Heterogeneity of phospholipid composition in the bacterial membrane

A motive for killing: effector functions of regulated lytic cell death

Immunological responses activated by pathogen recognition come in many guises. The proliferation, differentiation and recruitment of immune cells, and the production of inflammatory cytokines and chemokines are central to lifelong immunity. Cell death serves as a key function in the resolution of innate and adaptive immune responses. It also coordinates cell-intrinsic effector functions to restrict infection. Necrosis was formally considered a passive form of cell death or a consequence of pathogen virulence factor expression, and necrotic tissue is frequently associated with infection. However, there is now emerging evidence that points to a role for regulated forms of necrosis, such as pyroptosis and necroptosis, driving inflammation and shaping the immune response.

Comparison of the effects of subinhibitory concentrations of ciprofloxacin and colistin on the morphology of cardiolipin domains in Escherichia coli membranes

Membrane domains characterized by unique protein and lipid composition allow for compartmentalization and regulation of various biological processes. In Escherichia coli cardiolipin domains play a key role in the dynamic organization of bacterial membranes, and their distribution depends on the stage of the cell cycle. We studied the influence of subinhibitory concentrations of ciprofloxacin and colistin on the morphology and distribution of E. coli cardiolipin domains. Using the fluorescent dye 10-N-nonyl acridine orange we found that exposure of bacteria to ciprofloxacin significantly increased the percentage of filamentous cells with altered morphology of the cardiolipin domains, while colistin did not induce any significant changes. These results allow us to conclude that inhibition of DNA gyrase causes effects even at the bacterial membrane level and those changes can be easily visualized using 10-N-nonyl acridine orange.

Heterogeneity in lipid composition of the outer membrane and cytoplasmic membrane and cytoplasmic membrane of Pseudomonas BAL-31

The outer membranes and cytoplasmic membranes of the marine bacterium Pseudomonas BAL-31 were separated by washing the cells three times in 0.5 M NaCl and twice in 0.5 M sucrose. Electron microscopy during the removal of membranes revealed that the outer membranes fragmented in a regular manner to give rise to fairly uniform vesicles measuring approximately 140 nm in diameter. Isolated outer membranes had a buoyant density in sucrose of 1.230 g per cm(3), whereas the cytoplasmic membranes had a density of 1.194 g per cm(3). The removal of the outer membrane during the application of this procedure was monitored by measuring the release of 2-keto-3-deoxyoctulosonic acid and phospholipid. The cells lost 85.5% of their 2-keto-3-deoxyoctulosonic acid and 47.3% of their phospholipid during this treatment. Complete recovery of outer membrane material could be achieved. The removal of 25.5% of the 2-keto-3-deoxyoctulosonic acid and 0.9% of the phospholipid rendered the cells sensitive to lysis with Triton X-100. The phospholipid composition of the outer membrane was calculated to be 78.9% phosphatidylethanolamine and 16.1% phosphatidylglycerol. The phospholipid composition of the cytoplasmic membrane proved to be 71.5% phosphatidylethanolamine and 23.5% phosphatidylglycerol. The fatty acid composition was also found to be quantitatively heterogeneous between the two membranes.

Turnover of phosphatidylglycerol in Escherichia coli

In growing cultures of Escherichia coli, the nonacylated glycerol of phosphatidylglycerol (PG) is labeled more rapidly than is the acylated glycerol. This is, in part, due to a rapid exchange reaction of the nonacylated glycerol. Only some of the PG molecules undergo this reaction while others are stable. Using a mutant unable to make glycerophosphate, we have shown that the nonacylated glycerol of PG can exchange with non-phosphorylated glycerol.

Metabolism of phosphatidylglycerol, phosphatidylethanolamine, and cardiolipin of Bacillus stearothermophilus

The total phospholipid content of Bacillus stearothermophilus was constant during exponential growth, increased during the transition from the exponential to stationary phase of growth, and then slowly increased during the stationary phase. The first increase was a result of an increase in phosphatidylethanolamine; the second was a result of an increase in cardiolipin. Cessation of aeration of an exponentially growing culture or suspension in a nongrowth medium resulted in an immediate reduction in the rate of total phospholipid and phosphatidylethanolamine synthesis and a quantitative conversion of phosphatidylglycerol to cardiolipin. Cardiolipin appeared to be synthesized by the direct conversion of two molecules of phosphatidylglycerol to cardiolipin. After a 20-min pulse of (32)P, phosphatidylglycerol showed the most rapid loss of (32)P followed by cardiolipin, whereas phosphatidylethanolamine did not lose (32)P. The loss of (32)P from the total lipid pool, phosphatidylglycerol, and cardiolipin was biphasic, with rapid loss during the first two bacterial doublings followed by a greatly reduced rate of loss. The major loss of (32)P from the total phospholipid pool appeared to be by breakdown of cardiolipin. The loss of (32)P from the lipid pool was energy dependent (i.e., did not occur under anaerobic conditions or in the absence of an energy source) and was dependent on some factor other than the concentration of cardiolipin in the cells. The apparent conversion of phosphatidylglycerol to cardiolipin was independent of energy metabolism. Chloramphenicol reduced the rate of turnover of both phosphatidylglycerol and cardiolipin. The rate of lipid synthesis (all phospholipid components) was constant for about 10 min after the addition of chloramphenicol but diminished markedly after 20 min. Turnover of (32)P incorporated into phospholipid during a 30-min period prior to the addition of chloramphenicol was more rapid after the removal of chloramphenicol than that of (32)P incorporated during a 30-min period in the presence of chloramphenicol.

Phospholipid composition and metabolism of Micrococcus denitrificans

The phospholipid composition of Micrococcus denitrificans was unusual in that phosphatidyl choline (PC) was a major phospholipid (30.9%). Other phospholipids were phosphatidyl glycerol (PG, 52.4%), phosphatidyl ethanolamine (PE, 5.8%), an unknown phospholipid (5.3%), cardiolipin (CL, 3.2%), phosphatidyl dimethylethanolamine (PDME, 0.9%), phosphatidyl monomethylethanolamine (PMME, 0.6%), phosphatidyl serine (PS, 0.5%), and phosphatidic acid (0.4%). Kinetics of (32)P incorporation suggested that PC was formed by the successive methylations of PE. Pulse-chase experiments with pulses of (32)P or acetate-1-(14)C to exponentially growing cells showed loss of isotopes from PMME, PDME, PS, and CL with biphasic kinetics suggesting the same type of multiple pools of these lipids as proposed in other bacteria. The major phospholipids, PC, PG, and PE, were metabolically stable under these conditions. The fatty acids isolated from the complex lipids were also unusual in being a simple mixture of seven fatty acids with oleic acid representing 86% of the total. Few free fatty acids and no non-extractable fatty acids associated with the cell wall or membrane were found.

Detection of a rapidly metabolizing portion of the membrane cardiolipin in Haemophilus parainfluenzae

Heterogeneity in the metabolism of cardiolipin (CL) has been detected in Haemophilus parainfluenzae. Pulse-chase experiments showed that a portion of the total CL incorporated and then lost (32)P much more rapidly than the rest of the CL in the cells. The metabolism of each phosphate of the CL differed. The phosphate of the phosphatidyl glycerol (PG) portion of the CL had a more active metabolism than the phosphate of the phosphatidic acid portion of the molecule. Only a portion of the PG pool contributed to the formation of CL. Ethylenediaminetetraacetic acid inhibited the CL-specific phospholipase D in vitro and, when added to growing cells, resulted in more rapid PG metabolism, suggesting that CL hydrolysis contributed to the PG pool.

Consequences of the inhibition of cardiolipin metabolism in Haemophilus parainfluenzae

Examination of phospholipid metabolism in Haemophilus parainfluenzae with inhibitors of various cellular functions indicated that macromolecular synthesis and lipid metabolism can be dissociated at least for a short time. Two classes of inhibitors have relatively specific effects on cardiolipin (CL) metabolism. Pentachlorophenol and p-hydroxymercuribenzoate blocked CL synthesis but allowed CL hydrolysis to phosphatidic acid and phosphatidyl glycerol (PG); 3,3',4,5'-tetrachlorosalicylanilide (TCS) and carbonyl cyanide m-chlorophenylhydrazone (m-CCCP) blocked CL hydrolysis with the stoichiometric accumulation of CL. It appeared as if TCS and m-CCCP inhibited a vital activity coupled with the hydrolysis of CL by the highly active, CL-specific phospholipase D found in this organism. Because TCS and m-CCCP are thought to act by destroying the proton gradient thereby interrupting energy-dependent transport, it is possible that a highly active portion of the cellular CL could be coupled to some phase of this process.

Effect of benzo(a) pyrene and piperonyl butoxide on formation of respiratory system, phospholipids, and carotenoids of Staphylococcus aureus

Staphylococcus aureus formed an electron transport system when exponentially growing cells were aerated. Formation of the electron transport system occurred concomitantly with increases in the phospholipids and the carotenoids. The addition of piperonyl butoxide or benzo(a)pyrene at the onset of aeration (i) slowed the formation of the electron transport system, (ii) both inhibited cytochrome oxidase o synthesis and decreased its stability, (iii) simultaneously depressed the increase in total phospholipid (especially cardiolipin), and (iv) depressed the synthesis of the carotenoid rubixanthin. Benzo(a)pyrene was the more inhibitory of the two, both on the rate of synthesis of the electron transport system and on rubixanthin formation. Evidence obtained with the inhibitors suggested that inhibition of the lipid synthesis was related to the formation of the electron transport system.

Cardiolipin-specific phospholipase D of Haemophilus parainfluenzae. II. Characteristics and possible significance

A phospholipase specific for cardiolipin (CL) was found in the membrane of Haemophilus parainfluenzae. The enzyme hydrolyzed CL to phosphatidic acid (PA) and phosphatidylglycerol (PG), indicating that it was a phospholipase D (an enzyme activity believed to be confined to higher plants). In addition to its substrate specificity, this enzyme was unusual in its requirement for Mg(2+) (K(m) of 1.3 mm) for maximal activity and its inhibition by chelating agents, heavy metals, some detergents, and organic solvents. When inhibitors of phospholipase activity were added to the growth medium, CL accumulated and PG disappeared in the membrane, suggesting that the phospholipase D was active in vivo. The activity of phospholipase D in cell-free homogenates was greater than expected from earlier studies of CL metabolism and greater than the other phospholipase activities detected in the homogenate. The high activity of the CL-specific phospholipase D suggests there might be a very active degradation of CL to PG and PA and an active resynthesis of CL from the hydrolysis products.

Phospholipid metabolism during penicillinase production in Bacillus licheniformis

During membrane-bound penicillinase production, Bacillus licheniformis forms vesicles and tubules that do not appear in the absence of penicillinase production. The major lipids of B. licheniformis were shown to be phospholipids. The proportions, metabolism, and the total phospholipid per cell were shown to be essentially the same in the uninduced control, induced and constitutive penicillinase forming cells during both the exponential and stationary growth phases. Membrane phospholipids were not secreted into the medium during penicillinase formation. In the shift from the exponential to the stationary growth phase, there was an accumulation of phosphatidyl glycerol and a marked decrease in cardiolipin. These two lipids had the most active turnover of their phospholipid phosphate of all the lipids studied.

Metabolism of the glycosyl diglycerides and phosphatidylglucose of Staphylococcus aureus

A glucose containing lipid, phosphatidylglucose (probably 3-sn-phosphatidyl-1'-glucose) and a lipid tentatively identified as phosphatidylethanolamine have been characterized in the lipids of Staphylococcus aureus. These lipids together comprise less than 2% of the total phospholipids of exponentially growing S. aureus and accumulate to 14% of the total phospholipid in stationary-phase cells. These lipids lost no (32)P when cells grown with H(3) (32)PO(4) were transferred to nonradioactive medium during the exponential growth phase. This was in marked contrast to the other phospholipids which lost (32)P rapidly. The loss of (32)P from phosphatidic acid and cardiolipin in exponentially growing cells was biphasic, suggesting heterogeneity of phospholipid phosphate metabolism. The mono- and diglucosyl diglycerides showed a rapid loss of (14)C-glucose during growth in nonradioactive medium but no loss of (14)C from the fatty acids of these lipids. The (14)C in the glucose and fatty acids of the glucosyl diglycerides was derived from glucose.

Metabolism of phospholipid 2-linked fatty acids during the release of membrane fragments from Haemophilus parainfluenzae by ethylenediaminetetraacetic acid-tris(hydroxymethyl)-aminomethane

Membrane fragments containing diacyl phospholipids were released from viable cells of Haemophilus parainfluenzae during incubation in ethylenediaminetetraacetic acid (EDTA)- tris(hydroxymethyl)aminomethane (Tris) buffer. The phospholipids located in the part of the membrane that was released during the EDTA-Tris treatment had markedly different proportions of fatty acids than the lipids remaining in the cell residue. Very little metabolism of the 1-linked fatty acid occurred. After a short pulse with (14)C, the specific activity of the 1-linked fatty acid was lower in the phospholipids released than in the phospholipids of the residue, indicating an earlier time of synthesis of those lipids released in the membrane fragments. During the EDTA-Tris treatment, the 2-linked fatty acid was metabolized. This metabolism may have involved phospholipase A(2) which stimulates the synthesis of fatty acids and the transfer of acyl groups to the lysophospholipid.

Release of membrane components from viable Haemophilus parainfluenzae by ethylenediaminetetraacetic acid-tris(hydroxymethyl)-aminomethane

Logarithmically growing Haemophilus parainfluenzae lost 15 to 20% of the phospholipids, demethyl vitamin K(2), cytochrome b, and cytochrome c, and 50% of the lipopolysaccharide when incubated in ethylenediaminetetraacetic acid (EDTA)-tris-(hydroxymethyl)aminomethane (Tris) for 10 min. This loss of membrane components occurred without loss in viability, and the lost components were recovered as membrane fragments in the surrounding buffer. The phospholipids recovered in the membrane fragments had a slightly lower specific activity than the phospholipids in the residue. Lysis of a portion of the cells could not account for the release of membrane components, as the cells lost neither glucose-6-phosphate dehydrogenase activity not deoxyribonucleic acid. The treated cells were osmotically stable and contained the same proportions of the individual phospholipids as pretreatment cells. Prolongation of the EDTA-Tris treatment did not induce further loss of phospholipid or demethyl vitamin K(2), but caused a decrease in viability. If the cells were returned to the growth medium after 10 min, the cells immediately resumed growth at the pretreatment rate. During growth in the recovery period, the phospholipids increased logarithmically in the pretreatment rate. During growth in the recovery period, the phospholipids increased logarithmically in the pretreatment proportions, although there was a marked decrease in the turnover and a shift from the use of extracellular lipid precursors to the use of intracellular pools of precursors.