Comparative aspects of bacterial lipids

Differential protein expression during growth on model and commercial mixtures of naphthenic acids in Pseudomonas fluorescens Pf-5

Naphthenic acids (NAs) are carboxylic acids with the formula (Cn H2n+Z O2 ) and are among the most toxic, persistent constituents of oil sands process-affected waters (OSPW), produced during oil sands extraction. Currently, the proteins and mechanisms involved in NA biodegradation are unknown. Using LC-MS/MS shotgun proteomics, we identified proteins overexpressed during the growth of Pseudomonas fluorescens Pf-5 on a model NA (4'-n-butylphenyl)-4-butanoic acid (n-BPBA) and commercial NA mixture (Acros). By day 11, >95% of n-BPBA was degraded. With Acros, a 17% reduction in intensity occurred with 10-18 carbon compounds of the Z family -2 to -14 (major NA species in this mixture). A total of 554 proteins (n-BPBA) and 631 proteins (Acros) were overexpressed during growth on NAs, including several transporters (e.g., ABC transporters), suggesting a cellular protective response from NA toxicity. Several proteins associated with fatty acid, lipid, and amino acid metabolism were also overexpressed, including acyl-CoA dehydrogenase and acyl-CoA thioesterase II, which catalyze part of the fatty acid beta-oxidation pathway. Indeed, multiple enzymes involved in the fatty acid oxidation pathway were upregulated. Given the presumed structural similarity between alkyl-carboxylic acid side chains and fatty acids, we postulate that P. fluorescens Pf-5 was using existing fatty acid catabolic pathways (among others) during NA degradation.

Identification by mass spectrometry of glucosaminylphosphatidylglycerol, a phosphatidylglycerol derivative, produced by Pseudomonas aeruginosa

RATIONALE

Pseudomonas aeruginosa is an opportunistic pathogen bacterium widely considered to be an excellent research model in several areas of molecular studies, namely genomics and proteomics. However, its lipid metabolism is still not totally decrypted. While it is known that this bacterium has the particularity to produce phosphatidylcholine, a lipid mainly found in eukaryotes, other singularities are still to be discovered.

METHODS

P. aeruginosa was grown as planktonic cultures to the stationary state. Membrane pellets were collected and lipids were extracted using the Bligh and Dyer protocol. Lipid extracts were analyzed by Electrospray Ionization Mass Spectrometry (ESI-MS) using high-resolution mass spectrometer (LTQ Orbitrap Elite, Thermo Scientific) in the negative mode. MSⁿ spectra were recorded both in the Orbitrap and in the ion trap analyzer (collision-induced dissociation (CID) or higher energy collision-induced dissociation (HCD) mode).

RESULTS

We observed by mass spectrometry and thin layer chromatography that P. aeruginosa produced an unreferenced lipid in classical growth conditions. MS² analysis of the unknown ion indicates that it is a phosphatidylglycerol derivative. The exact mass shift corresponds to glucosamine which is largely found in the metabolism of this bacterium. MS³ analysis of secondary ions allowed us to conclude that this lipid is a glucosaminylphosphatidylglycerol, a phosphatidylglycerol derivative containing a glucosamine substituted at C4.

CONCLUSIONS

We show here that P. aeruginosa is able to produce glucosaminylphosphatidylglycerols via a probable esterification of phosphatidylglycerols by glucosamine.

A coarse-grained approach to studying the interactions of the antimicrobial peptides aurein 1.2 and maculatin 1.1 with POPG/POPE lipid mixtures

In the present work we investigated the differential interactions of the antimicrobial peptides (AMPs) aurein 1.2 and maculatin 1.1 with a bilayer composed of a mixture of the lipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE). We carried out molecular dynamics (MD) simulations using a coarse-grained approach within the MARTINI force field. The POPE/POPG mixture was used as a simple model of a bacterial (prokaryotic cell) membrane. The results were compared with our previous findings for structures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a representative lipid of mammalian cells. We started the simulations of the peptide-lipid system from two different initial conditions: peptides in water and peptides inside the hydrophobic core of the membrane, employing a pre-assembled lipid bilayer in both cases. Our results show similarities and differences regarding the molecular behavior of the peptides in POPE/POPG in comparison to their behavior in a POPC membrane. For instance, aurein 1.2 molecules can adopt similar pore-like structures on both POPG/POPE and POPC membranes, but the peptides are found deeper in the hydrophobic core in the former. Maculatin 1.1 molecules, in turn, achieve very similar structures in both kinds of bilayers: they have a strong tendency to form clusters and induce curvature. Therefore, the results of this study provide insight into the mechanisms of action of these two peptides in membrane leakage, which allows organisms to protect themselves against potentially harmful bacteria. Graphical Abstract Aurein pore structure (green) in a lipid bilayer composed by POPE (blue) and POPG (red) mixture. It is possible to see water beads (light blue) inside the pore.

Bioconversion of natural gas to liquid fuel: opportunities and challenges

Natural gas is a mixture of low molecular weight hydrocarbon gases that can be generated from either fossil or anthropogenic resources. Although natural gas is used as a transportation fuel, constraints in storage, relatively low energy content (MJ/L), and delivery have limited widespread adoption. Advanced utilization of natural gas has been explored for biofuel production by microorganisms. In recent years, the aerobic bioconversion of natural gas (or primarily the methane content of natural gas) into liquid fuels (Bio-GTL) by biocatalysts (methanotrophs) has gained increasing attention as a promising alternative for drop-in biofuel production. Methanotrophic bacteria are capable of converting methane into microbial lipids, which can in turn be converted into renewable diesel via a hydrotreating process. In this paper, biodiversity, catalytic properties and key enzymes and pathways of these microbes are summarized. Bioprocess technologies are discussed based upon existing literature, including cultivation conditions, fermentation modes, bioreactor design, and lipid extraction and upgrading. This review also outlines the potential of Bio-GTL using methane as an alternative carbon source as well as the major challenges and future research needs of microbial lipid accumulation derived from methane, key performance index, and techno-economic analysis. An analysis of raw material costs suggests that methane-derived diesel fuel has the potential to be competitive with petroleum-derived diesel.

Choline kinase II is present only in nodules that synthesize stable peribacteroid membranes

Host-cell cytoplasm from soybean plants infected with the peribacteroid membrane (PBM)-building Rhizobium japonicum strain 61-A-101 (effective, N(2)-fixing) had much higher choline kinase activity than cytoplasm from either uninfected tissue or tissue infected with the non-PBM-building (ineffective, non-N(2)-fixing) strain 61-A-24. Ion-exchange chromatography showed that both types of nodule and root tissue possessed constitutive choline kinase I activity that had a K(m) for choline of approximately 150 muM. The nodules of the effective symbiosis had another activity, choline kinase II (K(m) = 81 muM). Nondenaturing and NaDodSO(4) electrophoresis revealed no multimeric subunit structure of the two enzyme forms but did show the molecular sizes for choline kinase I, 58-59 kDa, and choline kinase II, 60 kDa. Choline kinase I and II and pI values of 8.1 and 8.5, respectively, and two-dimensional gel electrophoresis of whole cytoplasm from control and infected tissue showed a spot corresponding to choline kinase II only in the case of the effective symbiosis, whereas both tissue types had spots corresponding to choline kinase I. Choline kinase II is presumed to be encoded by the plant as neither free-living nor symbiotic (bacteroid) forms of the prokaryote showed any choline kinase activity.

Use of lipid composition and metabolism to examine structure and activity of estuarine detrital microflora

Earlier studies have shown that the activity of the estuarine detrital microflora measured by various enzyme activities, muramic acid and adenosine 5'-triphosphate (ATP) content, heterotrophic potentials, and respiratory activities correlates with the incorporation of C and P into the microbial lipids. In this study, these lipids were reproducibly fractionated into neutral lipid, glycolipid, and phospholipid classes. Distinct differences between the active microflora of oak leaves, sweet gum leaves, and pine needles were evidenced both in the rate of lipid synthesis and in the proportions of neutral lipids, glycolipids, and phospholipids. Successional changes in the microflora of leaves incubated in a semitropical estuary, previously suggested by ATP-to-muramic acid ratios and scanning electron micrography, were reflected in changes in the proportions of C in major lipid classes when analyzed from the same type of detritus. Short incubation times with C gave lipid compositions rich in phospholipids that are typical for the faster-growing bacterial populations; longer incubation with C gave lipid compositions richer in neutral and glycolipids, more characteristic of slower-growing eukaryotes or morphologically more complex prokaryotes. The metabolism of the lipids of the estuarine detrital microflora was examined by a pulse-chase experiment with C. Glycolipids lost C at a rate equal to the loss of C of the slow component of muramic acid. Individual phospholipids lost C from their backbone glycerol esters at different rates.

Mass spectrometry of membrane transporters reveals subunit stoichiometry and interactions

We describe a general mass spectrometry approach to determine subunit stoichiometry and lipid binding in intact membrane protein complexes. By exploring conditions for preserving interactions during transmission into the gas phase and for optimally stripping away detergent, by subjecting the complex to multiple collisions, we released the intact complex largely devoid of detergent. This enabled us to characterize both subunit stoichiometry and lipid binding in 4 membrane protein complexes.

Identification of cyclopropyl fatty acids in walnut (Juglans regia L.) oil

AIM

Identification of cyclopropyl fatty acids in walnut oil.

METHOD

GC/MS method was developed for the determination of eight cyclopropyl fatty acids in walnut (Juglans regia) oil.

RESULTS

Monocyclopropane acids: methyl 9-cyclopropyl-nonanoate, 6,7-methylene-, 8,9-methylene-, 9,10-methylene-, 11,12-methylene octadecanoates, and dicyclic acid - methyl 9,10,12,13-dimethylene octadecanoate, tricyclic acid - methyl 9,10,12,13,15,16-trimethylene octadecanoate, and unsaturated - methyl 2-octylcyclopropene-1-octanoate were detected in walnut oil by GC-MS and their mass spectra studied. Four cyclic fatty acids were identified for the fist time in seed oils.

CONCLUSIONS

Eight cyclopropyl fatty acids were detected in the Mediterranean nuts for the first time.

Protegrin interaction with lipid monolayers: Grazing incidence X-ray diffraction and X-ray reflectivity study

Interactions of the antimicrobial peptide protegrin-1 (PG-1) with phospholipid monolayers have been investigated by using grazing incidence X-ray diffraction (GIXD) and specular X-ray reflectivity (XR). The structure of a PG-1 film at the air-aqueous interface was also investigated by XR for the first time. Lipid A, dipalmitoyl-phosphatidylglycerol (DPPG) and dipalmitoyl-phosphatidylcholine (DPPC) monolayers were formed at the air-aqueous interface to mimic the surface of the bacterial cell wall and the outer leaflet of the erythrocyte cell membrane, respectively. Experiments were carried out under constant area conditions where the pressure changes upon insertion of peptide into the monolayer. GIXD data suggest that the greatest monolayer disruption produced by PG-1 is seen with the DPPG system at 20 mN/m since the Bragg peaks completely disappear after introduction of PG-1 to the system. PG-1 shows greater insertion into the lipid A system compared to the DPPC system when both films are held at the same initial surface pressure of 20 mN/m. The degree of insertion lessens at 30 mN/m with both DPPC and DPPG monolayer systems. XR data further reveal that PG-1 inserts primarily in the head group region of lipid monolayers. However, only the XR data of the anionic lipids suggest the existence of an additional adsorbed peptide layer below the head group of the monolayer. Overall the data show that the extent of peptide/lipid interaction and lipid monolayer disruption depends not only on the lipid composition of the monolayer, but the packing density of the lipids in the monolayer prior to the introduction of peptide to the subphase.

Lipid headgroup discrimination by antimicrobial peptide LL-37: insight into mechanism of action

Interaction of the human antimicrobial peptide LL-37 with lipid monolayers has been investigated by a range of complementary techniques including pressure-area isotherms, insertion assay, epifluorescence microscopy, and synchrotron x-ray scattering, to analyze its mechanism of action. Lipid monolayers were formed at the air-liquid interface to mimic the surface of the bacterial cell wall and the outer leaflet of erythrocyte cell membrane by using phosphatidylglycerol (DPPG), phosphatidylcholine (DPPC), and phosphatidylethanolamine (DPPE) lipids. LL-37 is found to readily insert into DPPG monolayers, disrupting their structure and thus indicating bactericidal action. In contrast, DPPC and DPPE monolayers remained virtually unaffected by LL-37, demonstrating its nonhemolytic activity and lipid discrimination. Specular x-ray reflectivity data yielded considerable differences in layer thickness and electron-density profile after addition of the peptide to DPPG monolayers, but little change was seen after peptide injection when probing monolayers composed of DPPC and DPPE. Grazing incidence x-ray diffraction demonstrated significant peptide insertion and lateral packing order disruption of the DPPG monolayer by LL-37 insertion. Epifluorescence microscopy data support these findings.

Effects of pure n-alkanes and crude oil on bacterial phospholipid classes and molecular species determined by electrospray ionization mass spectrometry

Phospholipids are major components of bacterial membrane. Furthermore, the growth in vitro on xenobiotics such as n-alkanes, aromatic compounds or alkanols bring about to a bacterial membrane adaptive response. Concerning this work, we studied the membrane lipid composition of a hydrocarbon-degrading gram-positive bacterium (Corynebacterium sp.) on a soluble substrate and we detected four different phospholipid classes: phosphatidylglycerol, phosphatidylinositol, cardiolipin and acyl phosphatidylglycerol. In addition, a study of the lipid composition was performed after an in vitro culture on either pure n-alkane or crude oil. The growths on such hydrophobic substrates showed major qualitative and quantitative modifications. In the case of a growth on either heneicosane or crude oil, an increase of odd-numbered fatty acids was observed. Furthermore, the phospholipid polar head group composition was highly influenced by the crude oil addition. These modifications were, respectively, interpreted as the consequence of hydrocarbon assimilation and membrane fluidity adaptation. Finally, Corynebacterium sp. was taken back on the initial ammonium acetate substrate in order to determine its restoration abilities after a petroleum contamination.

The formation of cyclopropane fatty acids in Salmonella enterica serovar Typhimurium

The formation of cyclopropane fatty acid (CFA) and its role in the acid shock response inSalmonella entericaserovar Typhimurium (S. typhimurium) was investigated. Data obtained by GC/MS demonstrated that the CFA level inS. typhimuriumincreased upon its entry to the stationary phase, as in other bacteria. Thecfagene encoding CFA synthase was cloned, and mutants of thecfagene were constructed by allelic exchange. Acfamutant could not produce CFA and was sensitive to low pH. Introduction of a functionalcfagene into acfamutant cell made the mutant convert all unsaturated fatty acids to CFAs and partially restored resistance to low pH. Interestingly, the alternative sigma factor RpoS, which was induced during the stationary phase, affected the production of C19CFA but not C17CFA. Western blotting analysis showed that the increase in expression of CFA synthase at early stationary phase was due to the alternative sigma factor RpoS.

Use of electrospray ionization mass spectrometry for profiling of crude oil effects on the phospholipid molecular species of two marine bacteria

We investigated the membrane lipid composition of two hydrocarbon-degrading gram-negative bacterial strains (Pseudomonas nautica IP 617 and Marinobacter hydrocarbonoclasticus) initially cultured on a soluble substrate, then on petroleum hydrocarbons, and finally taken back onto the soluble substrate. For the two strains, the growth on petroleum and the return to the initial medium showed major, but comparable, qualitative and quantitative modifications of the intact phospholipid molecular species (IPMS) composition. Furthermore, since bacterial membranes are mainly made up of phospholipids, these modifications reflected hydrocarbon assimilation, restoration abilities and membrane fluidity adaptation. The electrospray ionization mass spectrometry (ESI-MS) analysis of intact phospholipid provided some new information (e.g. sn fatty acyl chain distribution) that could not be assessed by the classical fatty acid analysis. Moreover, such information should be particularly helpful with regards to bacterial taxonomy and xenobiotic toxicity studies.

Inhibition of hyaluronan synthesis in Streptococcus equi FM100 by 4-methylumbelliferone

As observed previously in cultured human skin fibroblasts, a decrease of hyaluronan production was also observed in group C Streptococcus equi FM100 cells treated with 4-methylumbelliferone (MU), although there was no effect on their growth. In this study, the inhibition mechanism of hyaluronan synthesis by MU was examined using Streptococcus equi FM100, as a model. When MU was added to a reaction mixture containing the two sugar nucleotide donors and a membrane-rich fraction as an enzyme source in a cell-free hyaluronan synthesis experiment, there was no change in the production of hyaluronan. On the contrary, when MU was added to the culture medium of FM100 cells, hyaluronan production in the isolated membranes was decreased in a dose-dependent manner. However, when the effect of MU on the expression level of hyaluronan synthase was examined, MU did not decrease either the mRNA level of the has operon containing the hyaluronan synthase gene or the protein level of hyaluronan synthase. Solubilization of the enzyme from membranes of MU-treated cells and addition of the exogenous phospholipid, cardiolipin, rescued hyaluronan synthase activity. In the mass spectrometric analysis of the membrane phospholipids from FM100 cells treated with MU, changes were observed in the distribution of only cardiolipin species but not of the other major phospholipid, PtdGro. These results suggest that MU treatment may cause a decrease in hyaluronan synthase activity by altering the lipid environment of membranes, especially the distribution of different cardiolipin species, surrounding hyaluronan synthase.

Characterization of methanotrophic bacteria on the basis of intact phospholipid profiles

The intact phospholipid profiles (IPPs) of seven species of methanotrophs from all three physiological groups, type I, II and X, were determined using liquid chromatography/electrospray ionization/mass spectrometry. In these methanotrophs, two major classes of phospholipids were found, phosphatidylglycerol (PG) and phosphatidylethanolamine (PE) as well as its derivatives phosphatidylmethylethanolamine (PME) and phosphatidyldimethylethanolamine (PDME). Specifically, the type I methanotrophs, Methylomonas methanica, Methylomonas rubra and Methylomicrobium album BG8 were characterized by PE and PG phospholipids with predominantly C16:1 fatty acids. The type II methanotrophs, Methylosinus trichosporium OB3b and CSC1 were characterized by phospholipids of PG, PME and PDME with predominantly C18:1 fatty acids. Methylococcus capsulatus Bath, a representative of type X methanotrophs, contained mostly PE (89% of the total phospholipids). Finally, the IPPs of a recently isolated acidophilic methanotroph, Methylocella palustris, showed it had a preponderance of PME phospholipids with 18:1 fatty acids (94% of total). Principal component analysis showed these methanotrophs could be clearly distinguished based on phospholipid profiles. Results from this study suggest that IPP can be very useful in bacterial chemotaxonomy.

Metabolism and genetics of Helicobacter pylori: the genome era

The publication of the complete sequence of Helicobacter pylori 26695 in 1997 and more recently that of strain J99 has provided new insight into the biology of this organism. In this review, we attempt to analyze and interpret the information provided by sequence annotations and to compare these data with those provided by experimental analyses. After a brief description of the general features of the genomes of the two sequenced strains, the principal metabolic pathways are analyzed. In particular, the enzymes encoded by H. pylori involved in fermentative and oxidative metabolism, lipopolysaccharide biosynthesis, nucleotide biosynthesis, aerobic and anaerobic respiration, and iron and nitrogen assimilation are described, and the areas of controversy between the experimental data and those provided by the sequence annotation are discussed. The role of urease, particularly in pH homeostasis, and other specialized mechanisms developed by the bacterium to maintain its internal pH are also considered. The replicational, transcriptional, and translational apparatuses are reviewed, as is the regulatory network. The numerous findings on the metabolism of the bacteria and the paucity of gene expression regulation systems are indicative of the high level of adaptation to the human gastric environment. Arguments in favor of the diversity of H. pylori and molecular data reflecting possible mechanisms involved in this diversity are presented. Finally, we compare the numerous experimental data on the colonization factors and those provided from the genome sequence annotation, in particular for genes involved in motility and adherence of the bacterium to the gastric tissue.

Role of efflux pump(s) in intrinsic resistance of Pseudomonas aeruginosa: active efflux as a contributing factor to beta-lactam resistance

Wild-type strains of Pseudomonas aeruginosa are more resistant to various beta-lactam antibiotics as well as other agents than most enteric bacteria. Although resistance to compounds of earlier generations is explained by the synergism between the outer membrane barrier and the inducible beta-lactamase, it was puzzling to see significant levels of resistance to compounds that do not act as inducers or are not hydrolyzed rapidly by the chromosomally encoded enzyme. This intrinsic-resistance phenotype becomes enhanced in those strains with the so-called intrinsic carbenicillin resistance. In the accompanying paper (X.-Z. Li, D. M. Livermore, and H. Nikaido, Antimicrob. Agents Chemother. 38:1732-1741, 1994), we showed that active efflux played a role in the resistance, to various non-beta-lactam agents, of P. aeruginosa strains in general and that the efflux was enhanced in intrinsically carbenicillin-resistant strains. We show in this paper that, in comparison with the drug-hypersusceptible mutant K799/61, less benzylpenicillin was accumulated in wild-type strains of P. aeruginosa and that the accumulation levels were even lower in intrinsically carbenicillin-resistant strains. Deenergization by the addition of a proton conductor increased the accumulation level to that expected for equilibration across the cytoplasmic membrane. In intrinsically carbenicillin-resistant isolates, there was no evidence that either nonspecific or specific permeation rates of beta-lactams across the outer membrane were lowered in comparison with those of the more susceptible isolates. Furthermore, these carbenicillin-resistant isolates were previously shown to have no alteration in the level or the inducibility of beta-lactamase and in the affinity of penicillin-binding proteins. These data together suggest the involvement of an active efflux mechanism also in the resistance to beta-lactams. Hydrophilic beta-lactams with more than one charged group did not cross the cytoplasmic membrane readily. Yet one such compound, ceftriaxone, appeared to be extruded from the cells of more-resistant strains, although with this compound effects of proton conductors could not be shown. We postulate that wild-type strains of P. aeruginosa pump out such hydrophilic beta-lactams either from the periplasm or from the outer leaflet of the lipid bilayer of the cytoplasmic membrane, in a manner analogous to that hypothesized for multidrug resistance protein of human cancer cells (M.M. Gottesman and I. Pastan, Annu. Rev. Biochem. 62:385-427, 1993).

The growth phase-dependent synthesis of cyclopropane fatty acids in Escherichia coli is the result of an RpoS(KatF)-dependent promoter plus enzyme instability

The formation of cyclopropane fatty acids (CFAs) in Escherichia coli is a post-synthetic modification of the phospholipid bilayer that occurs predominantly as cultures enter the stationary phase of growth. The mechanism of this growth phase-dependent regulation of CFA synthesis was unclear, since log-phase and stationary-phase cultures had been reported to contain similar levels of the enzyme catalysing the reaction (CFA synthase). We report that the timing of CFA synthesis can be explained by two unusual features. Fist, the gene encoding CFA synthase (cfa) was found to be transcribed from two promoters and the 5' ends of both transcripts were mapped by primer extension. One of the promoters was active only during the log-to-stationary phase transition and depended on the putative sigma factor encoded by the rpoS(katF) gene whereas the other promoter had a standard sigma 70 promoter consensus sequence and was expressed throughout the growth curve. Second, CFA synthase activity was shown to be unstable in vivo and a Cfa fusion protein was found to have a half life of < 5 min. The combination of these factors meant that, although CFA synthase was synthesized throughout the growth curve, a large increase in activity occurred during the log-to-stationary phase transition. As stationary phase progressed, the increased CFA synthase activity rapidly declined to the basal level. This transient increase in CFA synthase activity coupled with the cessation of net phospholipid synthesis in stationary phase provides an explanation for the unusual time course of CFA synthesis.

Microbial fatty acids and thermal adaptation

The existing literature on the role of fatty acids in microbial temperature adaptation is reviewed. Several modes of change of cellular fatty acids at varying environmental temperatures are shown to exist in yeasts and fungi, Gram-negative bacteria, and bacteria containing iso- and anteiso-branched fatty acids, as well as in a few Gram-positive bacteria. Consequently, the degree of fatty acid unsaturation and cyclization, fatty acid chain length, branching, and cellular fatty acid content increase, decrease, or remain unaltered on lowering the temperature. Moreover, microorganisms seem to be able to change from one mode or alter the cellular fatty acid profile temperature dependently to another on lowering the temperature, as well as even within the same growth temperature range, depending on growth conditions. Therefore, the effect of the temperature on cellular fatty acids appears to be more complicated than known earlier. However, similarities found in the modes of change of cellular fatty acids at varying environmental temperatures in several microorganisms within the above mentioned groups support the existence of a limited amount of common regulatory mechanisms. The models presented enable the prediction of temperature-induced changes occurring in the fatty acids of microorganisms, and enzymatic steps of the fatty acid biosynthesis that possibly are under temperature control.

Lipid metabolism in anaerobic ecosystems

In anaerobic ecosystems, acyl lipids are initially hydrolyzed by microbial lipases with the release of free fatty acids. Glycerol, galactose, choline, and other non-fatty acid components released during hydrolysis are fermented to volatile fatty acids by the fermentative bacteria. Fatty acids are not degraded further in the rumen or other parts of the digestive tract but are subjected to extensive biohydrogenation especially in the rumen. However, in environments such as sediments and waste digestors, which have long retention times, both long and short chain fatty acids are beta-oxidized to acetate by a special group of bacteria, the H2-producing syntrophs. Long chain fatty acids can also be degraded by alpha-oxidation. Biotransformation of bile acids, cholesterol, and steroids by intestinal microorganisms is extensive. Many rumen bacteria have specific growth requirements for fatty acids such as n-valeric, iso-valeric, 2-methylbutyric, and iso-butyric acids. Some species have requirements for C13 to C18 straight-chain saturated or monoenoic fatty acids for growth.

Brucella abortus 16S rRNA and lipid A reveal a phylogenetic relationship with members of the alpha-2 subdivision of the class Proteobacteria

On the basis of ribosomal 16S sequence comparison, Brucella abortus has been found to be a member of the alpha-2 subdivision of the class Proteobacteria (formerly named purple photosynthetic bacteria and their nonphototrophic relatives). Within the alpha-2 subgroup, brucellae are specifically related to rickettsiae, agrobacteria, and rhizobiae, organisms that also have the faculty or the obligation of living in close association to eucaryotic cells. The composition of Brucella lipid A suggests a close phylogenetical relationship with members of the alpha-2 group. The chemical analysis of the lipid A fraction revealed that Brucella species contain both glucosamine and diaminoglucose, thus suggesting the presence of a so-called mixed lipid A type. The serological analysis with polyclonal and monoclonal antibodies is in agreement with the existence of mixed lipid A type in B. abortus. The amide-linked fatty acid present as acyl-oxyacyl residues were 3-O-C(16:0)12:0, 3-O-C(16:0)13:0, 3-O-C(16:0)14:0, and 3-O-C(18:0)14:0. The only amide-linked unsubstituted fatty acid detected was 3-OH-C16:0. The ester-linked fatty acids are 3-OH-C16:0, 3-OH-C18:0, C16:0, C17:0, and C18:0. Significant amounts of the large-chain 27-OH-C28:0 were detected together with traces of 25-OH-C26:0 and 29-OH-C30:0. Comparison of the Brucella lipid composition with that of the other Proteobacteria also suggests a close phylogenetical relationship with members of the alpha-2 subdivision. The genealogical grouping of Brucella species with pericellular and intracellular plant and animal pathogens as well as with intracellular plant symbionts suggests a possible evolution of Brucella species from plant-arthropod-associated bacteria.

Morphological detection of filipin-sterol complexes in the cytoplasmic membrane of staphylococcal L-form

Filipin, a sterol-specific antibiotic, and freeze-fracture electron microscopy were used to study the presence and distribution of sterol in the cytoplasmic membrane of stable staphylococcal L-form cells. Fixed cells were treated with filipin, and then observed by freeze-fracture electron microscopy. Freeze-fractured profiles of the L-form cells treated with filipin demonstrated irregular distribution of protuberances or pits of 25-30 nm, representing filipin-sterol complexes, on the proto-plasmic fracture face (PF) and exoplasmic fracture face (EF) of the cytoplasmic membrane. In contrast, no such structure was detected in the filipin-treated parent cells or protoplasts. The results suggest that some sterol molecules, which are usually not found in staphylococcal or other bacterial cells, emerged on the cytoplasmic membrane after the cells were converted to the stable L-form.

Effect of acceptor membrane phosphatidylcholine on the catalytic activity of bovine liver phosphatidylcholine transfer protein

Protein-mediated transfer of phosphatidylcholine (PC) by bovine liver phosphatidylcholine transfer protein (PC-TP) was examined using a vesicle-vesicle assay system. Donor and acceptor membranes were prepared from Escherichia coli phospholipids and limiting amounts of egg yolk PC. PC transfer between vesicles of E. coli lipid/egg PC was markedly higher than transfer of PC from vesicles of E. coli lipid/egg PC to vesicles of E. coli lipid. Kinetic parameters of the interaction between PC-TP and E. coli lipid vesicles with or without PC was investigated. The apparent dissociation constants of the complex formed between PC-TP and these vesicles were determined kinetically and from double-reciprocal plots of intrinsic PC-TP fluorescence intensity increase versus vesicle concentration. The magnitude of the dissociation constant decreased as the PC content of the vesicles increased from 0 to 5 mol%. In addition, kinetic analysis revealed that the presence of PC in acceptor vesicles increased both the association and dissociation of PC-TP from vesicles. The effect of membrane PC molecules on transfer rates was examined using bis-phosphatidylcholine, a dimeric PC molecule which is not transferred by PC-TP. Rates of PC transfer to acceptor vesicles comprised of E. coli lipid/bis-PC were virtually identical to rates observed with acceptors vesicles prepared from E. coli lipid. The results suggest that transfer of PC by PC-TP is enhanced only when insertion of protein-bound PC occurs concurrently with the extraction of a molecule of membrane PC, i.e., a concerted, one-step catalytic mechanism for phospholipid exchange.

Chlorinated fatty acid distribution in Mycobacterium convolutum phospholipids after growth on 1-chlorohexadecane

The composition of phospholipids from Mycobacterium convolutum R22 was determined after growth at two temperatures (20 and 30 degrees C) with 1-chlorohexadecane as the substrate. Comparisons were made with the phospholipids of cells grown on n-hexadecane. Phosphatidylinositolmannosides and phosphatidylethanolamine (PE) were the major phospholipids in n-hexadecane-grown cells. In 1-chlorohexadecane-grown cells, phosphatidylinositolmannosides were approximately half of the total phospholipids, with lesser amounts of PE and cardiolipin (CL). The relative level of PE was greater at 20 degrees C (versus that at 30 degrees C) after growth on either substrate. A determination was made of structure and positional distribution of constituent fatty acid in both CL and PE. The relative amount of unsaturated fatty acid was higher at 20 degrees C. There were two C16:1 fatty acids (C16:1 delta 9 and C16:1 delta 11), and these had positional preferences in both CL and PE. The positional sites of chlorinated fatty acids differed in both CL and PE at the two temperatures. The results confirm that microorganisms can specifically distribute chlorinated fatty acids into cellular phospholipids.

Enhanced chlorine resistance of tap water-adapted Legionella pneumophila as compared with agar medium-passaged strains

Previous studies have shown that bacteria maintained in a low-nutrient "natural" environment such as swimming pool water are much more resistant to disinfection by various chemical agents than strains maintained on rich media. In the present study a comparison was made of the chlorine (Cl2) susceptibility of hot-water tank isolates of Legionella pneumophila maintained in tap water and strains passaged on either nonselective buffered charcoal-yeast extract or selective differential glycine-vancomycin-polymyxin agar medium. Our earlier work has shown that environmental and clinical isolates of L. pneumophila maintained on agar medium are much more resistant to Cl2 than coliforms are. Under the present experimental conditions (21 degrees C, pH 7.6 to 8.0, and 0.25 mg of free residual Cl2 per liter, we found the tap water-maintained L. pneumophila strains to be even more resistant than the agar-passaged isolates. Under these conditions, 99% kill of tap water-maintained strains of L. pneumophila was usually achieved within 60 to 90 min compared with 10 min for agar-passaged strains. Samples from plumbing fixtures in a hospital yielded legionellae which were "super"-chlorine resistant when assayed under natural conditions. After one agar passage their resistance dropped to levels of comparable strains which had not been previously exposed to additional chlorination. These studies more closely approximate natural conditions than our previous work and show that tap water-maintained L. pneumophila is even more resistant to Cl2 than its already resistant agar medium-passaged counterpart.

Role of granulocyte oxygen products in damage of Schistosoma mansoni eggs in vitro

The objectives of this study were to describe the ultrastructure of granulocyte-Schistosoma mansoni egg interaction and to determine the role of reduced oxygen products as effectors of cell-mediated damage to the parasite target. Granulocytes attached to the parasites and closely applied their plasma membranes to the microspicules of the egg shell 30 min after mixing in the presence of immune serum. By 4 h, the egg shell was fractured and granulocyte pseudopodia extended toward the underlying miracidium. Granulocyte attachment to eggs resulted in release of O2- (0.30-0.52 nmol/min per 2 X 10(6) cells) and accumulation of H2O2 (0.14-0.15 nmol/min) in the presence of antibody or complement. Granulocytes reduced egg tricarboxylic-acid cycle activity and hatching by 28.3 +/- 0.9 and 35.2 +/- 2.8%, respectively (cell-egg ratio of 1,000: 1). Exogenous superoxide dismutase (10 micrograms/ml) inhibited granulocyte toxicity for egg metabolic activity (3.0 +/- 2.1% reduction in acetate metabolism vs. 28.3 +/- 0.9% decrease in controls without superoxide dismutase, P less than 0.0005) and hatching (12.5 +/- 1.8% reduction, P less than 0.0005), whereas catalase and heparin had no effect. Inhibitors of myeloperoxidase (1 mM azide, cyanide, and methimazole) augmented granulocyte-mediated toxicity of egg tricarboxylic-acid cycle activity (44-58% reduction in activity vs. 31 and 35% reduction in controls), suggesting that H2O2 released from cells was degraded before reaching the target miracidium. Oxidants generated by acetaldehyde (2 mM)-xanthine oxidase (10 mU/ml) also decreased egg metabolic activity and hatching by 62.0 +/- 9.0 and 38.7 +/- 7.3%, respectively. Egg damage by the cell-free system was partially prevented by superoxide dismutase (26.5 +/- 4.2% reduction in egg tricarboxylic-acid activity) and completely blocked by catalase (0% reduction in activity). These data suggest that granulocyte-mediated toxicity for S. mansoni eggs is dependent on release of O2- or related molecules. These oxygen products, unlike H2O2, may readily reach the target miracidium where they may be converted to H2O2 or other microbicidal effector molecules.

Phosphoglycerides and phospholipase C in membrane fractions of Escherichia coli B

The phospholipid composition and the phospholipase C activity of envelope fractions of Escherichia coli B were determined with special consideration of fractions containing sites at which an attachment of inner and outer membranes had been observed in the electron microscope (Int.M). Phosphoglycerides labeled with [14C]palmitic acid and [3H]serine were extracted from membrane fractions and identified by two-dimensional thin-layer chromatography. The amount of phosphatidylethanolamine was highest in the outer membrane, whereas the amounts of phosphatidylglycerol and cardiolipin were highest in the inner membrane. The Int.M fractions were observed to have concentrations of phospholipids intermediate to those of the inner and outer membranes. This result supports the assumption that a concentration gradient of inner membrane-outer membrane lipids might exist at the membrane contact sites. The highest phospholipase C activity was detected in the inner membrane and Int.M fractions. The presence of phospholipase C and other lipolytic enzymes in the Int.M fractions suggests a possible involvement of adhesion sites in lipid metabolism, adding a further set of activities to the function of these domains.

Effects of replacement of a double bond by a cyclopropane ring in phosphatidylethanolamines: a 2H NMR study of phase transitions and molecular organization

The thermotropic behavior and molecular properties of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-dihydrosterculoyl-sn-glycero-3-phosphoethanolamine (PDSPE) have been investigated by 2H NMR spectroscopy using samples selectively labeled at the 5'-, 9'-, 10'-, and 16'-positions of the sn-2 chains. Comparison with the corresponding phosphocholine analogues (POPC and PDSPC), obtained as intermediate synthetic products, was used to monitor the role of the polar head group. Replacement of the choline moiety by ethanolamine increased the gel to liquid-crystal transition temperature by 10-32 degrees C and led to a significantly higher ordering of the fatty acyl chains in the liquid-crystalline bilayer state. The lateral compression effect, due to the smaller area per polar head group in PE, results in a bilayer to hexagonal phase transition at elevated temperatures. The effects on both PC and PE due to replacement of the olefinic group by a cyclopropane unit are similar. A decrease in the temperature of the gel to liquid-crystal phase transition, Tc, is observed upon introduction of a cyclopropane ring; it goes from 26 degrees C in POPE to approximately 10 degrees C in PDSPE. In addition, a very significant broadening of the transition profile is observed. These observations are consistent with the poor packing ability of mixed saturated and cyclopropane-containing chains due to the bulky substituent effect. The temperature of the bilayer-hexagonal phase transition of PE samples was decreased by 15-20 degrees C on replacement of oleoyl chains by dihydrosterculoyl chains at the sn-2 position.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of the Legionella pneumophila outer membrane

A whole cell lysate of Legionella pneumophila was fractionated into five membrane fractions by sucrose gradient centrifugation. Membranes were characterized by enzymatic, chemical, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Two forms of cytoplasmic membrane (CM-1, CM-2), a band of intermediate density (IM), and two forms of outer membrane (OM-1, OM-2) were detected. The CM-1 fraction was the purest form of cytoplasmic membrane, and fraction CM-2 was primarily cytoplasmic membrane associated with small amounts of peptidoglycan. The IM, CM-1, and CM-2 fractions were enriched in peptidoglycan, and the amount of carbohydrate and 2-keto-3-deoxyoctonic acid was not appreciably greater in outer membrane relative to cytoplasmic membrane. Phosphatidylethanolamine and phosphatidylcholine were found to be the major phospholipids in the membrane fractions. The major outer membrane proteins had molecular sizes of 29,000 and 33,000 daltons and were both modified by heating. The 29,000-dalton protein was tightly associated with the peptidoglycan and was equally distributed in the IM, OM-1, and OM-2.

Cloning and manipulation of the Escherichia coli cyclopropane fatty acid synthase gene: physiological aspects of enzyme overproduction

Like many other eubacteria, cultures of Escherichia coli accumulate cyclopropane fatty acids (CFAs) at a well-defined stage of growth, due to the action of the cytoplasmic enzyme CFA synthase. We report the isolation of the putative structural gene, cfa, for this enzyme on an E. coli-ColE1 chimeric plasmid by the use of an autoradiographic colony screening technique. When introduced into a variety of E. coli strains, this plasmid, pLC18-11, induced corresponding increases in CFA content and CFA synthase activity. Subsequent manipulation of the cfa locus, facilitated by the insertion of pLC18-11 into a bacteriophage lambda vector, allowed genetic and physiological studies of CFA synthase in E. coli. Overproduction of this enzyme via multicopy cfa plasmids caused abnormally high levels of CFA in membrane phospholipid but no discernable growth perturbation. Infection with phage lambda derivatives bearing cfa caused transient overproduction of the enzyme, although pL-mediated expression of cfa could not be demonstrated in plasmids derived from such phages. CFA synthase specific activities could be raised to very high levels by using cfa runaway-replication plasmids. A variety of physiological factors were found to modulate the levels of CFA synthase in normal and gene-amplified cultures. These studies argue against several possible mechanisms for the temporal regulation of CFA formation.

Lipids of supragingival calculus

The matrix of supragingival calculus constitutes 15.7% of the calculus dry weight and contains 54.9% protein and 10.2% lipids. Of the total lipids, 61.8% are represented by neutral lipids, 28% by glycolipids, and 10.2% by phospholipids. The neutral lipids exhibit a high content of free fatty acids (63.9%) and triglycerides (15.8%). The glycolipids are comprised of simple glycosphingolipids (17.2%), mainly lactosyl- and glucosylceramides, and of neutral and sulfated glyceroglucolipids (82.8%). The phospholipids contain large quantities of phosphatidylethanolamine (34.2%) and diphosphatidylglycerol (25.5%). Comparison with salivary and submandibular stone lipids indicates that both saliva and bacteria contribute to the lipid content of supragingival calculus.

Ethanol-induced changes in the membrane lipid composition of Clostridium thermocellum

When ethanol is added to the growth medium of Clostridium thermocellum ATCC 27405 and C9, a different membrane composition is observed after the period of growth arrest. Changes in fatty acid composition and some unsaturated, branched hydrocarbons have been monitored by GLC-MS. There is a marked increase in normal and anteiso-branched fatty acids at the expense of isobranched fatty acids and an increase in short and unsaturated fatty acids. Thus, an adaptive response to growth in the presence of ethanol induces a membrane containing fatty acids with lower melting points and produces a more 'fluid' membrane. The suggestion is made that these membrane changes may be maladaptive to the performance of C. thermocellum.