Isolation of the saturated fatty acids of some marine lipids with particular reference to normal odd-numbered fatty acids and branched-chain fatty acids

Probing fatty acid metabolism in bacteria, cyanobacteria, green microalgae and diatoms with natural and unnatural fatty acids

In both eukaryotes and prokaryotes, fatty acid synthases are responsible for the biosynthesis of fatty acids in an iterative process, extending the fatty acid by two carbon units every cycle. Thus, odd numbered fatty acids are rarely found in nature. We tested whether representatives of diverse microbial phyla have the ability to incorporate odd-chain fatty acids as substrates for their fatty acid synthases and their downstream enzymes. We fed various odd and short chain fatty acids to the bacterium Escherichia coli, cyanobacterium Synechocystis sp. PCC 6803, green microalga Chlamydomonas reinhardtii and diatom Thalassiosira pseudonana. Major differences were observed, specifically in the ability among species to incorporate and elongate short chain fatty acids. We demonstrate that E. coli, C. reinhardtii, and T. pseudonana can produce longer fatty acid products from short chain precursors (C3 and C5), while Synechocystis sp. PCC 6803 lacks this ability. However, Synechocystis can incorporate and elongate longer chain fatty acids due to acyl-acyl carrier protein synthetase (AasS) activity, and knockout of this protein eliminates the ability to incorporate these fatty acids. In addition, expression of a characterized AasS from Vibrio harveyii confers a similar capability to E. coli. The ability to desaturate exogenously added fatty acids was only observed in Synechocystis and C. reinhardtii. We further probed fatty acid metabolism of these organisms by feeding desaturase inhibitors to test the specificity of long-chain fatty acid desaturases. In particular, supplementation with thia fatty acids can alter fatty acid profiles based on the location of the sulfur in the chain. We show that coupling sensitive gas chromatography mass spectrometry to supplementation of unnatural fatty acids can reveal major differences between fatty acid metabolism in various organisms. Often unnatural fatty acids have antibacterial or even therapeutic properties. Feeding of short precursors now gives us easy access to these extended molecules.

Saturated Branched Chain, Normal Odd-Carbon-Numbered, and n-3 (Omega-3) Polyunsaturated Fatty Acids in Freshwater Fish in the Northeastern United States

The fatty acid profiles of wild freshwater fish are poorly characterized as a human food source for several classes of fatty acids, particularly for branched chain fatty acids (BCFA), a major bioactive dietary component known to enter the US food supply primarily via dairy and beef fat. We evaluated the fatty acid content of 27 freshwater fish species captured in the northeastern US with emphasis on the BCFA and bioactive polyunsaturated fatty acids (PUFA) most associated with fish, specifically n-3 (omega-3) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Mean BCFA content across all species was 1.0 ± 0.5% (mean ± SD) of total fatty acids in edible muscle, with rainbow smelt (Osmerus mordax) and pumpkinseed (Lepomis gibbosus) the highest at >2% BCFA. In comparison, EPA + DHA constituted 28% ± 7% of total fatty acids. Across all fish species, the major BCFA were iso-15:0, anteiso-15:0, iso-16:0, iso-17:0 and anteiso-17:0. Fish skin had significantly higher BCFA content than muscle tissues, at 1.8% ± 0.7%, but lower EPA and DHA. Total BCFA in fish skins was positively related with that in muscle (r² = 0.6). The straight chain saturates n-15:0 and n-17:0 which have been identified previously as markers for dairy consumption were relatively high with means of 0.4% and 0.6%, respectively, and may be an underappreciated marker for seafood intake. Consuming a standardized portion, 70 g (2.5 oz), of wild freshwater fish contributes only small amounts of BCFA, 2.5-24.2 mg, to the American diet, while it adds surprisingly high amounts of EPA + DHA (107 mg to 558 mg).

Branched-chain Fatty acids in sediments

Branched-chain (iso and anteiso) fatty acids were isolated from marine sediments from several environments. The relatively high ratio of branched-chain to straight-chain fatty acids for the even-numbered carbon molecules suggests a bacterial origin for the branched-chain isomers. The branched-chain fatty acids are present in the Green River shale. Possible geochemical implications are suggested.

Lipid composition of the epidermal gel secretion from the Arabian Gulf catfish (Arius thalassinus Ruppell)

Lipids associated with a threat induced epidermal gel secretion from the catfish, Arius thalassinus, have been analyzed. Phospholipids, neutral lipids and glycolipids are all present and each of these subclasses has been analyzed by thin layer and gas chromatography with a general similarity with membrane lipids being noted. The epidermal gel lipids differed from total liver lipids of the catfish. Fatty acid analysis showed the gel lipid to be rich in the unsaturated fatty acids: oleate (omega 7, C18:1), arachidonate (omega 6, C20:4), and docosahexaenoate (omega 3, C22:6). Some prostaglandins were quantitated in lipid extracts from the epidermal gel.

Occurrence of cis-9,10-methylenehexadecanoic and cis-9, 10-methyleneoctadecanoic acids in the lipids of immature and mature Fundulus heteroclitus (L.), and in roe

Analysis of saturated fatty acids in the mummichog Fundulus heteroclitus (L.) by argentation chromatography and open-tubular gas-liquid chromatography detected cyclopropanoid fatty acids as well as all of the anticipated saturated fatty acids, including a variety of branched-chain saturated fatty acids previously found in fish. Cyclopropanoid fatty acids were identified in juveniles, male and female bodies, and roe. When the levels of these acids in eviscerated male and female bodies were compared with roe, roe had the highest concentration, followed by female and then male fish. Whole immature mummichog had almost twice the proportion of cyclopropanoid fatty acids found in whole mature male fish. The cyclic acids probably originate indirectly in the diet of the mummichog. This consists mainly of invertebrates probably consuming bacteria associated with plant detritus. The Atlantic silversides Menidia menidia collected from the same habitat had lower proportions of odd-chain methyl-branched fatty acids, and lower proportions of cyclopropanoid fatty acids, indicating differences in sources of dietary fatty acids.

Halosphaera viridis: Fatty Acid Composition and Taxonomical Relationships

The total fatty acids of a natural bloom of Halosphaera viridis have been determined. A readily extractable lipid fraction, mostly triglyceride, showed additional monoethylenic fatty acid isomers not obvious in the total lipid. Comparisons are made on the usefulness of this data in distinguishing Chlorophyceae and Prasinophyceae within the Chlorophyta.

The occurrence of diastereomers of phytanic and pristanic acids and their determination by gas-liquid chromatography

The methyl esters of phytanic (3,7,11,15-tetramethylhexadecanoic) and pristanic (2,6,10,14-tetramethylpentadecanoic) acids derived from phytol each can be resolved into two diastereomers by gas-liquid chromatography on an efficient open-tubular, gas-liquid chromatographic column with a polyester coating. Authentic D,D,D isomers prepared from the lipids of bacteriumH. cutirubrum gave only one peak. In mammals the D,D,D isomers usually predominate, but in marine life the L,D,D isomers apparently are the principal forms. The origin and metabolic roles of the diastercomers are discussed.

A quantitation problem in the open tubular gas chromatography of fatty acid esters from cod liver lipids

Methyl esters of fatty acids of marine origin contain large amounts of highly unsaturated long-chain fatty acids. It is shown that, although esters of saturated and monounsaturated fatty acids can be quantitatively analyzed on open tubular columns with a flame ionization detector there are serious losses of the long-chain highly unsaturated fatty acids of marine oils on the column. Through comparison of chain-length composition and iidine value some correction factors are suggested for the highly unsaturated fatty acids which permit reasonably accurate analyses.

Isomeric monoethylenic fatty acids in herring oil

Monoethylenic fatty acids from herring oil were concentrated by chromatography by chromatography on silver nitratesilicic acid columns. Examination of consecutive fractions by open tubular gas chromatography confirmed the preferential elution of longer chain length esters and of esters within one chain length with the double bond closer to the terminal methyl group. Isomeric monoethylenic fatty acids with double bonds in the positions closer to the carboxyl group than the approximate midpoint of the even-numbered fatty acid chains could not be adequately separated by gas chromatography and were determined by ozonolysis. The isomers observed are consistent with primary formation from saturated acids through the action of an enzyme specifically removing hydrogen atoms in positions Delta(9) and Delta(10) relative to the carboxyl group. Chain extension of particular monoethylenic isomers by two carbon atoms in the C(20) and longer chain lengths is apparently influenced by the position of the double bond.