Docosahexaenoic Acid Biosynthesis Research Articles

Biosynthetic deficiency of docosahexaenoic acid causes nonalcoholic fatty liver disease and ferroptosis-mediated hepatocyte injury

Exogenous omega-3 fatty acids, particularly docosahexaenoic acid (DHA), have shown to exert beneficial effects on nonalcoholic fatty liver disease (NAFLD), which is characterized by the excessive accumulation of lipids and chronic injury in the liver. However, the effect of endogenous DHA biosynthesis on the lipid homeostasis of liver is poorly understood. In this study, we used a DHA biosynthesis-deficient zebrafish model, elovl2 mutant, to explore the effect of endogenously biosynthesized DHA on hepatic lipid homeostasis. We found the pathways of lipogenesis and lipid uptake were strongly activated, while the pathways of lipid oxidation and lipid transport were inhibited in the liver of elovl2 mutants, leading to lipid droplet accumulation in the mutant hepatocytes and NAFLD. Furthermore, the elovl2 mutant hepatocytes exhibited disrupted mitochondrial structure and function, activated endoplasmic reticulum (ER) stress, and hepatic injury. We further unveiled that the hepatic cell death and injury was mainly mediated by ferroptosis, rather than apoptosis, in elovl2 mutants. Elevating DHA content in elovl2 mutants, either through introduction of an omega-3 desaturase (fat1) transgene or feeding with a DHA-rich diet, could strongly alleviate NAFLD features and ferroptosis-mediated hepatic injury. Together, our study elucidates the essential role of endogenous DHA biosynthesis in maintaining hepatic lipid homeostasis and liver health, highlighting that DHA deficiency can lead to NAFLD and ferroptosis-mediated hepatic injury.

Contribution of elovl5a to Docosahexaenoic Acid (DHA) Synthesis at the Transcriptional Regulation Level in Common Carp, Cyprinus carpio.

Docosahexaenoic acid (DHA) is an essential nutrient for humans and plays a critical role in human development and health. Freshwater fish, such as the common carp (Cyprinus carpio), have a certain degree of DHA biosynthesis ability and could be a supplemental source of human DHA needs. The elongase of very-long-chain fatty acid 5 (Elovl5) is an important enzyme affecting polyunsaturated fatty acid (PUFA) biosynthesis. However, the function and regulatory mechanism of the elovl5 gene related to DHA synthesis in freshwater fish is not clear yet. Previous studies have found that there are two copies of the elovl5 gene, elovl5a and elovl5b, which have different functions. Our research group found significant DHA content differences among individuals in Yellow River carp (Cyprinus carpio var.), and four candidate genes were found to be related to DHA synthesis through screening. In this study, the expression level of elovl5a is decreased in the high-DHA group compared to the low-DHA group, which indicated the down-regulation of elovl5a in the DHA synthesis pathways of Yellow River carp. In addition, using a dual-luciferase reporter gene assay, we found that by targeting the 3'UTR region of elovl5a, miR-26a-5p could regulate DHA synthesis in common carp. After CRISPR/Cas9 disruption of elovl5a, the DHA content in the disrupted group was significantly higher than in the wildtype group; meanwhile, the expression level of elovl5a in the disrupted group was significantly reduced compared with the wildtype group. These results suggest that elovl5a may be down-regulating DHA synthesis in Yellow River carp. This study could provide useful information for future research on the genes and pathways that affect DHA synthesis.

Between family variation in EPA and DHA storage among Atlantic salmon (Salmo salar) fed a fish oil-free diet

Biosynthesis and storage of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is under dietary and genetic control in Atlantic salmon (Salmo salar). Enhanced EPA and DHA biosynthesis and storage may improve utilization, and thus reduce marine forage fish oil use in aquafeeds. To determine phenotypic variability in EPA and DHA tissue content and growth performance, 50 families (n = 30 salmon/family, 48 g/fish initial weight) of Atlantic salmon (Saint John River strain) were reared in freshwater and fed either a fish oil (FO) control diet or FO-free diet. After 16 weeks, body size was recorded. Salmon fed the FO-free diet overall showed significantly lower growth performance compared to salmon fed the FO control diet, regardless of family. To determine the relationship between growth and FA content, the five families with the highest and the five families with the lowest weight gain were sampled for tissue and liver FA analysis. There was a significant interaction between growth and diet. The family x diet interaction was significant for final weight, final length, weight gain, growth rate and feed conversion ratio. Among the five fastest growing families, there was a significant family effect for EPA and DHA storage in the liver but not for muscle. Among the five slowest growing families, by comparison salmon had similar liver DHA and EPA content, independent of diet treatment. Family and diet were interacting factors that determine EPA and DHA storage in liver. Certain fast-growing families also had significantly higher DHA content in liver and muscle. This study demonstrates the potential for selecting families that can better utilize a diet without marine forage fish oil.

Dietary LC-PUFA and environmental salinity modulate the fatty acid biosynthesis capacity of the euryhaline teleost thicklip grey mullet (Chelon labrosus).

The capacity to biosynthesise long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA) depends upon the complement and function of key enzymes commonly known as fatty acyl desaturases and elongases. The presence of a Δ5/Δ6 desaturase enabling the biosynthesis of docosahexaenoic acid (22:6n-3, DHA) through the "Sprecher pathway" has been reported in Chelon labrosus. Research in other teleosts have demonstrated that LC-PUFA biosynthesis can be modulated by diet and ambient salinity. The present study aimed to assess the combined effects of partial dietary replacement of fish oil (FO) by vegetable oil (VO) and reduced ambient salinity (35ppt vs 20ppt) on the fatty acid composition of muscle, enterocytes and hepatocytes of C. labrosus juveniles. Moreover, the enzymatic activity over radiolabelled [1-14C] 18:3n-3 (α-linolenic acid, ALA) and [1-14C] 20:5n-3 (eicosapentaenoic acid, EPA) to biosynthesise n-3 LC-PUFA in hepatocytes and enterocytes, and the gene regulation of the C. labrosus fatty acid desaturase-2 (fads2) and elongation of very long chain fatty acids protein 5 (elovl5) in liver and intestine was also investigated. Recovery of radiolabelled products including stearidonic acid (18:4n-3, SDA), 20:5n-3, tetracosahexaenoic acid (24:6n-3, THA) and 22:6n-3 in all treatments except FO35-fish, provided compelling evidence that a complete pathway enabling the biosynthesis of EPA and DHA from ALA is present and active in C. labrosus. Low salinity conditions upregulated fads2 in hepatocytes and elovl5 in both cell types, regardless of dietary composition. Interestingly, FO20-fish showed the highest amount of n-3 LC-PUFA in muscle, while no differences in VO-fish reared at both salinities were found. These results demonstrate a compensatory capacity of C. labrosus to biosynthesise n-3 LC-PUFA under reduced dietary supply, and emphasise the potential of low salinity conditions to stimulate this pathway in euryhaline fish.

Endogenous biosynthesis of docosahexaenoic acid (DHA) regulates fish oocyte maturation by promoting pregnenolone production.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), particularly docosahexaenoic acid (22:6n-3, DHA), play crucial roles in the reproductive health of vertebrates, including humans. Nevertheless, the underlying mechanism related to this phenomenon remains largely unknown. In this study, we employed two zebrafish genetic models, i.e., elovl2 -/- mutant as an endogenous DHA-deficient model and fat1 (omega-3 desaturase encoding gene) transgenic zebrafish as an endogenous DHA-rich model, to investigate the effects of DHA on oocyte maturation and quality. Results show that the elovl2 -/- mutants had much lower fecundity and poorer oocyte quality than the wild-type controls, while the fat1 zebrafish had higher fecundity and better oocyte quality than wild-type controls. DHA deficiency in elovl2 -/- embryos led to defects in egg activation, poor microtubule stability, and reduced pregnenolone levels. Further study revealed that DHA promoted pregnenolone synthesis by enhancing transcription of cyp11a1, which encodes the cholesterol side-chain cleavage enzyme, thereby stabilizing microtubule assembly during oogenesis. In turn, the hypothalamic-pituitary-gonadal axis was enhanced by DHA. In conclusion, using two unique genetic models, our findings demonstrate that endogenously synthesized DHA promotes oocyte maturation and quality by promoting pregnenolone production via transcriptional regulation of cyp11a1.

BZIP transcription factor FabR: Redox-dependent mechanism controlling docosahexaenoic acid biosynthesis and H2O2 stress response in Schizochytrium sp.

Schizochytrium sp. is an important industrial strain for commercial production of docosahexaenoic acid (DHA), which plays essential physiological roles in infant development and human health. The regulatory network for DHA biosynthesis and lipid accumulation in Schizochytrium remains poorly understood. FabR (fatty acid biosynthesis repressor), a basic leucine zipper (bZIP) transcription factor, was transcriptionally downregulated under low-nitrogen condition. Deletion of fabR gene (mutant ΔfabR) increased production of total lipids and DHA by 30.1% and 46.5%, respectively. ΔfabR displayed H2O2 stress resistance higher than that of parental strain or complementation strain CfabR. FabR bound specifically to 7-bp pseudo-palindromic sequence 5′-ATTSAAT-3′ in upstream regions and repressed transcription of fatty acid biosynthesis genes (acl, fas, pfa) and antioxidant defense genes (cat, sod1, sod2, gpx). DNA binding activity of FabR was regulated in a redox-dependent manner. Under oxidative condition, FabR forms intermolecular disulfide bonds between two Cys46 residues of dimers; its DNA binding activity is thereby lost, and the transcription of its target genes is enhanced through derepression. Our findings clarify the redox-dependent mechanism that modulates FabR activity governing lipid and DHA biosynthesis and H2O2 stress response in Schizochytrium.

Uncovering global lipid accumulation routes towards docosahexaenoic acid (DHA) production in Aurantiochytrium sp. SW1 using integrative proteomic analysis

Aurantiochytrium sp., a marine thraustochytrid possesses a remarkable ability to produce lipid rich in polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid (DHA). Although gene regulation underlying lipid biosynthesis has been previously reported, proteomic analysis is still limited. In this study, high DHA accumulating strain Aurantiochytrium sp. SW1 has been used as a study model to elucidate the alteration in proteome profile under different cultivation phases i.e. growth, nitrogen-limitation and lipid accumulation. Of the total of 5146 identified proteins, 852 proteins were differentially expressed proteins (DEPs). The largest number of DEPs (488 proteins) was found to be uniquely expressed between lipid accumulating phase and growth phase. Interestingly, there were up-regulated proteins involved in glycolysis, glycerolipid, carotenoid and glutathione metabolism which were preferable metabolic routes towards lipid accumulation and DHA production as well as cellular oxidative defence. Integrated proteomic and transcriptomic data were also conducted to comprehend the gene and protein regulation underlying the lipid and DHA biosynthesis. A significant up-regulation of acetyl-CoA synthetase was observed which suggests alternative route of acetate metabolism for acetyl-CoA producer. This study presents the holistic routes underlying lipid accumulation and DHA production in Aurantiochytrium sp. SW1 and other relevant thraustochytrid.

Capability of DHA biosynthesis in a marine teleost, Pacific saury Cololabis saira: functional characterization of two paralogous Fads2 desaturases and Elovl5 elongase

The Pacific saury Cololabis saira is an important fishery resource in the Far East, where it is appreciated for its high lipid content, which includes long-chain polyunsaturated fatty acids (LC-PUFAs) such as docosahexaenoic acid (DHA). Although it has been hypothesized that these fatty acids are derived from their prey items, this study focused on evaluating the capacity of saury for endogenous production of LC-PUFAs. To describe its LC-PUFA biosynthetic pathway, we characterized fatty acid desaturase 2 (Fads2) and elongation of very long-chain fatty acid protein 5 (Elovl5) in Pacific saury. Two paralogous fads2 genes, namely fads2a and fads2b, were isolated from the saury and their recombinant protein showed ∆6∆8 and ∆4∆5 desaturase activities, respectively. Meanwhile, saury Elovl5 had elongase activity toward C18 and C20 PUFA. These three enzyme genes were expressed in the brain and liver, although fads2a was absent in the latter. Our results suggest that the saury has sufficient enzymatic functions, particularly in its brain, for DHA biosynthesis through the ∆4 pathway even from α-linolenic acid. This information provides novel insights into the origin of LC-PUFAs in Pacific saury and the future perspective for its potential as a source of such vital fatty acids for human consumption.

Eliminating the accumulation of reactive oxygen species through periodic hypoxic stress control for effective DHA production by Schizochytrium sp

Nitrogen starvation has been widely used for increasing docosahexaenoic acid (DHA) production by Schizochytrium sp. cells. However, dissolved oxygen concentration (DO) would be kept at rich and excessive levels due to the shortage of nitrogen source and the severe accumulation of reactive oxygen species (ROS) was induced by the oxygen-rich environment, leading to a failure of DHA production. To solve above problems, a periodic hypoxic stress control strategy was proposed and carried out through periodically switching the environments from “nitrogen-limited/oxygen-rich” to “nitrogen-rich/oxygen-limited”. When using this strategy, the lowest distribution of glucose to cells maintenance (0.0046 vs 0.0166 1/h) and the highest activities of key enzymes in DHA biosynthesis metabolisms were achieved by repressing the severe accumulation of ROS (251.24 ± 12.61 vs 175.66 ± 10.51 FI/g-DCW). As a result, DHA concentration increased over 30% as compared to control group and reached the highest level of 23.19 ± 1.29 g/L.

Development of Schizochytrium sp. strain HS01 with high-DHA and low-saturated fatty acids production by multi-pronged adaptive evolution.

Docosahexaenoic acid (DHA) is an important omega-3 unsaturated fatty acid and has been widely applied in medicine, food additives, and feed ingredients. The fermentative production of DHA using microorganisms, including Schizochytrium sp., attracted much attention due to its high production efficiency and environment friendly properties. An efficient laboratory evolution approach was used to improve the strain's performance in this study. A multi-pronged laboratory evolution approach was applied to evolve high-yield DHA-producing Schizochytrium strain. We further employed comparative transcriptional analysis to identify transcriptional changes between the screened strain HS01 and its parent strain GS00. After multiple generations of ALE, a strain HS01 with higher DHA content and lower saturated fatty acids content was obtained. Low nitrogen conditions were important for enhancing DHA biosynthesis in HS01. The comparative transcriptional analysis results indicated that during the fermentation process of HS01, the expression of key enzymes in the glycolysis, the pentose phosphate pathway and the tricarboxylic acid cycle were up-regulated, while the expression of polyketide synthase genes and fatty acid synthesis genes were similar to those in GS00. The results suggest that the improved DHA production capacity of HS01 is not due to enhancement of the DHA biosynthesis pathway, but rather related to modulation of central metabolism pathways.

Transcriptome analysis of malate-induced Schizochytrium sp. FJU-512 reveals a novel pathway for biosynthesis of docosahexaenoic acid with enhanced expression of genes responsible for acetyl-CoA and NADPH accumulation.

Schizochytrium is one of the few oleaginous microalgae that produce docosahexaenoic acid (DHA)-rich lipids. In this study, global changes in gene expression levels of Schizochytrium sp. FJU-512 cultured with malate in a 15 l-bioreactor was analyzed using comparative transcriptomics. The changes were found mainly in the genes involved in oxidative phosphorylation, β-oxidation, and pentose phosphate pathways. Consequently, the global changes in genes associated with the pathways could lead to an increase in the influx throughputs of pyruvate, branched-chain amino acids, fatty acids, and vitamin B6. Our transcriptome analysis indicated pyruvate dehydrogenase E2 component and acetolactate synthase I/II/III large subunit as major contributors to acetyl-CoA biosynthesis, whereas glucose-6-phosphate dehydrogenase was indicated as the major contributor to the biosynthesis of NADPH. An increase in DHA titer of up to 22% was achieved with the addition of malate to the fed-batch culture of Schizochytrium sp. FJU-512. This study provides an alternate method to enhance DHA production in Schizochytrium sp. FJU-512 through malate induced upregulation of genes responsible for acetyl-CoA and NADPH biosynthesis.

Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations.

Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.

Strategic Development of Aurantiochytrium sp. Mutants With Superior Oxidative Stress Tolerance and Glucose-6-Phosphate Dehydrogenase Activity for Enhanced DHA Production Through Plasma Mutagenesis Coupled With Chemical Screening.

Thraustochytrids, such as Aurantiochytrium and Schizochytrium, have been shown as a promising sustainable alternative to fish oil due to its ability to accumulate a high level of docosahexaenoic acid (DHA) from its total fatty acids. However, the low DHA volumetric yield by most of the wild type (WT) strain of thraustochytrids which probably be caused by the low oxidative stress tolerance as well as a limited supply of key precursors for DHA biosynthesis has restricted its application for industrial application. Thus, to enhance the DHA production, we aimed to generate Aurantiochytrium SW1 mutant with high tolerance toward oxidative stress and high glucose-6 phosphate dehydrogenase (G6PDH) activities through strategic plasma mutagenesis coupled with chemical screening. The WT strain (Aurantiochytrium sp. SW1) was initially exposed to plasma radiation and was further challenged with zeocin and polydatin, generating a mutant (YHPM1) with a 30, 65, and 80% higher overall biomass, lipid, and DHA production in comparison with the parental strains, respectively. Further analysis showed that the superior growth, lipid, and DHA biosynthesis of the YHMP1 were attributed not only to the higher G6PDH and enzymes involved in the oxidative defense such as superoxide dismutase (SOD) and catalase (CAT) but also to other key metabolic enzymes involved in lipid biosynthesis. This study provides an effective approach in developing the Aurantiochytrium sp. mutant with superior DHA production capacity that has the potential for industrial applications.

Zinc Finger Protein LipR Represses Docosahexaenoic Acid and Lipid Biosynthesis in Schizochytrium sp.

The heterotrophic marine microalgae Schizochytrium sp. is an important industrial producer of docosahexaenoic acid (DHA). Increased production of DHA and lipids in Schizochytrium sp. has been achieved by standard fermentation optimization and metabolic engineering methods; however, regulatory mechanisms for DHA and lipid biosynthesis remain unknown. In this study, the C2H2 zinc finger protein LipR was identified in Schizochytrium sp. ATCC 20888 by transcriptional analysis. Deletion of the lipR gene significantly (P < 0.001) increased production of total lipids and DHA by 33% and 48%, respectively. LipR repressed DHA and lipid production by directly inhibiting transcription of polyunsaturated fatty acid (PUFA) and fatty acid synthase (FAS) genes (pfa1, pfa2, pfa3, and fas). Specific binding of LipR to 9-bp recognition sequence 5'-(C/A)(A/G)CCATCTT-3' in upstream regions of target genes was demonstrated by electrophoretic mobility shift assays (EMSAs) and DNase I footprinting assays. Expression of several key genes (acc, acl, ampD, fabD, mae, zwf, and dga1) related to levels of precursors and NADPH, and to triacylglycerol storage rate, were also directly repressed by LipR. Our findings, taken together, indicate that the evolutionarily unique regulator LipR is an essential repressor of DHA and saturated fatty acid biosynthesis in Schizochytrium sp. IMPORTANCE Regulatory mechanisms for DHA and saturated fatty acid biosynthesis in the heterotrophic marine microalgae Schizochytrium sp. are unclear. We demonstrate here that deletion of the gene (lipR) encoding the C2H2 zinc finger protein LipR promotes DHA and saturated fatty acid production in this genus. LipR acts as a key repressor of such production by binding to 9-bp consensus sequence 5'-(C/A)(A/G)CCATCTT-3' in the upstream regions of polyunsaturated fatty acid and fatty acid synthase genes (pfa1, pfa2, pfa3, and fas), and genes related to levels of precursors and NADPH (acc, acl, ampD, fabD, mae, and zwf), and to triacylglycerol storage rate (dga1). This is the first demonstration that a regulator inhibits synthesis of DHA and lipids in Schizochytrium sp. by directly controlling transcription of PUFA synthase and fas genes. Manipulation of the lipR gene provides a potential strategy for enhancing accumulation of polyunsaturated fatty acids and lipids in thraustochytrids.

PUFA synthase-independent DHA synthesis pathway in Parietichytrium sp. and its modification to produce EPA and n-3DPA

The demand for n-3 long-chain polyunsaturated fatty acids (n-3LC-PUFAs), such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), will exceed their supply in the near future, and a sustainable source of n-3LC-PUFAs is needed. Thraustochytrids are marine protists characterized by anaerobic biosynthesis of DHA via polyunsaturated fatty acid synthase (PUFA-S). Analysis of a homemade draft genome database suggested that Parietichytrium sp. lacks PUFA-S but possesses all fatty acid elongase (ELO) and desaturase (DES) genes required for DHA synthesis. The reverse genetic approach and a tracing experiment using stable isotope-labeled fatty acids revealed that the ELO/DES pathway is the only DHA synthesis pathway in Parietichytrium sp. Disruption of the C20 fatty acid ELO (C20ELO) and ∆4 fatty acid DES (∆4DES) genes with expression of ω3 fatty acid DES in this thraustochytrid allowed the production of EPA and n-3docosapentaenoic acid (n-3DPA), respectively, at the highest level among known microbial sources using fed-batch culture.

Food and Feed Safety of NS-B5ØØ27-4 Omega-3 Canola (Brassica napus): A New Source of Long-Chain Omega-3 Fatty Acids.

DHA canola, a genetically engineered Brassica napus (OECD Unique Identifier NS-B5ØØ27-4), has been developed as one of the first land-based production systems for omega-3 long-chain polyunsaturated fatty acids (LCPUFA), whose health benefits are well-established. Yet, the marine sources of these nutrients are under high pressures due to over-fishing and increasing demand. DHA canola is a plant-based source for these essential fatty acids that produces a high level of docosahexaenoic acid (DHA). This terrestrial system allows for sustainable, scalable and stable production of omega-3 LCPUFA that addresses not only the increasing market demand, but also the complex interplay of agriculture, aquaculture, and human nutrition. The vector used to produce the desired oil profile in DHA canola contains the expression cassettes of seven genes in the DHA biosynthesis pathway and was specifically designed to convert oleic acid to DHA in canola seed. The characterization and safety evaluation of food and feed produced from DHA canola are described and supported by a detailed nutritional analysis of the seed, meal, and oil. Aside from the intended changes of the fatty acid profile, none of the other compositional analytes showed biologically meaningful differences when compared to conventional canola varieties. In addition, the meal from DHA canola is compositionally equivalent to conventional canola meal. Further evidence of nutritional value and safety of DHA canola oil have been confirmed in fish feeding studies. Given that most human populations lack sufficient daily intakes of omega-3 LCPUFA, a dietary exposure assessment is also included. In conclusion, the results from these studies demonstrate it is safe to use products derived from DHA canola in human foods, nutraceuticals, or animal feeds.

Evaluation of diverse biochemical stimulants to enhance growth, lipid and docosahexaenoic acid (DHA) production of Aurantiochytrium Sp. ATCC PRA-276

In the current investigation, the efficacy of five different biochemical stimulants; 2-phenylacetic acid (PAA), humic acid (HA), spermidine (SPD), 1-methylcyclopropene (1-MCP), and ferric chlorides (FC), as potential stimulant in augmenting the growth/biomass, lipid and docosahexaenoic acid (DHA) production of Aurantiochytrium sp. ATCC PRA-276 were elucidated. After 120 h of cultivation, the individual supplementation of PAA, HA, SPD, 1-MCP, and FC, elevates the biomass, total lipid and DHA production of Aurantiochytrium sp. ATCC PRA-276 by 32%–76%, 23%–34%, and 53%–86% in comparison to the control, respectively. The highest biomass and DHA productivities was observed with the supplementation of PAA and FC achieving 76% and 67% and 86% and 66%, compared to the control, respectively. PAA supplementation may have increased biomass production by reducing the lag period and extending the log phase. While only a marginal increment on biomass and DHA contents of Aurantiochytrium sp. ATCC PRA-276 was observed with the supplementation of 1-MCP. This study suggests the potential application of biochemical stimulants for improved growth, lipid and DHA productivities of Aurantiochytrium sp. ATCC PRA-276. • The effects of biochemical stimulants on Aurantiochytrium sp. ATCC PRA-276 growth, lipid, and DHA biosynthesis were studied. • Individual supplements of PAA, HA, and FC enhanced biomass, lipid, and DHA by 32%–76%, 23%–34%, and 53%–86%, respectively. • With the addition of PAA and FC, the maximum biomass and DHA productivities were achieved. • The addition of 1-MCP resulted in just a slight increase in the biomass and DHA contents of Aurantiochytrium sp. ATCC PRA-276.

Obtaining High-Purity Docosahexaenoic Acid Oil in Thraustochytrid Aurantiochytrium through a Combined Metabolic Engineering Strategy.

High-purity docosahexaenoic acid (DHA) resources are insufficient in the pharmaceutical and food industries. Although many efforts have attempted to obtain the high-purity DHA production, few reports have been successful. Here, a combined metabolic engineering strategy was employed to increase the DHA purity in the oleaginous thraustochytrid Aurantiochytrium. The strategy includes both partial deactivation of the competing pathway of DHA biosynthesis, by disrupting one copy of the fatty acid synthase gene, and strengthening of substrate supply and triacylglycerol synthesis, by the overexpression of acetyl-CoA carboxylase and diacylglycerol acyltransferase. With this strategy, a final mutant was obtained with a DHA purity of 61% in total fatty acids and a content of 331 mg/g dry cell weight. This study provides an advanced strategy for sustainable high-purity DHA production and highlights the strategy for producing designer oils in industrial oleaginous microorganisms.

Copy number variation of a fatty acid desaturase geneFads2associated with ecological divergence in freshwater stickleback populations

Fitness of aquatic animals can be limited by the scarcity of nutrients such as long-chain polyunsaturated fatty acids, especially docosahexaenoic acid (DHA). DHA availability from diet varies among aquatic habitats, imposing different selective pressures on resident animals to optimize DHA acquisition and synthesis. For example, DHA is generally poor in freshwater ecosystems compared to marine ecosystems. Our previous work revealed that, relative to marine fishes, several freshwater fishes evolved higher copy numbers of the fatty acid desaturase2 (Fads2) gene, which encodes essential enzymes for DHA biosynthesis, likely compensating for the limited availability of DHA in freshwater. Here, we demonstrate that Fads2 copy number also varies between freshwater sticklebacks inhabiting lakes and streams with stream fish having higher Fads2 copy number. Additionally, populations with benthic-like morphology possessed higher Fads2 copy number than those with planktivore-like morphology. This may be because benthic-like fish mainly feed on DHA-deficient prey such as macroinvertebrates whereas planktivore-like fish forage more regularly on DHA-rich prey, like copepods. Our results suggest that Fads2 copy number variation arises from ecological divergence not only between organisms exploiting marine and freshwater habitats but also between freshwater organisms exploiting divergent resources.

Health benefits of docosahexaenoic acid and its bioavailability: A review.

Docosahexaenoic acid (DHA) is the predominant omega‐3 long‐chain polyunsaturated fatty acid found in human brain and eyes. There are a number of studies in the literature showing the health benefits of DHA. It is critical throughout all life stages from the need for fetal development, the prevention of preterm birth, and the prevention of cardiovascular disease to the improvements in the cognitive function and the eye health of adults and elderly. These benefits might be related to the modulation of gut microbiota by DHA. In addition, there are some discrepancies in the literature regarding certain health benefits of DHA, and this review is intended to explore and understand these discrepancies. Besides the variations in the DHA contents of different supplement sources, bioavailability is crucial for the efficacy of DHA supplements, which depends on several factors. For example, DHA in phospholipid and triglyceride forms are more readily to be absorbed by the body than that in ethyl ester form. In addition, dietary lipids in meals and emulsification of DHA oil can increase the bioavailability of DHA. Estrogens stimulated the biosynthesis of DHA, whereas testosterone stimulus induced a decrease in DHA. The roles of DHA through human lifespan, the sources, and its recommended daily intake in different countries are also discussed to provide a better understanding of the importance of this review.