The effect of salt on the lipid composition of Ectothiorhodospira

Major components of polar lipids of halophilic phototrophic Ectothiorhodospira species were PG, CL, PC and PE. PA was only present in minor amounts. According to ¹⁴C-incorporation, polar lipids approximated to 75%–93% of the total lipid carbon. With increasing salinity, a strong increase in the portion of PG and a decrease in that of PE (especially in Ectothiorhodospira mobilis BN 9903) and CL (especially in E. halophila strains) were observed. Moreover, there was a significant increase in the excess negative charges of phospholipids upon increasing medium salinity. This increase was most dramatic in the slightly halophilic E. mobilis BN 9903, but quantitatively less important in both strains of E. halophila which had, however, a higher percentage of negative charges of their lipids. During salt-shift experiments, E. halophila BN 9630 responded to suddenly increased salinity by promoting the biosynthesis of PG and decreasing that of PC, CL and PE. Upon dilution stress, responses were reversed and resulted in a strong increase in PE biosynthesis. The effects of lipid charges and bilayer forming forces in stabilizing the membranes of Ectothiorhodospira species during salt stress are discussed.Abbreviations PC phosphatidylcholine - PG, PG-1, PG-2 phosphatidylglycerol - CL, CL-1, Cl-2 cardiolipin - PE phosphatidylethanol-amine - PA phosphatidic acid - NL nonpolar lipids - ori origin - TLC thin layer chromatography     

Occurrence and dynamics of phototrophic purple nonsulphur bacteria compared with other asymbiotic nitrogen fixers in ricefields of Egypt

The occurrence and the dynamics of phototrophic purple nonsulphur bacteria (PPNSB) as well as Azospirillum, Azotobacter, Clostridium, and cyanobacteria at different rice growth stages were studied in two ricefields, at Kafr-El-Shiekh and Al-Fayoum in Egypt.The PPNSB existed in the both rice fields examined, but their numbers varied according to field conditions, habitat and rice growth stage. After transplanting, the number of PPNSB increased gradually, reached its maximum at maximum tillering stage, and thereafter declined toward harvest time. Numbers of PPNSB were generally comparable with that of the heterotrophic N₂-fixers namely Azospirillum, Azotobacter, Clostridium and cyanobacteria, while that of phototrophic purple and green sulphur bacteria were relatively lower.The highest PPNSB numbers were generally found in rhizosphere (10³–10⁶ per g^–1 dw soil) followed by soil (10³–10⁵ per g^–1 dw soil) and floodwater (10–10² per ml). Rice plants showed a positive rhizosphere effect on PPNSB, clostridia, Azotobacter and Azospirillum, negative rhizosphere effect on cyanobacteria and green sulphur bacteria, and no effect on purple sulphur bacteria.     

DNA-DNA and rRNA-DNA hybridization studies in the genus Ectothiorhodospira and other purple sulfur bacteria

DNA-DNA hybridization reveals low DNA homologies (about 14%) between the species of Ectothiorhodospira genus and indicate clearly that the degree of divergence within this genus exceeds the interspecific level. The degree of genome similarities of E. mobilis and E. vacuolata (more than 80% homology) is high and characteristic for the strains of one and the same species.The results of rRNA-DNA and secondary DNA-DNA hybridization indicate the following: Ectothiorhodospira and Thiocapsa are far less related than the genera of one and the same family; the genus Ectothiorhodospira is equidistant from both families of purple sulfur and nonsulfur bacteria. Thus Ectothiorhodospira is a taxon of a higher rank than a genus; we agree with Imhoff's proposal of a new family Ectothiorhodospiraceae.     

The lipopolysaccharide of the phototrophic bacterium Ectothiorhodospira vacuolata

The lipopolysaccharide of Ectothiorhodospira vacuolata was obtained by the phenol-water procedure. It contained a 3-O-methyl-hexose, glucose, galacturonic and glucuronic acids. The finding of d-glycero-d-mannoheptose and 2-keto-3-deoxyoctonate (tentatively identified) suggested a core-structure. The lipid fraction of the lipopolysaccharide contained phosphate and both, 2,3-diamino-2,3-dideoxy-d-glucose and d-glucosamine. The major fatty acids were amine-bound 3-OH-10:0 and 3-OH-12:0 and esterbound 14:0 and 16:0 Sodium deoxycholate gel-electrophoresis, showing a single band only, indicated R-type character of the lipopolysaccharide of Ectothiorhodospira vacuolata.Abbreviations DOC sodium deoxycholate - GC/MS combined gasliquid chromatography - PAGE polyacrylamide gel-electrophoresis     

Expression study with the Escherichia coli lep gene for leader peptidase in phototrophic purple bacteria

Synthesis and assembly of leader peptidase of Escherichia coli (signal peptidase I), was studied by heterologous expression of its lep gene in three species of phototrophic purple bacteria. Cell extracts of the recipient species showed neither cross reaction with antibodies against E. coli leader peptidase nor cleavage of the model substrate M13-procoat in vitro. The lep gene was transferred via conjugation using the plasmid expression vector for phototrophic bacteria pJAJ9. Plasmidborne leader peptidase enzyme was identified by immunochemical means. However, extracts of transconjugant cells showed no cleavage function. Trypsin digestion studies revealed that the enzyme was not properly integrated across the host membranes. The data suggest that cleaving enzymes for protein export and/or their assembly pathway in purple bacteria differ from the E. coli type.Abbreviations DMSO dimethylsulfoxide - EDTA ethylenediamine tetraacetic acid - PAGE polyacrylamide gel electrophoresis - PMSF phenylmethylsulfonyl fluoride - SDS sodium dodecyl sulfate     

Association of a new type of gliding,filamentous, purple phototrophic bacterium inside bundles of Microcoleus chthonoplastes in hypersaline cyanobacterial mats

An unidentified filamentous purple bacterium, probably belonging to a new genus or even a new family, is found in close association with the filamentous, mat-forming cyanobacterium Microcoleus chthonoplastes in a hypersaline pond at Guerrero Negro, Baja California Sur, Mexico, and in Solar Lake, Sinai, Egypt. This organism is a gliding, segmented trichome, 0.8–0.9 m wide. It contains intracytoplasmic stacked lamellae which are perpendicular and obliquely oriented to the cell wall, similar to those described for the purple sulfur bacteria Ectothiorhodospira. These bacteria are found inside the cyanobacterial bundle, enclosed by the cyanobacterial sheath. Detailed transmission electron microscopical analyses carried out in horizontal sections of the upper 1.5 mm of the cyanobacterial mat show this cyanobacterial-purple bacterial association at depths of 300–1200 m, corresponding to the zone below that of maximal oxygenic photosynthesis. Sharp gradients of oxygen and sulfide are established during the day at this microzone in the two cyanobacterial mats studied. The close association, the distribution pattern of this association and preliminary physiological experiments suggest a co-metabolism of sulfur by the two-membered community. This probable new genus of purple bacteria may also grow photoheterotrophically using organic carbon excreted by the cyanobacterium. Since the chemical gradients in the entire photic zone fluctuate widely in a diurnal cycle, both types of metabolism probably take place. During the morning and afternoon, sulfide migrates up to the photic zone allowing photoautotrophic metabolism with sulfide as the electron donor. During the day the photic zone is highly oxygenated and the purple bacteria may either use oxidized species of sulfur such as elemental sulfur and thiosulfate in the photoautotrophic mode or grow photoheterotrophically using organic carbon excreted by M. chthonoplastes. The new type of filamentous purple sulfur bacteria is not available yet in pure culture, and its taxonomical position cannot be fully established. This organism is suggested to be a new type of gliding, filamentous, purple phototroph.     

Effect of growth temperature on the fatty acid composition of Mycobacterium phlei

In Mycobacterium phlei, fatty acid unsaturation increased with decreasing temperature. The 10-hexadecenoic acid content increased as the temperature was reduced from 35°C to 26–20°C. At lower temperatures tuberculostearic acid decreased while oleic and linoleic acids increased, the latter being found in M. phlei for the first time. Concomitantly palmitic acid content decreased, and the 6- and 9-hexadecenoic acids increased slightly on reducing the temperature from 35 to 10°C. Thus, down to 26–20°C palmitic acid was mainly replaced by 10-hexadecenoic acid. From this range down to 10°C, palmitic and tuberculostearic acids were replaced by oleic and linoleic acids. Consequently, fatty acid branching decreased and mean chain length increased, as the temperature was reduced. These observations support the view that regulation of membrane fatty acid composition is part of microbial temperature adaptation, and that themechanism behind the responses might be more complex than generally believed.Abbreviations ACP acyl carrier protein - FAS I (Type I) fatty acid synthetase I - FAS II (Type II) fatty acid synthetase II - MGLP methylglucose containing lipopolysaccharide - MMP methylmannose containning polysaccharide     

Effect of growth phase on the fatty acid composition of Thermus spp.

Two yellow and two red pigmented strains of Thermus were monitored for changes in fatty acid content and composition with reference to growth phase at the optimum temperature. Fatty acid content per mg of dry weight increased as the cultures aged. In addition the quantities of iso C 15:0, iso C 17:0 and iso C 16:0 increased in yellow pigmented strains, but in red pigmented strains, an increase was seen in iso C 15:0, but C 16:0 and iso C 16:0 levels decreased. Thus the fatty acid composition of these organisms varies with growth phase, and shows also strain specific variability.     

-Amino acid contents of mitochondria and some purple bacteria

The endosymbiont most likely to have given rise to mitochondria is an aerobic bacterium belonging to the α subdivision of the so-called purple bacteria such as Rickettsia, Bradythizobium and Agrobacterium [1 and 2]. Contents of the -enantiomers of serine, alanine, proline, glutamate and aspartate in rat liver whole mitochondria, mitochondrial outer membranes, inner membranes and matrix, soluble proteins and free amino acids were detected. These values for -amino acid content were compared with those in soluble proteins and free amino acids from the purple bacteria Paracoccus denitrificans, Pseudomonas aeruginosa and Escherichia coli, members, respectively of the α, β, and γ subdivisions, to find any similarity between mitochondria and these purple bacteria. A similarity was observed in protein -amino acid contents which were low (<1.5%, D-type/D-type+L-type) both in the membrane and soluble protein fractions from mitochondria and in soluble protein from bacteria. Oddly, substantial amounts of free -serine and free -aspartate (around 2%) were found for the first time in mitochondria. The contents of -serine and -aspartate were higher than those of -alanine, -proline and -glutamate. In purple bacteria, the concentration of -serine (<2%) was the lowest of the five amino acids examined, and those of -alanine (27–32%) and -glutamate (7–26%) were high. Therefore, no similarity was shown in the free -amino acid content between mitochondria and any of the three purple bacteria.     

Influence of culture temperature on the growth,biochemical composition and fatty acid profiles of six Antarctic microalgae

The growth, biochemical composition and fatty acid profiles of six Antarctic microalgae cultured at different temperatures, ranging from 4, 6, 9, 14, 20 to 30 ^∘C, were compared. The algae were isolated from seawater, freshwater, soil and snow samples collected during our recent expeditions to Casey, Antarctica, and are currently deposited in the University of Malaya Algae Culture Collection (UMACC). The algae chosen for the study were Chlamydomonas UMACC 229, Chlorella UMACC 234, Chlorella UMACC 237, Klebsormidium UMACC 227, Navicula UMACC 231 and Stichococcus UMACC 238. All the isolates could grow at temperatures up to 20 ^∘C; three isolates, namely Navicula UMACC 231 and the two Chlorella isolates (UMACC 234 and UMACC 237) grew even at 30 ^∘C. Both Chlorella UMACC 234 and Stichococcus UMACC 238 had broad optimal temperatures for growth, ranging from 6 to 20 ^∘C (μ = 0.19 – 0.22 day^–1) and 4 to 14 ^∘C (μ = 0.13 – 0.16 day^–1), respectively. In contrast, optimal growth temperatures for NaviculaUMACC 231 and Chlamydomonas UMACC 229 were 4 ^∘C (μ = 0.34 day^–1) and 6–9 ^∘C (μ = 0.39 – 0.40 day^–1), respectively. The protein content of the Antarctic algae was markedly affected by culture temperature. All except Navicula UMACC 231 and Stichococcus UMACC 238 contained higher amount of proteins when grown at low temperatures (6–9 ^∘C). The percentage of PUFA, especially 20:5 in Navicula UMACC 231 decreased with increasing culture temperature. However, the percentages of unsaturated fatty acids did not show consistent trend with culture temperature for the other algae studied.     

Effect of choline chloride on fatty acid chain ordering in membranes of wheat (Triticum aestvium L. cv. Miranovskaja 808)

A winter variety (Miranovskaja 808) of wheat (Triticum aestivum L.) was grown in water cultures containing 0, 5, 15, 30, and 60 mM choline chloride. There was an increase in the phosphatidylcholine level at the expense of phosphatidic acid, parallel with an increasing choline concentration in the cultivating medium. While the ratio of free sterols to phospholipids remained essentially constant in the seedlings, there was an increase in the ratio of saturated-to-unsaturated fatty acids of the phospholipid fraction. Probing the protoplasts obtained from the leaves of the seedlings, with spin labeled 5-doxyl- and 16-doxyl stearic acids, indicated a progressive rigidifying of the hydrophobic core of the plasmalemma. It is suggested that this is a manifestation of compensatory mechanisms by which plants attempt to maintain unchanged average membrane fluidity across their membranes in response to the fluidizing effect of choline head groups.     

Impact of salt adaptation on esterified fatty acids and cytochrome oxidase in plasma and thylakoid membranes from the cyanobacterium Anacystis nidulans

During adaptation of photoautotrophically growing fresh water cyanobacterium Anacystis nidulans to high salinity the cells showed a pronounced increase of proton-sodium antiporter activity, and of cytochrome c oxidase in isolated and purified plasma membrane. At the same time the concentrations of plasma membrane-bound EDTA-resistant copper and iron (determined by inductively coupled plasma atomic emission spectrometry) rose proportionately, accompanied by an increase in whole cell respiration. In plasma membranes from salt adapted cells lipid/protein ratios were markedly higher than in control cells, levels of esterified saturated and long-chain fatty acids being significantly higher than the respective levels of unsaturated and short-chain fatty acids which explains the higher lipid-phase transition temperatures derived from Arrhenius plots. Immunoblotting of the membrane proteins with antisera raised against the cytochrome c oxidases from Paracoccus denitrificans and A. nidulans gave two cross-reacting bands with apparent molecular weights around 50000 and 30000 (subunits I and II, respectively) which were more pronounced in plasma membranes from salt adapted cells when compared to control cells. The protein pattern of plasma membranes from salt adapted cells also showed the appearance of bands at apparent molecular weights of 44000–48000 and 54000–56000 which might stem from the proton/sodium-antiporter in this membrane.Abbreviations CM cytoplasmic or plasma membrane - ICM intracytoplasmic or thylakoid membrane - cyt cytochrome - DCCD N,N-dicyclohexylcarbodiimide - Hepes N-2-hydroxyethylpiperazine-N-2-ethanesulfonate - ICP-AES inductively coupled plasma atomic emission spectrometry - SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis - EPR electron paramagnetic resonance spectrometry     

Degradation of the compatible solute trehalose in Ectothiorhodospira halochloris: isolation and characterization of trehalase

Trehalase, which hydrolyzes the disaccharide trehalose to -d-glucose was isolated and partially purified (124-fold) from the phototrophic halo-alkaliphilic bacterium Ectothiorhodospira halochloris. The molecular mass was determined to be 480,000 and the isoelectric point pH 5.6. Temperature optimum was found to be 40°C and the pH-optimum 7.8–8.1. In spite of its high K _m-value of 0.5 M, trehalase of E. halochloris was shown to be specific for trehalose. Trehalase is activated by phosphate which is, however, not involved in the reaction mechanism. The enzyme is activated by the compatible solute betaine and inhibited by salts. In the presence of betaine the K _m-value is lowered from 0.5 M to 0.16 M; moreover, betaine partially protects enzymatic activity from salt inhibition. The findings indicate that betaine might regulate the trehalose level in the cells by affecting trehalase activity.     

Fatty acid composition of selected prosthecate bacteria

The cellular fatty acid composition of 14 strains of Caulobacter species and types, two species of Prosthecomicrobium, and two species of Asticcacaulis was determined by gas-liquid chromatography. In most of these bacteria, the major fatty acids were octadecenoic acid (C18:1), hexadecenoic acid (C16:1) and hexadecanoic acid (C16:0). Some cyclopropane and branched chain fatty acids were detected in addition to the straight chained acids. Hydroxytetradecanoic acid was an important component of P. enhydrum but significant amounts of hydroxy acids were not detected in other prosthecate bacteria examined.Abbreviations DEGS diethylene glycol succinate - A measare of association Dedicated to Prof. R. Y. Stanier on the occasion of his 60th birthday     

Salt-induced changes in lipid composition and membrane fluidity of halophilic yeast-like melanized fungi

The halophilic melanized yeast-like fungi Hortaea werneckii, Phaeotheca triangularis, and the halotolerant Aureobasidium pullulans, isolated from salterns as their natural environment, were grown at different NaCl concentrations and their membrane lipid composition and fluidity were examined. Among sterols, besides ergosterol, which was the predominant one, 23 additional sterols were identified. Their total content did not change consistently or significantly in response to raised NaCl concentrations in studied melanized fungi. The major phospholipid classes were phosphatidylcholine and phosphatidylethanolamine, followed by anionic phospholipids. The most abundant fatty acids in phospholipids contained C₁₆ and C₁₈ chain lengths with a high percentage of C18:2^9,12. Salt stress caused an increase in the fatty acid unsaturation in the halophilic H. werneckii and halotolerant A. pullulans but a slight decrease in halophilic P. triangularis. All the halophilic fungi maintained their sterol-to-phospholipid ratio at a significantly lower level than did the salt-sensitive Saccharomyces cerevisiae and halotolerant A. pullulans. Electron paramagnetic resonance (EPR) spectroscopy measurements showed that the membranes of all halophilic fungi were more fluid than those of the halotolerant A. pullulans and salt-sensitive S. cerevisiae, which is in good agreement with the lipid composition observed in this study.Communicated by W.D. Grant     

Phospholipid composition and fatty acid desaturation in the roots of rye during acclimatization of low temperature

When the roots of rye plants grown at 20°C were cooled to 8°C the concentration of phospholipid in them more than doubled over a 7 d period in comparison with that in roots remaining at 20°C. The relative abundance of lecithin (PC) declined while that of phosphatidyl ethanolamine (PE) increased; this change was completed after 2 d cooling. Labelling with ³²P suggested that turnover of phospholipids may be inhibited by low temperature. Acyl lipids contained an increased proportion of linolenic acid (18:3) and reduced proportion of linoleic acid (18:2) when roots were cooled at 8°C for 7 d. The ratio of these acids is a relatively more sensitive indicator of desaturation than is the double bond index. Cooling brought about no change in the abundance of the principal saturated acid, palmitic (16:0). In the first 3 days of cooling PC and PE desaturated markedly while there was no change in galactosyl and neutral lipids. Desaturation did not appear to be greatly sensitive to the concentration of dissolved O₂ and was only partly inhibited in 8°C solutions where the oxygen concentration was lowered to 0.5–2.0%. Positional analysis of acyl chains in PC and PE showed that more than 90% of all 16:0 is associated with position I while 65% of the 18:2+18:3 is associated with position II. When roots are cooled the abundance of 18:3 increases in both chains but the relative distribution of saturated and unsaturated fatty acids remains constant in positions I and II. At both 20°C and 8°C there is a high probability that a saturated chain in position I will be paired with the polyunsaturated one in position II.Abbreviations PC Lecithin - PE phosphatidyl ethanolamine - TLC thin layerchromatography - BHT butylatedhydroxytoluene     

The role of fatty acid unsaturation in minimizing biophysical changes on the structure and local effects of bilayer membranes

Studying the effects of saturated and unsaturated fatty acids on biological and model (liposomes) membranes could provide insight into the contribution of biophysical effects on the cytotoxicity observed with saturated fatty acids. In vitro experiments suggest that unsaturated fatty acids, such as oleate and linoleate, are less toxic, and have less impact on the membrane fluidity. To understand and assess the biophysical changes in the presence of the different fatty acids, we performed computational analyses of model liposomes with palmitate, oleate, and linoleate. The computational results indicate that the unsaturated fatty acid chain serves as a membrane stabilizer by preventing changes to the membrane fluidity. Based on a Voronoi tessellation analysis, unsaturated fatty acids have structural properties that can reduce the lipid ordering within the model membranes. In addition, hydrogen bond analysis indicates a more uniform level of membrane hydration in the presence of oleate and linoleate as compared to palmitate. Altogether, these observations from the computational studies provide a possible mechanism by which unsaturated fatty acids minimize biophysical changes and protect the cellular membrane and structure. To corroborate our findings, we also performed a liposomal leakage study to assess how the different fatty acids alter the membrane integrity of liposomes. This showed that palmitate, a saturated fatty acid, caused greater destabilization of liposomes (more “leaky”) than oleate, an unsaturated fatty acid.     

Changing fatty acid composition during somatic embryogenesis in cultures of Daucus carota

The fatty acid composition of five embryo stages following the induction of embryogenesis in cultures of Daucus carota have been studied. Quantitative rather than qualitative changes in fatty acid content were observed, although globular embryos do possess some fatty acids of long (C 20 and above) chain length not observed in earlier or later stages in development. The major fatty acids present were C 16:0, 18:0, 18:1, 18:2 and 18:3.Abbreviations SM small meristematic - LV large vacuolated - GLC gas-liquid chromatography - TLC thin lager chromatography     

Variation of lipid and fatty acid compositions of the marine microalga Pavlova viridis (Prymnesiophyceae) under laboratory and outdoor culture conditions

The marine microalga Pavlova viridis (Prymnesiophyceae) is widely used in marine aquaculture industries of China for feeding bivalves and has been proposed as an alternative source of eicosapentaenoic acid (EPA). To investigate variation of its lipid and fatty acid compositions during laboratory and outdoor cultivation, a 60-1 photobioreactor was established in Nanjing, China. Outdoor cultivation, paralleled with laboratory cultures in mid-October, was performed from autumn through midwinter. The results showed that the total lipid and EPA contents of outdoor cultures were both lower than those of indoor cultures. When the outdoor temperature and illumination decreased, total lipid experienced no significant change. Although the level of saturated fatty acids decreased, polyunsaturated fatty acids, especially EPA, increased.     

Fatty acid compositions of arthropod and cephalopod photoreceptors: interspecific,seasonal and developmental studies

Fatty acid compositions of the compound eyes of insects (soldier-bug, Hemiptera, and silk moth, Lepidoptera), crustaceans (crayfish and grapsid crab, Decapoda) and inner and outer segments of visual cells of a squid (Cephalopoda, Mollusca) were analyzed by gaschromatography for interspecific comparison. Fatty acid compositions showed great variation among species. In insect compound eyes, 16:0 and 18:0 were the main saturated fatty acids, and 18:1 was the dominant unsaturated fatty acid. Silk moth eyes contained, in addition, considerable amounts of 18:2 and 20:5. In crustacean compound eyes, the main saturated fatty acids were 16:0 and 18:0, and 14:0 (5.0%) was only detected in grapsid crabs; the main unsaturated fatty acids were 20:4, 20:5 and 22:6. Both whole eyes and rhabdom fraction of crayfish showed similar profiles of fatty acid compositions. Both inner and outer segments of squid retinae were characterized by high amounts of unsaturated fatty acids, especially 22:6. Compound eyes of grapsid crabs were used for the experiments on seasonal changes of fatty acid compositions. UFA/SFA ratios (weight in % of unsaturated fatty acids saturated fatty acids) were lowest (1.0) in July and highest (2.5) in March, and unsaturation indexes (average number of double bonds per molecule) were lowest (1.5) in July and highest (2.3) in March. Fatty acids 18:0 and 20:1 showed a significant correlation with the changes of seasonal temperature. Fatty acid analysis of the developing compound eyes of silk moths during the pupal stage revealed that eicosapentanoic acid (20:5) increased remarkably in parallel with the development of photoreceptive membranes, the rhabdoms. This suggests that eicosapentaenoic acid may play an important role in formation and function of rhabdoms.