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.     

Competition between cis,trans and Cyclopropane Fatty Acid Formation and its Impact on Membrane Fluidity

The impact of cis, trans and cyclopropane fatty acids on membrane fluidity was investigated using batch‐grown Pseudomonas putida P8 and Comamonas testosteroni ATCC 17454. A major difference observed between the two investigated strains is the absence of the ability to synthesize trans‐unsaturated fatty acids in Comamonas. When grown exponentially at 30 °C, a shift to 35 °C increased the trans/cis ratios of the fatty acids of P. putida P8 from 0 to 0.81 and 0 to 1.07, in lipid extracts and cell hydrolyzates, respectively. After prolonged growth followed by nutrient deprivation for 48 h, both at 30 °C, trans fatty acids were absent, but the cyclo/cis ratios rose from 0.1 to 1.55 in lipid extracts, and from 0.1 to 1.54 in cell hydrolyzates. C. testosteroni ATCC 17454 contained no cyclo fatty acids when harvested in the exponential phase after 6 h, whereas after 72 h cultivation, the cyclo/cis ratios rose to 0.49 and 0.47, in lipid extracts and cell hydrolyzates, respectively. Trans fatty acids were never observed in this strain. Increased cyclo/cis and trans/cis ratios correlated with decreased fluidity measured by the fluorescence anisotropy of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) intercalated in the bilayers of liposomes and by Fourier Transform Infrared (FTIR) spectroscopy of lipids prepared from the cells. The specific effect of cyclopropane fatty acids on membrane fluidity was much smaller than that of trans fatty acids. FTIR‐measurements of intact cells of P. putida P8 confirmed the high potency of trans fatty acids to decrease the fluidity. In cells with induced cyclopropane fatty acid synthesis, the membranes remained more fluidized, indicating the lower importance of these fatty acids for homeoviscosis.     

Synthesis of trans unsaturated fatty acids in Pseudomonas putida P8 by direct isomerization of the double bond of lipids

The phospholipids of Pseudomonas putida P8 contain monounsaturated fatty acids in the cis and trans configuration. Cells of this phenol-degrading bacterium change the proportions of these isomers in response to the addition or elimination of a membrane active compound such as 4-chlorophenol. This study undoubtedly reveals that the cis unsaturated fatty acids are directly converted into trans isomers without involvement of de novo synthesis of fatty acids. Oleic acid, which cannot be synthesized by this bacterium, was incorporated as a cis unsaturated fatty acid marker in the membrane lipids of growing cells. The conversion of this fatty acid into the corresponding trans isomer was demonstrated by gas chromatographic-mass spectrometric analysis and use of ¹⁴C-labeled oleic acid. Separation and isolation of the cellular membranes showed that the fatty acid isomerase is located in the cytoplasmic membrane of P. putida P8.Abbreviation 4-CP 4-chlorophenol     

Adaptation of Pseudomonas putida S12 to ethanol and toluene at the level of fatty acid composition of membranes.

Pseudomonas putida S12 was more tolerant to ethanol when preadapted to supersaturating concentrations of toluene. Cellular reactions at the membrane level to the toxicities of both compounds were different. In growing cells of P. putida S12, sublethal concentrations of toluene resulted in an increase in the degree of saturation of the membrane fatty acids, whereas toxically equivalent concentrations of ethanol led to a decrease in this value. Contrary to this, cells also reacted to both substances with a strong increase of the trans unsaturated fatty acids and a corresponding decrease of the cis unsaturated fatty acids under conditions where growth and other cellular membrane reactions were totally inhibited. While the isomerization of cis to trans unsaturated fatty acids compensates for the fluidizing effect caused by ethanol, a decrease in the degree of saturation is antagonistic with respect to the chemo-physical properties of the membrane. Consequently, the results support the hypothesis that the decrease in the degree of saturation induced by ethanol is not an adaptation mechanism but is caused by an inhibitory effect of the compound on the biosynthesis of saturated fatty acids.     

Formation of trans Fatty Acids Is Not Involved in Growth-Linked Membrane Adaptation of Pseudomonas putida

Fatty acid compositions in growing and resting cells of several strains of Pseudomonas putida (P8, NCTC 10936, and KT 2440) were studied, with a focus on alterations of the saturation degree, cis-trans isomerization, and cyclopropane formation. The fatty acid compositions of the strains were very similar under comparable growth conditions, but surprisingly, and contrary to earlier reports, trans fatty acids were not found in either exponentially growing cells or stationary-phase cells. During the transition from growth to the starvation state, cyclopropane fatty acids were preferentially formed, an increase in the saturation degree of fatty acids was observed, and larger amounts of hydroxy fatty acids were detected. A lowered saturation degree and concomitant higher membrane fluidity seemed to be optimal for substrate uptake and growth. The incubation of cells under nongrowth conditions rapidly led to the formation of trans fatty acids. We show that harvesting and sample preparation for analysis could provoke the enzyme-catalyzed formation of trans fatty acids. Freeze-thawing of resting cells and increased temperatures accelerated the formation of trans fatty acids. We demonstrate that cis-trans isomerization only occurred in cells that were subjected to an abrupt disturbance without having the possibility of adapting to the changed conditions by the de novo synthesis of fatty acids. The cis-trans isomerization reaction was in competition with the cis-to-cyclopropane fatty acid conversion. The potential for the formation of trans fatty acids depended on the cyclopropane content that was already present.     

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.     

Conversion of cis unsaturated fatty acids to trans, a possible mechanism for the protection of phenol-degrading Pseudomonas putida P8 from substrate toxicity.

A trans unsaturated fatty acid was found as a major constituent in the lipids of Pseudomonas putida P8. The fatty acid was identified as 9-trans-hexadecenoic acid by gas chromatography, argentation thin-layer chromatography, and infrared absorption spectrometry. Growing cells of P. putida P8 reacted to the presence of sublethal concentrations of phenol in the medium with changes in the fatty acid composition of the lipids, thereby increasing the degree of saturation. At phenol concentrations which completely inhibited the growth of P. putida, the cells were still able to increase the content of the trans unsaturated fatty acid and simultaneously to decrease the proportion of the corresponding 9-cis-hexadecenoic acid. This conversion of fatty acids was also induced by 4-chlorophenol in nongrowing cells in which the de novo synthesis of lipids had stopped, as shown by incorporation experiments with labeled acetate. The isomerization of the double bond in the presence of chloramphenicol indicates a constitutively operating enzyme system. The cis-to-trans modification of the fatty acids studied here apparently is a new way of adapting the membrane fluidity to the presence of phenols, thereby compensating for the elevation of membrane permeability induced by these toxic substances.     

Conversion of cis unsaturated fatty acids to trans, a possible mechanism for the protection of phenol-degrading Pseudomonas putida P8 from substrate toxicity.

A trans unsaturated fatty acid was found as a major constituent in the lipids of Pseudomonas putida P8. The fatty acid was identified as 9-trans-hexadecenoic acid by gas chromatography, argentation thin-layer chromatography, and infrared absorption spectrometry. Growing cells of P. putida P8 reacted to the presence of sublethal concentrations of phenol in the medium with changes in the fatty acid composition of the lipids, thereby increasing the degree of saturation. At phenol concentrations which completely inhibited the growth of P. putida, the cells were still able to increase the content of the trans unsaturated fatty acid and simultaneously to decrease the proportion of the corresponding 9-cis-hexadecenoic acid. This conversion of fatty acids was also induced by 4-chlorophenol in nongrowing cells in which the de novo synthesis of lipids had stopped, as shown by incorporation experiments with labeled acetate. The isomerization of the double bond in the presence of chloramphenicol indicates a constitutively operating enzyme system. The cis-to-trans modification of the fatty acids studied here apparently is a new way of adapting the membrane fluidity to the presence of phenols, thereby compensating for the elevation of membrane permeability induced by these toxic substances.     

Mechanism for phenol tolerance in phenol-degrading Comamonas testosteroni strain

Comamonas testosteroni P15 and its mutant strain E23 can tolerate and utilize phenol as the sole source of carbon and energy at up to 15 mM and 20 mM, respectively. Compared to the wild type P15, mutant E23 showed higher values of K _s and K _i but a lower μ_max value, and had lower phenol hydroxylase and catechol 2,3-dioxygenase activities. Without phenol exposure, mutant E23 demonstrated a two-fold greater amount of cardiolipin than the wild type P15. Upon exposure to phenol, an increase in cardiolipin at the expense of phosphatidylethanolamine was observed in the wild type P15. However, there was no significant difference in major phospholipid contents between mutant E23 cells grown in the presence or absence of phenol. It was noted that the ratio of trans/cis fatty acids of phosphatidylethanolamine and cardiolipin in mutant E23 was 65–70% higher than that in the wild type P15. In the absence of phenol, the degree of saturation of cardiolipin in mutant E23 was 33% higher than that in wild type P15. In contrast to earlier findings, an increase in C16:1 9trans with a simultaneous decrease in C18:1 11cis instead of C16:1 9cis was observed in specific classes of phospholipids. Received: 30 July 1998 / Received last revision: 16 November 1998 / Accepted: 12 December 1998     

Diferulic acid as a component of cell walls of Lolium multiflorum

Trans,trans-, cis,trans- and cis,cis-diferulic acids were released from cell walls of Lolium multiflorum by treatment with sodium hydroxide. The isomers were apparently bound via ester links to the structural carbohydrates of the cell walls. Sodium hydroxide treatment gave, per g of wall, 0.18 mg trans,trans-diferulic, 0.02 mg cis,trans-diferulic and a trace of cis,cis-diferulic acids compared with 5.3 mg trans-ferulic, 1.2 mg cis-ferulic, 0.78 mg trans-p-coumaric and 0.12 mg cis-p-coumaric acids. The significance of these acids in lignin biosynthesis is discussed. The effect of UV light on the trans,trans isomer and its fully silylated trimethylsilyl either derivative was also investigated.     

The response of Pseudomonas putida CP1 cells to nutritional, chemical and environmental stresses

Summary The response of a pollutant-degrading bacterium P. putida CP1 to stresses was investigated. The growth on the mono-chlorophenols resulted in a decrease in dry weight of the organism, although there was an increase in cell number. There was a change of bacterial shape from rod to round as well as the reduction of cell size when grown on phenol and chlorophenols. Changes in cell shape and size were also evident in glucose-free medium, which suggested that alteration of cell shape from rod to round as well as reduction of cell size were due to nutritional stress. The increase in cell number but a drop in dry weight correlated with the reduction of cell size and shape. The organism flocculated with chlorophenols but not with phenol. The cause of flocculation was due to the toxicity of chlorophenol. Isomerization of cis to trans forms of the unsaturated fatty acids in P. putida CP1 occurred under conditions of environmental stress. Trace amounts of the polyunsaturated fatty acid linoleic acid (cis-9, cis-12-octadecadienoic acid) rarely found in bacterial membranes and oleic acid (cis-9-octadecanoic acid), which is a typical product of aerobic fatty acid synthesis, were found in P. putida CP1.     

The trans/cis ratio of unsaturated fatty acids is not applicable as biomarker for environmental stress in case of long-term contaminated habitats

Cis-trans isomerization of unsaturated fatty acids is a crucial adaptive reaction of Pseudomonas and Vibrio species to toxic organic compounds or other environmental stress factors. In order to test the long-term performance of this adaptive mechanism as well as to assess its application as biomarker for environmental contamination studies were performed in batch cultures and in continuously running sand columns, simulating long-term contamination with bisphenol A (BPA). In short-term grown batch cultures a high correlation between trans/cis ratio and added BPA concentration and toxicity was observed. In contrary, this did not occur in the case of long-term sand columns. An increase in trans/cis ratio of unsaturated fatty acids only appeared in a limited period of time. Afterwards the trans/cis ratio reached the values measured for non-stressed cultures. Cis-trans isomerization is only an urgent response mechanism that is later substituted by other adaptive mechanisms. Therefore, it can be concluded that the trans/cis ratio of unsaturated fatty acids was shown not to be an appropriate biomarker for durable stress in the environment.     

Effect of supplementation with exogenous fatty acid on the biological properties of a fatty acid requiring auxotroph ofSalmonella typhimurium

The effects of changes in fatty acid composition of the cell membrane on different biological functions ofSalmonella typhimurium have been studied with the help of a temperature sensitive fatty acid auxotroph which cannot synthesise unsaturated fatty acids at high temperature. On being shifted to nonpermissive temperature the cells continue growing for another one and half to two generations. The rates of protein and DNA syntheses run parallel to the growth rate but the rate of RNA synthesis is reduced. Further, there is a gradual reduction in the rate of transport of exogenous uridine and thymidine into the soluble pool. The transport process can be restored by supplementing the growth medium with cis-unsaturated fatty acids but not trans-unsaturated ones although the growth of the cells is resumed by supplementation with eithercis or trans-unsaturated fatty acids. However, supplementation withtrans, trans-unsaturated fatty acids leads to only partial recovery of the transport process. The rate of oxygen uptake is also affected in cells grown in the presence of thetrans-unsaturated fatty acids, elaidic acid and palmitelaidic acid. Analysis of cells grown under different fatty acid supplementation indicate that fatty acid composition of the cell membrane, especially the ratio of unsaturated to saturated fatty acids varies with temperature shift and supplementation of the growth media with fatty acids.     

Effect of Environmental Factors on the trans/cis Ratio of Unsaturated Fatty Acids in Pseudomonas putida S12

The membrane reactions of Pseudomonas putida S12 to environmental stress were investigated. Cells reacted to the addition of six different heavy metals with an increase in the ratio of trans to cis unsaturated fatty acids. A correlation among the increase in the trans/cis ratio, the toxic effects of the heavy metals, and nonspecific permeabilization of the cytoplasmic membrane, as indicated by an efflux of potassium ions, was measured. Cells previously adapted to toxic concentrations of toluene exhibited increased tolerance to all applied concentrations of zinc compared with nonadapted cells. Cells exposed to different temperatures grew optimally at 30(deg)C. The degree of saturation of the membrane fatty acids of these cells decreased with decreasing temperature. An increase in the trans/cis ratio of unsaturated fatty acids took place only at higher temperatures. Osmotic stress, expressed as reduced water activity, was obtained by using different types of solutes. Only in the presence of toxic concentrations of sodium chloride or sucrose did the trans/cis ratio increase. At no applied water activity a significant effect of glycerol on the trans/cis ratio was measured. When cells were exposed to different pHs, a distinct optimum cis/trans isomerase activity was measured at pHs between 4.0 and 5.0, whereas at higher or lower pHs no reaction occurred. This optimum coincided with a loss of viability between pH 4 and 5.     

Long-chain fatty acid assimilation By rhodopseudomonas sphaeroides

Exogenously supplied long-chain fatty acids have been shown to markedly alleviate the inhibition of phototrophic growth of cultures of Rhodopseudomonas sphaeroides caused by the antibiotic cerulenin. Monounsaturated and polyunsaturated C18 fatty acids were most effective in relieving growth inhibition mediated by cerulenin. Medium supplementation with saturated fatty acids (C14 to C18) failed to influence the inhibitory effect of cerulenin. The addition of mixtures of unsaturated and saturated fatty acids to the growth medium did not enhance the growth of cerulenin-inhibited cultures above that obtained with individual unsaturated fatty acids as supplements. Resolution and fatty acid analysis of the extractable lipids of R. sphaeroides revealed that exogenously supplied fatty acids were directly incorporated into cellular phospholipids. Cells treated with cerulenin displayed an enrichment in their percentage of total saturated fatty acids irrespective of the presence of exogenous fatty acids. Cerulenin produced comparable inhibitions of the rates of both fatty acid and phospholipid synthesis and was further found to preferentially inhibit unsaturated fatty acid synthesis.     

Carbon isotope fractionation during <Emphasis Type="Italic">cis</Emphasis>–<Emphasis Type="Italic">trans</Emphasis> isomerization of unsaturated fatty acids in <Emphasis Type="Italic">Pseudomonas putida</Emphasis>

The molecular mechanism of the unique cis to trans isomerization of unsaturated fatty acids in the solvent-tolerant bacterium Pseudomonas putida S12 was studied. For this purpose, the carbon isotope fractionation of the cis–trans isomerase was estimated. In resting cell experiments, addition of 3-nitrotoluene for activation of the cis–trans isomerase resulted in the conversion of the cis-unsaturated fatty acids into the corresponding trans isomers. For the conversion of C16:1 cis to its corresponding trans isomer, a significant fractionation was measured. The intensity of this fractionation strongly depended on the rate of cis–trans isomerization and the added concentration of 3-nitrotoluene, respectively. The presence of a significant fractionation provides additional indication for a transition from the sp² carbon linkage of the cis-double bond to an intermediate sp³ within an enzyme–substrate complex. The sp² linkage is reconstituted after rotation to the trans configuration has occurred. As cytochrome c plays a major role in the catabolism of Cti polypeptide, these findings favour a mechanism for the enzyme in which electrophilic iron (Fe³⁺), provided by a heme domain, removes an electron of the cis double bond thereby transferring the sp² linkage into sp³.     

Differential Effects of Permeating and Nonpermeating Solutes on the Fatty Acid Composition of Pseudomonas putida

We examined the effect of reduced water availability on the fatty acid composition of Pseudomonas putida strain mt-2 grown in a defined medium in which the water potential was lowered with the permeating solutes NaCl or polyethylene glycol (PEG) with a molecular weight of 200 (PEG 200) or the nonpermeating solute PEG 8000. Transmission electron microscopy showed that −1.0-MPa PEG 8000-treated cells had convoluted outer membranes, whereas −1.0-MPa NaCl-treated or control cells did not. At the range of water potential (−0.25 to −1.5 MPa) that we examined, reduced water availability imposed by PEG 8000, but not by NaCl or PEG 200, significantly altered the amounts of trans and cis isomers of monounsaturated fatty acids that were present in whole-cell fatty acid extracts. Cells grown in basal medium or under the −0.25-MPa water potential imposed by NaCl or PEG 200 had a higher trans:cis ratio than −0.25-MPa PEG 8000-treated cells. As the water potential was lowered further with PEG 8000 amendments, there was an increase in the amount of trans isomers, resulting in a higher trans:cis ratio. Similar results were observed in cells grown physically separated from PEG 8000, indicating that these changes were not due to PEG toxicity. When cells grown in −1.5-MPa PEG 8000 amendments were exposed to a rapid water potential increase of 1.5 MPa or to a thermodynamically equivalent concentration of the permeating solute, NaCl, there was a decrease in the amount of trans fatty acids with a corresponding increase in the cis isomer. The decrease in the trans/cis ratio following hypoosomotic shock did not occur in the presence of the lipid synthesis inhibitor cerulenin or the growth inhibitors chloramphenicol and rifampicin, which indicates a constitutively operating enzyme system. These results indicate that thermodynamically equivalent concentrations of permeating and nonpermeating solutes have unique effects on membrane fatty acid composition.     

Adaptation mechanisms of bacteria during the degradation of polychlorinated biphenyls in the presence of natural and synthetic terpenes as potential degradation inducers

In this study, we examined the effect of polychlorinated biphenyls (PCBs) in the presence of natural and synthetic terpenes and biphenyl on biomass production, lipid accumulation, and membrane adaptation mechanisms of two PCB-degrading bacterial strains Pseudomonas stutzeri and Burkholderia xenovorans LB400. According to the results obtained, it could be concluded that natural terpenes, mainly those contained in ivy leaves and pine needles, decreased adaptation responses induced by PCBs in these strains. The adaptation processes under investigation included growth inhibition, lipid accumulation, composition of fatty acids, cis/trans isomerization, and membrane saturation. Growth inhibition effect decreased upon addition of these natural compounds to the medium. The amount of unsaturated fatty acids that can lead to elevated membrane fluidity increased in both strains after the addition of the two natural terpene sources. The cells adaptation changes were more prominent in the presence of carvone, limonene, and biphenyl than in the presence of natural terpenes, as indicated by growth inhibition, lipid accumulation, and cis/trans isomerization. Addition of biphenyl and carvone simultaneously with PCBs increased the trans/cis ratio of fatty acids in membrane fractions probably as a result of fluidizing effects of PCBs. This stimulation is more pronounced in the presence of PCBs as a sole carbon source. This suggests that PCBs alone have a stronger effect on bacterial membrane adaptation mechanisms than when added together with biphenyl or natural or synthetic terpenes.     

Effect of Animal and Industrial Trans Fatty Acids on HDL and LDL Cholesterol Levels in Humans – A Quantitative Review

Background

Trans fatty acids are produced either by industrial hydrogenation or by biohydrogenation in the rumens of cows and sheep. Industrial trans fatty acids lower HDL cholesterol, raise LDL cholesterol, and increase the risk of coronary heart disease. The effects of conjugated linoleic acid and trans fatty acids from ruminant animals are less clear. We reviewed the literature, estimated the effects trans fatty acids from ruminant sources and of conjugated trans linoleic acid (CLA) on blood lipoproteins, and compared these with industrial trans fatty acids.

Methodology/Principal Findings

We searched Medline and scanned reference lists for intervention trials that reported effects of industrial trans fatty acids, ruminant trans fatty acids or conjugated linoleic acid on LDL and HDL cholesterol in humans. The 39 studies that met our criteria provided results of 29 treatments with industrial trans fatty acids, 6 with ruminant trans fatty acids and 17 with CLA. Control treatments differed between studies; to enable comparison between studies we recalculated for each study what the effect of trans fatty acids on lipoprotein would be if they isocalorically replaced cis mono unsaturated fatty acids. In linear regression analysis the plasma LDL to HDL cholesterol ratio increased by 0.055 (95%CI 0.044–0.066) for each % of dietary energy from industrial trans fatty acids replacing cis monounsaturated fatty acids The increase in the LDL to HDL ratio for each % of energy was 0.038 (95%CI 0.012–0.065) for ruminant trans fatty acids, and 0.043 (95% CI 0.012–0.074) for conjugated linoleic acid (p = 0.99 for difference between CLA and industrial trans fatty acids; p = 0.37 for ruminant versus industrial trans fatty acids).

Conclusions/Significance

Published data suggest that all fatty acids with a double bond in the trans configuration raise the ratio of plasma LDL to HDL cholesterol.     

Membrane fatty acids adaptive profile in the simultaneous presence of arsenic and toluene in <Emphasis Type="Italic">Bacillus</Emphasis> sp. ORAs2 and <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. ORAs5 strains

Bacillus sp. ORAs2 and Pseudomonas sp. ORAs5, two arsenic-resistant bacterial strains previously isolated from sediments of the Orbetello Lagoon, Italy, were tested for their adaptation to mixed contaminants on the level of membrane fatty acid composition. The two bacterial strains were characterized by high levels of arsenic resistance, and Pseudomonas sp. ORAs5 was also shown to be solvent-tolerant. The bacterial strains were exposed to mixtures of two toxic compounds: arsenic at fixed concentrations and toluene in variable amounts or, alternatively, toluene at constant values along with arsenic added at variable concentrations. Both strains react to the contaminants by changing the composition of their membrane fatty acids. Bacillus sp. strain ORAs2 showed a correlation between growth rate decreases and fatty acids degree of saturation increases in both cases, although pointedly in the presence of 1, 2, and 3 mM of toluene and different additions of arsenic, counteracting membranes fluidity induced by toxic compounds. In Pseudomonas sp. ORAs5, adaptive changes in membrane composition was observed both in terms of increases in the degree of saturation and in the trans/cis ratio of unsaturated fatty acids in the presence of varying toluene and constant arsenic concentrations, whereas only minor changes occurred with increasing arsenic and constant toluene concentrations. Thus, on the level of membrane composition, Bacillus sp. ORAs2 showed a higher potential for adaptation to the presence of mixed pollutants, suggesting its probable suitability for bioremediation purposes.