Effect of age on the membrane lipid composition of Streptococcus sanguis

The cell membrane of Streptococcus sanguis contains three classes of lipid: neutral lipid, glycolipid and phospholipid. A striking difference in membrane lipid composition between cells in the exponential and in the stationary phases of growth was observed. During the exponential phase, approx. 37–45%, 14–19% and 37–45% of the lipids synthesized were found to be neutral lipid, glycolipid and phospholipid, respectively. The amount of lipid synthesized reached a maximum at the early stationary phase. The amount of phospholipid drastically declined thereafter and that of neutral lipid slightly declined. In contrast, the amount of glycolipid markedly increased and exceeded the amount of phospholipid. The phospholipid present during the exponential phase was found to be mainly phosphatidylglycerol (82–88%) and a small amount of cardiolipin (12–18%). At the stationary phase, the amount of phosphatidylglycerol greatly decreased and reached approx. 16% of that in the early stationary phase, while cardiolipin steadily increased and became the major phospholipid in the late stationary phase. The glycolipid was found to be composed of mainly mono- and diglucosyldiglycerides. At the end of the experiment (after 8 h incubation), the distribution of lipids was found to be: neutral lipid, 46%; glycolipid (monoglucosyldiglyceride, 28%; diglucosyldiglyceride, 13%) 41%; and phospholipid (phosphatidylglycerol, 3%, cardiolipin, 8%) 13%.     

Influence of growth temperature on cryotolerance and lipid composition of Lactobacillus acidophilus

In order to correlate the lipid composition of the membrane of Lactobacillus acidophilus CRL 640 with the freeze-thaw behaviour of the cultures grown at different temperatures, fatty acid methyl esters (FAMEs) from extracts grown at 25, 30, 37 and 40 degrees C were obtained and compared. Cultures grown at 25 degrees C (M25) exhibited more resistance to the freeze-thaw process probably because of an increase in C18:2 and C16:0 fatty acids. This culture also exhibited a lesser amount of phospholipids as shown by the sugar: phosphorus ratio. In all cases, the presence of the uncommon 10-hydroxyoctadecanoic acid was determined. From the extracts of the M25 and M37 cultures, diacylphosphatidylglycerol, cardiolipin, diglycosyldiglycerides, triglycosyldiglycerides and neutral lipids were isolated and identified. The structural elucidation was carried out by FAMEs and sugar analysis and by mass spectrometry using fast atom bombardment ionization. The changes in lipid composition due to different growth temperatures could be indicative of the resistance of the bacteria to freeze-thaw processes.     

Unsaturated diether lipids in the psychrotrophic archaeon Halorubrum lacusprofundi

The major phospholipids of Halorubrum lacusprofundi grown at 25 degrees C were archaeol phosphatidylglycerol, archaeol phosphatidylglycerylsulphate and archaeol phosphatidylglycerylphosphate methyl ester. Glycolipids included a monoglycosyl archaeol and the sulphate ester of a diglycosyl archaeol. Cultures grown at 12 degrees C contained the same suite of phospho- and glycolipids, with the addition of a series of unsaturated analogues with up to six double bonds. The patterns of unsaturation were similar for all the phospholipid series, but a different pattern occurred in the glycolipids. The analytical techniques used in this study allow facile detection of unsaturated archaeal cell membrane lipids that are degraded by commonly used chemical derivatization procedures.     

The effects of temperature acclimation on membrane sterols and phospholipids of Neurospora crassa

Experiments were conducted to examine the effects of temperature acclimation on sterol and phospholipid biosynthesis in Neurospora crassa. Cultures grown at high (37 degrees C) and low (15 degrees C) temperatures show significant differences in free and total sterol content, sterol/phospholipid ratios and distribution of major phospholipid species in total lipids and two functionally distinct membrane fractions. The ratio of free sterols to phospholipids in total cellular lipids from 15 degrees C cultures was found to be about one-half that found at 37 degrees C, whereas sterol/phospholipid ratios of mitochondrial and microsomal membranes were found to be higher at the low growth temperature. Total sterol and phospholipid biosynthetic rates showed parallel reductions in cultures acclimating to a shift from 37 to 15 degrees C growth conditions. Distribution of [14C]acetate label into free sterols was significantly lower under these conditions, however; indicating an increase in the conversion rate of sterols to sterol esters at the lower temperature. Mitochondrial and microsomal membrane fractions showed distinct phospholipid distributions which also differed from total lipid distributions at the two growth temperatures. In each case there was a consistent decrease in phosphatidylcholine and a corresponding increase in phosphatidylethanolamine as growth temperatures were lowered.     

Polar lipids from the radiation resistant bacterium Deinococcus radiodurans: structural investigations on glucosaminyl and N-acetyl glucosaminyl lipids

Deinococcus radiodurans, although a gram-positive bacterium, has a complex cell wall with multiple layers and associates to this structural particularity, a quite unusual lipid composition for gram-positive bacteria. The conventional phospholipids (phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl glycerol...) are absent. Among the nine polar lipids detected in the R1 Anderson strain, three are glycolipids only one is a phospholipid, the other ones are glycophospholipids. One of the latter compounds contains one free amino group. Analysis by aminoacid autoanalyser enables to identify glucosamine in one glycolipid and in two glycophospholipids. Sugar analysis by gas-liquid chromatography after acid methanolysis and trifluoroacetylation, reveals the occurrence of N-acetyl glucosaminyl residues in one glycolipid and in one phospholipid. The following identification for the two lipids of D. radiodurans is proposed: phosphatidyl glucosaminyl glycerol and phosphatidyl N-acetyl glucosaminyl glycerol.     

Thermal adaptation of Tetrahymena membranes with special reference to mitochondria. Role of cardiolipin in fluidity of mitochondrial membranes

During temperature acclimation of Tetrahymena pyriformis, the changes in fluidity and composition of total lipids from three membrane fractions, mitochondria, pellicles and microsomes were studied by a spin-label technique using a stearate probe and thin-layer and gas-liquid chromatography. The increase of fluidity observed in microsomal and pellicular lipids following the temperature shift from 39 to 15 degrees C corresponds with the increase of the ratio of total unsaturated to saturated fatty acid content. However, despite the increase of this ratio, the fluidity of mitochondrial lipids was found to be constant up to 10 h after the temperature shift. The fluidity of total lipids of mitochondria isolated from Tetrahymena cells grown at 39 degrees C was not changed by removal of cardiolipin, whereas cardiolipin-depleted lipids of mitochondria from 15 degrees C-acclimated cells showed a decrease in fluidity. The re-addition of cardiolipin to the mitochondrial lipids depleted of cardiolipin restored the fluidity to the initial level, thereby confirming the rigidifying effect of cardiolipin in cold-acclimated cells. These results suggest that cardiolipin may be implicated in maintaining consistent fluidity of mitochondrial membranes against change in thermal environment.     

l-Acylimidazoles with Broad-spectrum Fungicidal Activity

The membrane lipids of six higher plants that differ in salt tolerance were analyzed and compared. The root lipids increased in a ratio of glycolipid/phospholipid with increasing salt- tolerance. A similar increase in the ratio was observed with increasing external salinity when halophytic orach and salt-sensitive cucumber were exposed to varying salinity, although the latter plant was limited to only a little increase. Measurements of ion-transport rates with artificial lipid membranes revealed that the root lipids from a salt-resistant plant formed a more permeable membrane than those from a salt-sensitive species. It was found that the membrane permeability was related to the glycolipid/phospholipid ratio in the membrane lipids, where the glycolipids were stimulative and the phospholipids were repressive for ion-flow. These different effects of the two lipid classes may be attributed to their molecular species and head groups.     

Bleaching herbicide effects on plastids of dark-grown plants: lipid composition of etioplasts in amitrole and norflurazon-treated barley leaves

The effects of the bleaching herbicides amitrole (125 micro M) and norflurazon (100 micro M) on etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 degrees C or 30 degrees C in darkness. Total lipid, glycolipid and phospholipid contents of control etioplasts were increased at 30 degrees C in comparison with those at 20 degrees C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 degrees C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 degrees C and norflurazon at 30 degrees C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of etioplasts and the interaction between the pigment-protein complex, protochlorophyllide-NADPH-protochlorophyllide oxidoreductase, and polar lipids are discussed.     

Effects of temperature acclimation on Neurospora phospholipids. Fatty acid desaturation appears to be a key element in modifying phospholipid fluid properties

Experiments were conducted on the effect of growth temperature on phospholipids of Neurospora. Strains grown at high (37 degrees C) and low (15 degrees C) temperatures show large differences in the proportions of phospholipid fatty acid alpha-linolenate (18 : 3) which can vary by 10-fold over this temperature range. Changes in the phospholipid base composition are less dramatic; the most significant is an increase in phosphatidylethanolamines at low temperatures accompanied by a concomitant decrease in phosphatidylcholine. It appears that phospholipid fatty acid desaturation is closely regulated with respect to growth temperature. Over the 37 to 15 degrees C growth temperature range there appear to be at least two desaturase systems in Neurospora which are under different controls. Production of 18 : 1 and 18 : 2 species appears to occur at high levels over the entire temperature range, whereas the production of 18 : 3 seems to be inversely related to growth temperature. Shifting 37 degrees C-acclimated cultures to 15 degrees C produces a growth lag period of approximately 3 h, during which the level of 18 : 3 increases markedly. Differential scanning calorimetry of phospholipids from 37 degrees C cells shows a phase transition at -22 degrees C while lipids from 15 degrees C cultures exhibit a phase transition with reduced enthalpy at about -41 degrees C. The data are consistent with the idea that phospholipid composition in Neurospora is under strict control and suggest that membrane fluidity is regulated with respect to growth temperature through changes in membrane lipid composition.     

Lipid modulation by environmental stresses in two models of extremophiles isolated from Antarctica

Thermoacidophilic and halotolerant microorganisms from the Antarctic continent were studied for their lipid modulation under stress growth conditions. Temperature-induced changes in complex lipids and fatty acids of four strains belonging to the genus Alicyclobacillus involved the relative proportions of different polar lipids and the synthesis of ω-cyclohexyl-acyl chains, which were favoured by high temperatures. Studies were carried out on the lipid composition of four strains of extremely halotolerant bacteria belonging to the genus Micrococcus grown at different salt concentrations from 0 up to 4.5 M NaCl. The main lipids found were two unidentified glycolipids and two phospholipids: 1,2 diacylglycero-3-phosphoryl-glycerol (PG) and cardiolipin (DPG). Among the strains analysed, the lipids of the Micrococcus strain Erebus were shown to be strongly influenced by salt concentrations, in that DPG and one glycolipid were absent at a low salt molarity while, under these conditions, PG was the main lipid found. The predominant fatty acids in all halotolerant strains were of the anteiso type; growth under increasing salinity gave rise to an increase in long chain fatty acids and of straight chain fatty acids, while a decrease in iso fatty acids occurred. Accepted: 20 May 2000     

Structure of membrane lipids and physico-biochemical properties of the plasma membrane from Thermoplasma acidophilum, adapted to growth at 37 degrees C.

Thermoplasma acidophilum, a mycoplasma-like organism, grows optimally at 56 degrees C and pH2. The low temperature extreme of growth is 37 degrees C. The plasma membrane of cells grown at 37 degrees C was isolated and characterized physicobiochemically. Membrane lipids which comprise 25% of the membrane dry weight consist mainly of two repetitively methyl-branched C40 side chains that were ether-linked to two glycerol molecules. The lipid structures were elucidated by combined gas chromatography-mass spectroscopy, direct probe mass spectroscopy and 13C NMR. 37 degrees C-grown cells contained lipids with 42% more pentane cyclization than the 56 degrees C-grown cells. In 37 degrees C-grown cells, phospholipid and serine content decreased by about 10% each, carbohydrate content increased by 5%. EPR studies demonstrated an increase in membrane lipid fluidity of 37 degrees C-grown cells with an upper transition temperature at 35 degrees C which was shifted down by 10 degrees C compared with cells grown at 56 degrees C. Membrane-bound ATPase activities also indicated similar changes upon adaptation. There is a close correlation between membrane fluidity and physiological functioning of this membrane-bound enzyme.     

Thermal adaptation of Tetrahymena membranes with special reference to mitochondria. II. Preferential interaction of cardiolipin with specific molecular species of phospholipid

A specific effect of cardiolipin on fluidity of mitochondrial membranes was demonstrated in Tetrahymena cells acclimated to a lower temperature in the previous report (Yamauchi, T., Ohki, K., Maruyama, H. and Nozawa, Y. (1981) Biochim. Biophys. Acta 649, 385-392). This study was further confirmed by the experiment using fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). Anisotropy of DPH for microsomal and pellicular total lipids from Tetrahymena cells showed that membrane fluidity of these lipids increased gradually as the cells were incubated at 15 degrees C after the shift down of growth temperature from 39 degrees C. However, membrane fluidity of mitochondrial total lipids was kept constant up to 10 h. This finding is compatible with the result obtained using spin probe in the previous report. Additionally, the break-point temperature of DPH anisotropy was not changed in mitochondrial lipids whereas those temperatures in pellicular and microsomal lipids lowered during the incubation at 15 degrees C. Interaction between cardiolipins and various phospholipids, which were isolated from Tetrahymena cells grown at 39 degrees C or 15 degrees C and synthesized chemically, was investigated extensively using a spin labeling technique. The addition of cardiolipins from Tetrahymena cells grown at either 39 degrees C or 15 degrees C did not change the membrane fluidity (measured at 15 degrees C) of phosphatidylcholine from whole cells grown at 39 degrees C. On the other hand, both cardiolipins of 39 degrees C-grown and 15 degrees C-grown cells decreased the membrane fluidity of phosphatidylcholine from Tetrahymena cells grown at 15 degrees C. The same results were obtained for phosphatidylcholines of mitochondria and microsomes. Membrane fluidity of phosphatidylethanolamine, isolated from cells grown at 15 degrees C, was reduced to a small extent by Tetrahymena cardiolipin whereas that of 39 degrees C-grown cells was not changed. Representative molecular species of phosphatidylcholines of cells grown at 39 degrees C and 15 degrees C were synthesized chemically; 1-palmitoyl-2-oleoylphosphatidylcholine for 39 degrees C-grown cells and dipalmitoleoylphosphatidylcholine for 15 degrees C-grown ones. By the addition of Tetrahymena cardiolipin, the membrane fluidity of 1-palmitoyl-2-oleoylphosphatidylcholine was not changed but that of dipalmitoleoylphosphatidylcholine was decreased markedly. These phenomena were caused by Tetrahymena cardiolipin. However, bovine heart cardiolipin, which has a different composition of fatty acyl chains from the Tetrahymena one, exerted only a small effect.     

Lipid requirement of the branched-chain amino acid transport system of Streptococcus cremoris

The role of the membrane lipid composition on the transport protein of branched-chain amino acids of the homofermentative lactic acid bacterium Streptococcus cremoris has been investigated. The major membrane lipid species identified in S. cremoris were acidic phospholipids (phosphatidylglycerol and cardiolipin), glycolipids, and glycerophosphoglycolipids. Phosphatidylethanolamine (PE) was completely absent. Protonmotive force-driven and counterflow transport of leucine was assayed in fused membranes of S. cremoris membrane vesicles and liposomes composed of different lipids obtained by the freeze/thaw-sonication technique. High transport activities were observed with natural S. cremoris and Escherichia coli lipids, as well as with mixtures of phosphatidylcholine (PC) with PE or phosphatidylserine. High transport activities were also observed with mixtures of PC with monogalactosyl diglyceride, digalactosyl diglyceride, or a neutral glycolipid fraction isolated from S. cremoris. PC or mixtures of PC with phosphatidylglycerol, phosphatidic acid, or cardiolipin showed low activities. In mixtures of PC and methylated derivatives of PE, both counterflow and protonmotive force-driven transport activities decreased with increasing degree of methylation of PE. The decreased transport activity in membranes containing PC could be restored by refusion with PE-containing liposomes. These results demonstrate that both aminophospholipids and glycolipids can be activators of the leucine transport system from S. cremoris. It is proposed that aminophospholipids in Gram-negative bacteria and glycolipids in Gram-positive bacteria have similar functions with respect to solute transport.     

The effect of osmotic stress on the biophysical behavior of the Bacillus subtilis membrane studied by dynamic and steady-state fluorescence anisotropy

The thermotropic behavior of intact bacterial membranes and vesicles prepared from total and polar lipids isolated from Bacillus subtilis cultures grown at 37 degrees C in normal (LB) and hyperosmotic (LBN) conditions was studied using 1,6-diphenyl-1,3,5-hexatriene (DPH), 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate (TMA-DPH), and 2-diethylamino-6-lauroyl-naphthalene (Laurdan) as fluorescent probes. No phase transition of bulk lipids was observed in these preparations at the range of temperature studied. The anisotropy values (r(s)) for DPH and TMA-DPH in purified membranes showed significant differences between the LB and LBN conditions, suggesting that there was an increase in membrane packing during the adaptation to osmotic stress. Furthermore, generalized polarization (GP) parameters for Laurdan indicated small but significant changes in water relaxation at the membrane hydrophobic/hydrophilic interface. Membrane preparations showed r(s) higher values than those of lipid vesicles and a higher temperature dependence of the Laurdan GP parameter. This fact indicates that membrane proteins increase the lipid packing and keep the membrane more sensitive to temperature changes.     

Evidence for a Composite State of an F′his,gnd Element and a Cryptic Plasmid in a Derivative of Salmonella typhimurium LT2

The zoospores of Blastocladiella emersonii, when derived from cultures grown on solid media, contain about 11% total lipid. This lipid was separated chromatographically on silicic acid into neutral lipid (46.6%), glycolipid (15.8%), and phospholipid (37.6%). Each class was fractionated further on columns of silicic acid, Florisil, or diethylaminoethyl-cellulose, and monitored by thin-layer chromatography. Triglycerides were the major neutral lipids, mono- and diglycosyldiglycerides were the major glycolipids, and phosphatidylcholine and phosphatidylethanolamine were the major phospholipids. Other neutral lipids and phospholipids detected were: hydrocarbons, free fatty acids, free sterols, sterol esters, diglycerides, monoglycerides, lysophosphatidylcholine, lysophosphatidylethanolamine, phosphatidic acid, phosphatidylserine, and phosphatidylinositol. Palmitic, palmitoleic, stearic, oleic, gamma-linolenic, and arachidonic acids were the most frequently occurring fatty acids. When B. emersonii was grown in (14)C-labeled liquid media, lipid again accounted for 11% of both mature plants and zoospores released from them. The composition of the lipid extracted from such plants and spores was also the same; however, it differed markedly from that of the lipid in spores harvested from solid media, consisting of 28.3% neutral lipid, 12.0% glycolipid, and 59.7% phospholipid. The major lipids were again triglycerides for neutral lipids, mono- and diglycosyldiglycerides for glycolipids, and phosphatidyl choline and phosphatidylethanolamine for phospholipids.     

Temperature-induced modifications of glycosphingolipids in plasma membranes of Neurospora crassa

Plasma membranes isolated from a cell-wall-less mutant of Neurospora crassa grown at 37 and 15 degrees C display large differences in lipid compositions. A free sterol-to-phospholipid ratio of 0.8 was found in 37 degrees C membranes, while 15 degrees C plasma membranes exhibited a ratio of nearly 2.0. Membranes formed under both growth conditions were found to contain glycosphingolipids. Cultures grown at the low temperature, however, were found to contain 6-fold higher levels of glycosphingolipids and a corresponding 2-fold reduction of phospholipid levels. The high glycosphingolipid content at 15 degrees C compensates for the reduced levels of phospholipids in such a way that sterol/polar lipid ratios are almost the same in plasma membranes under the two growth conditions. Temperature-dependent changes in plasma-membrane phospholipid and glycosphingolipid species were also observed. Phosphatidylethanolamine levels were sharply reduced at 15 degrees C, in addition to a moderate increase in levels of unsaturated phospholipid fatty acids. Glycosphingolipids contained high levels of long-chain hydroxy fatty acids, which constituted 75% of the total fraction at 37 degrees C, but only 50% at 15 degrees C. Compositional changes were also observed in the long-chain base component of glycosphingolipids with respect to growth temperature. Fluorescence polarization studies indicate that the observed lipid modifications in 15 degrees C plasma membranes act to modulate bulk fluidity of the plasma-membrane lipids with respect to growth temperature. These studies suggest that coordinate modulation of glycosphingolipid, phospholipid and sterol content may be involved in regulation of plasma-membrane fluid properties during temperature acclimation.     

Mycolipenates and mycolipanolates of trehalose from mycobacterium tuberculosis

Analysis of the lipids of Mycobacterium tuberculosis, by thin-layer chromatography, revealed the presence of two families of novel glycolipids each having two closely-related members but differing widely in polarity. The least and most polar families of lipids were characterized from M. tuberculosis strains C and H37Rv, respectively; all were based on trehalose, the least polar pair of glycolipids having more long-chain substituents than the more polar pair. The acyl substituents of the least polar of the four glycolipids were mainly straight-chain C16 and C18 acids and 2,4,6-trimethyltetracos-2-enoic (C27-mycolipenic) acid, and the second least polar glycolipid contained major amounts of 3-hydroxy-2,4,6-trimethyltetracosanoic (C27-mycolipanolic) acid in addition to these non-hydroxylated acids. The relatively polar pair of glycolipids were analysed together and released mainly straight-chain C16 and C18 acids, C27-mycolipanolic acid, minor amounts of C25- and C27-mycolipenic acids and major proportions of an acid having the chromatographic properties of 2,4-dimethyldocosanoic acid. The most polar pair of glycolipids co-chromatographed with glycolipid antigens previously detected in Mycobacterium bovis BCG.     

Lipid composition and thermotropic phase behavior of boar, bull, stallion, and rooster sperm membranes.

Composition and thermotropic phase behavior of sperm membrane lipids from species ranging in sensitivity to cold shock were determined. Lipids from whole sperm and sperm plasma membrane were fractionated into neutral lipid, glycolipid, and phospholipid fractions. Compositional analyses were completed for free sterols, phospholipids and phospholipid-bound fatty acids. Phase transition temperatures were determined for phospholipid and glycolipid fractions using differential scanning calorimetry. Cholesterol was the major sterol in sperm lipids of all species. Cholesterol to phospholipid molar ratios were 0.26, 0.30, 0.36, and 0.45 for sperm plasma membrane of the boar, rooster, stallion, and bull, respectively. Choline and ethanolamine phosphoglycerides and sphingomyelin were the major phospholipid classes in sperm and their proportions differed across species. Phospholipid-bound fatty acyl compositions of choline and ethanolamine phosphoglycerides were characterized by a high proportion of docosapentanoyl and docosahexanoyl groups in mammalian sperm and shorter, more saturated groups in rooster sperm. Glycolipids represented less than 10% of total polar lipids for all species. Thin-layer chromatographic analysis indicated that the major glycolipid component of rooster sperm was different from that of mammalian sperm. Peak phase transition temperatures (Tm) for sperm membrane phospholipids were 24.0, 25.4, 20.7 and 24.5, for the boar, stallion, and rooster, respectively. Corresponding Tm's for glycolipids were 36.2, 42.8, and 33.4 with no exotherm for rooster sperm glycolipids. These results demonstrate a difference in both composition and thermotropic phase behavior of glycolipids between rooster and mammalian sperm which may be related to the greater tolerance of rooster sperm to rapid cooling.     

Replacement of the aliphatic chains of Clostridium acetobutylicum by exogenous fatty acids: regulation of phospholipid and glycolipid composition.

The membrane lipid aliphatic chains of Clostridium acetobutylicum ATCC 4259 have been extensively modified by growth in biotin-free medium containing vitamin-free casein hydrolysate supplemented with either elaidic acid, oleic acid, or mixtures of palmitic and oleic acids. Growth with elaidic acid resulted in polar lipids containing 88.6% 18:1 acyl chains and 94.5% 18:1 ether-linked chains. Growth with oleic acid resulted in comparable levels of enrichment of the lipids with 18:1 chains and C19 chains containing cyclopropane rings. When cells were grown with mixtures of palmitic and oleic acids, the ether-linked chains of the plasmalogens were greater than or equal to 64% 18:1 plus C19 chains containing cyclopropane rings at all ratios of oleic to palmitic acid in the medium. The acyl chains reflected the palmitic acid content of the medium more closely. Marked changes were observed in both phospholipid and glycosyldiglyceride compositions as the lipid acyl and ether-linked chains became more enriched with unsaturated and cyclopropane chains. The ratio of the glycerol acetal of plasmenylethanolamine to phosphatidylethanolamine increased, the ratio of cardiolipin to phosphatidylglycerol decreased, and the ratio of diglycosyldiglyceride to monoglycosyldiglyceride increased. However, the monoglycosyldiglyceride/diglycosyldiglyceride ratio was lower for cells grown on 100% oleic acid than for cells grown on 60 or 80% oleic acid. In the membranes of cells grown on 100% oleic acid, the ratio of glycolipids to phospholipids was lower than that found in cells grown on 60% oleic acid. These results indicate that C. acetobutylicum regulates its polar lipid composition in a complex manner involving phospholipids and glycosyldiglycerides. These changes can affect the equilibria between those lipids that form bilayers and those lipids that tend to form nonlamellar phases when enriched with unsaturated aliphatic chains. Phosphoglycolipids of unknown structure were also observed in cells grown either with biotin or with fatty acids. The content of the most abundant phosphoglycolipid also varied with the degree of unsaturation of the cellular lipids.     

Physiology of biosurfactant synthesis by Rhodococcus species H13-A

The physiology of biosurfactant synthesis by a soil isolate, identified as a Rhodococcus species, is described. The biosurfactant is a surface-active glycolipid produced during the stationary growth phase of Rhodococcus species H13-A on n-alkanes and fatty alcohols in response to limiting ammonium ion concentrations. Hexadecane-grown cells produced increasing amounts of extracellular glycolipid when the carbon to nitrogen ratio (C/N) was increased from 1.7 to 3.4. The increase in extracellular glycolipid in hexadecane-grown cells correlated with a decrease in the interfacial tension of the spent growth medium to values less than 5?mN/m. Significant levels of extracellular glycolipid were not detected in the spent growth medium of cells grown on triglycerides, fatty acids, ethanol, organic acids, or carbohydrates. Rhodococcus species H13-A contains the three indigenous plasmids pMVS100, pMVS200, and pMVS300, with neither pMVS200 nor pMVS300 being involved in glycolipid synthesis or hexadecane dissimilation. The role of pMVS100 remains undetermined. Key words: biosurfactants, glycolipids, trehalose lipids, Rhodococcus.