Translocation and de novo synthesis of eicosapentaenoic acid (EPA) during nitrogen starvation in Nannochloropsis gaditana

The microalga Nannochloropsis gaditana is known for accumulating fatty acids, including the commercially interesting eicosapentaenoic acid (EPA) within the polar lipids (PL) and neutral lipids (NL). During microalgal growth EPA is mainly present in the PL. Upon nitrogen starvation N. gaditana accumulates large amounts of TAG in lipid bodies. The neutral lipid fraction will mainly consist of triacylglycerol (TAG). When expressed per total cell dry weight, the NL-localized EPA increased while the PL-localized EPA decreased, suggesting that EPA is translocated from the PL into the NL lipids during nitrogen starvation. Here, we elucidated the origin of EPA in NL of N. gaditana by firstly growing this microalga under optimal growth conditions with 13CO2 as the sole carbon source followed by nitrogen starvation with 12CO2 as the sole carbon source. By measuring both 12C and 13C fatty acid isotope species in time, the de novo synthesized fatty acids and the already present fatty acids can be distinguished. For the first time, we proved that actual translocation of EPA from the PL into the NL occurs during nitrogen starvation of N. gaditana. Next to being translocated, EPA was synthesized de novo in both PL and NL during nitrogen starvation. EPA was made by carbon reshuffling within the cell as well. EPA was the main fatty acid translocated, suggesting that the enzyme responsible for fatty acid translocation has a high specificity for EPA.publishedVersio

Time-dependent transcriptome profile of genes involved in triacylglycerol (TAG) and polyunsaturated fatty acid synthesis in Nannochloropsis gaditana during nitrogen starvation

In this research, the gene expression of genes involved in lipid metabolism of the eustigmatophyte alga Nannochloropsis gaditana was measured by transcriptomic data. This microalga can be used as a source of triacylglycerol (TAG) and the omega-3 fatty acid eicosapentaenoic acid (EPA). Insight in TAG and EPA production and regulation are needed to improve their productivity. Nitrogen starvation induces TAG accumulation in N. gaditana. Previous research showed that during nitrogen starvation, EPA was translocated from the polar lipids to TAG and de novo synthesized in N. gaditana. Therefore, the expression levels of genes involved in fatty acid translocation and de novo TAG synthesis were measured. Furthermore, the genes involved in de novo EPA synthesis such as elongases and desaturases were studied. The expression levels were measured during the first hours of nitrogen starvation and the subsequent period of 14 days. One phospholipid:diacylglycerol acyltransferase (PDAT) gene involved in translocation of fatty acids from membrane lipids to TAG was upregulated. In addition, several lipases were upregulated, suggesting that these enzymes might be responsible for the translocation of EPA to TAG. Most desaturases and elongases involved in de novo EPA synthesis were downregulated during nitrogen starvation, except for Δ9 desaturase which was upregulated. This upregulation correlates with the increase in oleic acid. Due to the presence of many hypothetical genes, improvement in annotation is needed to increase our understanding of these pathways and their regulation.</p

An assessment of heterosexuals\u27 perceived risk for HIV infection

Microalgae are a sustainable source of lipids. A commonly used strategy for lipid accumulation in microalgae is a two-step batch cultivation, with a growth phase followed by a nitrogen starvation phase. A problem with this process is the decrease in photosynthetic efficiency during the nitrogen starvation phase, which leads to low lipid productivities. In this research, a new process strategy was studied with the aim to improve lipid productivity of the microalgae Nannochloropsis gaditana. The nitrogen concentrations were chosen to assure consumption of most part of the nitrogen during the night. An improvement of the photosystem II maximum quantum yield and an increase in the dry weight and TAG concentration was achieved from day 7 of nitrogen starvation onwards when the culture was fed with nitrogen each night compared to a culture without nitrogen addition. Consequently, the time-average TAG yield on light was also higher after 7 days of nitrogen starvation. However, since the maximal time-averaged triacylglycerol (TAG) yield on light was reached after 3 days of nitrogen starvation, the improved photosynthetic activity did not lead to an increase of the maximal time-averaged TAG yield on light. The culture with nitrogen addition had a higher protein concentration (1.1 compared to 0.7 g L−1), showing that the added nitrogen was mainly used for protein production. A higher chlorophyll a content (2.0 compared to 0.8 μg mg−1) showed improved photosystem and that a small part of nitrogen was used for chlorophyll a. Small nightly nitrogen additions during batch cultivation of nitrogen starved N. gaditana did result in improvement in photosystem II maximal quantum yield, biomass concentration, TAG production and a higher time-averaged maximal TAG yield on light, after 7 days of nitrogen starvation.</p

Lipid metabolism in Nannochloropsis gaditana during nitrogen starvation

Microalgae are unicellular photosynthetic microorganisms, which can convert light, carbon dioxide and nutrients into multiple products like lipids, proteins and pigments. Even though they are a sustainable source of lipids, higher lipid yields are required to turn the production into an economical feasible process. The microalgae Nannochloropsis gaditana can accumulate large amount of lipids upon nitrogen starvation and it is a natural producer of the omega-3 fatty acid eicosapentaenoic acid (EPA). This thesis focusses on understanding the cellular mechanisms underlying lipid accumulation and developing a process with improved lipid production for Nannochloropsis gaditana. Upon nitrogen starvation Nannochloropsis gaditana can accumulate large amounts of lipids in triacylglycerol (TAG) lipid bodies. EPA can accumulate in both TAG and polar lipid fraction. In this research, we used labelled carbon to measure de novo synthesis and transport of fatty acids during starvation. The expression levels of the genes involved in the pathways were measured for more insight in the active pathways. Furthermore, a strategy to improve lipid accumulation by addition of small amounts of nitrogen to a nitrogen starved culture was tested. Next to that, the amount of light per biomass upon nitrogen starvation was found to be important for TAG accumulation under outdoor light conditions. The research of this thesis was performed within the EU FP7 MIRACLES project under grant agreement No. 613588

Lipid production in Nannochloropsis gaditana during nitrogen starvation

The microalga Nannochloropsis gaditana is a natural producer of triacylglycerol (TAG) and the omega-3 fatty acid eicosapentaenoic acid (EPA). TAG accumulation is induced by nitrogen starvation. The biomass-specific photon supply rate used had an effect on EPA and TAG accumulation during nitrogen starvation as well as on the localization of EPA accumulation. Clear differences in TAG yield on light were found for different biomass-specific photon supply rates and light regimes during nitrogen starvation. De novo EPA synthesis or the translocation of EPA between lipid fractions might be limiting for EPA accumulation in TAG. Further studies are needed to fully understand EPA accumulation in TAG during nitrogen starvation. To elucidate the function of EPA in TAG nitrogen recovery, experiments are suggested. The overexpression of genes involved in de novo EPA synthesis and translocation is proposed to elucidate the exact metabolic routes involved in these processes during nitrogen starvation. This work addresses future opportunities to increase EPA accumulation

Lipid production in nannochloropsis gaditana during nitrogen starvation

The microalga Nannochloropsis gaditana is a natural producer of triacylglycerol (TAG) and the omega-3 fatty acid eicosapentaenoic acid (EPA). TAG accumulation is induced by nitrogen starvation. The biomass-specific photon supply rate used had an effect on EPA and TAG accumulation during nitrogen starvation as well as on the localization of EPA accumulation. Clear differences in TAG yield on light were found for different biomass-specific photon supply rates and light regimes during nitrogen starvation. De novo EPA synthesis or the translocation of EPA between lipid fractions might be limiting for EPA accumulation in TAG. Further studies are needed to fully understand EPA accumulation in TAG during nitrogen starvation. To elucidate the function of EPA in TAG nitrogen recovery, experiments are suggested. The overexpression of genes involved in de novo EPA synthesis and translocation is proposed to elucidate the exact metabolic routes involved in these processes during nitrogen starvation. This work addresses future opportunities to increase EPA accumulation

Lipid production in nannochloropsis gaditana during nitrogen starvation

The microalga Nannochloropsis gaditana is a natural producer of triacylglycerol (TAG) and the omega-3 fatty acid eicosapentaenoic acid (EPA). TAG accumulation is induced by nitrogen starvation. The biomass-specific photon supply rate used had an effect on EPA and TAG accumulation during nitrogen starvation as well as on the localization of EPA accumulation. Clear differences in TAG yield on light were found for different biomass-specific photon supply rates and light regimes during nitrogen starvation. De novo EPA synthesis or the translocation of EPA between lipid fractions might be limiting for EPA accumulation in TAG. Further studies are needed to fully understand EPA accumulation in TAG during nitrogen starvation. To elucidate the function of EPA in TAG nitrogen recovery, experiments are suggested. The overexpression of genes involved in de novo EPA synthesis and translocation is proposed to elucidate the exact metabolic routes involved in these processes during nitrogen starvation. This work addresses future opportunities to increase EPA accumulation.</p

Mi ciudad sorpresa : estrategias de visibilización y movilización política del movimiento LGBTI en Pasto.

El objetivo del siguiente trabajo es analizar las diversas estrategias de visibilización y movilización política del movimiento LGBTI (Lesbianas, Gays, Bisexuales, Trans e Intersexuales) en la ciudad de Pasto, Colombia, teniendo en cuenta que se trata de un movimiento social heterogéneo y cuyas acciones responden a distintos intereses, preocupaciones y problemáticas. De modo que esta propuesta de investigación parte de la discusión teórica en torno al movimiento LGBTI y las diversidades sexuales y de género, cuyo enfoque tiene que ver con las demandas de acceso a derechos, entendida como ciudadanía plena y no solo como ciudadanía sexual

Translocation and de novo synthesis of eicosapentaenoic acid (EPA) during nitrogen starvation in Nannochloropsis gaditana

The microalga Nannochloropsis gaditana is known for accumulating fatty acids, including the commercially interesting eicosapentaenoic acid (EPA) within the polar lipids (PL) and neutral lipids (NL). During microalgal growth EPA is mainly present in the PL. Upon nitrogen starvation N. gaditana accumulates large amounts of TAG in lipid bodies. The neutral lipid fraction will mainly consist of triacylglycerol (TAG). When expressed per total cell dry weight, the NL-localized EPA increased while the PL-localized EPA decreased, suggesting that EPA is translocated from the PL into the NL lipids during nitrogen starvation. Here, we elucidated the origin of EPA in NL of N. gaditana by firstly growing this microalga under optimal growth conditions with 13CO2 as the sole carbon source followed by nitrogen starvation with 12CO2 as the sole carbon source. By measuring both 12C and 13C fatty acid isotope species in time, the de novo synthesized fatty acids and the already present fatty acids can be distinguished. For the first time, we proved that actual translocation of EPA from the PL into the NL occurs during nitrogen starvation of N. gaditana. Next to being translocated, EPA was synthesized de novo in both PL and NL during nitrogen starvation. EPA was made by carbon reshuffling within the cell as well. EPA was the main fatty acid translocated, suggesting that the enzyme responsible for fatty acid translocation has a high specificity for EPA

Time-dependent transcriptome profile of genes involved in triacylglycerol (TAG) and polyunsaturated fatty acid synthesis in Nannochloropsis gaditana during nitrogen starvation

In this research, the gene expression of genes involved in lipid metabolism of the eustigmatophyte alga Nannochloropsis gaditana was measured by transcriptomic data. This microalga can be used as a source of triacylglycerol (TAG) and the omega-3 fatty acid eicosapentaenoic acid (EPA). Insight in TAG and EPA production and regulation are needed to improve their productivity. Nitrogen starvation induces TAG accumulation in N. gaditana. Previous research showed that during nitrogen starvation, EPA was translocated from the polar lipids to TAG and de novo synthesized in N. gaditana. Therefore, the expression levels of genes involved in fatty acid translocation and de novo TAG synthesis were measured. Furthermore, the genes involved in de novo EPA synthesis such as elongases and desaturases were studied. The expression levels were measured during the first hours of nitrogen starvation and the subsequent period of 14 days. One phospholipid:diacylglycerol acyltransferase (PDAT) gene involved in translocation of fatty acids from membrane lipids to TAG was upregulated. In addition, several lipases were upregulated, suggesting that these enzymes might be responsible for the translocation of EPA to TAG. Most desaturases and elongases involved in de novo EPA synthesis were downregulated during nitrogen starvation, except for Δ9 desaturase which was upregulated. This upregulation correlates with the increase in oleic acid. Due to the presence of many hypothetical genes, improvement in annotation is needed to increase our understanding of these pathways and their regulation