Modulation of Polar Lipid Profiles in Chlorella sp. in Response to Nutrient Limitation

Does cobalt antagonize P limitation effects on photosynthetic parameters on the freshwater microalgae Raphidocelis subcapitata (Chlorophyceae), or does P limitation acclimation antagonize cobalt effects? More questions than answers

Phosphorus (P; macronutrient) and cobalt (Co; micronutrient) are essential for algal healthy metabolism. While P provides energy, Co is a co-factor of several enzymes and component of B12 vitamin. However, in concentrations higher or lower than required, P and Co alter algal metabolism, impacting physiological processes (e.g., growth and photosynthesis), usually in a harmful way. In the environment, algae are exposed to multiple stressors simultaneously and studies evaluating the algal response to the combination of macronutrient limitation and micronutrient excess are still scarce. We assessed the effects of P limitation and Co excess, isolated and combined, in Raphidocelis subcapitata (Chlorophyceae), in terms of growth, pigments production, and photosynthetic parameters. Except for the photochemical quenching (qP) and the efficiency in light capture (α) under P limitation, all parameters were affected by both stressors, isolated and combined. Under P limitation, chlorophyll a was the most sensitive parameter; while excess of Co affected most the photoprotective mechanisms of algae, altering the non-photochemical quenchings qN and NPQ, influencing the light use and dissipation of heat by algae. The combination of two stressors resulted in a significant decrease in algal growth, with synergistic responses in growth and pigments production, and antagonism in the photosynthetic parameters. We suggest that algal metabolism was altered during P limitation acclimation and the excess of Co was used in a beneficial way by P-limited algae in photosynthesis, resulting in the well-functioning of the photosynthetic apparatus in the combination of both stressors. However, more studies are needed to understand which mechanisms are involved in this adaptation which resulted in antagonism in photosynthetic processes and synergism in growth and pigments production.

Adaptive traits of cysts of the snow alga Sanguina nivaloides unveiled by 3D subcellular imaging

Sanguina nivaloides is the main alga forming red snowfields in high mountains and Polar Regions. It is non-cultivable. Analysis of environmental samples by X-ray tomography, focused-ion-beam scanning-electron-microscopy, physicochemical and physiological characterization reveal adaptive traits accounting for algal capacity to reside in snow. Cysts populate liquid water at the periphery of ice, are photosynthetically active, can survive for months, and are sensitive to freezing. They harbor a wrinkled plasma membrane expanding the interface with environment. Ionomic analysis supports a cell efflux of K+, and assimilation of phosphorus. Glycerolipidomic analysis confirms a phosphate limitation. The chloroplast contains thylakoids oriented in all directions, fixes carbon in a central pyrenoid and produces starch in peripheral protuberances. Analysis of cells kept in the dark shows that starch is a short-term carbon storage. The biogenesis of cytosolic droplets shows that they are loaded with triacylglycerol and carotenoids for long-term carbon storage and protection against oxidative stress.

Lipidomic Characterization and Antioxidant Activity of Macro- and Microalgae Blend

Macro- and microalgae are currently recognized sources of lipids with great nutritional quality and attractive bioactivities for human health promotion and disease prevention. Due to the lipidomic diversity observed among algae species, giving rise to different nutritional and functional characteristics, the mixture of macro- and microalgae has the potential to present important synergistic effects resulting from the complementarity among algae. The aim of this work was to characterize for the first time the lipidome of a blend of macro- and microalgae and evaluate the antioxidant capacity of its lipid fraction. Fatty acids were profiled by GC-MS, the polar lipidome was identified by high resolution LC-MS, and ABTS^+• and DPPH^• assays were used to assess the antioxidant potential. The most abundant fatty acids were oleic (18:1 n-9), α-linolenic (18:3 n-3), and linoleic (18:2 n-6) acids. The lipid extract presented a beneficial n-6/n-3 ratio (0.98) and low values of atherogenic (0.41) and thrombogenic indices (0.27). The polar lipidome revealed 462 lipid species distributed by glycolipids, phospholipids, and betaine lipids, including some species bearing PUFA and a few with reported bioactivities. The lipid extract also showed antioxidant activity. Overall, the results are promising for the valorization of this blend for food, nutraceutical, and biotechnological applications.

Lipid turnover and SQUAMOSA promoter-binding proteins mediate variation in fatty acid desaturation under early nitrogen deprivation revealed by lipidomic and transcriptomic analyses in Chlorella pyrenoidosa

Nitrogen deprivation induces variations in fatty acid desaturation in microalgae, which determines the performance of biodiesel and the nutritional value of bioproducts. However, the detailed scenario and the underlying regulatory mechanism remain unclear. In this study, we attempt to outline these scenario and mechanisms by performing biochemical, lipidomic, and transcriptomic analyses in Chlorella pyrenoidosa and functional characterization of transcription factors in Yarrowia lipolytica. We found that early nitrogen deprivation dramatically reduced fatty acid desaturation without increasing lipid content. The contents of palmitic acid (16:0) and oleic acid (18:1) dramatically increased to 2.14 and 2.87 times that of nitrogen repletion on the second day, respectively. Lipidomic analysis showed the transfer of polyunsaturated fatty acids from phospholipids and glycolipids to triacylglycerols, and an increase in lipid species with 16:0 or 18:1 under nitrogen deprivation conditions. Upregulated stearoyl-ACP desaturase and oleyl-ACP thioesterase promoted the synthesis of 18:1, but restricted acetyl-CoA supply revealed that it was the intensive lipid turnover instead of an attenuated Kennedy pathway that played an important role in the variation in fatty acid composition under early nitrogen deprivation. Finally, two differentially expressed SQUAMOSA promoter-binding proteins (SBPs) were heterologously expressed in Y. lipolytica, demonstrating their role in promoting the accumulation of total fatty acid and the reduction in fatty acid desaturation. These results revealed the crucial role of lipid turnover and SBPs in determining fatty acid desaturation under early nitrogen deprivation, opening new avenues for the metabolic engineering of fatty acid desaturation in microalgae.

Applications of lipidomics in marine organisms: Progresses, challenges and future perspectives

Marine ecosystems comprise a high diversity of life forms, such as algae, invertebrates, and vertebrates. These organisms have adapted their physiology according to the conditions of the environments in which...

Recycling of the major thylakoid lipid MGDG and its role in lipid homeostasis in Chlamydomonas reinhardtii

Monogalactosyldiacylglycerol (MGDG), the most abundant lipid in thylakoid membranes, is involved in photosynthesis and chloroplast development. MGDG lipase has an important role in lipid remodeling in Chlamydomonas reinhardtii. However, the process related to turnover of the lysogalactolipid that results from MGDG degradation, monogalactosylmonoacylglycerol (MGMG), remains to be clarified. Here we identified a homolog of Arabidopsis thaliana lysophosphatidylcholine acyltransferase (LPCAT) and characterized two independent knockdown (KD) alleles in C. reinhardtii. The enzyme designated as C. reinhardtiiLysolipid Acyltransferase 1 (CrLAT1) has a conserved membrane-bound O-acyl transferase domain. LPCAT from Arabidopsis has a key role in deacylation of phosphatidylcholine (PC). Chlamydomonas reinhardtii, however, lacks PC, and thus we hypothesized that CrLAT1 has some other important function in major lipid flow in this organism. In the CrLAT1 KD mutants, the amount of MGMG was increased, but triacylglycerols (TAGs) were decreased. The proportion of more saturated 18:1 (9) MGDG was lower in the KD mutants than in their parental strain, CC-4533. In contrast, the proportion of MGMG has decreased in the CrLAT1 overexpression (OE) mutants, and the proportion of 18:1 (9) MGDG was higher in the OE mutants than in the empty vector control cells. Thus, CrLAT1 is involved in the recycling of MGDG in the chloroplast and maintains lipid homeostasis in C. reinhardtii.

Microalgal Lipid Extracts Have Potential to Modulate the Inflammatory Response: A Critical Review

Noncommunicable diseases (NCD) and age-associated diseases (AAD) are some of the gravest health concerns worldwide, accounting for up to 70% of total deaths globally. NCD and AAD, such as diabetes, obesity, cardiovascular disease, and cancer, are associated with low-grade chronic inflammation and poor dietary habits. Modulation of the inflammatory status through dietary components is a very appellative approach to fight these diseases and is supported by increasing evidence of natural and dietary components with strong anti-inflammatory activities. The consumption of bioactive lipids has a positive impact on preventing chronic inflammation and consequently NCD and AAD. Thus, new sources of bioactive lipids have been sought out. Microalgae are rich sources of bioactive lipids such as omega-6 and -3 polyunsaturated fatty acids (PUFA) and polar lipids with associated anti-inflammatory activity. PUFAs are enzymatically and non-enzymatically catalyzed to oxylipins and have a significant role in anti and pro-resolving inflammatory responses. Therefore, a large and rapidly growing body of research has been conducted in vivo and in vitro, investigating the potential anti-inflammatory activities of microalgae lipids. This review sought to summarize and critically analyze recent evidence of the anti-inflammatory potential of microalgae lipids and their possible use to prevent or mitigate chronic inflammation.

Polar lipidomic profile shows Chlorococcum amblystomatis as a promising source of value-added lipids

There is a growing trend to explore microalgae as an alternative resource for the food, feed, pharmaceutical, cosmetic and fuel industry. Moreover, the polar lipidome of microalgae is interesting because of the reports of bioactive polar lipids which could foster new applications for microalgae. In this work, we identified for the first time the Chlorococcum amblystomatis lipidome using hydrophilic interaction liquid chromatography-high resolution electrospray ionization- tandem mass spectrometry (HILIC-HR-ESI-MS/MS). The Chlorococcum amblystomatis strain had a lipid content of 20.77% and the fatty acid profile, determined by gas chromatography-mass spectrometry, has shown that this microalga contains high amounts of omega-3 polyunsaturated fatty acids (PUFAs). The lipidome identified included 245 molecular ions and 350 lipid species comprising 15 different classes of glycolipids (6), phospholipids (7) and betaine lipids (2). Of these, 157 lipid species and the main lipid species of each class were esterified with omega-3 PUFAs. The lipid extract has shown antioxidant activity and anti-inflammatory potential. Lipid extracts also had low values of atherogenic (0.54) and thrombogenic index (0.27). In conclusion, the lipid extracts of Chlorococcum amblystomatis have been found to be a source of lipids rich in omega-3 PUFAs for of great value for the food, feed, cosmetic, nutraceutical and pharmaceutical industries.

Effects of light-emitting diodes (LEDs) on lipid production of the aerial microalga Coccomyxa sp. KGU-D001 under liquid- and aerial-phase conditions

Algal biofuels are a promising alternative to fossil fuels, but their widespread use is hindered by problems with mass production. Light-emitting diodes (LEDs) with specific light wavelengths could be used as an energy source for algal growth and lipid synthesis. In this study, the effects of light source on the biomass and lipid production of the aerial microalga Coccomyxa sp. KGU-D001 were evaluated using LEDs. The integration of two-phase cultures, including growth and lipid production under the stress of nitrate depletion, was assessed for efficient lipid production under liquid- or aerial-phase conditions. Different wavelengths of light (blue, green, and red) were tested under liquid- and aerial-phase conditions. Under aerial-phase culture, the fatty acid contents in biofilm reached 320 mg g DWC^-1 with the red LEDs. In view of these findings, we describe a one-step culture method for growth and lipid accumulation in algal biofilm under aerial-phase culture with red LED irradiation. When Coccomyxa biofilm was cultured on wet cotton wool with BBM in a petri dish under the red LED, it was able to grow and accumulate lipids under the aerial-phase condition. Based on the results of this study, a potential method for a continuous biodiesel production system is proposed.

Surviving Starvation: Proteomic and Lipidomic Profiling of Nutrient Deprivation in the Smallest Known Free-Living Eukaryote

Marine phytoplankton, comprising cyanobacteria, micro- and pico-algae are key to photosynthesis, oxygen production and carbon assimilation on Earth. The unicellular green picoalga Ostreococcus tauri holds a key position at the base of the green lineage of plants, which makes it an interesting model organism. O. tauri has adapted to survive in low levels of nitrogen and phosphorus in the open ocean and also during rapid changes in the levels of these nutrients in coastal waters. In this study, we have employed untargeted proteomic and lipidomic strategies to investigate the molecular responses of O. tauri to low-nitrogen and low-phosphorus environments. In the absence of external nitrogen, there was an elevation in the expression of ammonia and urea transporter proteins together with an accumulation of triglycerides. In phosphate-limiting conditions, the expression levels of phosphokinases and phosphate transporters were increased, indicating an attempt to maximise scavenging opportunities as opposed to energy conservation conditions. The production of betaine lipids was also elevated, highlighting a shift away from phospholipid metabolism. This finding was supported by the putative identification of betaine synthase in O. tauri. This work offers additional perspectives on the complex strategies that underpin the adaptive processes of the smallest known free-living eukaryote to alterations in environmental conditions.