Turnover of phospholipids in an unsaturated fatty acid auxotroph of Escherichia coli

Coexistence of domains with distinct order and polarity in fluid bacterial membranes

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 degrees 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 proteolipid 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.

Excretion of extracellular lipids by Streptococcus mutans BHT and FA-1

Streptococcus mutans BHT and FA-1, when grown to log phase on chemically defined medium containing [14C]glycerol, excreted 15% of the total biosynthesized 14C-lipid into the medium. When grown to early stationary phase, 28 to 33% of the 14C-lipid was found in the medium. The radioactive lipids of these varieties of S. mutans were identified as diacylglycerol, diglucosyl diacylglycerol (DGD), monoglucosyl diacylglycerol, diphosphatidylglycerol, phosphatidylglycerol (PG), and smaller amounts of two other lipids tentatively were identified as amino acyl-PG and glycerol phosphoryl-DGD. All lipids were found as extracellular and intracellular components from cells grown to either log or stationary phase. However, there were some shifts in the relative percentage of these lipids as the cells changed from log to stationary phase. For example, the intracellular lipid content of log-phase S. mutans BHT was composed of 49% PG and 19% DGD, but these percents shifted to 18% PG and 57% DGD when the cells were grown to stationary phase. However, the extracellular lipids of this organism contained 50 to 60% PG and 20% DGD in both log and stationary phases.

Biochemical changes in Bifidobacterium bifidum var. pennsylvanicus after cell wall inhibition. IX. Metabolism and release of cellular lipids in the presence of antibiotics

Inhibiton of cell wall synthesis caused simultaneously an increase in cellular phospho-and glycolipids and a marked release of these compounds to the medium. The composition of the cellular and the released glyco-and phospholipids was almost the same. Antibiotics, which inhibit cell wall synthesis, did not influence glycolipid composition, but increased the relative and absolute amounts of disphosphatidylglycerol and its lysoderivatives. Incorporation and chase experiments demonstrated a considerable stimulation of phospholipid metabolism, and of diphosphatidylglycerol synthesis especially. Release of lipids was not accompanied by loss of cellular protein. Omission of Tween 80 from the medium decreased the release by about 50% and increased the relative amounts of the phosphogalactolipids in the cells and in the culture fluid. Inhibitors of protein synthesis and valinomycin caused a decrease in cellular lipidphosphorus content, and a relative increase of the phosphogalactolipids. No release of lipids was observed under these conditions.

Effects of antibiotics on metabolism of peptidoglycan, protein, and lipids in Bifidobacterium bifidum subsp. pennsylvanicus

The formation of cell envelope components of Bifidobacterium bifidum subsp. pennsylvanicus was studied by measuring the incorporation of [(3)H]glycine, (14)C-labeled fatty acids, and N-benzoyl-[(14)C]glucosamine into the membrane protein, membrane lipids, and cell wall peptidoglycan, respectively. Inhibition of peptidoglycan synthesis by antibiotics (penicillin G, vancomycin, d-cycloserine, and bacitracin) and by the omission of glucosamine-containing growth factors caused a marked decrease in glycine incorporation into cellular as well as membrane protein, which was accompanied by a considerable enhancement of fatty acid incorporation. The uncoupling of protein and lipid synthesis led to the release of marked amounts of lipids from the cell under these conditions. Arrestment of protein synthesis by antibiotics (chloramphenicol, tetracycline, and actinomycin D) decreased peptidoglycan and lipid synthesis only partially, but did not lead to lipid release. Mg(2+) deficiency of the medium caused about 60% inhibition of growth and lipid synthesis, but protein synthesis and especially peptidoglycan synthesis were much less inhibited. Staphylococcin 1580 arrested the growth and also the synthesis of protein and peptidoglycan. However, the synthesis and turnover of lipids were considerably increased and a release of large amounts of lipids was observed. Peptidoglycan and cellular protein did not show any turnover either during normal growth or after the inhibition of cell wall and protein synthesis.

Altered phospholipid metabolism in a temperature-sensitive mutant of a thermophilic bacillus

The phospholipid metabolism of a temperature-sensitive mutant of a thermophilic bacillus was studied after the shift from a permissive (58 degrees C) to a restrictive (65 degrees C) growth temperature. During the short period of growth of the mutant at 65 degrees C, the proportions of cardiolipin and its 3-acyl derivative (lyso-cardiolipin) increased, and the proportions of phosphatidylglycerol and phosphatidylethanolamine decreased on cell dry weight basis. In 32P incorporation and turnover experiments, phosphatidylglycerol showed the most rapid uptake and loss of the label. Turnover of cardiolipin, limited to a short period, ceased 18 min after the shift, as did the turnover of phosphatidylethanolamine. In the absence of net phospholipid synthesis, there was a quantitative conversion of phosphatidylglycerol to cardiolipin and an increase in the proportion of lyso-cardiolipin. Chloramphenicol, added to the medium at the time of the shift, reduced the rate of phospholipid synthesis, prevented the increase in the proportions of cardiolipin and lyso-cardiolipin, and slowed the decrease in the proportions of the other two phospholipids. The results indicated a defect in the regulatory mechanism(s) of phospholipid metabolism in the mutant at the restrictive temperature.

Relation between protein synthesis and phospholipid synthesis and turnover in Escherichia coli

Turnover of phospholipids occurred continuously in a fatty acid auxotroph of Escherichia coli, but in the wild-type parent strain significant turnover occurred only under conditions where protein synthesis was inhibited but lipid synthesis continued. Both strains gave a stringent response of ribonucleic acid accumulation to amino acid starvation, but only in the wild type was lipid synthesis also inhibited. A revertant strain of the auxotroph resembled the wild type in this respect. The phospholipid that accumulates in the culture medium as a result of the lipid turnover appears to be part of a loosely bound low-density complex arising from the cell envelope.