Low Molecular Weight Fatty Acids Research Articles

Quantification of low molecular weight fatty acids in cave drip water and speleothems using HPLC-ESI-IT/MS — development and validation of a selective method

This study presents a novel method for the analysis of low molecular weight (LMW) fatty acids in cave drip water and speleothems. The method development included optimization of sample preparation procedures, e.g., blank reduction, solid phase extraction, concentration of extracts as well as liquid chromatography coupled to electrospray ion-trap mass spectrometry (HPLC-ESI-IT/MS) measurement parameters. Retention times for five analytes (lauric acid, myristic acid, palmitic acid, stearic acid and arachidic acid) were between 5 and 13.5 min. Spiking experiments were performed to accomplish external calibrations which ranged from 12.5 to 75 ng per spiked water sample. The correlation coefficient ranged from 0.9558 to 0.9989. Inter-batch precision, expressed as the relative standard deviation of three replicates, was <7 %. Limits of detection ranged from 0.77 to 55.97 ng for the diverse analytes; obtained recoveries varied from 30 to 103 %. For a first application, cave drip water and stalagmite samples from Herbstlabyrinth-Adventhöhle cave system were analyzed. Concentrations ranged from 38.37 to 9,982.54 ng L(-1) for water samples and 2.52 to 1,344.96 ng g(-1) for the stalagmite. Thereby, the different fatty acids showed a distinctive variation. Whereas shorter-chained fatty acids exhibited similarities, arachidic acid showed opposite trends. Diverse correlations were found, which could improve the understanding of different organic sources of the lipids transported by drip water and preserved in speleothems. This new method provides a more selective extraction process, particularly adjusted to LMW fatty acids and therefore reduces the required sample size. Furthermore, it is applicable to stalagmite as well as cave drip water samples.

Two-step thermal conversion of oleaginous microalgae into renewable hydrocarbons

The aim of this study was to evaluate the conversion of microalgal biomass to renewable chemicals and fuels through a two-step reaction and separation process. High density Chlorella protothecoides culture with 40% lipid accumulation (dwb) was produced in 10 L bioreactors and hydrolyzed in batch stainless steel reactors under subcritical conditions. After hydrolysis, fatty acids free of sulfur and low in nitrogen and salts, were recovered by hexane extraction. The fatty acids were pyrolyzed at 410°C for 2h under N2 yielding n-alkanes, α-olefins and internal olefins and low molecular weight fatty acids. This study demonstrated the direct conversion of microalgal biomass into valuable platform chemicals and fuels compatible with the existing industrial hydrocarbon infrastructure.

Biomarker records in penguin droppings and observed changes in penguin communities and their response to the ENSO in the Western Antarctic

Lipid biomarkers in AD2 penguin droppings-amend soil core from the Ardley Island, Western Antarctic, were dated using 210Pb. Changes in the fatty acid ratios of nC18:2/nC18:0 from the penguin droppings reflect climate changes coincident with ENNO events during 1931–2006. The occurrence of the minimum values in the depth of 2–3 and 6–7 cm are consistent with the end of ENSO in 1958 and 1983, respectively, reflecting a lag of the biomarker records in AD2 penguin droppings-amend soil in climatic signatures. This study also reveals that the changes in the relative concentration of n-alkanes nC23, the ratios of nC23/nC17 and ΣnC21−/ΣnC22+, and carbon preferential index (CPI) values collectively indicate the variations of soil microorganism and lower plant, which are closely related to climate changes. The ratios of bacterial fatty acids iC15:0/aC15:0 reflect the increasing significance of microorganism activities during the two periods that occurred at the end years of ENSO. Decrease in CPIA value and increase in ΣnC21t-/ΣnC22+ indicate that low molecular weight fatty acids are derived from microorganism; and their insignificant correlation with Pr/Ph suggests microorganisms play an important role in the relatively simply ecosystem in the Antarctic and are closely linked to climatic conditions. In addition, the observed penguin community indicates the population of penguin can largely reflect the impacts of global climate changes on the ecosystem.

Biorefinery approach for coconut oil valorisation: A statistical study

The biorefinery approach, consisting in transesterification using methanol and potassium hydroxide as catalyst, has been used to assess coconut oil valorisation. Due to the fatty acid composition of coconut oil, low (LMWME) and high (HMWME) molecular weight fatty acid methyl esters were obtained. Methyl laurate (78.30 wt.%) is the major component of the low molecular weight fraction. The influence of variables such as temperature and catalyst concentration on the production of both fractions has been studied and optimized by means of factorial design and response surface methodology (RSM). Two separate optimum conditions were found to be a catalyst concentration of 0.9% and 1% and an operation temperature of 42.5 °C and 57 °C for LMWME and HMWME, respectively, obtaining conversion rates of 77.54% and 25.41%. The valuable components of LMWME may be recovered for sale as biolubricants or biosolvents, the remaining fraction could be used as biodiesel, matching the corresponding European Standard.

Sodium 4-phenylbutyrate protects against liver ischemia reperfusion injury by inhibition of endoplasmic reticulum-stress mediated apoptosis

Evidence is emerging that the endoplasmic reticulum (ER) participates in initiation of apoptosis induced by the unfolded protein response and by aberrant Ca(++) signaling during cellular stress such as ischemia/reperfusion injury (I/R injury). ER-induced apoptosis involves the activation of caspase-12 and C/EBP homologous protein (CHOP), and the shutdown of translation initiated by phosphorylation of eIF2alpha. Sodium 4-phenylbutyrate (PBA) is a low molecular weight fatty acid that acts as a chemical chaperone reducing the load of mutant or unfolded proteins retained in the ER during cellular stress and also exerting anti-inflammatory activity. It has been used successfully for treatment of urea cycle disorders and sickle cell disease. Thus, we hypothesized that PBA may reduce ER-induced apoptosis triggered by I/R injury to the liver. Groups of male C57BL/6 mice were subjected to warm ischemia (70% of the liver mass, 45 minutes). Serum aspartate aminotransferase was assessed 6 hours after reperfusion; apoptosis was evaluated by enzyme-linked immunosorbent assays of caspase-12 and plasma tumor necrosis factor alpha, Western blot analyses of eIF2alpha, and reverse transcriptase-polymerase chain reaction of CHOP expression. A dose-dependent decrease in aspartate aminotransferase was demonstrated in mice given intraperitoneal PBA (1 hour before and 12 hours after reperfusion), compared with vehicle-treated controls; this effect was associated with reduced pyknosis, parenchymal hemorrhages, and neutrophil infiltrates in PBA-treated mice, compared with controls. In a lethal model of total liver I/R injury, all vehicle-treated controls died within 3 days after reperfusion. In contrast, 50% survival (>30 days) was observed in animals given PBA. The beneficial effects of PBA were associated with a greater than 45% reduction in apoptosis, decreased ER-mediated apoptosis characterized by significant reduction in caspase-12 activation, and reduced levels of both phosphorylated eIF2alpha and CHOP. Significant reductions in plasma levels of tumor necrosis factor alpha and liver myeloperoxidase content were demonstrated after PBA treatment. Reduction in ER stress-induced hepatocellular injury was achieved by the administration of PBA. Targeting the ER-associated cell death pathway might offer a novel approach to reduce I/R injury to the liver.

Crude Oil Emulsion Properties and Their Application to Heavy Oil Transportation

Many advances have been made in the field of emulsions in recent years. Emulsion behavior is largely controlled by the properties of the adsorbed layers that stabilize the oil-water surfaces. The knowledge of surface tension alone is not sufficient to understand emulsion properties, and surface rheology plays an important role in a variety of dynamic processes. The complexity of petroleum emulsions comes from the oil composition in terms of surface-active molecules contained in the crude, such as low molecular weight fatty acids, naphthenic acids and asphaltenes. These molecules can interact and reorganize at oil/water interfaces. The pronounced nonlinear behavior of surface rheology for asphaltene layers might explain differences in behavior between surfactant and asphaltene emulsions. These effects are very important in the case of heavy oils because this type of crude contains a large amount of asphaltene and surface-active compounds. This article reviews different petroleum emulsion properties and the transport of high viscosity hydrocarbon as a crude oil in water emulsion.

Sodium 4-phenylbutyrate protects against cerebral ischemic injury.

Sodium 4-phenylbutyrate (4-PBA) is a low molecular weight fatty acid that has been used for treatment of urea cycle disorders in children, sickle cell disease, and thalassemia. It has been demonstrated recently that 4-PBA can act as a chemical chaperone by reducing the load of mutant or mislocated proteins retained in the endoplasmic reticulum (ER) under conditions associated with cystic fibrosis and liver injury. In the present study, we evaluated the neuroprotective effect of 4-PBA on cerebral ischemic injury. Pre- or post-treatment with 4-PBA at therapeutic doses attenuated infarction volume, hemispheric swelling, and apoptosis and improved neurological status in a mouse model of hypoxia-ischemia. Moreover, 4-PBA suppressed ER-mediated apoptosis by inhibiting eukaryotic initiation factor 2alpha phosphorylation, CCAAT/enhancer-binding protein homologous protein induction, and caspase-12 activation. In neuroblastoma neuro2a cells, 4-PBA reduced caspase-12 activation, DNA fragmentation, and cell death induced by hypoxia/reoxygenation. It protected against ER stress-induced but not mitochondria-mediated cell death. Additionally, 4-PBA inhibited the expression of inducible nitric-oxide synthase and tumor necrosis factor-alpha in primary cultured glial cells under hypoxia/reoxygenation. These results indicate that 4-PBA could protect against cerebral ischemia through inhibition of ER stress-mediated apoptosis and inflammation. Therefore, the multiple actions of 4-PBA may provide a strong effect in treatment of cerebral ischemia, and its use as a chemical chaperone would provide a novel approach for the treatment of stroke.

Four years' observations of terrestrial lipid class compounds in marine aerosols from the western North Pacific

In order to understand the long‐range atmospheric transport of terrestrial organic matter over the open ocean, marine aerosol samples were collected on a biweekly basis from 1990 to 1993 in a remote island, Chichi‐Jima, in the western North Pacific. The samples were analyzed for lipid class compounds using a capillary gas chromatography (GC) and GC/mass spectrometry (GC/MS). A homologous series of n‐alkanes (C20‐C40), alcohols (C13‐C34), fatty acids (C9‐C34) and α,ω‐dicarboxylic acids (C7‐C28) were detected in the aerosol samples. Distributions of n‐alkanes (0.17–14 ngm−3, average 1.7 ngm−3) are characterized by a strong odd‐carbon number predominance (CPI ratios, average 4.5) with a maximum at C29 or C31, indicating that n‐alkanes are mainly derived from terrestrial higher plant waxes. Fatty alcohols (0.19–23 ngm−3, average 2.0 ngm−3) show an even‐carbon number predominance with a maximum generally at C26 or C28, again indicating a contribution from terrestrial higher plants. On the other hand, fatty acids (2.5–38 ngm−3, average 14 ngm−3) show a bimodal distribution with two maxima at C16 and C24 or C28. Lower molecular weight fatty acids (generally &lt;C20) that are mainly derived from marine organisms showed higher concentrations in summer. In contrast, higher molecular weight fatty acids (C21‐C34) derived from terrestrial higher plants, together with C25‐C35 alkanes, C20‐C34 alcohols and C20‐C28 dicarboxylic acids, generally showed higher concentrations in winter to spring seasons. This seasonal trend is most likely interpreted as atmospheric transport of terrestrial organic matter from Asian continent in winter/spring, when westerly winds dominate over the western North Pacific. Backward trajectory analyses supported the long‐range atmospheric transport of higher plant‐ and soil‐derived organic matter from the Asian continent over the Pacific Ocean. This study also suggested that the atmospheric transport is the main pathway for the terrestrial lipid compounds that are abundantly present in the deep‐sea sediments in the Central Pacific.

Supercritical CO 2 fractionation of crude palm oil

Crude palm oil was fractionated using supercritical CO 2 (SC–CO 2) in a semi batch apparatus. The fractionation conditions studied were at 40, 50 and 60°C and at 110, 140 and 200 bars, respectively. System pressure was found to be more significant rather than temperature for increasing the solubility of palm oil triglycerides in SC–CO 2. The solubility of crude palm in SC–CO 2 was generally low for triglycerides rich in the saturated and lower molecular weight fatty acids, i.e. C12:0, C14:0 and C16:0. These fatty acids were fractionated first followed by the heavier and mainly unsaturated fatty acids, i.e. C18:1, C18:3 and C20:0. The initial extracted fractions were white to yellow in colour and solid like. The later fractions however were more intense in colour and semi-liquid. It was difficult to extract β-carotene from the palm oil in the fractions even at high pressures because it is concentrated in the raffinate. The del Valle-Aguilera correlation was found to over estimated solubility of crude palm oil in supercritical CO 2.

Compound-Specific Radiocarbon Ages of Fatty Acids in Marine Sediments from the Western North Pacific

Compound-specific radiocarbon analysis of five fatty-acid biomarkers was conducted for marine sediments collected from the western North Pacific. The fatty acids (C12 to C34) showed a typical bimodal distribution pattern with two maxima at C16 and C26. Their carbon isotopic compositions ranged from −25.1‰ (C16) to −31.8‰ (C28), suggesting that they derived from terrestrial higher plants and marine organisms. A large variations of 14C ages were found among the fatty acids detected in the same sedimentary horizon of the core, ranging from 530 BP (C18) to 3250 BP (C28). The results of 14C analysis of fatty acids could be divided into two groups, i.e., lower molecular weight (LMW) fatty acids (C16, C18) derived from marine organisms and higher molecular weight (HMW) fatty acids (C24, C26, C28) derived from terrestrial higher plants. The HMW fatty acids showed older ages, ranging from 2550 BP (C24) to 3250 BP (C28), than LMW fatty acids (530 BP [C18] to 1,820 years BP [C16]). On the other hand, bulk-phase total organic matter (TOM) showed the age of 2260 BP that is between those two groups, suggesting that it was likely a mixture of organic matter derived from marine and terrestrial sources. The compound specific 14C ages and δ13C data of sedimentary fatty acids presented here could provide useful information to decipher the fate and transport process of terrestrial organic matter to marine sediments.

Purification and characterization of rat hepatic microsomal low molecular weight fatty acid ethyl ester synthase and its relationship to carboxylesterases.

We reported purification of a high molecular weight (HMW) (ca. 180 kD) and a low molecular weight (LMW) (ca. 60 kD) protein fractions from digitonized rat liver microsomes using ammonium sulfate precipitation followed by ion exchange and gel filtration column chromatography. Both fractions expressed fatty acid ethyl ester (FAEE) synthase as well as p-nitrophenyl acetate (PNPA)-hydrolyzing (esterase) activities. The HMW fraction was found to be a trimer with subunit molecular weight ca. 60 kD and structurally and functionally similar to rat hepatic microsomal carboxylesterase (CE, pI 6.1) and adipose tissue FAEE synthase. In this article, we report further purification and characterization of the LMW (minor) fraction expressing FAEE synthase activity and its structural and functional relationship to hepatic microsomal CEs. Using isoelectric focusing (IEF) followed by gel filtration-high-performance liquid chromatography (GF-HPLC), five proteins were purified, which expressed FAEE synthase as well as PNPA-hydrolyzing activity. The isoelectric point values of 6.5, 5.8, 5.6, 5.3, and 5.0 were found for the purified LMW proteins by IEF and each showed a peak corresponding to ca. 60 kD molecular weight by GF-HPLC, which expressed FAEE synthase as well as PNPA-hydrolyzing activity. Sodium dodecyl sulfate-polyacrylamide gel elecrophoresis (SDS-PAGE) analysis of the GF-HPLC purified LMW proteins revealed that these proteins are monomers (ca. 60 kD). All the purified LMW proteins cross-reacted with antibodies to rat adipose tissue FAEE synthase. Coelution of PNPA-hydrolyzing and FAEE synthase activity at each step of purification and cross-reactivity with rat adipose tissue FAEE synthase antibodies suggest that the purified proteins are related to various hepatic microsomal CEs. This conclusion is further supported by the homology of N-terminal amino acid sequence of the purified LMW proteins to various hepatic microsomal CEs and protease precursors. Therefore, LMW FAEE synthase activity most probably is expressed by various isozymes of hepatic microsomal CEs, which are also involved in the biotransformation of xenobiotic alcohols and amines.

Improving phase equilibrium calculation with the Peng–Robinson EOS for fats and oils related compounds/supercritical CO 2 systems

Several predictive methods for normal boiling point, critical temperature, critical pressure, and acentric factor, applied to fatty acids and fatty acid esters of high molecular weight were evaluated. The properties estimated by the selected methods were used to analyze the ability of the Peng–Robinson equation of state (EOS) to predict the vapor–liquid equilibria of binary and ternary systems of fats and oils related compounds with CO 2. Van der Waals mixing rules with the combining rules proposed by Kwak and Mansoori and Park et al. were used. For fatty acids, the method of Constantinou and Gani was selected for the prediction of the critical temperature and that of Somayajulu for the prediction of the critical pressure when experimental boiling temperatures were available. In the absence of experimental data, the method of Constantinou and Gani was selected for the prediction of critical and boiling temperatures, as well as for the critical pressure. For fatty acid esters, the method of Joback and Reid was chosen for the prediction of the critical and boiling temperatures, and that of Constantinou and Gani was selected for the prediction of the critical pressure. The indirect method of Tu was preferred for the prediction of the acentric factors of high molecular weight fatty acids. The correlation of Vetere was chosen for the prediction of the acentric factors of low molecular weight fatty acid esters, and the indirect method of Tu was selected for the prediction of the acentric factors for the methyl ester family. The results for the phase equilibria suggest that the Peng–Robinson equation, with the quadratic mixing rules for the three combining rules tested, is capable of predicting vapor–liquid equilibrium with quality comparable to the results obtained with the mixing rules for more complex models like MHV1 and LCVM.

N‐Alkanes and free fatty acids in humus and A1 horizons of soils under beech, spruce and grass in the Massif‐Central (Mont‐Lozère), France

SummarySoil profiles under beech, spruce and a grassland have been analysed to study the evolution of natural n‐alkanes in pollution‐free ecosystems. The soils had all developed on granitic bedrock, at an altitude of 1300–1500 m in the region of Mont‐Lozère (southern Massif‐Central, France). In contrast to the grassland soil, the two forest soils both possessed a well‐developed acidic moder humus‐type horizon. This could be subdivided as follows: fresh litter (OL), fragmentation (OF) and humification (OH) layers; two litters, one fresh (OL1) and one old (OL2) could actually be distinguished in the beech forest soil. The n‐alkane signature of the parent plants was preserved in the top litter. Immediately underneath, in the OF layer(s) the original n‐alkane signatures were progressively but rapidly replaced by a common signature composed of n‐C27 and n‐C25 with larger proportions of the former than of the latter. These two hydrocarbons were most probably produced in situ by fungi. These results appear to illustrate the action of soil microorganisms which metabolize the inherited n‐alkanes and produce new compounds of the same family. Unlike the alkanes and the low molecular weight fatty acids ≤ C20 (which increase greatly in the OL2 layer under beech as a result of intense microbial activity), the heavy fatty acids (&gt; C20) show no significant change in the organic horizon.

Sulfate reduction rates and low molecular weight fatty acid concentrations in the water column and surficial sediments of the Black Sea

Sulfate reduction rates and concentrations of low molecular weight organic acids were measured in the water column and surficial sediments at two sites in the central Black Sea. Water column sulfate reduction rates were much lower than previously reported. The highest rate measured was 3.5 nM day −1 and on a depth integrated basis values of 1.2 and 0.22 mmol m −2 day −1 were obtained for the two sites. Sediment sulfate reduction rates were within the ranges previously reported but were higher than some for comparable abyssal sites. Rates were about 21 μM day −1 in the flocculent layer at the sediment-water interface, decreasing to 2–3μM day −1 at 20 cm depth. On an areal, depth integrated basis, rates at the two sites were 1.45 and 1.29 mmol m −2 day −1. Thus, the water column and sediments have comparable areal rates, but on a volume basis the sediment rates are several thousand times higher than the water column rates. Organic acid concentrations in the anoxic Black Sea water column were surprisingly high, reaching several μM in some cases. One deep sample contained 60μM acetate. Lactate, acetate and formate were the only acids detected in the water column. Some propionate was seen in sediment porewaters. Apparent turnover times of the organic acids in the water column, calculated for utilization solely by sulfate reducing bacteria, are tens to hundred of years. This suggests that sulfate reduction rates in the water column were not limited by organic substrate supply. In the sediments, apparent acid turnover times calculated in this way are generally less than one day, suggesting that sulfate reduction may be limited to by the supply of these substrates through fermentation reactions.

Biological removal of organic nitrogen and fatty acids from metal-cutting-fluid wastewater

The anaerobic, anaerobic/aerobic (anaerobic followed by aerobic) and straight aerobic treatments of a simulated metal-cutting-fluid wastewater were evaluated in terms of the removal of organic nitrogen (primarily alkanolamines and heterocyclic compounds) and fatty acids, the two major constituents of many water-based metal-cutting fluids. The organic nitrogen was not well adsorbed on activated carbon but was degraded through the anaerobic/aerobic or straight aerobic treatment. It was also found that an acclimation period was necessary before the organic nitrogen could be anaerobically degraded. 2-Methylhexanoic, heptanoic, 3,5,5-trimethylhexanoic and benzoic acid, which were found in the wastewater, were degraded well both anaerobically and aerobically. The wastewater also contained a group of unidentified organic compounds that consisted of five gas chromatographic peaks (probably branched C 8–C 10 fatty acids or their esters). These unidentified organics were partially degraded and persisted in the effluents, contributing to the non-biodegradable portion of organics. Several low molecular weight fatty acids (acetic acid, propanoic acid, 2-methylpropanoic acid, butanoic acid, 3-methylbutanoic acid and pentanoic acid) were produced during the periods when the influent chemical oxygen demand (COD) loading was varied to study the response of an anaerobic reactor to the variation. The anaerobic/aerobic treatment produced an effluent similar to that of the straight aerobic treatment with respect to fatty acid concentrations.

Interesterification of Butter Fat by Lipase fromMucor mieheiin Organic Solvent Media

Summary Butter fat was interesterified in three organic solvent media, hexane, hexane‐chloroform (70:30, v/v), and hexane‐ethyl acetate (70:30, v/v), at different water contents, using commercial immobilized lipase from Mucor miehei. The results indicate that the addition of 30% of either chloroform or ethyl acetate to the hexane resulted in a 25% increase in the interesterification yield; moreover, the addition of 0.8 to 1% water shifted the hydrolytic affinity of lipase towards low molecular weight fatty acids. However, the addition of a small portion of water in hexane, 0.4%, increased the amount of free fatty acids from 0.30 to 7.98 mmole per gram of butter.

Modification of the fatty acid binding profile of liver fatty acid binding protein (L-FABP)

Low molecular-weight fatty acid binding protein (L-FABP) was purified from rat liver by a combination of gel filtration and affinity chromatography. The purified protein had a molecular weight of 14,000 Daltons as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fast protein liquid chromatography (FPLC) gel filtration chromatography. Isoelectric focusing of delipidated preparations gave a major protein band with a pl of 7.5. Delipidated L-FABP was used to determine binding constants for individual saturated, monounsaturated, and polyunsaturated fatty acids. For fatty acids of chain length greater than C14 there was no apparent selectivity based on chain length or degree of unsaturation. When delipidated L-FABP was incubated with an equimolar (0.3 mmol/L) mixture of fatty acids; 16:0, 18:1 (n-9), 18:2(n-6), 20:3(n-6), 20:4(n-6), and 22:6(n-3) were bound at equivalent levels (0.18 mol/mol L-FABP). However, stearic acid was bound to a greater extent (approximately two fold) and 18:3(n-6) and 18:3(n-3) were bound to a lesser extent (50%). 12:0, 14:0, and 20:5(n-3) bound poorly to L-FABP. Thus, under these conditions fatty acid binding protein exhibits a selectivity that is not apparent from individual binding constants. When rats were maintained on different diets for 6 weeks, the concentration of L-FABP was reduced only in animals maintained on a fat-free diet. The apparent binding capacity of L-FABP (0.71 mol fatty acid per mol L-FABP) was the same for all diets. However, the endogenous fatty acid composition of L-FABP was strongly influenced by dietary fatty acid composition.

Biochemical Models for Phosphate Accumulating Microorganisms

Although biochemical models for the Pi accumulation of Acinetobacter have been discussed in the literature, attention should be given to the fact that a wastewater treatment plant implies a mixed population of microorganisms and acetate and other low molecular weight fatty acids are not the only nor the most abundant carbon source available. Other microorganisms known to be present in activated sludge plants are able to accumulate polyP, PHB and/or carbohydrates. These bacteria (Pseudomonas, Aeromonas, Moraxella, Klebsiella, and others) may use acetate, but also glucose and other monosaccharides, amino acids, fatty acids and other substances as carbon sources, not only for a fermentation process, but also for the intracellular synthesis of polyP in an aerobic stage, and the release of Pj in the anaerobic one. Though most of the experimental work found in the literature was done using mixed cultures, it is proposed that the main differences in the biochemical models is due to the lack of the definition of the specific substrate transport mechanism across the cellular membrane.

Fatty acid oxidation in anoxic marine sediments: the importance of hydrogen sensitive reactions

In anoxic marine sediments fatty acids may be oxidized directly by sulfate reducing bacteria, or may be oxidized by pathways which result in hydrogen production. Some of these latter reactions are quite sensitive to hydrogen concentrations ... in other words if hydrogen concentrations become elevated, fatty acid oxidation will cease. Thus sulfate reducers may actually play two important roles in the metabolism of fatty acids in marine sediments. The sulfate reducers both can utilize fatty acids directly, and also can oxidize hydrogen and thus control hydrogen partial pressures in the sediments. Therefore sulfate reducers may act indirectly to facilitate fatty acid oxidation by hydrogen-producing pathways. We carried out a series of incubations of slurried salt marsh sediment under high and low hydrogen partial pressures and in the presence and absence of molybdate to investigate the relative importance of sulfate reducers and other bacteria mediating hydrogen-sensitive reactions. Our results suggest that both classes of bacteria contribute significantly to fatty acid turnover in marine sediments. Studies of low molecular weight fatty acid turnover in sediment must explicitly recognize that manipulation of sediment (including addition of molydbate to inhibit sulfate reducers) may have a large impact on hydrogen partial pressures in sediment, and may thus significantly alter the pathways and/or rates of fatty acid turnover.

Comparison by capillary SFC and SFC‐MS of soxhlet and supercritical fluid extraction of hamster feces

AbstractComponents of hamster feces ranging from low molecular weight fatty acids through the expected range of triglycerides have been eluted in a single SFC run with simultaneous pressure and temperature programming. Temperature programming from 140°C to 240°C was required to provide optimum conditions for separation of the fatty acids and to move the elution region of the sterol esters away from that of the triglycerides. Data from chemical ionization and electron impact mass spectrometry of compounds separated by SFC were used to confirm identities suggested by retention measurements and to provide tentative identities of unknown compounds.SFC with flame ionization detection was used to compare Soxhlet extraction, off‐line supercritical fluid extraction (SFE), and on‐line SFE of the feces. Although samples obtained by Soxhlet extraction and SFE produced very similar chromatograms, SFE required far less time and consumed much smaller quantities of organic solvent.