Changes in fatty acid composition and degree of unsaturation of (brady)rhizobia as a response to phases of growth, reduced water activities and mild desiccation

The effects of growth phase, reductions in the water activity (a _w) of the growth medium and mild desiccation on the composition and the degree of unsaturation of cellular fatty acids (CFA) of Sinorhizobium meliloti, Bradyrhizobium elkaniiand Bradyrhizobium japonicum were studied. During the course of growth, an interchange of cis-vaccenic with lactobacillic acid and a slight increase in palmitic acid were observed while other fatty acids remained constant. The degree of unsaturation was significantly higher in the exponential phase of growth. Reductions in the a _w of the medium led to an increase in lag phase, a reduction in growth rate and maximal optical densities (OD) in stationary phase cells. A decrease in the degree of unsaturation of CFA was also observed as the a _w was reduced from 0.999 to 0.969 and after desiccation to 83.5% relative humidity (R.H.). The changes in the degree of unsaturation of CFA observed after growth at reduced a _w may be one of the pre-adaptation steps to endure more severe desiccation.     

Desiccation responses and survival of Sinorhizobium meliloti USDA 1021 in relation to growth phase, temperature, chloride and sulfate availability

AIMS: To identify physical and physiological conditions that affect the survival of Sinorhizobium meliloti USDA 1021 during desiccation. METHODS AND RESULTS: An assay was developed to study desiccation response of S. meliloti USDA 1021 over a range of environmental conditions. We determined the survival during desiccation in relation to (i) matrices and media, (ii) growth phase, (iii) temperature, and (iv) chloride and sulfate availability. CONCLUSIONS: This study indicates that survival of S. meliloti USDA 1021 during desiccation is enhanced: (i) when cells were dried in the stationary phase, (ii) with increasing drying temperature at an optimum of 37 degrees C, and (iii) during an increase of chloride and sulfate, but not sodium or potassium availability. In addition, we resolved that the best matrix to test survival was nitrocellulose filters. SIGNIFICANCE AND IMPACT OF THE STUDY: The identification of physical and physiological factors that determine the survival during desiccation of S. meliloti USDA 1021 may aid in (i) the strategic development of improved seed inocula, (ii) the isolation, and (iii) the development of rhizobial strains with improved ability to survive desiccation. Furthermore, this work may provide insights into the survival of rhizobia under drought conditions.     

Evidence of membrane lipid oxidation of spray-dried Lactobacillus bulgaricus during storage

P. TEIXEIRA, H. CASTRO AND R. KIRBY. 1996. Membrane fatty acids of Lactobacillus bulgaricus were analysed by gas-liquid chromatography before and after spray drying. The ratio unsaturated/saturated fatty acids decreased following spray drying, indicating the formation of lesions in cellular lipid-containing structures. The same method was used to analyse membrane lipids of Lact. bulgaricus during storage. Similarly the ratio of unsaturated/saturated fatty acids in dried cells decreased further during storage in air, presenting evidence of lipid oxidation after prolonged storage. The mechanisms of cell death during storage in the dried state are still unknown, but from these results and those presented in the literature, it seems evident that lipid oxidation and survival during storage may be related.     

The NodA proteins of Rhizobium meliloti and Rhizobium tropici specify the N-acylation of Nod factors by different fatty acids

Rhizobia synthesize mono- N -acylated chitooligosaccharide signals, called Nod factors, that are required for the specific infection and nodulation of their legume hosts. The biosynthesis of Nod factors is under the control of nodulation ( nod ) genes, including the nodABC genes present in all rhizobial species. The N -acyl substitution can vary between species and can play a role in host specificity. In Rhizobium meliloti , an alfalfa symbiont, the acyl chain is a C16 unsaturated or a (ω-1) hydroxylated fatty acid, whereas in Rhizobium tropici , a bean symbiont, it is vaccenic acid (C18:1). We constructed R. meliloti derivatives having a non-polar deletion of nodA , and carrying a plasmid with either the R. meliloti or the R. tropici nodA gene. The strain with the R. tropici nodA gene produced Nod factors acylated by vaccenic acid, instead of the C16 unsaturated or hydroxylated fatty acids characteristic of R. meliloti Nod factors, and infected and nodulated alfalfa with a significant delay. These results show that NodA proteins of R. meliloti and R. tropici specify the N -acylation of Nod factors by different fatty acids, and that allelic variation of the common nodA gene can contribute to the determination of host range.     

Effect of ammonium ions on spiramycin biosynthesis in Streptomyces ambofaciens

The physiological significance of trans unsaturated fatty acids, which are constituents of membrane lipids of the phenol-degrading bacterium Pseudomonas putita P8, was studied. The addition of phenol or phenol derivatives to the cells induced the formation of trans unsaturated fatty acids, yielding an overall maximal amount of 41.3% of total fatty acids. The inhibition of de-novo lipid synthesis by cerulenin prevented the change in the degree of saturation in the lipids. However, the cells could still respond to phenols with an amplified conversion of cis into trans unsaturated fatty acids, which is apparently a post-synthesis mechanism of isomerization of the double bond. The cis/trans conversion correlated with growth inhibition induced by toxic concentrations of 4-chlorophenol, whereas only growing cells were able to change the degree of saturation. In cells that were protected against phenol by immobilization in calcium alginate, the conversion of cis into trans fatty acids occurred at higher toxin concentrations compared with free cells. Cells entering the stationary growth phase increased the prodortion of saturated to unsaturated fatty acids but maintained a constant trans/cis ratio.P. putida P8 reacted to an increase or decrease in the growth temperature with an appropriate change in the ratio of saturated to unsaturated fatty acids and in cells inhibited by cerulenin with a change in the trans/cis ratio. This study shows that the physiological role of the cis/trans conversion is probably the regulation of membrane fluidity when the most important mechanism for this, the modification of the degree of saturation, cannot by used by the cells due to inhibition of growth and lipid biosynthesis. Correspondence to: H. Keweloh     

Early recognition in the Rhizobium meliloti-alfalfa symbiosis: root exudate factor stimulates root adsorption of homologous rhizobia.

Adsorption of Rhizobium meliloti to alfalfa roots before their infection and nodule formation shows the specificity of the symbiotic association (G. Caetano-Anollés and G. Favelukes, Appl. Environ. Microbiol. 52:377-382, 1986). The time course of specific adsorption of R. meliloti (10(3) to 10(4) cells per ml) to roots shows an initial lag period of 3 h, suggesting that either or both symbionts must become conditioned for the adsorption process. Preincubation of R. meliloti L5-30 for 3 h with dialyzed alfalfa root exudate (RE) markedly increased early adsorption of rhizobia to alfalfa roots. The activity in RE was linked to a nondialyzable, thermolabile, trypsin-sensitive factor(s), very different from the root-exuded flavonoid compounds also involved in early Rhizobium-legume interactions. The lack of activity in the RE from plants grown in 5 mM NO3- suggested its negative regulation by the nitrogen nutritional status of the plant. Preincubation of R. meliloti with heterologous clover RE did not stimulate adsorption of rhizobial cells to roots. A short pretreatment of RE with homologous (but not heterologous) strains eliminated the stimulatory activity from solution. The stimulation of adsorption of R. meliloti to alfalfa roots was strongly dependent on the growth phase of the rhizobia, being greater at the late exponential stage. Nevertheless, the capacity of R. meliloti L5-30 to eliminate from solution the stimulatory activity in RE appeared to be constitutive in the rhizobia. The low concentration of rhizobial cells used in these experiments was critical to detect the stimulation of adsorption. The early interaction of spontaneously released alfalfa root macromolecular factor(s) and free-living R. meliloti, which shows the specificity and regulatory properties characteristic of infection and nodulation, would be an initial recognition event in the rhizosphere which triggers the process of symbiotic association.     

Modulation of Opioid Receptor Binding by Cis and Trans Fatty Acids

In synaptosomal brain membranes, the addition of oleic acid (cis), elaidic acid (trans), and the cis and trans isomers of vaccenic acid, at a concentration of 0.87 mumol of lipid/mg of protein, strongly reduced the Bmax and, to a lesser degree, the binding affinity of the mu-selective opioid [3H]Tyr-D-Ala-Gly-(Me)Phe-Gly-ol ([3H]DAMGO). At comparable membrane content, the cis isomers of the fatty acids were more potent than their trans counterparts in inhibiting ligand binding and in decreasing membrane microviscosity, both at the membrane surface and in the core. However, trans-vacenic acid affected opioid receptor binding in spite of just marginally altering membrane microviscosity. If the receptors were uncoupled from guanine nucleotide regulatory protein, an altered inhibition profile was obtained: the impairment of KD by the fatty acids was enhanced and that of Bmax reduced. Receptor interaction of the delta-opioid [3H](D-Pen2,D-Pen5)enkephalin was modulated by lipids to a greater extent than that of [3H]DAMGO: saturable binding was abolished by both oleic and elaidic acids. The binding of [3H]naltrexone was less susceptible to inhibition by the fatty acids, particularly in the presence of sodium. In the absence of this cation, however, cis-vaccenic acid abolished the low-affinity binding component of [3H]naltrexone. These findings support the membrane model of opioid receptor sequestration depicting different ionic environments for the mu- and delta-binding sites. The results of this work show distinct modulation of different types and molecular states of opioid receptor by fatty acids through mechanisms involving membrane fluidity and specific interactions with membrane constituents.     

Comparison of the effect of individual saturated and unsaturated fatty acids on cell growth and death induction in the human pancreatic beta-cell line NES2Y

We tested the effects of various types of fatty acids, differing in the degree of saturation and in the cis/trans configuration of the double bond, on the growth and viability of NES2Y cells (a human pancreatic beta-cell line). We found that during a 48-hour incubation period, saturated fatty acids, i.e. palmitic and stearic acids, at a physiologically relevant concentration of 1 mM and higher concentrations induced death of the beta-cells while their counterpart unsaturated fatty acids, i.e. palmitoleic and oleic acids, did not induce cell death at concentrations up to 3 mM. We also found that unsaturated elaidic acid with a trans double bond exerted significant inhibition of growth of the beta-cells at a concentration approximately ten times lower, i.e. 0.1 mM vs. 1 mM, than counterpart oleic acid with a cis double bond. This is the first direct evidence that a trans unsaturated fatty acid is significantly more effective in inhibiting beta-cell growth than a counterpart cis unsaturated fatty acid. Furthermore, we newly demonstrated that beta-cell death induced by saturated fatty acids is related to significant increase of caspase-2 activity (2 to 5-fold increase) but not to caspase-3 activation. The growth-inhibiting effect of saturated fatty acids at concentrations lower than death-inducing concentrations correlates with certain increase of caspase-2 activity.     

Poly-3-hydroxybutyrate (PHB) supports survival and reproduction in starving rhizobia

The carbon that rhizobia in root nodules receive from their host powers both N₂ fixation, which mainly benefits the host, and rhizobium reproduction. Rhizobia also store energy in the lipid poly-3-hydroxybutyrate (PHB), which may enhance rhizobium survival when they are carbon limited, either in nodules or in the soil between hosts. There can be a conflict of interest between rhizobia and legumes over the rate of PHB accumulation, due to a metabolic tradeoff between N₂ fixation and PHB accumulation. To quantify the benefits of PHB to carbon-limited rhizobia, populations of genetically uniform rhizobia with high vs. low PHB (confirmed by flow cytometry) were generated by fractionating Sinorhizobium meliloti via density gradient centrifugation, and also by harvesting cells at early vs. late stationary phase. These rhizobia were starved for 165 days. PHB use during starvation was highly predictive of both initial reproduction and long-term population maintenance. Cultured S. meliloti accumulated enough PHB to triple their initial population size when starved, and to persist for c . 150 days before the population fell below its initial value. During the first 21 days of nodule growth, undifferentiated S. meliloti within alfalfa nodules accumulated enough PHB to support significant increases in reproduction and survival during starvation.     

Wastewater sludge as a substrate for growth and carrier for rhizobia: the effect of storage conditions on survival of Sinorhizobium meliloti

The inoculation of legumes with rhizobia is used to maximise nitrogen fixation and enhance the plant yield without using N fertilisers. For this reason many inoculant types were developed and optimised. In our study, the effects of the growth medium, the carrier, the temperature and the storage period were determined on the survival of Sinorhizobium meloliti. Secondary sludge from Communauté Urbaine de Quebec wastewater treatment plant and standard medium (YMB) were used for rhizobial growth. Dehydrated sludge from Jonquière wastewater treatment plant, peat and a mixture of peat and sludge were used as carrier materials. Results showed that the wastewater sludge offered better protection for rhizobia survival during freezing and thawing at -20 degrees C than the standard medium. In general, results also showed the suitability of using sludge as a carrier because it had the same or a higher potential than peat to support survival of S. meliloti. In the case of YMB-grown rhizobia, peat- and sludge-based carriers appeared to be similar in terms of survival rate during the storage at 4 and 25 degrees C. For secondary sludge-grown rhizobia, the survival was better in sludge than in peat based carrier. Generally, the cell count remained higher than 10(8) cells/g for up to 80 days at 4 and 25 degrees C in both carriers (sludge and peat). However, for the secondary sludge-grown cells stored in peat-based carrier at 4 degrees C, the viable cells decreased under 10(8) cells/g at the 81st day of storage but remained acceptable compared to the standard (10(7) cells/g of carrier).     

Pseudomonas putida NCTC 10936 balances membrane fluidity in response to physical and chemical stress by changing the saturation degree and the trans/cis ratio of fatty acids

This study explored the capability of Pseudomonas putida NCTC 10936 to maintain homeoviscosity after changing the growth temperature, incubating resting cells at different temperatures or at a constant temperature in the presence of 4-chlorophenol (4-CP). After raising the growth temperature from 20 to either 30 or 35 degrees C, the degree of saturation of the organism's fatty acids increased and the ratio of trans to cis unsaturated fatty acids decreased somewhat. In contrast, after the incubation temperature of resting cells was raised (grown at 30 degrees C) from 20 to 30 or 35 degrees C the degree of saturation of the fatty acids remained nearly constant, while the ratio of trans to cis unsaturated fatty acids increased. Incubating resting cells (grown at 30 degrees C) at 20 degrees C in the presence of 4-CP again caused no major changes in the degree of saturation, but cis to trans conversion of unsaturated fatty acids was induced, with a corresponding increase in the trans/cis ratios. Increases in both the saturation degree of the fatty acids and the trans/cis ratio of the unsaturated fatty acids correlated with increases in the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene intercalated in the bilayers of liposomes prepared from the cells of P. putida NCTC 10936. Electron transport phosphorylation (ETP) could be stabilized by adaptive adjustments in the fluidity of the cytoplasmic membrane mediated by changes in fatty acid composition such as those observed. Whether changes in the degree of saturation or in the trans/cis ratio are more effective can be decided by studying P. putida NCTC 10936.     

Temperature- and growth-phase-dependent changes in membrane fatty acid compositions of Brevibacterium ammoniagenes

Fatty acids newly synthesized by Brevibacterium ammoniagenes grown at different temperatures were analyzed. The assay temperature, not the growth temperature, was found to be the major factor affecting the unsaturated/saturated ratio of newly synthesized fatty acids in logarithmic-phase cells. However, in the stationary-phase cells the growth temperature also affected the product profile significantly; cells grown at 7 degrees C produced relatively more oleate and stearate and less palmitate and hexadecenoate when shifted up to 37 degrees C than did cells grown and assayed at 37 degrees C. The unsaturated/saturated ratio as well as average chain length of fatty acids also varied along with the progress of isothermal growth phase. These changes in fatty acid product profiles observed in vivo could be mimicked in vitro assays of the fatty acid synthetase by changing malonyl-CoA concentrations. Our results suggest that the malonyl-CoA concentration is a factor which, in addition to temperature, determines growth-phase-dependent and growth-temperature-dependent changes in the unsaturated/saturated ratios of fatty acids.     

Characteristics of a lipolytic and fatty acid-requiring Butyrivibrio sp. isolated from the ovine rumen.

A naturally occurring fatty acid-requiring Butyrivibrio sp. (strain S2), isolated from the ovine rumen, deacylates plant galactolipids, phospholipids and sulpholipids to obtain sufficient fatty acid for growth. Growth in vitro was promoted by adding to the growth medium a single straight-chain saturated fatty acid (C13 to C18) or vaccenic acid. Palmitoleic and oleic acids also supported growth but gave lengthy lag phases probably due to their toxicity. Linolenic and linoleic acids supported good growth but they were completely hydrogenated to trans-11-octadecenoic acid which was incorporated into the bacterial complex lipids. No chain elongation, chain shortening or desaturation of the added fatty acids occurred and all were substantially incorporated into bacterial lipids of the plasmalogen type, partially as a new type of hydrophobic grouping derived from two molecules of fatty acid. The absence of fatty acid unsaturation poses the question of the maintenance of membrane fluidity within this bacterium.     

Biochemical characterization of Sinorhizobium meliloti mutants reveals gene products involved in the biosynthesis of the unusual lipid A very long-chain fatty acid

Sinorhizobium meliloti forms a symbiosis with the legume alfalfa, whereby it differentiates into a nitrogen-fixing bacteroid. The lipid A species of S. meliloti are modified with very long-chain fatty acids (VLCFAs), which play a central role in bacteroid development. A six-gene cluster was hypothesized to be essential for the biosynthesis of VLCFA-modified lipid A. Previously, two cluster gene products, AcpXL and LpxXL, were found to be essential for S. meliloti lipid A VLCFA biosynthesis. In this paper, we show that the remaining four cluster genes are all involved in lipid A VLCFA biosynthesis. Therefore, we have identified novel gene products involved in the biosynthesis of these unusual lipid modifications. By physiological characterization of the cluster mutant strains, we demonstrate the importance of this gene cluster in the legume symbiosis and for growth in the absence of salt. Bacterial LPS species modified with VLCFAs are substantially less immunogenic than Escherichia coli LPS species, which lack VLCFAs. However, we show that the VLCFA modifications do not suppress the immunogenicity of S. meliloti LPS or affect the ability of S. meliloti to induce fluorescent plant defense molecules within the legume. Because VLCFA-modified lipids are produced by other rhizobia and mammalian pathogens, these findings will also be important in understanding the function and biosynthesis of these unusual fatty acids in diverse bacterial species.     

Synthesis and utilization of fatty acids by wild-type and fatty acid auxotrophs of Caulobacter crescentus.

The fatty acid composition of the dimorphic bacterium Caulobacter crescentus was found to consist primarily of 16- and 18-carbon fatty acids, both saturated and monounsaturated, in agreement with the findings of Chow and Schmidt (J. Gen. Microbiol. 83:359-373, 1974). In addition, two minor but as yet unidentified fatty acids were detected. Chromatographic mobilities suggested that these fatty acids may be a cyclopropane and a branched-chain fatty acid. In addition, we demonstrated that the fatty acid composition of wild-type C. crescentus can be altered by growing the cells in medium supplemented with any one of a variety of unsaturated fatty acids. Linoleic acid, a diunsaturated fatty acid which is not synthesized by C. crescentus, was incorporated into phospholipids without apparent modification. In addition, we found that C. crescentus, like Escherichia coli, synthesizes vaccenic acid (18:1 delta 11,cis) rather than oleic acid (18:1 delta 9,cis). This result allowed us to deduce that the mechanism of fatty acid desaturation in C. crescentus is anaerobic, as it is in E. coli. Finally, we examined the fatty acid biosynthesis and composition of two unsaturated fatty acid auxotrophs of C. crescentus. Neither of these mutants resembled the E. coli unsaturated fatty acid auxotrophs, which have defined enzymatic lesions in fatty acid biosynthesis. Rather, the mutants appeared to have defects relating to the complex coordination of membrane biogenesis and cell cycle events in C. crescentus.     

Phospholipid ester-linked fatty acid profile changes during nutrient deprivation of Vibrio cholerae: increases in the trans/cis ratio and proportions of cyclopropyl fatty acids

The phospholipid ester-linked fatty acids of 0-day-, 7-day-, and 30-day-starved cultures of Vibrio cholerae were compared. Statistically significant trends were noted in the fatty acid profiles as the cells starved. The amount of the cis-monoenoic fatty acids declined (e.g., 16:1 omega 7c: 0 day, 39%; 7 day, 18%; 30 day, 11%). In contrast, the saturated fatty acids, the cyclopropyl derivatives of the cis-monoenoic fatty acids, and trans-monoenoic fatty acids increased during starvation. For instance, the amounts of 16:1 omega 7t were: 0 day, 1%; 7 day, 13%; 30 day, 17%; which increased the trans/cis ratio for 16:1 omega 7 from 0.02 (0 day) to 0.70 (7 day) to 1.56 (30 day). This may be due to the reported high turnover rates of cis-monoenoic fatty acids of membrane phospholipids and the availability of enzymes for the metabolism of these isomers. During starvation-induced phospholipid loss, the cis-monoenoic fatty acids would, therefore, be preferentially utilized. The ability to either synthesize trans-monoenoic acids (which are not easily metabolized by bacteria) or modify the more volatile cis-monoenoic acids to their cyclopropyl derivatives may be a survival mechanism which helps maintain a functional (although structurally altered) membrane during starvation-induced lipid utilization. In addition, a trans/cis fatty acid ratio significantly greater than that reported for most bacterial cultures and environmental samples (less than 0.1) may be used as a starvation or stress lipid index. Such a ratio could help determine the nutritional status of ultramicrobacteria and other reported dormant cells in natural aquatic environments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phospholipid ester-linked fatty acid profile changes during nutrient deprivation of Vibrio cholerae: increases in the trans/cis ratio and proportions of cyclopropyl fatty acids.

The phospholipid ester-linked fatty acids of 0-day-, 7-day-, and 30-day-starved cultures of Vibrio cholerae were compared. Statistically significant trends were noted in the fatty acid profiles as the cells starved. The amount of the cis-monoenoic fatty acids declined (e.g., 16:1 omega 7c: 0 day, 39%; 7 day, 18%; 30 day, 11%). In contrast, the saturated fatty acids, the cyclopropyl derivatives of the cis-monoenoic fatty acids, and trans-monoenoic fatty acids increased during starvation. For instance, the amounts of 16:1 omega 7t were: 0 day, 1%; 7 day, 13%; 30 day, 17%; which increased the trans/cis ratio for 16:1 omega 7 from 0.02 (0 day) to 0.70 (7 day) to 1.56 (30 day). This may be due to the reported high turnover rates of cis-monoenoic fatty acids of membrane phospholipids and the availability of enzymes for the metabolism of these isomers. During starvation-induced phospholipid loss, the cis-monoenoic fatty acids would, therefore, be preferentially utilized. The ability to either synthesize trans-monoenoic acids (which are not easily metabolized by bacteria) or modify the more volatile cis-monoenoic acids to their cyclopropyl derivatives may be a survival mechanism which helps maintain a functional (although structurally altered) membrane during starvation-induced lipid utilization. In addition, a trans/cis fatty acid ratio significantly greater than that reported for most bacterial cultures and environmental samples (less than 0.1) may be used as a starvation or stress lipid index. Such a ratio could help determine the nutritional status of ultramicrobacteria and other reported dormant cells in natural aquatic environments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stable-isotope-based labeling of styrene-degrading microorganisms in biofilters

Deuterated styrene ([(2)H(8)]styrene) was used as a tracer in combination with phospholipid fatty acid (PLFA) analysis for characterization of styrene-degrading microbial populations of biofilters used for treatment of waste gases. Deuterated fatty acids were detected and quantified by gas chromatography-mass spectrometry. The method was evaluated with pure cultures of styrene-degrading bacteria and defined mixed cultures of styrene degraders and non-styrene-degrading organisms. Incubation of styrene degraders for 3 days with [(2)H(8)]styrene led to fatty acids consisting of up to 90% deuterated molecules. Mixed-culture experiments showed that specific labeling of styrene-degrading strains and only weak labeling of fatty acids of non-styrene-degrading organisms occurred after incubation with [(2)H(8)]styrene for up to 7 days. Analysis of actively degrading filter material from an experimental biofilter and a full-scale biofilter by this method showed that there were differences in the patterns of labeled fatty acids. For the experimental biofilter the fatty acids with largest amounts of labeled molecules were palmitic acid (16:0), 9,10-methylenehexadecanoic acid (17:0 cyclo9-10), and vaccenic acid (18:1 cis11). These lipid markers indicated that styrene was degraded by organisms with a Pseudomonas-like fatty acid profile. In contrast, the most intensively labeled fatty acids of the full-scale biofilter sample were palmitic acid and cis-11-hexadecenoic acid (16:1 cis11), indicating that an unknown styrene-degrading taxon was present. Iso-, anteiso-, and 10-methyl-branched fatty acids showed no or weak labeling. Therefore, we found no indication that styrene was degraded by organisms with methyl-branched fatty fatty acids, such as Xanthomonas, Bacillus, Streptomyces, or Gordonia spp.     

Production of butter fat rich in trans10-C18:1 for use in biomedical studies in rodents

Trans fatty acids are suspected to be detrimental to health, particularly to cardiovascular function. Trans fatty acids include a wide range of fatty acids, with isomers of C18:1, conjugated and non-conjugated C18:2 as major components. A vaccenic acid (trans11-C18:1) + rumenic acid (cis9,trans11-CLA)-rich butter has been shown previously to exhibit health beneficial effects, but less is known concerning another trans-C18:1 present in hydrogenated vegetable oil-based products and sometimes in milk fat, the trans10-isomer. The present experiment was conducted to produce butters from milk of variable fatty acid composition for use in biomedical studies with rodents, with the overall aim of evaluating the specific effect of trans10-C18:1 and trans11-C18:1 + cis9,trans11-CLA on cardiovascular function. Milks from lactating dairy cows fed two types of maize-based diets supplemented (5% of dry matter)--or not--with sunflower oil were collected, and used to manufacture butters either rich in trans10-C18:1 (14% of total fatty acids, 64.5% of fat content) or rich in trans11-C18:1 + cis9,trans11-CLA (7.4 and 3.1% of total fatty acids, respectively, 68.5% of fat content), or with standard fatty acid composition (70% of fat content). Additionally, total saturated fatty acid percentage was reduced by more than one third in the enriched butters compared with the standard butter. An understanding of the role of nutrition on milk fatty acid composition in cows allows for the production of dairy products of variable lipid content and composition for use in biomedical studies in animal models and human subjects.     

The hydrogenation of phospholipid-bound unsaturated fatty acids by a homogeneous, water-soluble, palladium catalyst

The hydrogenation of unsaturated phospholipids by palladium di(sodium alizarine monosulphonate) activated for 5 min under H2 proceeded rapidly at 20 degrees C and 1 atm. H2. Multibilayer liposomes of dioleoyl- and dilinolenoylphosphatidylcholine were hydrogenated at similar rates while dilinoleoyl- and 1-palmitoyl-2-oleoylphosphatidylcholine were hydrogenated at slightly slower rates. The reduction of polyunsaturated fatty acids gave rise to a variety of natural and unnatural positional cis and trans isomers which were largely reduced further to saturated fatty acids as the hydrogenation continued. Dioleoylphosphatidylethanolamine was attacked by the catalyst more slowly at 20 degrees C than was the equivalent phosphatidylcholine molecular species. Experiments conducted using mixtures of phosphatidylethanolamine and phosphatidylcholine in varying proportions also suggested that phospholipids are slightly more susceptible to catalytic hydrogenation in the bilayer phase than in the hexagonalII phase. Understanding the sequence of hydrogenation reactions involving these one and two component lipid preparations is useful in interpreting the action of the palladium catalyst on living cells under the same mild conditions.