The interrelation of phosphatidylethanolamine and glycosyl diglycerides in bacterial membranes

Unique Francisella Phosphatidylethanolamine Acts as a Potent Anti-Inflammatory Lipid

Virulent Francisella tularensis subsp. tularensis (Ftt) is a dynamic, intracellular, bacterial pathogen. Its ability to evade and rapidly suppress host inflammatory responses is considered a key element for its profound virulence. We previously established that Ftt lipids play a role in inhibiting inflammation, but we did not determine the lipid species mediating this process. Here, we show that a unique, abundant, phosphatidylethanolamine (PE), present in Francisella, contributes to driving the suppression of inflammatory responses in human and mouse cells. Acyl chain lengths of this PE, C24: 0 and C10: 0, were key to the suppressive capabilities of Francisella PE. Addition of synthetic PE 24: 0-10: 0 resulted in the accumulation of PE in host cells for up to 24 h of incubation, and recapitulated the inhibition of inflammatory responses observed with native Ftt PE. Importantly, this novel PE significantly inhibited inflammatory responses driven by a medically and globally important flavivirus, dengue fever virus. Thus, targeting these lipids and/or the pathways that they manipulate represents a new strategy to combat immunosuppression engendered by Ftt, but they also show promise as a novel therapeutic intervention for significant viral infections.

The potent in vitro skin permeation of archaeosome made from lipids extracted of Sulfolobus acidocaldarius

Archaeosomes are a new generation of liposomes that exhibit higher stabilities under different conditions, such as high temperatures, alkaline or acidic pH, and presence of bile salts in comparison with liposomes, and can be used in biotechnology including drug, gene, and vaccine delivery. The objective of this study was to prepare archaeosomes using lipid extracted from Sulfolobus acidocaldarius and evaluate their physicochemical properties. The lipids were extracted from S. acidocaldarius and assayed by High Performance Thin-Layer Chromatography (HPTLC). Archaeosomes were prepared using film method and methylene blue was used as drug model. They were characterized for their vesicle size and Differential Scanning Calorimetry (DSC) was used to investigate changes in their thermal behavior. The released amount of methylene blue was determined using a dialysis membrane and rat skin. HPTLC analysis of the extracted lipids showed that glycerol ether may be the major lipid with more than 78 percent probability. Results of particle size determination showed a mean size of 158.33 nm and the results of DSC indicated the possible interaction of methylene blue with lipids during the preparation of archaeosome. The addition of cholesterol significantly improved the encapsulation of methylene blue in the archaeosome so that the encapsulation efficiency was 61.66 ± 2.88%. The result of in vitro skin permeation showed that methylene blue could pass through skin model according to Peppas model and there was about 41.66% release after 6 h, whereas no release was observed through dialysis membrane. According to the results of the study, it is concluded that archaeosome may be successfully used as drug delivery system.

Phosphatidylethanolamine is required for in vivo function of the membrane-associated lactose permease of Escherichia coli

Experiments with mutant Escherichia coli cells lacking phosphatidylethanolamine (PE) as a membrane component (DeChavigny, A., Heacock, P. N., and Dowhan, W. (1991) J. Biol. Chem. 266, 5323-5332) were carried out to establish whether or not PE is necessary for full function of the lac permease in vivo. The Vmax for active transport of both lactose (in cells lacking beta-galactosidase, lacZ) and the unhydrolyzable lactose analog, methyl-beta-D-galactopyranoside (TMG), by mutant cells lacking PE was reduced 5-10-fold relative to cells containing PE, while the Km for the uptake of both substrates was the same in both types of cells. The low rate of TMG and lactose uptake by PE-deficient cells was unaffected by the presence of a protonophore (uncoupler) and for TMG uptake was on the order of the greatly reduced rate of uptake in uncoupler-treated cells containing PE. The rate of entry of lactose into lacZ+ derivatives of both types of cells, as a measure of facilitated diffusion, was nearly the same. The Km for lactose (lacZ cells) and TMG transport in PE-deficient cells was unaffected by the presence of an uncoupler which had a small effect on Vmax. In PE-containing cells these kinetic parameters for TMG transport were reduced by an uncoupler to the level found with PE-deficient cells while an uncoupler reduced lactose uptake by PE-containing (lacZ) cells to below measureable levels. Inverted membrane vesicles made from both types of cells could be loaded with TMG, but energizing TMG-loaded vesicles by ATP only induced rapid, uphill, permease-dependent efflux of TMG from PE-containing vesicles. The decrease in apparent active transport activity of cells with no PE was not due to a change in membrane permeability, to a reduced delta microH+ (proton electrochemical gradient) across the cell membrane, or to a reduced level of membrane-associated lac permease protein. These results suggest that in the absence of PE the lac permease cannot couple substrate uptake to delta microH+ in order to effect accumulation of substrate and as a result only carries out facilitated diffusion.

Secondary transport of amino acids by membrane vesicles derived from lactic acid bacteria

Lactococci are fastidious bacteria which require an external source of amino acids and many other nutrients. These compounds have to pass the membrane. However, detailed analysis of transport processes in membrane vesicles has been hampered by the lack of a suitable protonmotive force (pmf)-generating system in these model systems. A membrane-fusion procedure has been developed by which pmf-generating systems can be functionally incorporated into the bacterial membrane. This improved model system has been used to analyze the properties of amino acid transport systems in lactococci. Detailed studies have been made of the specificity and kinetics of amino acid transport and also of the interaction of the transport systems with their lipid environment. The properties of a pmf-independent, arginine-catabolism specific transport system in lactococci will be discussed.

Influence of specific growth rate and nutrient limitation upon the sensitivity of Escherichia coli towards chlorhexidine diacetate

The sensitivity of Escherichia coli to chlorhexidine has been assessed for cells grown in a chemostat at a variety of specific growth rates, under conditions of carbon, nitrogen, phosphorus and magnesium limitation. At slow rates of growth (ca 0.08/h) little difference in sensitivity was observed. As growth rate was increased, however, the sensitivity of nitrogen- and carbon-limited cells increased whilst that of magnesium- and phosphate-limited cells decreased. It was not possible to correlate the observed patterns of chlorhexidine sensitivity with any single measure of cell envelope composition (phospholipid content, lipopolysaccharide, envelope proteins, etc.). The results presented are not consistent, therefore, with any simple model for chlorhexidine binding or action and more probably reflect subtle interaction between chlorhexidine, phospholipid-lipopolysaccharide complexes and cations within the envelope.

Interaction of some polyhexamethylene biguanides and membrane phospholipids in Escherichia coli

The interaction between some polyhexamethylene biguanides and the cell envelope of Escherichia coli has been investigated. An amine-ended dimer, (AED, n = 2), a polydisperse mixture (ICI plc) available as the active ingredient of Vantocil IB, (PHMB, n = 5.5), and a high molecular weight fraction, (HMW, n = greater than or equal to 10) of PHMB were used. The sensitivity of batch cultures depleted of magnesium (M-dep), phosphorus (P-dep) or glycerol (C-dep) towards the biocides was assessed by monitoring the rate and extent of potassium ion leakage. P-dep suspensions were particularly resistant to all these agents and possessed less than half the quantity of phospholipid of other cell types. This was compensated for by a proportionate increase in fatty acid and neutral lipid content of the cells. The reduction in phospholipid content was accounted for by decreases in phosphatidylglycerol (PG) and phosphatidylethanolamine (PE). Diphosphatidylglycerol (DPG) and phosphatidylserine (PS) content of the cultures remained unaffected by the depleting nutrient. Fourier-transform n.m.r. spectroscopy was used to study proton nuclei during the interaction of HMW, AED and PHMB with various phospholipid-vesicle preparations. The results strongly suggest that the biocides acted preferentially on the acidic phospholipids PG and DPG, rather than towards PE or PS. Resistance of P-dep cultures therefore reflected reductions in PG content. A molecular basis for the interaction of these compounds and membranes is proposed.

Lipids of the Streptomycettes. Structural investigation and biological interrelation a review

During a systematic investigation of lipids of Streptomycetes a series of compounds of biochemical and microbiological interest have been isolated and characterized. These include several menaquinones, glycosyl diglycerides (glucuronosyl and isoladobinosym diglycerides), two ornithino lipids and a diol phospholipid. Some of these lipids were not known previously as constituents of streptomycete cells although they have been encountered elsewhere; others have proved to be novel lipids. The results of structural studies of these lipids are reviewed and some of their possible biological functions are discussed.

Effect of R-plasmid RP1 and nutrient depletion on the gross cellular composition of Escherichia coli and its resistance to some uncoupling phenols

The resistance of Escherichia coli batch cultures depleted of carbon (C-dep), magnesium (Mg-dep), or phosphate (P-dep) against low concentrations of 3-chlorophenol, 4-chlorophenol, or 2-phenoxyethanol varied. C-dep cultures were always significantly more sensitive than Mg-dep or P-dep cultures. The presence of R-plasmid RP1 increased the sensitivity of C-dep cultures to 3- and 4-chlorophenol, yet had little effect on those cultured depleted in magnesium or phosphate ions. Cultures with R-plasmid RP1 had increased levels of beta-polyhydroxybutyrate irrespective of the nature of the depleting nutrient. P-dep bacteria had less than one-third of the phospholipid of other cell types, this deficiency being compensated for by increases in fatty acid and neutral lipid content. The reduction in phospholipid content of P-dep cultures was entirely accounted for by decreased diphosphatidylglycerol and phosphatidylethanolamine levels in these cells.

Influence of growth rate and nutrient limitation on the gross cellular composition of Pseudomonas aeruginosa and its resistance to 3- and 4-chlorophenol

Concentrations of 3-chlorophenol and 4-chlorophenol below their minimal inhibitory concentrations were found to increase the permeability of Pseudomonas aeruginosa cells to protons. Levels of such activity were assessed in suspensions of cells prepared from chemostat-grown cultures, limited by either magnesium (Mg-lim) or glucose (G-lim), with the use of five growth rates. Drug concentrations required to produce the same levels of proton translocation varied with the growth rate and the nutrient limiting growth. Fast-growing cultures were more sensitive than slower-growing ones, and G-lim cells were generally more sensitive than Mg-lim ones. 3-Chlorophenol had greater activity than 4-chlorophenol at slow growth rates, but at faster rates of growth their activity was similar. Variation in these iso-effective concentrations for different cells probably reflected an alteration in the ease of drug penetration of the outer envelope. Uptake of the compounds by cells in suspension varied, drug-sensitive bacteria absorbing more than resistant ones. This variation in uptake persisted when bacteria were solvent-extracted to remove readily extractable lipids (REL). Since no significant alteration in cell size was observed among the growth conditions studied, variation in absorption probably resulted from an altered affinity of the cells to the drug, with little involvement of REL. Overall REL content did not alter significantly with growth rate or nutrient limitation. However, total phospholipid content decreased and fatty acid content increased with increasing growth rate. For G-lim and Mg-lim cultures phosphatidylcholine content remained constant, yet phosphatidylethanolamine and phosphatidylglycerol content decreased with increasing growth rate. Diphosphatidylglycerol content decreased with increasing growth rate for Mg-lim cultures and remained relatively constant for G-lim cultures. Lipopolysaccharide content of the cells was higher in Mg-lim than in G-lim cultures and decreased with increasing growth rate in both cases. Lipopolysaccharide content correlated significantly with drug uptake and sensitivity, and it appeared to determine the degree of penetration of the cell envelope by these chlorinated phenols.

Teichoic acids and lipids associated with the membrane of a Bacillus licheniformis mutant and the membrane lipids of the parental strain

Bacillus licheniformis 6346 MH-1 and a phosphoglucomutase-deficient poorly lytic mutant, B. licheniformis 6346 MH-5, both contain cardiolipin, phosphatidyl ethanolamine, and phosphatidyl glycerol but are devoid of phosphoglycolipids. Gentiobiosyl diglyceride is present in the parent organism but glycolipids are absent from the mutant. Lipoteichoic acid was extracted from the whole cells of MH-5 with hot aqueous phenol and contained fatty acids, glucosamine, and 1,3-polyglycerol phosphate. The fatty acids were predominantly of the branched-chain type and were esterified to hydroxyl groups of a terminal glycerol residue. The polyglycerol phosphate chains contained, on average, 32 to 40 glycerol residues, some of which were substituted at the secondary hydroxyl group with alpha-N-acylglucosaminyl residues. Phenol extraction of the supernatant fluid that remained when walls were removed from preparations of disrupted cells of MH-5 yielded membrane teichoic acid, which consisted of substituted polyglycerol phosphate but was devoid of fatty acids.

Effect of pH on the proportions of polar lipids, in chemostat cultures of Bacillus subtilis

Significant changes in the relative proportions of the individual polar lipids of two strains of Bacillus subtilis were observed when the pH of their chemostat cultures was varied. In phosphate- and magnesium-limited cultures of B. subtilis var. niger NCIB 8058. lysylphosphatidylglycerol was present in higher proportions at low pH (5.1) than at neutral pH. With magnesium-limited cultures of this strain harvested at pH 8.0, lysylphosphatidylglycerol and phosphatidylethanolamine were not detected. Phosphate-limited cultures of B. subtilis NCIB 3610 contained no phosphatidylethanolamine or lysylphosphatidylglycerol at neutral pH, but at low pH (5.1) both these lipids were present in substantial proportions. The proportions of phosphatidylglycerol in actively dividing cells of chemostat cultures of bacilli were always greater than those of lysylphosphatidylglycerol. The reverse is commonly found in batch cultures of bacilli and staphylococci harvested at low pH. Changes in the proportions of the other polar lipids present in these bacilli (diphosphatidylglycerol and diglucosyl diacylglycerol) with pH were also noted. Certain cultures of both strains of B. subtilis contained small proportions of a peptidolipid.

Action of phospholipase A 2 and phospholipase C on Bacillus subtilis protoplasts

Protoplasts prepared from Bacillus subtilis by lysozyme digestion lysed in the presence of pure pancreatic phospholipase A(2). The phospholipids cardiolipin, phosphatidylethanolamine, phosphatidylglycerol and lysylphosphatidylglycerol, which are present in the membrane, are degraded by phospholipase A(2) only after removal of the cell wall, giving free fatty acids and lyso derivatives. The four phospholipids are hydrolyzed equally well at a given enzyme concentration. Differences in the phospholipid composition of the protoplasts were obtained by variations in the growth medium, time of harvesting, and preincubation time with lysozyme. The extent of hydrolysis appeared to depend on the initial phospholipid composition. A relative increase in acidic phospholipids in the membrane facilitated the action of phospholipase A(2), whereas the rate of hydrolysis was diminished when protoplasts were tested which contained a relatively high amount of positively charged phospholipid. Pure phospholipase C from B. cereus preferentially hydrolyzed phosphatidyl-ethanolamine in the B. subtilis membrane. More than 80% of this phospholipid was converted into diglyceride, whereas only 30% of the cardiolipin was hydrolyzed. Such a loss of phospholipids, however, was not followed by lysis of the protoplasts. Liposomes were prepared from the lipid extracts of B. subtilis and incubated with both phospholipases. The hydrolysis pattern of the phospholipids in these model membrane systems was identical to the hydrolysis pattern of the phospholipids in the protoplast membrane. Phospholipase A(2) hydrolyzed all the phospholipids in the liposomes equally well, whereas phospholipase C preferentially degraded phosphatidylethanolamine.

Further studies on the lipids of corynebacteria. The mannolipids of Corynebacterium aquaticum

1. The major free lipids of Corynebacterium aquaticum were characterized as dimannosyl diglyceride, monomannophosphoinositide and phosphatidylethanolamine. Bisphosphatidylglycerol and phosphatidylglycerol were also tentatively identified. 2. We regard this as the only well-documented case of an organism containing monomannophosphoinositide to the exclusion of dimannophosphoinositides and the higher homologues. 3. The co-existence of the two mannolipids in one organism is a distinctive feature. So also is the presence of phosphatidylethanolamine in a corynebacterium. 4. The monomannophosphoinositide apparently does not utilize phosphatidylinositol as a precursor, unlike the monomannophosphoinositide of Propionibacterium shermanii. CDP-diglyceride may be necessary for its synthesis.