Unsaturated fatty acid biosynthesis in Tetrahymena. Evidence for two pathways

Biochemical composition of algivorous freshwater ciliates: you are not what you eat

The focus of our study was to determine whether the biochemical composition of two algivorous ciliates, both fed the same alga, resembles that of their diet. By comparing both ciliated protozoa we intended to identify species-specific differences in the metabolic features of these ciliates. Carbon- and cell-specific concentrations of fatty acids and essential amino acids were investigated for the ciliates Balanion planctonicum and Urotricha farcta grown on the cryptomonad Cryptomonas phaseolus. Stepwise discriminant analyses (SDA) indicated differences in the biochemical composition between ciliates and their diet and between the two ciliated protozoa. Carbon-specific fatty acid concentrations were usually higher in the ciliates than in their diet, especially concentrations of monounsaturated and some polyunsaturated fatty acids. Except for tryptophan, valine, and lysine, amino acid concentrations were higher in the ciliates than in C. phaseolus. Furthermore, differences in the polyunsaturated fatty acids accounted for the largest discrepancies between the two ciliated protozoa. The higher concentrations in the ciliates compared to their diet suggest that these species are capable of efficiently ingesting, assimilating or possibly synthesizing some fatty acids and amino acids. We conclude that dietary fatty acid and amino acid composition influences the composition of the two ciliated protozoa to a minor extent, and that species-specific differences in fatty acid and amino acid metabolism may be more important determinants of the biochemical composition of the studied ciliates. Moreover, the metabolism of polyunsaturated fatty acids seems to differ more profoundly between the two ciliated protozoa than the metabolism of other fatty acid classes or amino acids.

The effect of dietary sterol on the activity of fatty acid desaturases isolated from Tetrahymena setosa

Tetrahymena setosa has a nutritional requirement for micro amounts of sterol, a requirement which is also satisfied by relatively large amounts of either intact phospholipids or a mixture of unsaturated fatty acids normally found in these ciliates. Three microsomal fatty acyl-CoA desaturases have been isolated from T. setosa and partially characterized. These enzymes which can account for the formation of the majority of the ciliate's unsaturated fatty acids, include: a delta 9, a delta 12 and a delta 6 desaturase which catalyze the transformation of stearoyl-CoA to oleic acid, of oleoyl-CoA to linoleic acid and of linoleoyl-CoA to gamma-linolenic acid, respectively. The stearoyl CoA desaturase required NAD (or NADP), ATP and free CoA; the delta 6 and delta 12 desaturases required NADP, but not ATP or CoA. Cellular levels of the three desaturases were highest in mid-logarithmic phase cells and lowest in stationary phase cells. In order to determine if there was a relationship between the sterol requirement and the ability of the organism to desaturate, T. setosa was grown in a synthetic medium supplemented with either cholesterol or a phospholipid which permits growth in the absence of cholesterol, or with both phospholipid and cholesterol. Cells grown with phospholipid alone had only half as much stearoyl-CoA and oleoyl-CoA desaturase activity as cells of identical culture age grown either on cholesterol alone or on cholesterol plus phospholipid.

On the isolation of the new fatty acid 6,11-eicosadienoic (20:2) and related 6,11-dienoic acids from the sponge Euryspongia rosea

The phospholipid fatty acids from the sponge Euryspongia rosea were studied revealing the presence of the new 6,11-eicosadienoic (20:2) acid and the rare 6,11-octadecadienoic acid (18:2). The isolation of these 6,11-dienoic acids reveals the presence of new biosynthetic possibilities in sponges and suggests the presence of an active delta 6 desaturase in E. rosea. Other acids isolated from E. rosea include 12-eicosenoic (20:1) and 17-tetracosenoic acid (24:1). The major phospholipids encountered in the sponge were phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylcholine (PC).

Unsaturated fatty acid isomers: effects on the circadian rhythm of a fatty-acid-deficient Neurospora crassa mutant

The fatty acids oleic, linoleic, and linolenic, each of which has a cis double bond at the delta 9 position, are known to lengthen the circadian period of conidiation (spore formation) of strains of Neurospora crassa carrying the cel mutation. cel confers a partial fatty acid requirement on the organism and has been used to promote incorporation of exogenous fatty acids. To test whether a physical effect imparted by the cis double bonds, such as increased membrane fluidity, is critical for the perturbation of the rhythm, various isomers of these fatty acids were supplemented to the bd csp cel strain. Positional isomers of oleic acid, such as petroselinic (delta 6) and vaccenic (delta 11) acids, and longer-chain isomers, such as eicosenoic (delta 11) and erucic (delta 13) acids, did not lengthen the rhythm. The shorter-chain palmitoleic (delta 9) acid did not give a consistent lengthening of the rhythm; it may be elongated to vaccenic acid. In contrast, gamma-linolenic acid (delta 6,9,12) dramatically lengthened the period. Linoelaidic acid (the trans,trans isomer of linoleic acid) lengthened the period at 22 degrees C, but elaidic acid (the trans isomer of oleic acid) did not. Elaidic acid was shown to exert a lengthening effect, but only at lower temperatures. The data do not support a direct physical action as the source of the fatty acids' "chronobiotic" ability.

Fatty acid desaturase specificity of Tetrahymena

The ciliate, Tetrahymena, was provided a supplement of the fatty acid [1-14 C]18:2 delta 6.9. After a period of growth the cells were claimed, the lipids extracted, the polar lipids recovered and the mild alkali-labile fatty acid methyl esters generated. The fatty acids were resolved by high pressure liquid chromatography (HPLC), the 18:3 delta 6.9,12(gamma-linolenic acid) was recovered and its identity verified by high pressure liquid chromatography (HPLC), gas liquid chromatography (GLC), hydrogenation and oxidation. Fifty-three percent of the cell-associated label was found in gamma-linolenic acid; thus, a delta 12 fatty acid desaturase converts the 6,9 octadecadienoic acid to the 6,9,12 derivative. No carboxyl or methyl terminus restriction appears on delta 9 monoenoic or dienoic fatty acid desaturation in this cell as is found in higher plants and animals.

Studies on thermal adaptation in Tetrahymena membrane lipids. Changes in positional distribution of fatty acids in diacyl-phospholipids and alkyl-acyl-phospholipids during temperature acclimation

The positioning of acyl chains in both 1-O-alkyl-2-acyl- and 1,2-diacyl-phospholipids was analyzed at various time intervals for a thermotolerant strain (NT-1) of Tetrahymena pyriformis cells during cold acclimation. During the 10 h period of adaptation, cells were not able to grow but maintained the ability to divide. The content of palmitate (16 : 0) in phosphatidylcholine and phosphatidylethanolamine was decreased after temperature-shift, with a concurrent increase of palmitoleate (16 : 1 delta 9) and gamma-linolenate (18 : 3 delta 6,9,12). An increase in gamma-linolenate at the 1-position and linoleate at the 2-position was observed in diacyl-phospholipids (phosphatidylethanolamine, phosphatidylcholine and 2-aminoethylphosphonolipid). The 2-position of 1-O-alkyl-2-acyl-phosphatidylcholine and 1-O-alkyl-2-acyl-(2-aminoethyl)phosphonolipid was occupied mainly by gamma-linolenate together with cilienate (18 : 2 delta 6,11) and linoleate (18 : 2 delta 9,12). Cilienate and gamma-linolenate at the 2-position of 1-O-alkyl-2-acyl-phosphatidylcholine were increased after temperature shift, with a small decrease of linoleate. There are little significant changes in alkyl ether lipid content of phosphatidylcholine and 2-aminoethylphosphonolipid after temperature shift. The results indicate that phosphatidylethanolamine, which is most abundant and present only in the diacyl form, would play a crucial role in thermal adaptation of membrane lipids, by replacing palmitate with gamma-linolenate at its 1-position, and also that hexadecyl/gamma-linolenoyl phosphatidylcholine would be an important molecular species in the acclimation.

Isolation of a stearoyl CoA Desaturase form Tetrahymena thermophila

Cell free preparations of Tetrahymena thermophila contain an enzyme that catalyzes the direct desaturation of stearoyl CoA to octadecenoic acid. The enzyme is associated with the microsomal fraction of the ciliate. Substrate of the enzyme consists of either free stearic acid or stearoyl CoA. Both ATP and CoA are required when free stearate is the substrate and are also highly stimulatory when stearoyl CoA is the substrate. With stearoyl CoA as the substrate, either NADH or NADPH are required for desaturase activity. In presence of ATP and CoA, either NAD or NADP can replace NADH and NADPH. Desaturase activity is optimal when the enzyme is incubated at pH of 7.2 and a temperature of 30-35 degrees C. Highest levels of the stearoyl CoA desaturase are found in stationary phase ciliates grown at 35 degrees C.

Metabolism of odd-numbered, normal fatty acids in Tetrahymena pyriformis W

Tetrahymena pyriformis W cells were grown with short- and long-chain, odd and even normal fatty acid supplements. Tris acetate addition had no effect on the fatty acyl composition of the glycerophospholipids or sphingolipids, while Tris propionate supplementation led to a marked increase in odd normal fatty acids at the expense of even normal acids in both classes of complex lipids. This enhancement of odd normal acids permitted the identification of 17:1 delta 9(n), 17:2 delta 6,9(n), 17:2 delta 9,12(n), 17:3 delta 6,9,12(n), 19:1 delta 9(n), 19:2 delta 9,12(n) and 19:3 delta 6,9,12(n) by oxidation with periodate-permanganate and examination of the short-chain fragments. Supplementation with pentadecanoic acid (15:0(n)) led to an increase in the proportions of normal C15, C17 and C19 acids. The increase in C15 acids primarily reflected a rise in 15:0(n), whereas the rise in the levels of C17 and C19 acids was accounted for by an elevation of unsaturated acids. Growth with heptadecanoic acid (17:0(n)) resulted in substantial increases in unsaturated normal C17 and C19 fatty acids, while nonadecanoic acid (19:0(n)) addition led only to an increase in the proportion of unsaturated C19 acids. Retroconversion of these saturated, odd normal long chain fatty acid supplements was limited. Supplementation with arachidic acid (20:0(n)) resulted in only a marginal increase (1.4%) in normal C20 fatty acids of both the glycerophospholipids and the mild alkali labile neutral lipids and provided no evidence that desaturation occurred. The release of 14CO2 from [1-14C]arachidic acid when incubated with the ciliates indicated that this long-chain saturate is accumulated, activated and degraded. Normal C16-C19 saturated fatty acids are substrates for the delta 9 desaturase. The delta 11 isomers arise by chain elongation. Normal C16-C19 delta 9 monoenoic acids are substrates for the delta 12 desaturase. Normal C16-C18 delta 9 monoenes, normal C16-C19 delta 9,12 dienes and 18:1 delta 11(n) are desaturated at the C-6,7 position.

Modification of membrane lipid composition following the nutritional shift-up of starved cells. A comparison with membrane biogenesis in Tetrahymena

Detailed analyses of lipid composition have been made on various membrane fractions isolated at different intervals after 24 h-starved Tetrahymena cells were refed with nutrient-rich medium. During starvation there was a marked alteration in both phospholipid polar headgroup and acyl chain compositions: an increase in 2-aminoethylphospholipid and gamma-linolenic acid (18 : 3) with a concurrent decrease in phosphatidylethanolamine and palmitoleic acid (16 : 1). However, following refeeding, such an altered lipid composition was rather rapidly restored to the initial level of the control cell membranes prior to starvation. This membrane lipid modification was found to occur in good accordance with the recovery of cell size and lipid synthesis. The considerable changes in the principal unsaturated fatty acids, 16 : 1 and 18 : 3, which are formed via the palmitate and stearate desaturation pathways, respectively, were suggested to be accounted for by the levels of desaturases activities. The results of the labeling experiments with radioactive precursors have demonstrated that in the refed cells, there was a more rapid and dynamic transfer or exchange between membranes as compared with that in the exponentially growing control cells. Thus, rapid ameliorative modifications of membrane lipid composition are thought to be required for the urgent growth of membrane systems in the refed cell which should be ready to initiate new division.

Studies on thermal adaptation in Tetrahymena membrane lipids. Positional distribution of fatty acid in diacyl- and alkyl-acyl-phosphatidylcholines and -(2-aminoethyl)phosphonolipids from cells grown at different temperatures

Phosphatidylcholine and 2-aminoethylphosphonolipid, major membrane phospholipids in Tetrahymena, comprise 1,2-diacyl and 1-alkyl-2-acyl moieties, whereas phosphatidylethanolamine is solely in diacyl form. The overall fatty acid composition of phosphatidylcholine and 2-aminoethylphosphonolipid fractions from 15 degrees C-grown cells mainly consisted of linoleic (C18 : 2 delta 9,12) and gamma-linolenic (C18 : 3 delta 6,9,12) acids, except for the large amount of an usual fatty acid, cilienic acid (C18 : 2 delta 6,11) in 2-aminoethylphosphonolipids. When compared with 39.5 degrees C-grown cells, the 1-position of phosphatidylcholine and 2-aminoethylphosphonolipid from 15 degrees C-grown cells undergoes a large increase in palmitoleic (C16 : 1 delta 9) and gamma-linolenic acids with a corresponding decrease of myristic (C14 : 0) and palmitic (C16 : 0) acids. At the 2-position of 15 degrees C-grown cells, linoleic and gamma-linolenic acids in phosphatidylcholine, and cilienic and linoleic acids in 2-aminoethylphosphonolipid increase with a large decrease of palmitoleic acid in both phospholipids and of gamma-linolenic acid in 2-aminoethylphosphonolipid. There was quite a similarity in fatty acid composition between 1,2-diacylphosphatidylcholine and 1,2-diacyl-(2-aminoethyl)phosphonolipid in 39.5 degrees C- and 15 degrees C-grown cells. However, a marked increase of gamma-linolenic acid at the 1-position of 1,2-diacyl-phosphatidylcholine, and of linoleic acid at the 2-position of diacyl-aminoethylphosphonolipid was observed in 15 degrees C-grown cells. The 2-position of 1-alkyl-2-acyl-phosphatidylcholine and 1-alkyl-2-acyl-(2-aminoethyl)phosphonolipid was occupied mainly by unsaturated fatty acids. In 15 degrees C-grown cells, the sum of linoleic and gamma-linolenic acids accounted for 79.9% in 1-alkyl-2-acyl-phosphatidylcholine and 87.1% in 1-alkyl-2-acyl-(2-aminoethyl)phosphonolipid. These data support the hypothesis that 2-aminoethylphosphonolipid and phosphatidylcholine would play an important role as acceptors of polyunsaturated fatty acids (C18 : 2 delta 6,11, C18 : 2 delta 9,12 and C18: 3 delta 6,9,12) for temperature acclimation. Furthermore, changes in the ratio of diacyl- to alkyl-acylphosphatidylcholine may also be involved in thermal adaptation by regulating the number of fatty acid acceptor.

Modulation of membrane fluidity in a fatty acid auxotrophe of Tetrahymena thermophila

A mutant of Tetrahymena thermophila has been isolated which requires an unsaturated fatty acid for growth. Pellicles isolated from cultures supplemented with palmitoleic, elaidic, oleic, linoleic and gamma-linolenic acids show widely differing membrane fluidities, as measured by the polarisation of fluorescence technique. In contrast to the behaviour of the wild type organism, the changes in fluidity of the membrane, once induced by supplementation, are permanent. This mutant should prove extremely useful for studying structure-function relationships in the various membrane systems of Tetrahymena.

The effect of temperature on unsaturated fatty acid loss in Tetrahymena pyriformis

Cultures of Tetrahymena pyriformis W incorporate exogenous 3-[14C]-cilienic acid and gamma-[1(-14)C] linolenic acid, terminal products of unsaturated fatty acid synthesis, into glycerophosphatides without randomization of the radiolabel. There was no difference in the rate of loss of each of the two acids at 15 or 28.5 degrees C. Differential turnover of these fatty acids, therefore, does not appear to be the cause of the shift in fatty acid pattern observed with temperature reduction.

Differential biosynthesis of polyunsaturated fatty acids by Tetrahymena supplemented with ergosterol

Tetrahymena grown with foreign sterols such as ergosterol incorporate them into cellular membranes at the expense of the native compound, tetrahymanol. It is shown that cells grown with ergosterol have a lessened capacity to produce the polyunsaturated linoleic and gamma-linolenic acids from [14C]oleic acid. However, the same cells have normal capacities to introduce double bonds at C-6 into linoleate, alpha-linolenate, or cis-vaccenate. Thus, a presumed 12-desaturase is inhibited in the presence of ergosterol, while desaturation at C-6 is unaffected.