Changes in fatty acid profiles of thermo-intolerant and thermo-tolerant marine diatoms during temperature stress

Fatty acid composition and degree of fatty acid saturation during temperature stress in thermo-intolerant (Phaeodactylum tricornutum) and thermo-tolerant (Chaetoceros muelleri) marine diatoms were investigated. A greater number of fatty acids were observed in C. muelleri than in P. tricornutum regardless of treatment. The major fatty acids detected were 14:0, 16:0, 16:1, 16:2, 16:3, 18:0, 18:1(n-9)c, 18:2(n-6) and 20:5(n-3) with additional fatty acids 18:1(n-9)t and 20:4(n-6) detected in C. muelleri. Short duration (2 h) temperature increase above optimal growth temperature had a greater effect on fatty acid composition in C. muelleri than in P. tricornutum and the degree of fatty acid saturation was affected more by temperature in C. muelleri than in P. tricornutum during both short and long duration (24 h) treatments. Total protein assay results suggest that P. tricornutum, but not C. muelleri, was undergoing stress under our growing conditions although lipids in both diatoms were affected by increased temperature. Immunodetection of proteins with anti-rubisco indicates that the rubisco large subunit was undergoing greater turnover in C. muelleri than in P. tricornutum. However, the integrity of rubisco as a suitable indicator of lipid status needs further study. This work supports the hypothesis that a particular temperature, and not treatment duration, has the greater effect on changes in fatty acid composition. Furthermore, changes in fatty acid composition and degree of fatty acid saturation occurred more quickly in the diatoms in response to increased temperature than previously observed in nutrient starvation studies. Since diatom lipids represent an important resource for growth and reproduction of marine animals, the rapid alteration of their lipid composition under temperatures normally encountered in marine environments warrants further study.     

Biochemical dynamics of spermatogenesis and oogenesis in Eledone cirrhosa and Eledone moschata (Cephalopoda: Octopoda)

The effect of spermatogenesis and oogenesis on protein, lipid, glycogen, cholesterol and energy contents, total amino acid and fatty acid profiles of Eledone cirrhosa and Eledone moschata tissues (gonad, digestive gland and muscle) was investigated. A significant (p<0.05) increase in the amino acids and protein content of the gonad throughout sexual maturation (namely in oogenesis) was observed, but the allocation of these nitrogen compounds from the digestive gland and muscle was not evident. The major essential amino acids (EAA) in the three tissues were leucine, lysine and arginine. The major nonessential amino acids (NEAA) were glutamic acid, aspartic acid and alanine. A significant increase in lipid and fatty acid contents of gonad and digestive gland was observed. There was also little evidence of accumulated lipid storage reserves being used for egg production. It seems that for egg production Eledone species use energy directly from food, rather than from stored products. Most of saturated fatty acid (SFA) content of the three tissues was presented as 16:0 and 18:0, monounsaturated fatty acid (MUFA) content as 18:1 and 20:1 and polyunsaturated fatty acid (PUFA) content as 20:4n-6, 20:5n-3 and 22:6n-3. Cholesterol and glycogen contents significantly increased in gonad and digestive gland throughout maturation while the muscle revealed no obvious pattern. If Eledone's component sterols are of a dietary origin, a considerable variation in the cholesterol content between species might be expected on the basis of the sterol composition of their prey. Although spermatogenesis and oogenesis had a significant effect (p<0.05) in gonad and digestive gland energy content, the biochemical composition of digestive gland and muscle may not be primarily influenced by sexual maturation, but rather by other biotic factors such as feeding activity, food availability, spawning and brooding.     

Incorporation of bacterial fatty acids and changes in a wax ester-based omnivory index during a long-term incubation experiment with Calanus glacialis Jaschnov

We traced the incorporation of fatty acid biomarkers into Calanus glacialis Jaschnov (CV) during a long-term incubation experiment using bacterivorous dinoflagellates and diatoms as food. Copepods fed Oxyrrhis marina Dujardin during a 3-week acclimation period developed an omnivorous lipid composition, relative to wild-captured copepods, characterized by significant losses of polyunsaturated fatty acids (PUFA) and diatom fatty acids [16:4(n−1), 20:5(n−3)], and increases in saturated fatty acids (SFA) and 18:1(n−7). Levels of a wax ester-based omnivory index [unsaturation coefficient (UC)], verified by gas chromatography (GC), also decreased in response to the relatively PUFA-poor dinoflagellate. After half of the copepods were switched to a diet comprised of the diatom Thalassiosira hispida Syvertsen (PUFA-rich), the data showed reversal to a more herbivorous lipid composition (increases in UC and relative amounts of PUFA and diatom fatty acids). We assert that UC, derived from routine thin-layer chromatography analysis (Iatroscan) can quickly determine in situ feeding strategies (i.e., degree of omnivory) of wax ester-storing copepods. None of the eight odd and/or branched fatty acids (OBFA) initially detected in C. glacialis increased in response to a diet of O. marina which was rich in these compounds [mainly iso (i)-15:0 and anteiso (ai)-15:0]. Lack of transfer of these and other fatty acids [e.g., 22:6(n−3)] could be related to the physiological state of the copepods (early diapause). We suggest that the bacterial fatty acid 18:1(n−7) may be more useful in inferring connections between Calanus spp. and the microbial food web than the odd and/or branched chains.     

Hexadecenoic Fatty Acid Isomers in Human Blood Lipids and Their Relevance for the Interpretation of Lipidomic Profiles

Monounsaturated fatty acids (MUFA) are emerging health biomarkers, and in particular the ratio between palmitoleic acid (9cis-16:1) and palmitic acid (16:0) affords the delta-9 desaturase index that is increased in obesity. Recently, other positional and geometrical MUFA isomers belonging to the hexadecenoic family (C16 MUFA) were found in circulating lipids, such as sapienic acid (6cis-16:1), palmitelaidic acid (9trans-16:1) and 6trans-16:1. In this work we report: i) the identification of sapienic acid as component of human erythrocyte membrane phospholipids with significant increase in morbidly obese patients (n = 50) compared with age-matched lean controls (n = 50); and ii) the first comparison of erythrocyte membrane phospholipids (PL) and plasma cholesteryl esters (CE) in morbidly obese patients highlighting that some of their fatty acid levels have opposite trends: increases of both palmitic and sapienic acids with the decrease of linoleic acid (9cis,12cis-18:2, omega-6) in red blood cell (RBC) membrane PL were reversed in plasma CE, whereas the increase of palmitoleic acid was similar in both lipid species. Consequentially, desaturase enzymatic indexes gave different results, depending on the lipid class used for the fatty acid content. The fatty acid profile of morbidly obese subjects also showed significant increases of stearic acid (C18:0) and C20 omega-6, as well as decreases of oleic acid (9cis-18:1) and docosahexaenoic acid (C22:6 omega-3) as compared with lean healthy controls. Trans monounsaturated and polyunsaturated fatty acids were also measured and found significantly increased in both lipid classes of morbidly obese subjects. These results highlight the C16 MUFA isomers as emerging metabolic marker provided that the assignment of the double bond position and geometry is correctly performed, thus identifying the corresponding lipidomic pathway. Since RBC membrane PL and plasma CE have different fatty acid trends, caution must also be used in the choice of lipid species for the interpretation of lipidomic profiles.     

Light,nutrients and the fatty acid composition of stream periphyton

1. While the balance of light and nutrients is known to influence the food quality of herbivores by altering algal phosphorus and nitrogen content, the combined effects of light and nutrients on fatty acid synthesis in freshwater periphyton are relatively unknown. In this study, we manipulated light and phosphorus concentration in large, flow‐through experimental streams to examine their effects on both elemental stoichiometry and fatty acid content in periphyton. 2. Two levels of phosphorus (4 and 80 μg L^?1) and three of light (17, 40, 110 μmol photons m^?2 s^?1) were applied in a factorial design in two separate experiments. Diatoms dominated periphyton communities in both experiments, comprising >95% of algal biovolume. Periphyton growth in the streams was simultaneously affected by both resources, even at low rates of supply. 3. Periphyton C/P and C/N ratios increased with light augmentation and decreased with phosphorus enrichment, and consistent with the light : nutrient hypothesis (LNH). Light effects were strongest in streams with low phosphorus concentrations. 4. Periphyton fatty acids reflected the dominance of diatoms : palmitic (16 : 0), palmitoleic (16 : 1ω7) and eicosapentanoic (20 : 5ω3) were the principal saturated (SAFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), respectively. Linoleic (18 : 2ω6) and linolenic (18 : 3ω3) acids, characteristic of chlorophytes and cyanophytes, were rare, comprising <2% of total fatty acids. 5. Periphyton fatty acid profiles were highly sensitive to light and phosphorus. The proportion of fatty acids comprised by SAFA and MUFA increased with light augmentation and decreased with phosphorus enrichment, whereas PUFA decreased with light and increased with phosphorus. Light effects on fatty acid composition were strongest in phosphorus‐poor streams. PUFA declined with increasing light/phosphorus ratios in the streams, whereas ‘energy’ fatty acids (16 : 0 and 16 : 1) increased. The ratio of SAFA/PUFA was strongly and positively correlated with C/P and C/N ratios. SAFA and MUFA, normalised to dry mass, increased two‐ to threefold with increasing light, while PUFA normalised to dry mass was not significantly affected by light. 6. Similarities in the responses of fatty acids and elemental stoichiometry to light and phosphorus treatments suggested that they were influenced by a common mechanism. Both components of food quality appeared to be sensitive to light‐regulated rates of carbon fixation which, when coupled with insufficient supplies of phosphorus, caused diatom cells to store surplus carbon in SAFA, MUFA and other carbon‐rich compounds that diluted both essential fatty acids and mineral nutrients.     

Effect of different CO2 concentrations on biomass,pigment content,and lipid production of the marine diatom Thalassiosira pseudonana

The marine diatom Thalassiosira pseudonana grown under air (0.04% CO₂) and 1 and 5% CO₂ concentrations was evaluated to determine its potential for CO₂ mitigation coupled with biodiesel production. Results indicated that the diatom cultures grown at 1 and 5% CO₂ showed higher growth rates (1.14 and 1.29 div day⁻¹, respectively) and biomass productivities (44 and 48 mg_AFDWL⁻¹ day⁻¹) than air grown cultures (with 1.13 div day⁻¹ and 26 mg_AFDWL⁻¹ day⁻¹). The increase of CO₂ resulted in higher cell volume and pigment content per cell of T. pseudonana. Interestingly, lipid content doubled when air was enriched with 1–5% CO₂. Moreover, the analysis of the fatty acid composition of T. pseudonana revealed the predominance of monounsaturated acids (palmitoleic-16:1 and oleic-18:1) and a decrease of the saturated myristic acid-14:0 and polyunsaturated fatty acids under high CO₂ levels. These results suggested that T. pseudonana seems to be an ideal candidate for biodiesel production using flue gases.

     

Revealing the architecture of the photosynthetic apparatus in the diatom Thalassiosira pseudonana

Diatoms are a large group of marine algae that are responsible for about one-quarter of global carbon fixation. Light-harvesting complexes of diatoms are formed by the fucoxanthin chlorophyll a/c proteins and their overall organization around core complexes of photosystems (PSs) I and II is unique in the plant kingdom. Using cryo-electron tomography, we have elucidated the structural organization of PSII and PSI supercomplexes and their spatial segregation in the thylakoid membrane of the model diatom species Thalassiosira pseudonana. 3D sub-volume averaging revealed that the PSII supercomplex of T. pseudonana incorporates a trimeric form of light-harvesting antenna, which differs from the tetrameric antenna observed previously in another diatom, Chaetoceros gracilis. Surprisingly, the organization of the PSI supercomplex is conserved in both diatom species. These results strongly suggest that different diatom classes have various architectures of PSII as an adaptation strategy, whilst a convergent evolution occurred concerning PSI and the overall plastid structure.

The antenna organization of photosystem II in the diatom Thalassiosira pseudonana strongly differs from Chaetoceros gracilis, while the architecture of the photosystem I antenna remains the same.     

Lipid Content and fatty acid composition of algal communities in sea-ice and water from the Weddell Sea (Antarctica)

The lipid and fatty acid compositions of microalgae were investigated in sea-ice and water samples from six different habitats of the Weddell Sea (Antarctica). All sea-ice samples and ice-associated water contained high algal biomass dominated by centric and pennate diatoms. Cells partially filled with oil droplets and resting spores were found. In the cells from the ice platelet layer triacylglycerols formed the largest component of the lipids. The fatty acid composition of sea-ice microalgae was dominated by the 16:1(n-7), 16:0, 18:1(n-9) and 20:5 (n-3) fatty acids. Except 18:1, they are typical for diatom fatty acids. These fatty acids were most abundant in pieces of first year ice with a brown colouration (brown-ice) and in the water column directly below sea-ice (sub-ice water). The small amounts of non-diatom acids, as 22:6 (n-3) and 18:4 (n-3), clearly showed that the sea-ice communities were not purely composed of diatoms. The most striking difference, in comparison to the general fatty acid composition of diatoms, was the high proportion of the 18:1 fatty acid in all samples, which might be caused by detrital material or lipid accumulation within cells and resting spores. In general, no clear adaptation of the fatty acid composition to the Antarctic and sea-ice environment was found. The fatty acid composition of the particulate matter from the water column was totally different from all other samples dominated by the saturated fatty acids 16:0 and 18:0.     

Sterols and fatty acids of the marine diatom biddulphia sinensis

Nine sterols, most showing Δ⁵- or Δ^5,22-unsaturation, were identified in the marine diatom Biddulphia sinensis. One sterol, cholesta-5,22E-dien-3β-ol, comprised 70–80% of the total sterols which is the first such predominance noted in a diatom. The only Δ⁷-sterol detected was cholest-7-en-3β-ol and this was a very minor component. A sterol showing unusual side-chain alkylation,23,24-dimethylcholesta-5,22E-dien-3β-ol, was identified for the first time in a diatom. Total fatty acids exhibited a predominance of Δ⁹- 16:1, 14:0, 20:5 and 16:0, typical of diatoms, although the proportions of these acids were found to vary with culture maturity. n-Heneicosahexaene was the major hydrocarbon together with a small amount of squalene.     

Effect of sex,dietary glycerol or dietary fat during late fattening,on fatty acid composition and positional distribution of fatty acids within the triglyceride in pigs

The effect of sex, source of saturated fat (lard v. palm oil) and glycerol inclusion in the fattening diet on composition and fatty acid positional distribution in the triglyceride molecule was studied in pigs from 78 to 110 kg BW. Average daily gain and carcass characteristics, including ham and loin weight, were not affected by dietary treatment but sex affected backfat depth (P<0.01). A significant interaction between sex and glycerol inclusion was observed; dietary glycerol increased lean content in gilts but not in barrows (P<0.05 for the interaction). Individual and total saturated fatty acid (SFA) concentrations were greater in barrows than in gilts. In contrast, the concentration of total polyunsaturated fatty acids (PUFA) and of C18:2n-6, C18:3n-3, C20:3n-9 and C20:4n-6 in the intramuscular fat (IMF) was higher (P<0.05) in gilts than in barrows. Sex did not affect total monounsaturated fatty acids (MUFA) concentration in the IMF. The proportion of SFA in the subcutaneous fat (SF) was higher in barrows than in gilts (P<0.001). Within the individual SFA, sex affected only the concentrations of C14:0 and C16:0 (P<0.001). Dietary fat did not affect total SFA or PUFA concentrations of the IMF but the subcutaneous total MUFA concentration tended to be higher (P=0.079) in pigs fed lard than in pigs fed palm oil. Dietary glycerol increased total MUFA and C18:1n-9 concentration in the IMF and increased total MUFA and decreased C18:2n-6, C18:3n-3 and total PUFA concentrations in the SF. The data indicate that altering the fatty acid composition of the triglyceride molecule at the 2-position, by dietary intervention during the fattening phase, is very limited.     

Plastidial acyl carrier protein Δ9-desaturase modulates eicosapentaenoic acid biosynthesis and triacylglycerol accumulation in Phaeodactylum tricornutum

The unicellular marine diatom Phaeodactylum tricornutum accumulates up to 35% eicosapentaenoic acid (EPA, 20:5n3) and has been used as a model organism to study long chain polyunsaturated fatty acids (LC-PUFA) biosynthesis due to an excellent annotated genome sequence and established transformation system. In P. tricornutum, the majority of EPA accumulates in polar lipids, particularly in galactolipids such as mono- and di-galactosyldiacylglycerol. LC-PUFA biosynthesis is considered to start from oleic acid (18:1n9). EPA can be synthesized via a series of desaturation and elongation steps occurring at the endoplasmic reticulum and newly synthesized EPA is then imported into the plastids for incorporation into galactolipids via an unknown route. The basis for the flux of EPA is fundamental to understanding LC-PUFA biosynthesis in diatoms. We used P. tricornutum to study acyl modifying activities, upstream of 18:1n9, on subsequent LC-PUFA biosynthesis. We identified the gene coding for the plastidial acyl carrier protein Δ9-desaturase, a key enzyme in fatty acid modification and analyzed the impact of overexpression and knock out of this gene on glycerolipid metabolism. This revealed a previously unknown role of this soluble desaturase in EPA synthesis and production of triacylglycerol. This study provides further insight into the distinctive nature of lipid metabolism in the marine diatom P. tricornutum and suggests additional approaches for tailoring oil composition in microalgae.     

Ultraviolet radiation negatively affects growth and food quality of the pelagic diatom Skeletonema costatum

There are now compelling observations of the ecological impacts of global change on marine ecosystems. A predicted 10% increase in UVB doses at the Earth's surface has been shown to impair indirectly the reproductive output of marine copepods. Wild females of Calanus helgolandicus fed with UVB-irradiated diatoms produced fewer eggs and unhealthy offspring exhibiting a large proportion of high lethal naupliar deformities. By reproducing the same irradiative stress on the pelagic diatom Skeletonema costatum, we looked for potential modifications of the algal properties (cell size, biovolume, chlorophyll content) and biochemical characteristics (fatty acid and amino acid contents). Our results confirmed that the metabolism of S. costatum is adversely affected by enhanced UVB exposure: cell growth was reduced and the biochemical characteristics, and thus the algal nutritional quality, were significantly altered. UVB irradiation reduced cell division, leading to cell elongation and thus increasing the biovolume. Meanwhile, the amino acid and fatty acid contents did not increase concomitantly to the cell enlargement and were thus diluted in the cell. Because of this dilution, the irradiated S. costatum represents a poorer diet for its potential consumers. Moreover, UVB dramatically affects the relative contribution of certain essential fatty acids such as eicosapentanoic acid (EPA), which are essential for the development of marine invertebrates.     

Deep-water shrimp (Pandalus borealis, Krøyer 1838) as indicator organism for fish-farm waste

A feeding experiment was carried out with deep-water shrimp (Pandalus borealis), a common benthic inhabitant of Norwegian fjords. Shrimp were reared in tanks for three months, fed either salmon feed or cod, and the fatty acid profile of their muscle tissue was monitored. The salmon feed pellets and cod had completely different fatty acid compositions, with significant differences in most of the analysed fatty acids, eight of them, 14:0, iso16:0, 16:1n7, 16:2n11, 18:3n3, 20:0, 22:0 and 22:1n11, differing between the two diets by a factor of 10 or more. The levels of the fatty acids in the diets differed also substantially from the levels in the shrimp tissue at the start of the experiment. The shrimp were fed ad libitum and both groups increased significantly in total fatty acid content in the course of the experiment. Nevertheless, the fatty acids made up no more than 6.5 mg g^− 1 muscle tissue, with 88 ± 1% of them bound in polar, membrane lipids. Their composition in the tissue did also change to a certain extent, but the resulting tissue composition did not reflect the fatty acid composition of the diets. Only two fatty acids, 18:2n6 and 18:3n3, clearly followed the dietary level. They are abundant in commercial salmon feed since they are rich in plant oils used as additives to the commercial feed. Determination of fatty acid levels in shrimp tissue may enable shrimp to be used as indicator organisms for the influence of organic fish-farm waste on the food web in adjacent areas.     

Fatty acids as trophic markers of phytoplankton blooms in the Bahía Blanca estuary (Buenos Aires, Argentina) and in Trinity Bay (Newfoundland, Canada)

The fatty acid compositions of phytoplankton and major primary consumers were analyzed during the development of seasonal algal blooms in the Bahía Blanca estuary, situated on the southern coast of the province of Buenos Aires (Argentina), and Trinity Bay, at Sunnyside, on the eastern coast of Newfoundland (Canada). Primary consumers in the Bahía Blanca estuary were zooplankton dominated by the calanoid copepod Acartia tonsa. At Sunnyside, the primary consumers were the sea scallop Placopecten magellanicus, an ecological and economical important benthic bivalve. The study shows that in spite of obvious differences between the two environments and the analytical approaches employed in each case, the analyses of fatty acid biomarkers can provide relevant ecological information. The fatty acid composition of the lipids of Bahía Blanca phytoplankton (high concentrations of the fatty acids 14:0, 16:4ω1, and 20:5ω3) reflected the presence of diatoms as a major component throughout the bloom. Fatty acid markers of the post-bloom phytoplankton in Bahía Blanca indicated a decline of phytoplankton biomass, and a relatively high input of detritus and terrestrial plant materials to the particulate organic matter of the estuary. Linoleic acid (18:2ω6), a typical “terrestrial” fatty acid, was conspicuous in the lipids of the post-bloom particulate matter of the Bahía Blanca estuary; 18:2ω2 was subsequently incorporated into zooplankton lipids diatom markers were also prominent in the lipids of pre-bloom and bloom phytoplankton at Sunnyside; post-bloom phytoplankton showed higher proportions of 18:0, 18:1ω9, and 18:4ω3, characteristic and often major fatty acids of dinoflagellates. The fatty acids of the digestive gland of P. magellanicus reflected the fatty acid composition of the phytoplankton, whereas those of the adductor muscle were practically unaffected by the composition of the food. This organ-specific response of an animal to the fatty acid composition of the diet is examined in terms of different applications of the fatty acid marker concept.     

Characterization of the triacylglycerol profile in marine diatoms by ultra performance liquid chromatography coupled with electrospray ionization–quadrupole time-of-flight mass spectrometry

Diatoms are considered to have great potential as new biofuel sources because they can effectively accumulate triacylglycerols (TAGs). Detailed structure information of TAG in diatoms is much needed not only for the assessment of biofuel quality such as fatty acid chain length and unsaturation degree but also for the tracing of biosynthetic precursors because the biosynthesis of TAG is typically completed by utilizing the diacylglycerol acyltransferase in the cytoplasm. In this report, a comprehensive characterization of TAGs in marine diatoms was performed using ultra performance liquid chromatography–electrospray ionization–quadrupole time-of-flight mass spectrometry. Many types of major TAGs were identified for the first time in these diatoms: 12 TAGs in Chaetoceros debilis, 9 TAGs in Phaeodactylum tricornutum Bohlin, 16 TAGs in Nitzschia closterium f. minutissima, 16 TAGs in Thalassiosira weissflogii, 13 TAGs in Thalassiosira sp., 16 TAGs in Stephanodiscus asteaea and 7 TAGs in Skeletonema costatum. Semi-quantification of TAGs in these diatoms was also carried out, and it was found that the contents of individual TAGs ranged from 0.5?±?0.1 to 217.9?±?8.1 nmol mg^?1 total lipids. In addition, the total lipid contents in diatoms ranged from 143.6?±?16.3 to 201.1?±?16.3 mg g^?1 dry microalgae and the total TAG contents ranged from 36.8?±?9.5 to 793.2?±?54.4 nmol mg^?1 total lipids. By comparative analysis of the compositions and concentrations of major TAGs in the seven algal strains, N. closterium f. minutissima with high abundance of TAGs containing the most monounsaturated fatty acids (mainly palmitoleic acid) was considered as one of the most promising diatom strains for microalgal biofuel production. Additionally, based on the information of sn-2 fatty acid obtained (mainly C16 in the sn-2 position), we propose the hypothesis that TAGs in diatoms are mainly derived from lipids in chloroplasts through the prokaryotic biosynthesis pathway, including monogalactosyldiacylglycerol and digalactosyldiacylglycerol.     

Spatial and temporal variation of the fatty acid composition of Patella spp. (Gastropoda: Prosobranchia) soft bodies and gonads

This study evaluated the effects of season and spatial distribution on the fatty acid composition of Patella depressa gonads and Patella spp. soft body tissue. The results show that the quantitatively most important fatty acids were the saturated fatty acids (SFA) 16:0, 14:0 and 18:0; the monounsaturated fatty acids (MUFA) 18:1(n-7), 18:1(n-9), 16:1(n-7) and 20:1(n-9) and the polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA 20:5(n-3)), and arachidonic acid (ARA 20:4(n-6)). P. depressa and P. ulyssiponensis soft body fatty acid profiles revealed significant differences between sexes; males showed significantly higher percentages of PUFA, highly unsaturated fatty acids (HUFA), (n-3) fatty acids and ARA, while in females significantly higher proportions of MUFA were found. Analysis of variance on the fatty acid composition of P. depressa gonads revealed significant differences between sexes, which were more marked than when the whole body was analysed. Males showed a significantly higher percentage of PUFA, HUFA, fatty acids from the (n-3) and (n-6) series, ARA and EPA, while females were seen to have higher proportions of SFA, MUFA and total fatty acid methyl esters (FAME). Some variability was seen to occur due to shore location and seasons, but these effects were not so obvious.     

Assimilation and biosynthesis of lipids in Arctic Calanus species based on feeding experiments with a C labelled diatom

The dominant Arctic Ocean and North Atlantic copepods Calanus hyperboreus, Calanus glacialis, and Calanus finmarchicus were collected in the Greenland Sea and fed ¹³C labelled diatom Thalassiosira weissflogii to follow the transfer and assimilation of carbon, lipid, and individual fatty acids and alcohols. The diatom was grown with ¹³C for 3 to 5 days and fed then to the copepods. During the feeding period of 14 days, total carbon increased in the copepodite stages V of C. hyperboreus and C. finmarchicus, whereas carbon remained almost constant in C. glacialis females. However, total lipid increased in all species and stages. Highest lipid accumulation occurred in C. hyperboreus in which nearly all lipids were exchanged already after 11 days of feeding. In the other species lipid accumulation made up between 22% (C. finmarchicus) and 45% of total lipid (C. glacialis). The proportion of wax esters was high ranging from 76% of total lipid in C. glacialis to 92% in C. finmarchicus. The fatty acid composition of the alga was dominated by 16:1(n-7), 16:0, 20:5(n-3), and 22:6(n-3). The composition of the copepods was similar because of feeding already on diatoms in the field. In addition, the monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), were major components of the copepod lipids. During the feeding period the highest ¹³C labelling was always found in the C₁₆ polyunsaturated fatty acids and in the 16:1(n-7) alcohol. Because these components occurred only in trace amounts in the copepods they totally originated from the diet explaining the high labelling. It is noteworthy that the 16:1(n-7) alcohol originated only from the corresponding dietary and not from the abundant internal fatty acid. The long-chain monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), are not existent in phytoplankton and have to be produced de novo. They were less labelled in the smaller species but highly ¹³C enriched in C. hyperboreus. Although dietary fatty acids were generally retained by the copepods it seems that fatty acids or even lipids were selectively accumulated and turned over due to bodily requirements, and thus, essential polyunsaturated fatty acids were preferentially retained. During feeding mixing, accumulation, and exchange of internal and dietary fatty acids and alcohols occurred as well as utilisation of lipids from both sources for metabolic requirements. The differences in lipid assimilation fit to the different life strategies of the copepods.     

Seasonal changes in lipid classes and fatty acid composition in the digestive gland of Pecten maximus

Seasonal variations in lipid classes and fatty acid composition of triacylglycerols and phospholipids in the digestive gland of Pecten maximus were studied over a period of 16 months. Acylglycerols predominated (19-77% of total lipids), in accordance with the role of the digestive gland as an organ for lipid storage in scallops. Seasonal variations were mainly seen in the acylglycerol content, while phospholipids (2.5-10.0% of total lipids) and sterols (1.9-7.4% of total lipids) showed only minor changes. The most abundant fatty acids were 14:0, 16:0, 18:0, 16:1(n-7), 18:1(n-9), 18:1(n-7), 18:4(n-3), 20:5(n-3) and 22:6(n-3) and these showed similar seasonal profiles in both, triacylglycerol and phospholipid fractions. In contrast to the phospholipid fraction, the triacylglycerol fraction contained more 20:5(n-3) than 22:6(n-3). In three phospholipid samples we noted a high percentage of a 22-2-non-methylene-interrupted fatty acid, previously described to have a structural role in several bivalve species. The main polyunsaturated fatty acids displayed important seasonal variations parallel to those of the acylglycerols, suggesting good nutritional conditions. A positive correlation existed between the level of saturated fatty acids and temperature, whereas the levels of polyunsaturated fatty acids correlated negatively with temperature.     

Metabolic Analysis of Adaptation to Short-Term Changes in Culture Conditions of the Marine Diatom Thalassiosira pseudonana

This report describes the metabolic and lipidomic profiling of 97 low-molecular weight compounds from the primary metabolism and 124 lipid compounds of the diatom Thalassiosira pseudonana. The metabolic profiles were created for diatoms perturbed for 24 hours with four different treatments: (I) removal of nitrogen, (II) lower iron concentration, (III) addition of sea salt, (IV) addition of carbonate to their growth media. Our results show that as early as 24 hours after nitrogen depletion significant qualitative and quantitative change in lipid composition as well as in the primary metabolism of Thalassiosira pseudonana occurs. So we can observe the accumulation of several storage lipids, namely triacylglycerides, and TCA cycle intermediates, of which citric acid increases more than 10-fold. These changes are positively correlated with expression of TCA enzymes genes. Next to the TCA cycle intermediates and storage lipid changes, we have observed decrease in N-containing lipids and primary metabolites such as amino acids. As a measure of counteracting nitrogen starvation, we have observed elevated expression levels of nitrogen uptake and amino acid biosynthetic genes. This indicates that diatoms can fast and efficiently adapt to changing environment by altering the metabolic fluxes and metabolite abundances. Especially, the accumulation of proline and the decrease of dimethylsulfoniopropionate suggest that the proline is the main osmoprotectant for the diatom in nitrogen rich conditions.