The Chilean scallop Argopecten purpuratus (Lamarck, 1819): I. fatty acid composition and lipid content of six organs

Lipid droplets play versatile roles in ovarian development of the razor clam Sinonovacula constricta: Insights from proteomic and lipidomic analyses

Lipid droplet (LD) deposition is a common phenomenon during ovarian development across marine mollusks; however, studies on the protein and lipid composition of their ovarian LDs remain limited. Here, we purified LDs from the ovaries of Sinonovacula constricta and isolated proteins and lipids from these purified LDs for proteomic and lipidomic analyses. Our proteomic analysis identified 3243 proteins, with PLIN2 being the most abundant (37.03 ± 13.56 %). We subsequently conducted a functional analysis of the top 500 most abundant LD-associated proteins, categorizing them into 15 groups, including those involved in lipid metabolism, sterol biosynthesis, tricarboxylic acid cycle, carbohydrate metabolism, G protein superfamily, protein chaperones, transport proteins, nucleotide-catabolic process, protein processing and degradation, cytoskeletal proteins, oxidative stress and immunity, and ribosome-associated proteins. In our lipidomic analysis, we identified 1158 molecules across 52 lipid classes, with phosphatidylcholine (PC) exhibiting the greatest diversity at 209 varieties, followed by EtherPC with 177 varieties and triglyceride (TG) with 149 varieties. The fatty acid (FA) analysis of LDs revealed that 16:0 was the most abundant (30.01 ± 0.42 %). Additionally, LDs were found rich in long-chain polyunsaturated FAs (35.63 ± 4.36 %), particularly EPA and DHA. Moreover, we analyzed the FA composition of TGs, PCs, and EtherPCs derived from ovarian LDs. In PCs and TGs, the predominant FAs were 16:0, 16:1, and 18:3, while 16:0, 22:6, and 18:4 constituted the major FA species in EtherPCs. Together, our results suggest that ovarian LDs in S. constricta not only participate in lipid metabolism but also interact with other organelles and metabolic processes, thereby facilitating ovarian development.

Transcriptomic and metabolomic analyses reveal sex-related differences in the gonads of Pinctada fucata martensii

Pinctada fucata martensii is an economically important bivalve mollusk, as this species makes a major contribution to seawater pearl production. Pearl production efficiency varies between the sexes of P. f. martensii, but many aspects of the molecular mechanisms underlying sex determination and sex differentiation in P. f. martensii remain unclear. Here, transcriptomic and metabonomic analyses were conducted to identify the major genes and metabolic changes associated with sex determination and gametogenesis. We identified a total of 3426 differentially expressed genes (DEGs) between females and males. These included Fem-1c and Foxl2, which are involved in sex determination and sex differentiation, and SOHLH2, Nanos1 and TSSK4, which are involved in gametogenesis. We also identified a total of 5231 significant differential metabolites (SDMs) between females and males. These DEGs were enriched in 47 metabolic pathways, including "ABC transporters," "purine metabolism," and "glycerophospholipid metabolism." Our findings provide new insights into the molecular mechanisms underlying sex determination, sex differentiation, and gametogenesis and will aid future studies of P. f. martensii.

Sexual dimorphism in the gonad lipidome of blue mussels (Mytilus sp.): New insights from a global lipidomics approach

Blue mussels (Mytilus sp.) are an economically important species for European aquaculture. Their importance as a food source is expected to increase in the coming net-zero society due to their low environmental footprint; however, their production is affected by anthropogenic stressors and climate change. During reproduction, lipids are key molecules for mussels as they are the main source of energy on which newly hatched embryos depend in the first days of their development. In this work, blue mussels of different origins are analysed, focusing on the differences in lipid composition between the ovary (BMO) and the testis (BMT). The lipidome of blue mussel gonads (BMG) is studied here by combining traditional lipid profiling methods, such as fatty acid and lipid class analysis, with untargeted liquid chromatography-mass spectrometry (LC-MS) lipidomics. The approach used here enabled the identification of 770 lipid molecules from 23 different lipid classes in BMG. BMT, which consists of billions of spermatocytes, had greater amounts of cell membrane and membrane lipid components such as FA18:0, C20 polyunsaturated fatty acids (PUFA), free sterols (ST), ceramide phosphoethanolamines (CerPE), ceramide aminoethylphosphonates (CAEP), cardiolipins (CL), glycerophosphocholines (PC), glycerophosphoethanolamines (PE) and glycerophosphoserines (PS). In BMO, saturated fatty acids (FA14:0 and FA16:0), monounsaturated fatty acids (MUFA) and other storage components such as C18-PUFA accumulated in triradylglycerolipids (TG) and alkyldiacylglycerols (neutral plasmalogens, TG O-), which, together with terpenes, wax esters and cholesterol esters, make up most of oocytes yolk reserves. BMO also had higher levels of ceramides (Cer) and generally alkyl/alkenyl glycerophospholipids (mainly plasmanyl/plasmenyl PC), suggesting a role for these lipids in vitellogenesis. Non-methylene interrupted dienoic fatty acids (NMID FA), typically found in plasmalogens, were the only membrane-forming PUFA predominantly detected in BMO. The results of this study are of great importance for clarifying the lipid composition of BMG and provide an important basis for future studies on the reproductive physiology of these organisms.

A Diet Rich in HUFAs Enhances the Energetic and Immune Response Capacities of Larvae of the Scallop Argopecten purpuratus

Massive mortalities in farmed larvae of the scallop Argopecten purpuratus have been associated with pathogenic Vibrio outbreaks. An energetic trade-off between development-associated demands and immune capacity has been observed. Given that highly unsaturated fatty acids (HUFAs) are essential nutrients for larval development, we evaluated the effect of diets based on microalgae low and high in HUFAs (LH and HH, respectively) on the energetic condition and the immune response of scallop larvae. The results showed that the HH diet increased cellular membrane fluidity in veliger larvae. The routine respiration rate was 64% higher in the HH-fed veligers than in the LH-fed veligers. Additionally, the metabolic capacity tended to be higher in the HH-fed veligers than in the LH-fed veligers after the Vibrio challenge. After the challenge, the HH-fed veligers presented higher transcript induction of ApTLR (immune receptor) and ApGlys (immune effector) genes, and the HH-fed pediveligers presented higher induction of ApLBP/BPI1 (antimicrobial immune effector) gene, than the LH-fed larvae. Furthermore, the HH-fed veligers controlled total Vibrio proliferation (maintaining near basal levels) after the bacterial challenge, while the LH-fed veligers were not able to control this proliferation, which increased three-fold. Finally, the HH-fed larvae showed 20-25% higher growth and survival rates than the LH-fed veligers. Overall, the results indicated that the administration of a HH diet increases cell membrane fluidity and energy metabolic capacity, which in turn enhances immunity and the ability to control Vibrio proliferation. The administration of microalgae high in HUFAs would be a promising strategy for improving scallop larval production efficiency.

Effect of cadmium exposure on essential omega-3 fatty acids in the edible bivalve Donax trunculus

Donax trunculus is the most consumed bivalve by the local population of the Northeast Algeria for its nutritional value. Therefore, the aim of the current study was to determine the effects of cadmium (Cd), a known toxic metal, on the alterations in main essential omega-3 fatty acids, i.e., eicosapentaenoic acid (EPA; C20:5n-3) and docosahexaenoic acid (DHA; C22:6n-3), in male and female gonads of D. trunculus during the reproduction period at spring (before spawning). Additionally, this work seeks to describe the relation between EPA and DHA with non-methylene-interrupted dienoic (NMID) fatty acids, and explores their possible contribution of to protect against Cd stress. The samples were collected at El Battah, a relatively clean sea shore, and reared in the laboratory. Physico-chemical parameters such as temperature, pH, salinity, and dissolved oxygen were measured. Cd was added to the rearing water at two sublethal concentrations (LC₁₀ and LC₂₅-96h, as determined previously). A two-way ANOVA analysis indicated significant effects of concentrations and genders for both fatty acids. Our results showed a significant reduction in EPA and DHA concentrations in the both genders, with a strong effect in females. There was also a negative correlation between NMID fatty acids and the two essential omega-3 fatty acids for each gender.

Variation of content of lipid classes, sterols and fatty acids in gonads and digestive glands of Scrobicularia plana in relation to environment pollution levels

Lipids are central for energy metabolism and their fate in bivalves is closely linked to environmental conditions and gametogenic cycle. In order to assess the pollution impact on lipid metabolism of bivalves, storage and structure lipids from samples of Scrobicularia plana were studied. These samples were collected during sexual maturity both from estuaries considered contaminated (Goyen and Blavet) and from a reference site (Bay of St Brieuc) for comparison. Lipids were extracted from the gonads and the digestive glands and further separated by column chromatography. Fatty acids and sterols were then analyzed by gas chromatography-mass spectrometry. Correlations were shown between dioxin-like compounds (Eq-TCDD) and triacyglycerol levels (TAG). In the same way, glycolipids and contamination by polycyclic aromatic hydrocarbons (PAH) and pollutants with estrogenic activity seem to be closely related. In a second time, lipid indices (ratio between storage and structure lipids) were evaluated. Whereas these indices are often used in fish to assess habitat quality with regards to differential anthropogenic pressure, the ratio TAG/sterols was not here significantly influenced by the site of origin of S. plana. Intersite fluctuations of the ratio TAG/phospholipids also remained very limited. This could be explained by the limited contamination level in studied sites but also by a contrasted response from organisms in different taxa (bivalves vs. fish). Environmental pollution is not the only factor able to induce changes in lipid classes. The trophic wealth seemed to be different between the reference site and contaminated estuaries, the total organic carbon content being higher in muddy estuarine sediments.

Fatty acids from lipids of marine organisms: molecular biodiversity, roles as biomarkers, biologically active compounds, and economical aspects

Because of their characteristic living environments, marine organisms produce a variety of lipids. Fatty acids constitute the essential part of triglycerides and wax esters, which are the major components of fats and oils. Nevertheless, phospholipids and glycolipids have considerable importance and will be taken into account, especially the latter compounds that excite increasing interest regarding their promising biological activities. Thus, in addition to the major polyunsaturated fatty acids (PUFA) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, a great number of various fatty acids occur in marine organisms, e.g. saturated, mono- and diunsaturated, branched, halogenated, hydroxylated, methoxylated, non-methylene-interrupted. Various unprecedented chemical structures of fatty acids, and lipid-containing fatty acids, have recently been discovered, especially from the most primitive animals such as sponges and gorgonians. This review of marine lipidology deals with recent advances in the field of fatty acids since the end of the 1990s. Different approaches will be followed, mainly developing biomarkers of trophic chains in marine ecosystems and of chemotaxonomic interest, reporting new structures, especially those with biological activities or biosynthetic interest. An important part of this review will be devoted to the major PUFA, their relevance to health and nutrition, their biosynthesis, their sources (usual and promising) and market.

Incorporation and modification of dietary fatty acids in gill polar lipids by two bivalve species Crassostrea gigas and Ruditapes philippinarum

Two bivalve species Crassostrea gigas and Ruditapes philippinarum were fed eight weeks with three mono-specific algae diets: T-Isochrysis galbana, Tetraselmis suecica, Chaetoceros calcitrans, selected on the basis of their polyunsaturated fatty acid (PUFA) composition. The incorporation and the modification of dietary fatty acids in C. gigas and R. philippinarum gill lipids were analysed and compared. Essential PUFA (20:4n-6, 20:5n-3 and 22:6n-3) and non-methylene interrupted PUFAs (known to be synthesised from monounsaturated precursors) contents of gill polar lipid of both species were greatly influenced by the dietary conditioning. Interestingly, oysters and clams responded differentially to the mono-specific diets. Oysters maintained higher 20:5n-3 level and higher 22:2j/22:i and n-7/n-9 ratio in gill polar lipids than clams. To better discriminate dietary and species influences on the fatty acid composition, a Principal Component Analysis followed by a MANOVA on the two most explicative components was performed. These statistical analyses showed that difference in fatty acid compositions attributable to species were just as significant as the diet inputs. The differences of gill fatty acid compositions between oysters and clams are speculated to result of an intrinsic species characteristic and perhaps of a group characteristic: Fillibranch vs. Eulamellibranch.

Esterification of vertebrate-type steroids in the Eastern oyster (Crassostrea virginica)

Characteristics of acyl-coenzyme A (acyl-CoA):steroid acyltransferase from the digestive gland of the oyster Crassostrea virginica were determined by using estradiol (E2) and dehydroepiandrosterone (DHEA) as substrates. The apparent Km and Vmax values for esterification of E2 with the six fatty acid acyl-CoAs tested (C20:4, C18:2, C18:1, C16:1, C18:0, and C16:0) were in the range of 9-17 microM E2 and 35-74 pmol/min/mg protein, respectively. Kinetic parameters for esterification of DHEA (Km: 45-120 microM; Vmax: 30-182 pmol/min/mg protein) showed a lower affinity of the enzyme for this steroid. Formation of endogenous fatty acid esters of steroids by microsomes of digestive gland and gonads incubated in the presence of ATP and CoA was assessed, and at least seven E2 fatty acid esters and five DHEA fatty acid esters were observed. Some peaks eluted at the same retention times as palmitoleoyl-, linoleoyl-, oleoyl/palmitoyl-, and stearoyl-E2; and palmitoleoyl-, oleoyl/palmitoyl-, and stearoyl-DHEA. The same endogenous esters, although in different proportions, were produced by gonadal microsomes. The kinetic parameters for both E2 (Km: 10 microM; Vmax: 38 pmol/min/mg protein) and DHEA (Km: 61 microM; Vmax: 60 pmol/min/mg protein) were similar to those obtained in the digestive gland. Kinetic parameters obtained are similar to those observed in mammals; thus, fatty acid esterification of sex steroids appears to be a well-conserved conjugation pathway during evolution.

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.