Pathways of lipid metabolism in marine algae, co-expression network, bottlenecks and candidate genes for enhanced production of EPA and DHA in species of Chromista

The potential of Pavlovophyceae species as a source of valuable carotenoids and polyunsaturated fatty acids for human consumption

Microalgae are a group of microorganisms, mostly photoautotrophs with high CO2 fixation capacity, that have gained increased attention in the last decades due to their ability to produce a wide range of valuable metabolites, such as carotenoids and polyunsaturated fatty acids, for application in food/feed, pharmaceutical, and cosmeceutical industries. Their increasing relevance has highlighted the importance of identifying and culturing new bioactive-rich microalgae species, as well as of a thorough understanding of the growth conditions to optimize the biomass production and master the biochemical composition according to the desired application. Thus, this review intends to describe the main cell processes behind the production of carotenoids and polyunsaturated fatty acids, in order to understand the possible main triggers responsible for the accumulation of those biocompounds. Their economic value and the biological relevance for human consumption are also summarized. In addition, an extensive review of the impact of culture conditions on microalgae growth performance and their biochemical composition is presented, focusing mainly on the studies involving Pavlovophyceae species. A complementary description of the biochemical composition of these microalgae is also presented, highlighting their potential applications as a promising bioresource of compounds for large-scale production and human and animal consumption.

Impact of Climate Change on Dietary Nutritional Quality and Implications for Asthma and Allergy

Asthma and allergic disorders are common in childhood with genetic and environmental determinants of disease that include prenatal nutritional exposures such as long-chain polyunsaturated fatty acids and antioxidants. Global climate change is implicated in asthma and allergic disorder morbidity with potential mechanisms including perturbations of ecosystems. There is support that environmental and climatic changes such as increasing global temperate and carbon dioxide levels affect aquatic and agricultural ecosystems with subsequent alterations in long-chain polyunsaturated fatty acid availability and nutrient quality and antioxidant capacity of certain crops, respectively. This article discusses asthma epidemiology and the influence of global climate change.

Acyl-CoA binding protein is required for lipid droplet degradation in the diatom Phaeodactylum tricornutum

Diatoms (Bacillariophyceae) accumulate neutral storage lipids in lipid droplets during stress conditions, which can be rapidly degraded and recycled when optimal conditions resume. Since nutrient and light availability fluctuate in marine environments, storage lipid turnover is essential for diatom dominance of marine ecosystems. Diatoms have garnered attention for their potential to provide a sustainable source of omega-3 fatty acids. Several independent proteomic studies of lipid droplets isolated from the model oleaginous pennate diatom Phaeodactylum tricornutum have identified a previously uncharacterized protein with an acyl-CoA binding (ACB) domain, Phatrdraft_48778, here referred to as Phaeodactylum tricornutum acyl-CoA binding protein (PtACBP). We report the phenotypic effects of CRISPR-Cas9 targeted genome editing of PtACBP. ptacbp mutants were defective in lipid droplet and triacylglycerol degradation, as well as lipid and eicosapentaenoic acid synthesis, during recovery from nitrogen starvation. Transcription of genes responsible for peroxisomal β-oxidation, triacylglycerol lipolysis, and eicosapentaenoic acid synthesis was inhibited. A lipid-binding assay using a synthetic ACB domain from PtACBP indicated preferential binding specificity toward certain polar lipids. PtACBP fused to eGFP displayed an endomembrane-like pattern, which surrounded the periphery of lipid droplets. PtACBP is likely responsible for intracellular acyl transport, affecting cell division, development, photosynthesis, and stress response. A deeper understanding of the molecular mechanisms governing storage lipid turnover will be crucial for developing diatoms and other microalgae as biotechnological cell factories.

Lipidome Plasticity Enables Unusual Photosynthetic Flexibility in Arctic vs. Temperate Diatoms

The diatom lipidome actively regulates photosynthesis and displays a high degree of plasticity in response to a light environment, either directly as structural modifications of thylakoid membranes and protein-pigment complexes, or indirectly via photoprotection mechanisms that dissipate excess light energy. This acclimation is crucial to maintaining primary production in marine systems, particularly in polar environments, due to the large temporal variations in both the intensity and wavelength distributions of downwelling solar irradiance. This study investigated the hypothesis that Arctic marine diatoms uniquely modify their lipidome, including their concentration and type of pigments, in response to wavelength-specific light quality in their environment. We postulate that Arctic-adapted diatoms can adapt to regulate their lipidome to maintain growth in response to the extreme variability in photosynthetically active radiation. This was tested by comparing the untargeted lipidomic profiles, pigmentation, specific growth rates and carbon assimilation of the Arctic diatom Porosira glacialis vs. the temperate species Coscinodiscus radiatus during exponential growth under red, blue and white light. Here, we found that the chromatic wavelength influenced lipidome remodeling and growth in each strain, with P. glacialis showing effective utilization of red light coupled with increased inclusion of primary light-harvesting pigments and polar lipid classes. These results indicate a unique photoadaptation strategy that enables Arctic diatoms like P. glacialis to capitalize on a wide chromatic growth range and demonstrates the importance of active lipid regulation in the Arctic light environment.

Role of ERA protein in enhancing glyceroglycolipid synthesis and phosphate starvation tolerance in Synechococcus elongatus PCC 7942

Glyceroglycolipids are the primary thylakoid membrane lipids in cyanobacteria. Their diverse bioactivities have led to extensive utilization in the biomedical industry. In this study, we elucidated the role of ERA (E. coli Ras-like protein) in augmenting glyceroglycolipid synthesis and bolstering stress resilience in Synechococcus elongatus PCC 7942 during phosphate starvation. Notably, the ERA overexpression strain (ERA OE) outperformed the wild-type (WT) strain under phosphate-starved conditions, displaying an average 13.9 % increase in biomass over WT during the entire growth period, peaking at 0.185 g L-1 of dry cell weight on day 6. Lipidomic analysis using UHPLC-MS/MS techniques revealed that ERA OE exhibited a higher total glyceroglycolipid content compared to WT under phosphate starvation, representing a 7.95 % increase over WT and constituting a maximum of 5.07 % of dry cell weight on day 6. Transcriptomic analysis identified a significant up-regulation of the gldA gene (encoding glycerol dehydrogenase) involved in glycerolipid metabolism due to overexpression of ERA during phosphate starvation. These findings suggest a potential mechanism by which ERA regulates glyceroglycolipid synthesis through the up-regulation of GldA, thereby enhancing phosphate starvation tolerance in S. elongatus PCC 7942. Furthermore, lipidomic analysis revealed that ERA facilitated the production of glyceroglycolipid molecules containing C16:1 and C18:1 fatty acids. Additionally, ERA redirected lipid flux and promoted glyceroglycolipid accumulation while attenuating triacylglycerol production under phosphate starvation. This study represents the first demonstration of pivotal role of ERA in enhancing glyceroglycolipid synthesis and phosphate starvation tolerance in cyanobacteria, offering new insights into the effective utilization of glyceroglycolipids in various applications.

Resolving the dynamics of chrysolaminarin regulation in a marine diatom: A physiological and transcriptomic study

Diatom containing different active biological macromolecules are thought to be an excellent microbial cell factory. Phaeodactylum tricornutum, a model diatom, is a superb chassis organism accumulating chrysolaminarin with important bioactivities. However, the characteristic of chrysolaminarin accumulation and molecular mechanism of the fluctuated chrysolaminarin in diatom are still unknown. In this study, physiological data and transcriptomic analysis were carried out to clarify the mechanism involved in chrysolaminarin fluctuation. The results showed that chrysolaminarin content fluctuated, from 7.41 % dry weight (DW) to 40.01 % DW during one light/dark cycle, increase by day and decrease by night. The similar fluctuated characteristic was also observed in neutral lipid content. Genes related to the biosynthesis of chrysolaminarin and neutral lipid were up-regulated at the beginning of light-phase, explaining the accumulation of these biological macromolecules. Furthermore, genes involved in carbohydrate degradation, cell cycle, DNA replication and mitochondria-localized β-oxidation were up-regulated at the end of light phase and at the beginning of dark phase hinting an energy transition of carbohydrate to cell division during the dark period. Totally, our findings provide important information for the regulatory mechanism in the diurnal fluctuation of chrysolaminarin. It would also be of great help for the mass production of economical chrysolaminarin in marine diatom.

CRISPR/Cas9-mediated knock-in of masu salmon (Oncorhyncus masou) elongase gene in the melanocortin-4 (mc4r) coding region of channel catfish (Ictalurus punctatus) genome

Channel catfish, Ictalurus punctatus, have limited ability to synthesize Ω-3 fatty acids. The ccβA-msElovl2 transgene containing masu salmon, Oncorhynchus masou, elongase gene driven by the common carp, Cyprinus carpio, β-actin promoter was inserted into the channel catfish melanocortin-4 receptor (mc4r) gene site using the two-hit two-oligo with plasmid (2H2OP) method. The best performing sgRNA resulted in a knockout mutation rate of 92%, a knock-in rate of 54% and a simultaneous knockout/knock-in rate of 49%. Fish containing both the ccβA-msElovl2 transgene knock-in and mc4r knockout (Elovl2) were 41.8% larger than controls at 6 months post-hatch (p = 0.005). Mean eicosapentaenoic acid (EPA, C20:5n-3) levels in Elov2 mutants and mc4r knockout mutants (MC4R) were 121.6% and 94.1% higher than in controls, respectively (p = 0.045; p = 0.025). Observed mean docosahexaenoic acid (DHA, C22:6n-3) and total EPA + DHA content was 32.8% and 45.1% higher, respectively, in Elovl2 transgenic channel catfish than controls (p = 0.368; p = 0.025). To our knowledge this is the first example of genome engineering to simultaneously target transgenesis and knock-out a gene in a commercially important aquaculture species for multiple improved performance traits. With a high transgene integration rate, improved growth, and higher omega-3 fatty acid content, the use of Elovl2 transgenic channel catfish appears beneficial for application on commercial farms.

Promising Sources of Plant-Derived Polyunsaturated Fatty Acids: A Narrative Review

(1) Background: Polyunsaturated fatty acids (PUFAs) are known for their ability to protect against numerous metabolic disorders. The consumption of oily fish is the main source of PUFAs in human nutrition and is commonly used for supplement production. However, seafood is an overexploited source that cannot be guaranteed to cover the global demands. Furthermore, it is not consumed by everyone for ecological, economic, ethical, geographical and taste reasons. The growing demand for natural dietary sources of PUFAs suggests that current nutritional sources are insufficient to meet global needs, and less and less will be. Therefore, it is crucial to find sustainable sources that are acceptable to all, meeting the world population's needs. (2) Scope: This review aims to evaluate the recent evidence about alternative plant sources of essential fatty acids, focusing on long-chain omega-3 (n-3) PUFAs. (3) Method: A structured search was performed on the PubMed search engine to select available human data from interventional studies using omega-3 fatty acids of non-animal origin. (4) Results: Several promising sources have emerged from the literature, such as algae, microorganisms, plants rich in stearidonic acid and GM plants. However, the costs, acceptance and adequate formulation deserve further investigation.

Flashing lights affect the photophysiology and expression of carotenoid and lipid synthesis genes in Nannochloropsis gaditana

Nannochloropsis gaditana is a promising microalga for biotechnology. One of the strategies to stimulate its full potential in metabolite production is exposure to flashing lights. Here, we report how N. gaditana adapts to different flashing light regimes (5, 50, and 500 Hz) by changing its cellular physiology and the relative expression of genes related to critical cellular functions. We analyzed the differential mRNA abundance of genes related to photosynthesis, nitrogen assimilation and biosynthesis of chlorophyll, carotenoids, lipids, fatty acids and starch. Analysis of photosynthetic efficiency and high mRNA abundance of photoprotection genes supported the inference that excess excitation energy provided by light absorbance during photosynthesis was produced under low frequency flashing lights and was dissipated by photopigments via the xanthophyll-cycle. Increased relative expression levels of genes related to the synthesis of carotenoids and chlorophyll confirmed the accumulation of photopigments previously observed at low frequency flashing lights. Higher differential mRNA abundance of genes related to the triacylglycerol biosynthesis were observed at lower frequency flashing lights, possibly triggered by a poor nitrogen assimilation caused by low mRNA abundance of a nitrate reductase gene. This study advances a new understanding of algal physiology and metabolism leading to improved cellular performance and metabolite production.

Integrated Omics analysis of pig muscle metabolism under the effects of dietary Chlorella vulgaris and exogenous enzymes

Monogastric feeding is dependent on costly conventional feedstuffs. Microalgae such as Chlorella vulgaris are a sustainable alternative; however, its recalcitrant cell wall hinders monogastric digestion. Carbohydrate Active Enzyme (CAZyme) supplementation is a possible solution. The objective of this work was to evaluate the effect of 5% dietary C. vulgaris (CV) and enzymatic supplementation (CV + R-Rovabio® Excel AP; CV + M-four CAZyme mix) on muscle transcriptome and proteome of finishing pigs, in an integrated approach. Control pigs increased the abundance of contractile apparatus (MYH1, MYH2, MYH4) and energy metabolism (CKMT1, NDUFS3) proteins, demonstrating increased nutrient availability. They had increased expression of SCD, characteristic of increased glucose availability, via the activation of SREBP-1c and ChREBP. CV and CV + R pigs upregulated proteolytic and apoptotic genes (BAX, DDA1), whilst increasing the abundance of glucose (UQCRFS1) and fatty acid catabolism (ACADS) proteins. CV + R pigs upregulated ACOT8 and SIRT3 genes as a response to reduced nutrient availability, maintaining energy homeostasis. The cell wall specific CAZyme mix, CV + M, was able to comparatively reduce Omics alterations in the muscle, thereby reducing endogenous nutrient catabolism compared to the CV + R and CV.

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.

New Insights into Xanthophylls and Lipidomic Profile Changes Induced by Glucose Supplementation in the Marine Diatom Nitzschia laevis

Nitzschia laevis is a candidate microorganism for bioactive compounds (fucoxanthin and eicosapentaenoic acid (EPA)) production. In this study, the impacts of glucose-induced trophic transition on biomass, photosynthesis, pigments, and lipid profiles were examined. The specific growth rate was increased under glucose addition, achieved at 0.47 day−1 (0.26 ± 0.01 day−1 for the group without glucose in medium). However, the photosynthetic parameters and pigments including chlorophylls, fucoxanthin, and diatoxanthin were reduced. The net yield of EPA doubled under glucose addition, reaching 20.36 ± 1.22 mg/L in 4 days. In addition, the alteration in detailed lipid molecular species was demonstrated with a focus on EPA-enriched lipids. The effects of 2-deoxyglucose (2DG) indicated that glucose phosphorylation was involved in glucose-induced regulation. These findings provide novel data for guiding the application of this diatom strain in the functional food industries.

Comparative Proteomics Reveals Evidence of Enhanced EPA Trafficking in a Mutant Strain of Nannochloropsis oculata

The marine microalga Nannochloropsis oculata is a bioproducer of eicosapentaenoic acid (EPA), a fatty acid. EPA is incorporated into monogalactosyldiacylglycerol within N. oculata thylakoid membranes, and there is a biotechnological need to remodel EPA synthesis to maximize production and simplify downstream processing. In this study, random mutagenesis and chemical inhibitor-based selection method were devised to increase EPA production and accessibility for improved extraction. Ethyl methanesulfonate was used as the mutagen with selective pressure achieved by using two enzyme inhibitors of lipid metabolism: cerulenin and galvestine-1. Fatty acid methyl ester analysis of a selected fast-growing mutant strain had a higher percentage of EPA (37.5% of total fatty acids) than the wild-type strain (22.2% total fatty acids), with the highest EPA quantity recorded at 68.5 mg/g dry cell weight, while wild-type cells had 48.6 mg/g dry cell weight. Label-free quantitative proteomics for differential protein expression analysis revealed that the wild-type and mutant strains might have alternative channeling pathways for EPA synthesis. The mutant strain showed potentially improved photosynthetic efficiency, thus synthesizing a higher quantity of membrane lipids and EPA. The EPA synthesis pathways could also have deviated in the mutant, where fatty acid desaturase type 2 (13.7-fold upregulated) and lipid droplet surface protein (LDSP) (34.8-fold upregulated) were expressed significantly higher than in the wild-type strain. This study increases the understanding of EPA trafficking in N. oculata, leading to further strategies that can be implemented to enhance EPA synthesis in marine microalgae.

Climate change and n-3 LC-PUFA availability

Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) are essential fatty acids for the growth, development and survival of virtually all organisms. There is increasing evidence that anthropogenic climate change has a direct and indirect impact on the availability of natural n-3 LC-PUFA. However, this information is fragmented and not well organized. Therefore, this article reviewed published data from laboratory experiments, field experiments and model simulations to reveal the impact of climate change on the global supply of natural n-3 LC-PUFA and how this will limit the availability of n-3 LC-PUFA in the future food web. In general, climate change can significantly reduce the availability of natural n-3 LC-PUFA in grazing food webs in the following ways: 1) decrease the total biomass of phytoplankton and shift the plankton community structure to a smaller size, which also reduce the biomass of animals in higher trophics; 2) reduce the n-3 LC-PUFA content and/or quality (n-3: n-6 ratio) of all marine organisms; 3) reduce the transfer efficiency of n-3 LC-PUFA in grazing food web. In addition, as an anthropogenic climate adaptation measure, this review also proposed some alternative sources of n-3 LC-PUFA and determined the direction of future research. The information in this article is very useful for providing a critical analysis of the impact of climate change on the supply of natural n-3 LC-PUFA. Such information will aid to establish climate adaptation or management measures, and determine the direction of future research.

Bioactive Components in Traditional Foods Aimed at Health Promotion: A Route to Novel Mechanistic Insights and Lead Molecules?

Traditional foods and diets can provide health benefits beyond their nutrient composition because of the presence of bioactive compounds. In various traditional healthcare systems, diet-based approaches have always played an important role, which has often survived until today. Therefore, investigating traditional foods aimed at health promotion could render not only novel bioactive substances but also mechanistic insights. However, compared to pharmacologically focused research on natural products, investigating such nutrition-based interventions is even more complicated owing to interacting compounds, less potent and relatively subtle effects, the food matrix, and variations in composition and intake. At the same time, technical advances in 'omics' technologies, cheminformatics, and big data analysis create new opportunities, further strengthened by increasing insights into the biology of health and homeostatic resilience. These are to be combined with state-of-the-art ethnobotanical research, which is key to obtaining reliable and reproducible data. Unfortunately, socioeconomic developments and climate change threaten traditional use and knowledge as well as biodiversity. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Low light acclimation strategy of the brown macroalga Undaria pinnatifida: Significance of lipid and fatty acid remodeling for photosynthetic competence

Brown macroalgae, being important components of benthic communities in temperate regions, are frequently subjected to light limitation. To extend our understanding of their low light acclimation strategies to the regulation of membrane lipid environment, photosynthetic characteristics, lipid class, fatty acid profiles and chloroplast ultrastructure were compared in Undaria pinnatifida (Phaeophyceae, Ochrophyta) after long-term exposure to low and moderate light intensities (LL, 100 and ML, 280 µmol photons · m-2 · s-1 ). We show that light limitation significantly increased PSII quantum efficiency and photosynthetic electron transport rate, enhanced pigment contents and concentration of thylakoid membranes in chloroplasts but decreased the distance between the thylakoid stacks. These physiological alterations at LL were accompanied by a selective remodeling of thylakoid membrane lipids driven by increases in monogalactosyldiacylglycerol (MGDG) and phosphatidylglycerol (PG) contents. Light limitation also induced active production of PG specific trans-Δ3 -hexadecenoic acid and accumulation of n-3 polyunsaturated fatty acids (PUFA) mostly in PG and MGDG at the expense of the rise in 18:3n-3 and 20:5n-3, 18:4n-3, respectively. These changes in lipid and FA profiles are apparently responsible for supporting thylakoid biogenesis and efficient photosynthesis at light limitation, thus contributing to photoacclimation strategies in brown algae. The content of triacylglycerols (TAG) and the level of their PUFA were decreased at LL, suggesting the consumption of TAG as a source of PUFA and energy reserves. Thus, U. pinnatifida is able to successfully overcome periods of low irradiance through the effective light harvesting and utilization that are provided by high flexibility of lipid biosynthesis.

Research advancement and commercialization of microalgae edible oil: a review

The global food crisis has led to a great deal of attention being given to microalgal oil as a sustainable natural food source. This article provides an overview of the progress and future directions in promoting the commercialization of microalgal edible oils, including microalgal triglyceride accumulation, suitable edible oil culture strategies for high nutritional value, metabolic engineering, production, and downstream technologies. The integration of the production process, biosafety, and the economic sustainability of microalgal oil production are analyzed for their critical roles in the commercialization of microalgal edible oil to provide a theoretical and scientific basis for the comprehensive development and utilization of microalgal edible oil. © 2021 Society of Chemical Industry.

Lipid synthesis at the trophic base as the source for energy management to build complex structures

The review explores the ecological basis for bacterial lipid metabolism in marine and terrestrial ecosystems. We discuss ecosystem stressors that provoked early organisms to modify their lipid membrane structures, and where these stressors are found across a variety of environments. A major role of lipid membranes is to manage cellular energy utility, including how energy is used for signal propagation. As different environments are imbued with properties that necessitate variation in energy regulation, bacterial lipid synthesis has undergone incalculable permutations of functional trial and error. This may hold clues for how biotechnology can improvise a short-hand version of the evolutionary gauntlet to stimulate latent functional competences for the synthesis of rare lipids. Reducing human reliance on marine resources and deriving solutions for production of essential nutrients is a pressing problem in sustainable agriculture and aquaculture, as well as timely considering the increasing fragility of human health in an aging population.

Microalgae as Sustainable Biofactories to Produce High-Value Lipids: Biodiversity, Exploitation, and Biotechnological Applications

Microalgae are often called “sustainable biofactories” due to their dual potential to mitigate atmospheric carbon dioxide and produce a great diversity of high-value compounds. Nevertheless, the successful exploitation of microalgae as biofactories for industrial scale is dependent on choosing the right microalga and optimum growth conditions. Due to the rich biodiversity of microalgae, a screening pipeline should be developed to perform microalgal strain selection exploring their growth, robustness, and metabolite production. Current prospects in microalgal biotechnology are turning their focus to high-value lipids for pharmaceutic, nutraceutic, and cosmetic products. Within microalgal lipid fraction, polyunsaturated fatty acids and carotenoids are broadly recognized for their vital functions in human organisms. Microalgal-derived phytosterols are still an underexploited lipid resource despite presenting promising biological activities, including neuroprotective, anti-inflammatory, anti-cancer, neuromodulatory, immunomodulatory, and apoptosis inductive effects. To modulate microalgal biochemical composition, according to the intended field of application, it is important to know the contribution of each cultivation factor, or their combined effects, for the wanted product accumulation. Microalgae have a vital role to play in future low-carbon economy. Since microalgal biodiesel is still costly, it is desirable to explore the potential of oleaginous species for its high-value lipids which present great global market prospects.

Responses of Alpha-linolenic acid strain (C-12) from Chlorella sp. L166 to low temperature plasma treatment

LTP treatment was applied to induce a high-content alpha-linolenic acid (ALA) strain (C-12) from Chlorella sp. L166, the ALA content of C-12 was increased by 48.37%. The mechanism of LTP induction were examined. The results showed that LTP could facilitate pH change, induce malondialdehyde (MDA) production, cause protein leakage, and destroyed the microalgae cells. The genes of C-12 encoding pyruvate dehydrogenase (E₂) were up-regulated 2.47-fold, and acetyl-CoA carboxylase (ACCase) down-regulated 0.48-fold compared to the wild type, these changed in the direction of ALA accumulation. Furthermore, the enzymes in DNA replication were significantly up regulated. Take ALA and biomass accumulation into account, LTP technology had a positive effect on ALA accumulation. Global view of metabolic variation also suggested that C-12 had an excellent adaptability to the changes of pH and peroxidation of LTP production. C-12 could be a promising ALA source of alternative materials for it do not compete with land.

Diatoms and Plants Acyl-CoA:lysophosphatidylcholine Acyltransferases (LPCATs) Exhibit Diverse Substrate Specificity and Biochemical Properties

The search of the Phaeodactylum tricornutum genome database revealed the existence of six genes potentially encoding lysophospholipid acyltransferases. One of these genes, Phatr3_J20460, after introduction to yeast ale1 mutant disrupted in the LPCAT gene, produced a very active acyl-CoA:lysophosphatidylcholine (LPCAT) enzyme. Using in vitro assays applying different radioactive and non-radioactive substrates and microsomal fractions from such yeast, we have characterized the biochemical properties and substrate specificities of this PtLPCAT1. We have found that the substrate specificity of this enzyme indicates that it can completely supply phosphatidylcholine (PC) with all fatty acids connected with a biosynthetic pathway of very long-chain polyunsaturated fatty acids (VLC-PUFAs) used further for the desaturation process. Additionally, we have shown that biochemical properties of the PtLPCAT1 in comparison to plant LPCATs are in some cases similar (such as the dependency of its activity on pH value), differ moderately (such as in response to temperature changes), or express completely different properties (such as in reaction to calcium and magnesium ions or toward some acyl-CoA with 20C polyunsaturated fatty acids). Moreover, the obtained results suggest that cloned “Phatr3_J20460” gene can be useful in oilseeds plant engineering toward efficient production of VLC-PUFA as LPCAT it encodes can (contrary to plant LPCATs) introduce 20:4-CoA (n-3) to PC for further desaturation to 20:5 (EPA, eicosapentaenoic acid).

Influence of Carbohydrate Additives on the Growth Rate of Microalgae Biomass with an Increased Carbohydrate Content

Our study focused on investigating the possibilities of controlling the accumulation of carbohydrates in certain microalgae species (Arthrospira platensis Gomont, Chlorella vulgaris Beijer, and Dunaliella salina Teod) to determine their potential in biofuel production (biohydrogen). It was found that after the introduction of carbohydrates (0.05 g⋅L⁻¹) into the nutrient medium, the growth rate of the microalgae biomass increased, and the accumulation of carbohydrates reached 41.1%, 47.9%, and 31.7% for Arthrospira platensis, Chlorella vulgaris, and Dunaliella salina, respectively. Chlorella vulgaris had the highest total carbohydrate content (a mixture of glucose, fructose, sucrose, and maltose, 16.97%) among the studied microalgae, while for Arthrospira platensis and Dunaliella salina, the accumulation of total carbohydrates was 9.59% and 8.68%, respectively. Thus, the introduction of carbohydrates into the nutrient medium can stimulate their accumulation in the microalgae biomass, an application of biofuel production (biohydrogen).

The evolutionary ecology of fatty-acid variation: Implications for consumer adaptation and diversification

The nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. The omega-3 long-chain polyunsaturated fatty acids eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) have a high potential to affect consumer fitness, through their widespread effects on reproduction, growth and survival. However, few studies consider the evolution of fatty acid metabolism within an ecological context. In this review, we first document the extensive diversity in both primary producer and consumer fatty acid distributions amongst major ecosystems, between habitats and amongst species within habitats. We highlight some of the key nutritional contrasts that can shape behavioural and/or metabolic adaptation in consumers, discussing how consumers can evolve in response to the spatial, seasonal and community-level variation of resource quality. We propose a hierarchical trait-based approach for studying the evolution of consumers' metabolic networks and review the evolutionary genetic mechanisms underpinning consumer adaptation to EPA and DHA distributions. In doing so, we consider how the metabolic traits of consumers are hierarchically structured, from cell membrane function to maternal investment, and have strongly environment-dependent expression. Finally, we conclude with an outlook on how studying the metabolic adaptation of consumers within the context of nutritional landscapes can open up new opportunities for understanding evolutionary diversification.

Lipid Droplets in Unicellular Photosynthetic Stramenopiles

The Heterokonta or Stramenopile phylum comprises clades of unicellular photosynthetic species, which are promising for a broad range of biotechnological applications, based on their capacity to capture atmospheric CO₂ via photosynthesis and produce biomolecules of interest. These molecules include triacylglycerol (TAG) loaded inside specific cytosolic bodies, called the lipid droplets (LDs). Understanding TAG production and LD biogenesis and function in photosynthetic stramenopiles is therefore essential, and is mostly based on the study of a few emerging models, such as the pennate diatom Phaeodactylum tricornutum and eustigmatophytes, such as Nannochloropsis and Microchloropsis species. The biogenesis of cytosolic LD usually occurs at the level of the endoplasmic reticulum. However, stramenopile cells contain a complex plastid deriving from a secondary endosymbiosis, limited by four membranes, the outermost one being connected to the endomembrane system. Recent cell imaging and proteomic studies suggest that at least some cytosolic LDs might be associated to the surface of the complex plastid, via still uncharacterized contact sites. The carbon length and number of double bonds of the acyl groups contained in the TAG molecules depend on their origin. De novo synthesis produces long-chain saturated or monounsaturated fatty acids (SFA, MUFA), whereas subsequent maturation processes lead to very long-chain polyunsaturated FA (VLC-PUFA). TAG composition in SFA, MUFA, and VLC-PUFA reflects therefore the metabolic context that gave rise to the formation of the LD, either via an early partitioning of carbon following FA de novo synthesis and/or a recycling of FA from membrane lipids, e.g., plastid galactolipids or endomembrane phosphor- or betaine lipids. In this review, we address the relationship between cytosolic LDs and the complex membrane compartmentalization within stramenopile cells, the metabolic routes leading to TAG accumulation, and the physiological conditions that trigger LD production, in response to various environmental factors.

Pigment and Fatty Acid Production under Different Light Qualities in the Diatom Phaeodactylum tricornutum

Diatoms are microscopic biorefineries producing value-added molecules, including unique pigments, triglycerides (TAGs) and long-chain polyunsaturated fatty acids (LC-PUFAs), with potential implications in aquaculture feeding and the food or biofuel industries. These molecules are utilized in vivo for energy harvesting from sunlight to drive photosynthesis and as photosynthetic storage products, respectively. In the present paper, we evaluate the effect of narrow-band spectral illumination on carotenoid, LC-PUFAs and TAG contents in the model diatom Phaeodactylum tricornutum. Shorter wavelengths in the blue spectral range resulted in higher production of total fatty acids, namely saturated TAGs. Longer wavelengths in the red spectral range increased the cell’s content in Hexadecatrienoic acid (HTA) and Eicosapentaenoic acid (EPA). Red wavelengths induced higher production of photoprotective carotenoids, namely fucoxanthin. In combination, the results demonstrate how diatom value-added molecule production can be modulated by spectral light control during the growth. How diatoms could use such mechanisms to regulate efficient light absorption and cell buoyancy in the open ocean is discussed.

Microalgae n-3 PUFAs Production and Use in Food and Feed Industries

N-3 polyunsaturated fatty acids (n-3 PUFAs), and especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential compounds for human health. They have been proven to act positively on a panel of diseases and have interesting anti-oxidative, anti-inflammatory or anti-cancer properties. For these reasons, they are receiving more and more attention in recent years, especially future food or feed development. EPA and DHA come mainly from marine sources like fish or seaweed. Unfortunately, due to global warming, these compounds are becoming scarce for humans because of overfishing and stock reduction. Although increasing in recent years, aquaculture appears insufficient to meet the increasing requirements of these healthy molecules for humans. One alternative resides in the cultivation of microalgae, the initial producers of EPA and DHA. They are also rich in biochemicals with interesting properties. After defining macro and microalgae, this review synthesizes the current knowledge on n-3 PUFAs regarding health benefits and the challenges surrounding their supply within the environmental context. Microalgae n-3 PUFA production is examined and its synthesis pathways are discussed. Finally, the use of EPA and DHA in food and feed is investigated. This work aims to define better the issues surrounding n-3 PUFA production and supply and the potential of microalgae as a sustainable source of compounds to enhance the food and feed of the future.

Development of High-Level Omega-3 Eicosapentaenoic Acid (EPA) Production from Phaeodactylum tricornutum

Phaeodactylum tricornutum is a lipid-rich marine diatom that contains a high level of omega-3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA). In an effort to reduce costs for large-scale cultivation of this microalga, this study first established a New BBM medium (0.3 x strength BBM with only 3% of the initial phosphate level) to replace the traditional F/2 medium. Phaeodactylum tricornutum could grow in extremely low phosphate concentrations (25 µM), without compromising the EPA content. In the presence of sea salts, silicate addition was not necessary for high rate growth, high EPA content, or lipid accumulation in this species. Using urea as the sole nitrogen source tended to increase EPA contents per dry biomass (by 24.7%) while not affecting growth performance. The use of sea salts, rather than just sodium chloride, led to significantly improved biomass yields (20% increase) and EPA contents of total fatty acid (46-52% increase), most likely because it supplied sufficient essential elements such as magnesium. A salinity level of 35 led to significantly higher biomass yields compared with 20, but salinity had no significant influence on EPA content. EPA became the dominant fatty acid with average levels of 51.8% of total fatty acids during the exponential growth phase at 20 ppt in New BBM medium with sea salts.

The carbon partitioning of glucose and DIC in mixotrophic, heterotrophic and photoautotrophic cultures of Tetraselmis suecica

OBJECTIVE

Changes in the partitioning of dissolved inorganic (DIC) and glucose were elucidated by utilising ¹³C labelled DIC or glucose, and quantifying the biochemical profile of mixotrophic, heterotrophic and photoautotrophic cultures of the microalga Tetraselmis suecica.

RESULTS

Mixotrophic cultivation increases microalgal productivity and changes their biochemical profile, due to an alteration in the partitioning of carbon within the cell. When cultured mixotrophically and heterotrophically, there is enhanced incorporation of carbon into shorter chain saturated fatty acids and non-lipid biomass, compared to photoautotrophic cultivation. Autotrophic culture results in increased total fatty acid content of cultures (4.19% dry weight compared to 2.13%) and shifts the fatty acid profile in favour of long-chain unsaturated fatty acids, such as 18:2 n-(9,12), compared to mixotrophic culture. Quantifying the changes in partitioning between DIC and glucose facilitates tailoring of the biochemical profile to develop "designer" algae.

CONCLUSIONS

There is a condition specific shift in carbon partitioning into different fatty acid and biochemical fractions in T. suecica, with more inorganic carbon partitioned into 18:2 n-(9,12) in photoautotrophic rather than mixotrophic cultures.

Metabolomics-derived marker metabolites to characterize Phaeocystis pouchetii physiology in natural plankton communities

Phaeocystis pouchetii (Hariot) Lagerheim, 1893 regularly dominates phytoplankton blooms in higher latitudes spanning from the English Channel to the Arctic. Through zooplankton grazing and microbial activity, it is considered to be a key resource for the entire marine food web, but the actual relevance of biomass transfer to higher trophic levels is still under discussion. Cell physiology and algal nutritional state are suggested to be major factors controlling the observed variability in zooplankton grazing. However, no data have so far yielded insights into the metabolic state of Phaeocystis populations that would allow testing this hypothesis. Therefore, endometabolic markers of different growth phases were determined in laboratory batch cultures using comparative metabolomics and quantified in different phytoplankton blooms in the field. Metabolites, produced during exponential, early and late stationary growth of P. pouchetii, were profiled using gas chromatography-mass spectrometry. Then, metabolites were characterized that correlate with the growth phases using multivariate statistical analysis. Free amino acids characterized the exponential growth, whereas the early stationary phase was correlated with sugar alcohols, mono- and disaccharides. In the late stationary phase, free fatty acids, sterols and terpenes increased. These marker metabolites were then traced in Phaeocystis blooms during a cruise in the Barents Sea and North Norwegian fjords. About 50 endometabolites of P. pouchetii were detected in natural phytoplankton communities. Mannitol, scyllo-inositol, 24-methylcholesta-5,22-dien-3β-ol, and several free fatty acids were characteristic for Phaeocystis-dominated blooms but showed variability between them. Distinct metabolic profiles were detected in the nutrient-depleted community in the inner Porsangerfjord (< 0.5 µM NO₃^-, < 0.1 µM PO ₄ ^3- ), with high relative amounts of free mono- and disaccharides indicative for a limited culture. This study thereby shows how the variable physiology of phytoplankton can alter the metabolic landscape of entire plankton communities.

Marine heat waves alter gene expression of key enzymes of membrane and storage lipids metabolism in Phaeodactylum tricornutum

Across the globe, heat waves are getting more intense and frequent. Diatoms are a major group of microalgae at the base of the marine food webs and an important source of long chain polyunsaturated fatty acids that are transferred through the food web. The present study investigates the possible impacts of temperature increase on lipid classes and expression of genes encoding enzymes related to lipid metabolism in Phaeodactylum tricornutum. The heat wave exposure caused an increase in the relative amounts of plastidial lipids such as the glycolipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulphoquinovosyldiacylglycerol (SQDG) in parallel with a decrease in the neutral lipid fraction, which includes triacylglycerols. In agreement, gene expression analyses revealed an up-regulation of a gene encoding one MGDG synthase and down-regulation of a diacylglycerol acyltransferase (DGAT), a key enzyme in triacylglycerol synthesis. Our results show that heat waves not only negatively impact the abundance of unsaturated fatty acids such as eicosapentaenoic acid (20:5n-3, EPA) and hexadecatrienoic acid (16:3n-4) as observed by the decrease in their relative abundance in MGDG and neutral lipids, respectively, but also induce changes in the relative amounts of the diverse membrane lipids as well as the proportion of membrane/storage lipids. The expression study of key genes indicates that some of the aforementioned alterations are regulated at the transcription level whereas others appear to be post-transcriptional. The changes observed in plastidial lipids are related to negative impacts on the photosynthesis.

Fluoxetine Arrests Growth of the Model Diatom Phaeodactylum tricornutum by Increasing Oxidative Stress and Altering Energetic and Lipid Metabolism

Pharmaceutical residues impose a new and emerging threat to aquatic environments and its biota. One of the most commonly prescribed pharmaceuticals is the antidepressant fluoxetine, a selective serotonin re-uptake inhibitor that has been frequently detected, in concentrations up to 40 μg L^–1, in aquatic ecosystems. The present study aims to investigate the ecotoxicity of fluoxetine at environmentally relevant concentrations (0.3, 0.6, 20, 40, and 80 μg L^–1) on cell energy and lipid metabolism, as well as oxidative stress biomarkers in the model diatom Phaeodactylum tricornutum. Exposure to higher concentrations of fluoxetine negatively affected cell density and photosynthesis through a decrease in the active PSII reaction centers. Stress response mechanisms, like β-carotene (β-car) production and antioxidant enzymes [superoxide dismutase (SOD) and ascorbate peroxidase (APX)] up-regulation were triggered, likely as a positive feedback mechanism toward formation of fluoxetine-induced reactive oxygen species. Lipid peroxidation products increased greatly at the highest fluoxetine concentration whereas no variation in the relative amounts of long chain polyunsaturated fatty acids (LC-PUFAs) was observed. However, monogalactosyldiacylglycerol-characteristic fatty acids such as C16:2 and C16:3 increased, suggesting an interaction between light harvesting pigments, lipid environment, and photosynthesis stabilization. Using a canonical multivariate analysis, it was possible to evaluate the efficiency of the application of bio-optical and biochemical techniques as potential fluoxetine exposure biomarkers in P. tricornutum. An overall classification efficiency to the different levels of fluoxetine exposure of 61.1 and 88.9% were obtained for bio-optical and fatty acids profiles, respectively, with different resolution degrees highlighting these parameters as potential efficient biomarkers. Additionally, the negative impact of this pharmaceutical molecule on the primary productivity is also evident alongside with an increase in respiratory oxygen consumption. From the ecological point of view, reduction in diatom biomass due to continued exposure to fluoxetine may severely impact estuarine and coastal trophic webs, by both a reduction in oxygen primary productivity and reduced availability of key fatty acids to the dependent heterotrophic upper levels.

Nutritional evaluation and human health-promoting potential of compounds biosynthesized by native microalgae from the Peruvian Amazon

A plausible strategy to mitigate socioeconomic problems in the Peruvian Amazon is through the sustainable exploitation of biodiversity resources, such as native microalgae. Several studies worldwide affirm that these microorganisms are excellent sources of higher value products for human nutrition and possess health-promoting biochemicals, but these attributes are unknown for the native microalgae of Peru. Therefore, the aim of this investigation was to evaluate the nutritional and human health-promoting potential of compounds biosynthesized by native microalgae from the Peruvian Amazon. Ten native microalgae strains of the groups cyanobacteria and chlorophyta were cultured in BG-11 medium and their biomass harvested and dried. Standardized methods were then used to determine proximate composition, fatty acids and amino acids composition, antioxidant activity, and total phenolic content. All ten microalgae strains produce primary nutrients, the entire spectrum of essential amino acids, essential fatty acids, and 3 of the 10 microalgae strains produced eisosapentaenoic acid. Additionally, all microalgae strains exhibited antioxidant activities and contained phenolic compounds. In conclusion, native microalgae strains from the Peruvian Amazon analyzed in this study possess the ability to biosynthesize and accumulate several nutrients and compounds with human health-promoting potential.

Biochemical profiling of three indigenous Dunaliella isolates with main focus on fatty acid composition towards potential biotechnological application

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Biochemical composition of native isolates determined their potential application.

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The isolates tend to store energy and carbon mainly in lipid, not carbohydrate, form.

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The fatty acid profile of the isolates show appropriate n3:n6 and health lipid indices.

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Dunaliella sp. ABRIINW-B1 and -G2/1 are the proper options for nutraceutical purposes.

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Dunaliella sp. ABRIINW-I1 well suits pharmaceutical and aquaculture application.

This study describes the biochemical composition of three isolates, Dunaliella sp. ABRIINW-B1, -G2/1 and -I1 towards the biotechnological potential. Dunaliella sp. ABRIINW- G2/1 and -I1 had a remarkable protein content (∼40% dry weight). Dunaliella sp. ABRIINW-I1 contained a pigment fraction of 3.2% largely composed of chlorophyll a (1.9%) and carotenoid (1.1%). Dunaliella sp. ABRIINW-B1, -G2/1 and -I1 produced respectively 42, 36 and 47% lipid content. The occurrence of high lipid and low carbohydrate (4–7%) in the isolates demonstrated their cell tendency to store energy and carbon mainly in lipid form. The lipid profile of the isolates expressed adequate n3:n6 ratio and health indices. The biochemical analysis revealed that Dunaliella sp. ABRIINW-B1 and -G2/1 have potential applications in the food and freshwater aquafeed sector. While Dunaliella sp. ABRIINW-I1 owing to appropriate pigment, protein, and lipid level containing very-long-chain polyunsaturated fatty acids showed a great promise in nutritional, pharmaceutical and marine aquafeed industries.

Study of Synthesis Pathways of the Essential Polyunsaturated Fatty Acid 20:5n-3 in the Diatom Chaetoceros Muelleri Using 13C-Isotope Labeling

The present study sought to characterize the synthesis pathways producing the essential polyunsaturated fatty acid (PUFA) 20:5n-3 (EPA). For this, the incorporation of ¹³C was experimentally monitored into 10 fatty acids (FA) during the growth of the diatom Chaetoceros muelleri for 24 h. Chaetoceros muelleri preferentially and quickly incorporated ¹³C into C₁₈ PUFAs such as 18:2n-6 and 18:3n-6 as well as 16:0 and 16:1n-7, which were thus highly ¹³C-enriched. During the experiment, 20:5n-3 and 16:3n-4 were among the least-enriched fatty acids. The calculation of the enrichment percentage ratio of a fatty acid B over its suspected precursor A allowed us to suggest that the diatom produced 20:5n-3 (EPA) by a combination between the n-3 (via 18:4n-3) and n-6 (via 18:3n-6 and 20:4n-6) synthesis pathways as well as the alternative ω-3 desaturase pathway (via 20:4n-6). In addition, as FA from polar lipids were generally more enriched in ¹³C than FA from neutral lipids, particularly for 18:1n-9, 18:2n-6 and 18:3n-6, the existence of acyl-editing mechanisms and connectivity between polar and neutral lipid fatty acid pools were also hypothesized. Because 16:3n-4 and 20:5n-3 presented the same concentration and enrichment dynamics, a structural and metabolic link was proposed between these two PUFAs in C. muelleri.

Genome and Transcriptome Analyses Provide Insight Into the Omega-3 Long-Chain Polyunsaturated Fatty Acids Biosynthesis of Schizochytrium limacinum SR21

Schizochytrium sp. is the best natural resource for omega-3 long-chain polyunsaturated fatty acids. We report a high-quality genome sequence of Schizochytrium limacinum SR21, which has a 63 Mb genome size, with a contig N50 of 2.67 Mb and 6,838 protein-coding genes. Phylogenomic and comparative genomic analyses revealed that DHA-producing Schizochytrium and Aurantiochytrium strains were highly similar and possessed similar genes. Analysis of the fatty acid synthase (FAS) for LC-PUFAs production results in the annotation of all genes in map00062 and map01212. A gene cluster and 10 ORFs related to PKS pathway were found in the genome. 1,402 differentially expressed genes (DEGs) of the treated groups (0.5 g/L yeast extract) were identified by comparing with the control groups (1.0 g/L yeast extract) at 36 h. A weighted gene coexpression network analysis revealed that 2 of 7 modules correlated highly with the fatty acid and DHA contents. The DEGs and transcription factors were significantly correlated with fatty acid biosynthesis, including MYB, Zinc Finger and ACOX. The results showed that these hub genes are regulated by genes involved in fatty acid biosynthesis pathways. The results providing an important reference for further research on promoting fatty acid and DHA accumulation in S. limacinum SR21.

The Myb-like transcription factor phosphorus starvation response (PtPSR) controls conditional P acquisition and remodelling in marine microalgae

Phosphorus (P) is one of the limiting macronutrients for algal growth in marine environments. Microalgae have developed adaptation mechanisms to P limitation that involve remodelling of internal phosphate resources and accumulation of lipids. Here, we used in silico analyses to identify the P-stress regulator PtPSR (Phaeodactylum tricornutum phosphorus starvation response) in the diatom P. tricornutum. ptpsr mutant lines were generated using gene editing and characterised by various molecular, genetics and biochemical tools. PtPSR belongs to a clade of Myb transcription factors that are conserved in stramenopiles and distantly related to plant P-stress regulators. PtPSR bound specifically to a conserved cis-regulatory element found in the regulatory region of P-stress-induced genes. ptpsr knockout mutants showed reduction in cell growth under P limitation. P-stress responses were impaired in ptpsr mutants compared with wild-type, including reduced induction of P-stress response genes, near to complete loss of alkaline phosphatase activity and reduced phospholipid degradation. We conclude that PtPSR is a key transcription factor influencing P scavenging, phospholipid remodelling and cell growth in adaptation to P stress in diatoms.

An adjustable algal chloroplast plug-and-play model for genome-scale metabolic models

The chloroplast is a central part of plant cells, as this is the organelle where the photosynthesis, fixation of inorganic carbon, and other key functions related to fatty acid synthesis and amino acid synthesis occur. Since this organelle should be an integral part of any genome-scale metabolic model for a microalgae or a higher plant, it is of great interest to generate a detailed and standardized chloroplast model. Additionally, we see the need for a novel type of sub-model template, or organelle model, which could be incorporated into a larger, less specific genome-scale metabolic model, while allowing for minor differences between chloroplast-containing organisms. The result of this work is the very first standardized chloroplast model, iGR774, consisting of 788 reactions, 764 metabolites, and 774 genes. The model is currently able to run in three different modes, mimicking the chloroplast metabolism of three photosynthetic microalgae-Nannochloropsis gaditana, Chlamydomonas reinhardtii and Phaeodactylum tricornutum. In addition to developing the chloroplast metabolic network reconstruction, we have developed multiple software tools for working with this novel type of sub-model in the COBRA Toolbox for MATLAB, including tools for connecting the chloroplast model to a genome-scale metabolic reconstruction in need of a chloroplast, for switching the model between running in different organism modes, and for expanding it by introducing more reactions either related to one of the current organisms included in the model, or to a new organism.

Highest accumulated microalgal lipids (polar and non-polar) for biodiesel production with advanced wastewater treatment: Role of lipidomics

Microalgal lipids consist of non-polar and polar lipids. Triacyleglyceride (TAG), a non-polar lipid, is convertible to biodiesel, whereas glycolipids and phospholipids are polar and not convertible to biodiesel owing to their high degree of unsaturation (polyunsaturated fatty acids), which makes the production process insufficient and expensive. In this review, microalgal species that contain the highest lipid content (≥40%) in the literature till 2019 are highlighted. The differentiation between non-polar and polar lipids and the limitations in the conversion of polar lipids to biodiesel are reported. The basic and advanced factors contributing to the accumulation of lipids convertible to biodiesel is discussed. Microalgal species including Scenedesmus obliquus, Ourococcus multisporus, Chlamydomonas pitschmannii, Micractinium reisseri, and Botryococcus braunii with high lipid content are potential candidates for biomass/biodiesel production and nutrient removal from wastewater. Application of lipidomics and transcriptomics to manipulate the lipid associated gene acetyl-CoA synthetase in microalgae improves the accumulative lipid content.

Genome-Wide Association Study for Serum Omega-3 and Omega-6 Polyunsaturated Fatty Acids: Exploratory Analysis of the Sex-Specific Effects and Dietary Modulation in Mediterranean Subjects with Metabolic Syndrome

Many early studies presented beneficial effects of polyunsaturated fatty acids (PUFA) on cardiovascular risk factors and disease. However, results from recent meta-analyses indicate that this effect would be very low or nil. One of the factors that may contribute to the inconsistency of the results is that, in most studies, genetic factors have not been taken into consideration. It is known that fatty acid desaturase (FADS) gene cluster in chromosome 11 is a very important determinant of plasma PUFA, and that the prevalence of the single nucleotide polymorphisms (SNPs) varies greatly between populations and may constitute a bias in meta-analyses. Previous genome-wide association studies (GWAS) have been carried out in other populations and none of them have investigated sex and Mediterranean dietary pattern interactions at the genome-wide level. Our aims were to undertake a GWAS to discover the genes most associated with serum PUFA concentrations (omega-3, omega-6, and some fatty acids) in a scarcely studied Mediterranean population with metabolic syndrome, and to explore sex and adherence to Mediterranean diet (MedDiet) interactions at the genome-wide level. Serum PUFA were determined by NMR spectroscopy. We found strong robust associations between various SNPs in the FADS cluster and omega-3 concentrations (top-ranked in the adjusted model: FADS1-rs174547, p = 3.34 × 10-14; FADS1-rs174550, p = 5.35 × 10-14; FADS2-rs1535, p = 5.85 × 10-14; FADS1-rs174546, p = 6.72 × 10-14; FADS2-rs174546, p = 9.75 × 10-14; FADS2- rs174576, p = 1.17 × 10-13; FADS2-rs174577, p = 1.12 × 10-12, among others). We also detected a genome-wide significant association with other genes in chromosome 11: MYRF (myelin regulatory factor)-rs174535, p = 1.49 × 10-12; TMEM258 (transmembrane protein 258)-rs102275, p = 2.43 × 10-12; FEN1 (flap structure-specific endonuclease 1)-rs174538, p = 1.96 × 10-11). Similar genome-wide statistically significant results were found for docosahexaenoic fatty acid (DHA). However, no such associations were detected for omega-6 PUFAs or linoleic acid (LA). For total PUFA, we observed a consistent gene*sex interaction with the DNTTIP2 (deoxynucleotidyl transferase terminal interacting protein 2)-rs3747965 p = 1.36 × 10-8. For adherence to MedDiet, we obtained a relevant interaction with the ME1 (malic enzyme 1) gene (a gene strongly regulated by fat) in determining serum omega-3. The top-ranked SNP for this interaction was ME1-rs3798890 (p = 2.15 × 10-7). In the regional-wide association study, specifically focused on the FADS1/FASD2/FADS3 and ELOVL (fatty acid elongase) 2/ELOVL 5 regions, we detected several statistically significant associations at p < 0.05. In conclusion, our results confirm a robust role of the FADS cluster on serum PUFA in this population, but the associations vary depending on the PUFA. Moreover, the detection of some sex and diet interactions underlines the need for these associations/interactions to be studied in all specific populations so as to better understand the complex metabolism of PUFA.

Osmotrophic glucose and leucine assimilation and its impact on EPA and DHA content in algae

The uptake of dissolved organic compounds, that is, osmotrophy, has been shown to be an efficient nutritional strategy for algae. However, this mode of nutrition may affect the biochemical composition, for example, the fatty acid (FA) contents, of algal cells. This study focused on the osmotrophic assimilation of glucose and leucine by selected seven algal strains belonging to chlorophytes, chrysophytes, cryptophytes, dinoflagellates and euglenoids. Our laboratory experiments with stable isotope labeling showed that osmotrophy occurred in four of the selected seven strains. However, only three of these produced long chain omega-3 FAs eicosapentaenoic acid (EPA; 20:5ω3) and docosahexaenoic acid (DHA; 22:6ω3). High glucose content (5 mg L-1) affected negatively on the total FAs of Mallomonas kalinae and the total omega-3 FAs of Cryptomonas sp. Further, glucose assimilation explained 35% (negative effect) and leucine assimilation 48% (positive effect) of the variation of EPA, DHA and the FAs related to their synthesis in Cryptomonas sp. Moderate glucose concentration (2 mg L-1) was found to enhance the growth of Cryptomonas ozolinii, whereas low leucine (20 µg L-1) enhanced the growth of M. kalinae. However, no systematic effect of osmotrophy on growth rates was detected. Our study shows that osmotrophic assimilation of algae is species and compound specific, and that the effects of the assimilated compounds on algal metabolism also varies depending on the species.

Algae: Critical Sources of Very Long-Chain Polyunsaturated Fatty Acids

Polyunsaturated fatty acids (PUFAs), which are divided into n-3 and n-6 classes, are essential for good health in humans and many animals. They are metabolised to lipid mediators, such as eicosanoids, resolvins and protectins. Increasing interest has been paid to the 20 or 22 carbon very long chain PUFAs, since these compounds can be used to form lipid mediators and, thus, avoid inefficient formation of dietary plant PUFAs. The ultimate sources of very long chain PUFAs are algae, which are consumed by fish and then by humans. In this review, I describe the biosynthesis of very long chain PUFAs by algae and how this synthesis can be manipulated for commercial purposes. Ultimately, the production of algal oils is critical for ecosystems worldwide, as well as for human dietary lipids.

Phenomics reveals a novel putative chloroplast fatty acid transporter in the marine diatom Skeletonema marinoi involved in temperature acclimation

Diatoms are the dominant phytoplankton in temperate oceans and coastal regions and yet little is known about the genetic basis underpinning their global success. Here, we address this challenge by developing the first phenomic approach for a diatom, screening a collection of randomly mutagenized but identifiably tagged transformants. Based upon their tolerance to temperature extremes, several compromised mutants were identified revealing genes either stress related or encoding hypothetical proteins of unknown function. We reveal one of these hypothetical proteins is a novel putative chloroplast fatty acid transporter whose loss affects several fatty acids including the two omega-3, long-chain polyunsaturated fatty acids - eicosapentaenoic and docosahexaenoic acid, both of which have medical importance as dietary supplements and industrial significance in aquaculture and biofuels. This mutant phenotype not only provides new insights into the fatty acid biosynthetic pathways in diatoms but also highlights the future value of phenomics for revealing specific gene functions in these ecologically important phytoplankton.

Elevated CO2 improves both lipid accumulation and growth rate in the glucose-6-phosphate dehydrogenase engineered Phaeodactylum tricornutum

BACKGROUND

Numerous studies have shown that stress induction and genetic engineering can effectively increase lipid accumulation, but lead to a decrease of growth in the majority of microalgae. We previously found that elevated CO₂ concentration increased lipid productivity as well as growth in Phaeodactylum tricornutum, along with an enhancement of the oxidative pentose phosphate pathway (OPPP) activity. The purpose of this work directed toward the verification of the critical role of glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme in the OPPP, in lipid accumulation in P. tricornutum and its simultaneous rapid growth rate under high-CO₂ (0.15%) cultivation.

RESULTS

In this study, G6PDH was identified as a target for algal strain improvement, wherein G6PDH gene was successfully overexpressed and antisense knockdown in P. tricornutum, and systematic comparisons of the photosynthesis performance, algal growth, lipid content, fatty acid profiles, NADPH production, G6PDH activity and transcriptional abundance were performed. The results showed that, due to the enhanced G6PDH activity, transcriptional abundance and NAPDH production, overexpression of G6PDH accompanied by high-CO₂ cultivation resulted in a much higher of both lipid content and growth in P. tricornutum, while knockdown of G6PDH greatly decreased algal growth as well as lipid accumulation. In addition, the total proportions of saturated and unsaturated fatty acid, especially the polyunsaturated fatty acid eicosapentaenoic acid (EPA; C20:5, n-3), were highly increased in high-CO₂ cultivated G6PDH overexpressed strains.

CONCLUSIONS

The successful of overexpression and antisense knockdown of G6PDH well demonstrated the positive influence of G6PDH on algal growth and lipid accumulation in P. tricornutum. The improvement of algal growth, lipid content as well as polyunsaturated fatty acids in high-CO₂ cultivated G6PDH overexpressed P. tricornutum suggested this G6PDH overexpression-high CO₂ cultivation pattern provides an efficient and economical route for algal strain improvement to develop algal-based biodiesel production.