The type 1 fimbriae of Actinomyces viscosus mediate the adherence of this organism to saliva-treated hydroxyapatite. The gene encoding a putative subunit of this fimbrial adhesin was cloned in Escherichia coli, and its product was examined. A. viscosus T14V chromosomal DNA was partially restricted with Sau3AI and cloned into E. coli JM109 by using the plasmid vector pUC13. Two clones, each containing a different DNA insert with a common 4.1-kilobase region, reacted in colony immunoassays with specific polyclonal as well as monoclonal antibodies directed against A. viscosus T14V type 1 fimbriae. Western blot analysis revealed the expression of a 65-kilodalton protein that migrated slightly behind an antigenically similar protein from native type 1 fimbriae. Deletion analysis showed that the gene encoding the cloned protein was localized on a 1.9-kilobase PstI-BamHI fragment and that transcription was dependent on the lac promoter of the vector. The cloned fimbrial protein was purified from the E. coli cytoplasmic fraction by ion-exchange, immunoaffinity, and gel permeation chromatography. Rabbit antibodies prepared against the cloned protein and against purified A. viscosus type 1 fimbriae gave similar patterns with partially dissociated type 1 fimbriae after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The data therefore provide evidence that the gene cloned encodes a subunit of this fimbrial adhesin.

Isolation and characterization of the outer membrane and lipopolysaccharide from Eikenella corrodens

The chemical composition of the outer membrane fractions (OMFs) of Eikenella corrodens strains 23834 and 470 as well as the strain 23834 lipopolysaccharide (LPS) was determined. The OMFs were obtained by Triton X-100 treatment of the heavier membrane fraction from sucrose density centrifugation of the total membrane fraction. The resulting OMFs of strains 23834 and 470, free of cytoplasmic membrane components, were found to contain 69.6 and 75.0% (wt/wt) protein, 4.8 and 9.2% lipid, 4.6 and 4.7% carbohydrate, and 2.0 and 4.6% muramic acid, respectively. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis both OMFs contained one major peptide determined to be 33,500 daltons for the strain 23834 OMF, and 37,500 daltons for the strain 470 OMF. Analysis of the OMF fatty acids revealed hexadecanoic, hexadecenoic, octadecenoic, and lesser amounts of octadecanoic acids. Transmission electron microscopic examination of the OMFs revealed typical large sheets of membrane. Structures (10 nm in diameter) resembling pores were also evident. The E. corrodens LPS was found to be composed of 34.5% (wt/wt) carbohydrate and 25.0% lipid A. Only minute amounts of 2-keto-3-deoxyoctonate and heptose could be detected. Fatty acid analysis revealed primarily octadecanoic and hexadecanoic acids, with lesser amounts of octadecenoic acid. No hydroxy fatty acids were detected. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed the E. corrodens LPS to resemble other smooth-type LPSs. Transmission electron microscopic examination revealed a vesicle-like morphology. The E. corrodens LPS appears not to be a "classical," i.e., enteric, type of LPS.

Identification and characterization of Campylobacter jejuni outer membrane proteins

Outer membrane proteins from isolates of Campylobacter jejuni were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sarcosinate-insoluble membrane preparations were outer membrane enriched based on increased ketodeoxyoctonate concentrations, the presence of surface-exposed 125I-labeled proteins that were hydrophobic, and similarity to membrane vesicle (bleb) sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles. Most isolates contained a single major band with molecular weight of 41,000 to 45,000. Profiles of C. jejuni and Campylobacter coli isolates were indistinguishable, but either could be easily differentiated from Campylobacter fetus and Campylobacter faecalis. The profiles were stable for strains under a variety of growth, incubation and passage conditions. We classified 110 isolates from patients with sporadic campylobacter enteritis into nine subtypes based on differences in outer membrane sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles. Two categories accounted for 76% of the isolates. Complete concordance was observed in subtypes of strains obtained from epidemiologically related cases. Thus, comparison of the major outer membrane proteins of C. jejuni is a useful technique for investigating the transmission of this organism and may provide a basis for immunological characterization of the outer membrane proteins.

Effects of nonionic, ionic, and dipolar ionic detergents and EDTA on the Brucella cell envelope

Cell envelopes prepared from smooth and rough strains of Brucella were characterized on the basis of lipopolysaccharide and protein content. The action of three kinds of detergents on Brucella cell envelopes and Escherichia coli control cell envelopes was examined on the basis of the proteins and lipopolysaccharides that were extracted. As compared with those of E. coli, Brucella cell envelopes were resistant to nonionic detergents. Zwittergents 312 and 316 were most effective in extracting E. coli cell envelopes, and Zwittergent 316 was most effective in extracting Brucella cell envelopes. Sarkosyl extracted proteins but extracted only trace amounts of lipopolysaccharides from cell envelopes of both bacteria. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the Sarkosyl-resistant proteins revealed a composition similar to that of the proteins exposed on the surfaces of viable cells, as determined by the lactoperoxidase-125I radioiodination method. EDTA, with either Tris-HCl or Tris-HCl-Triton X-100, did not have detectable effects on Brucella cell envelopes. Ultracentrifugation of purified lipopolysaccharides in detergents and EDTA demonstrate that, in contrast to that of E. coli, Brucella lipopolysaccharide was not stabilized by divalent cations. Sarkosyl was ineffective in dispersing lipopolysaccharides, whereas the action of Zwittergents was related to the length of their alkyl chains.

Effect of iron limitation on growth, siderophore production, and expression of outer membrane proteins of Vibrio cholerae

Vibrio cholerae strains secrete a phenolate-type siderophore when grown in low-iron medium. The siderophore was detected as early as 3.5 h after downshift to iron-poor medium, and it continued to accumulate in the medium as the cells entered stationary phase. Two clinical isolates and an environmental isolate were examined for the amount of siderophore produced. The environmental isolate produced more siderophore and continued to secrete it at concentrations of iron that repressed synthesis in the clinical isolates. Concomitant with production of siderophore, at least six new proteins were seen in the outer membranes of iron starved cells. One of the proteins was large (200,000 Mr [220K]) and appeared to be loosely associated with the outer membrane. The other five proteins had approximate Mr values of 77K, 76K, 75K, 73K, and 62K. The 62K protein, like the 40K major outer membrane protein, was heat modifiable. One or more of these proteins may be a component of the receptor for the iron-siderophore complex.

Tetramethyl-p-phenylenediamine oxidase of Pseudomonas aeruginosa

An oxidase complex has been solubilized and partially purified from the membrane particle of Pseudomonas aeruginosa grown under limited oxygen condition. The oxidase consists of two major cytochrome components, cytochrome c554 and cytochrome o (b561), with a molar ratio of about 9:1 in terms of c-heme to protoheme content. Ninety percent of the cytochrome c+o complex, corresponding to all of the cytochrome c554, is reducible by reduced N,N,N',N'-tetramethyl-p-phenylenediamine. This partially purified oxidase exhibited a maximal specific activity about 5 mumol O2 uptake x min-1 x mg protein-1, with a Km (of reduced N,N,N',N'-tetramethyl-p-phenylenediamine) = 7.2 x 10(-4) M at 30 degrees C. The oxidase is sensitive to KCN, NaN3 and NaNO2. Oxidation-reduction potentiometric titration shows that cytochrome c554 has a midpoint potential of 289 mV and cytochrome o of + 25 mV at pH 7.2 in the partially purified oxidase preparation. The purity of the preparation has been estimated to be about 85--90% by gel electrophoresis.

Identification and preliminary characterization of Vibrio cholerae outer membrane proteins

Outer membrane proteins of Vibrio cholerae were purified by sucrose density centrifugation and Triton X-100 extraction at 10 mM Mg2+. The proteins were separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. V. cholerae outer membrane proteins presented a unique pattern when compared with the patterns of other gram-negative rods. There were 8 to 10 major bands (Mr 94,000 to 27,000), with most of the protein located in band 5 (Mr approximately 45,000), which thus appears to be the major structural protein of the outer membrane. Lipid and carbohydrate were associated with band 6.

Plasma membrane heterogeneity in ascites tumor cells. Isolation of a light and a heavy membrane fraction of the glycogen-free Ehrlich-Lettré substrain

In this work we report on the isolation of two plasma membrane fractions of a glycogen-free substrain of Ehrlich-Lettré ascites cells, a light fraction sedimenting in a sucrose gradient at 1.10 g/ml, and a heavy fraction sedimenting at nuclei by a combination of short-term swelling and mild Dounce homogenization. A 12 000 X g postnuclear pellet (PII) containing major portions of the plasma membrane marker enymes, 5'-nucleotidase, ouabain-sensitive (Na+ + K+)-ATPase and the alkaline phosphatase, was prepared by differential centrifugation. The two plasma membrane fractions were obtained by centrifugation on a discontinuous sucrose gradient, from which they were further purified on a linear sucrose gradient applying sedimentation velocity conditions only. Enrichment factors for the three marker enzymes were between 5- and 14-fold for the light fraction and between 3- and 7-fold for the heavy fraction with an overall yield of 1--4% and 0.5--1.7%, respectively, of cellular protein. Contamination of both fractions with nuclear material was minor. Mitochondrial contamination was about 8% for the light material and somewhat higher for the heavy material. In the light fraction, co-sedimentation of lysosomal and Golgi marker enzymes was detected. The presence of membrane structures of these organelles could not be confirmed definitely by electron microscopy. Differences in sialic acid content and phospholipid composition within the two fractions, especially in the relative proportion of lecithin to sphingomyelin, suggests differences in membrane fluidity. The light material showed mostly unit membrane vesicles in thin-section and freeze-etch electron microscopy, whereas the heavy fraction mainly consisted of sheet-like membrane fragments.

An antigen common to a wide range of bacteria. 2. A biochemical study of a "common antigen" from Pseudomonas aeruginosa

Common Antigen (CA) of Pseudomonas aeruginosa has been shown to be a protein composed of polypeptide subunits of a molecular weight (MW) of about 62 000. The MW of this protein was estimated to 665 000 by gel filtration on sepharose CL-6B, to 800 000 by electrophoresis on polyacrylamide gradient gels and to about 900 000 by ultracentrifugation, on a sucrose gradient. By analytical ultracentrifugation with Schlieren optics a sedimentation coefficient (S20 degrees, W) of 22.65 was calculated. The isoelectrical point was determined to pH 4.4. The antigen was decomposed on exposure to proteolytic enzymes. Polysaccharide, lipid, deoxyribonucleic acid or ribonucleic acid were not demonstrated in CA. The amino acid content of CA was determined, and no hexosamine or abnormal residues were observed. The amino acid content of CA was determined, and no hexosamine or abnormal residues were observed. The antigen was degraded when heated to 100 degrees C for 4 min or when exposed to pH below 4 or above 11 at 4 degree C. CA has been isolated from the cytoplasmic water-soluble fraction of disintegrated bacteria and only trace-amounts could be obtained from envelope fractions after solubilization with Triton X-100.

Membrane-bound respiratory chain of Pseudomonas aeruginosa grown aerobically

The electron transport chain of the gram-negative bacterium Pseudomonas aeruginosa, grown aerobically, contained a number of primary dehydrogenases and respiratory components (soluble flavin, bound flavin, coenzyme Q9, heme b, heme c, and cytochrome o) in membrane particles of the organism. Cytochrome o, about 50% of the b-type cytochrome, seemed to function as a terminal oxidase in the respiratory chain. The electron transport chain of P. aeruginosa grown aerobically was suggested to be lined up in order of primary dehydrogenase, b, c1, c, o, and oxygen.

Outer membrane of Pseudomonas aeruginosa: heat- 2-mercaptoethanol-modifiable proteins

A number of polyacrylamide gel systems and solubilization procedures were studied to define the number and nature of "major" polypeptide bands in the outer membrane of Pseudomonas aeruginosa. It was shown that five of the eight major outer membrane proteins were "heat modifiable" in that their mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was determined by the solubilization temperature. Four of these heat-modifiable proteins had characteristics similar to protein II of the Escherichia coli outer membrane. Addition of lipopolysaccharide subsequent to solubilization caused reversal of the heat modification. The other heat-modifiable protein, the porin protein F, was unusually stable to sodium dodecyl sulfate. Long periods of boiling in sodium dodecyl sulfate were required to cause conversion to the heat-modified form. This was demonstrated both with outer membrane-associated and purified lipopolysaccharide-depleted protein F. Furthermore, lipopolysaccharide treatment had no effect on the mobility of heat-modified protein F. Thus it is concluded that protein F represents a new class of heat-modifiable protein. It was further demonstrated that the electrophoretic mobility of protein F was modified by 2-mercaptoethanol and that the 2-mercaptoethanol and heat modification of mobility were independent of one another. The optimal conditions for the examination of the outer membrane proteins of P. aeruginosa by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis are discussed.

Outer membranes of gram-negative bacteria. XIX. Isolation from Pseudomonas aeruginosa PAO1 and use in reconstitution and definition of the permeability barrier

A method for separating the outer and inner membranes of Pseudomonas aeruginosa PAO1 in the absence of added ethylenediaminetetraacetic acid was devised. The method yields two outer membrane fractions which show the same protein pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but differ substantially in their relative contents of phospholipids. One of these outer membrane fractions and the inner membrane fraction are less than 4% cross-contaminated, as judged by the content of typical inner and outer membrane markers. The outer membrane contains four major protein bands with apparent molecular weights of 37,000, 35,000, 21,000 and 17,000. Vesicles reconstituted from lipopolysaccharide and phospholipids were impermeable to all saccharides included in the vesicles during vesicle formation. When the vesicles contained outer membrane proteins, they fully retained only those saccharides of greater than 9,000 molecular weight, suggesting that the exclusion limit of the outer membrane of P. aeruginosa for saccharides is substantially larger than the figure (500 to 600 daltons) obtained for certain enteric bacteria. The advantages and potential disadvantages of having an outer membrane with a higher exclusion limit for hydrophilic substances are discussed.