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This study employed 1-ethyl-3-methyl imidazolium chloride ([EMIM][Cl]) as an additive in an aqueous medium, combined with microwave-assisted extraction (IL-MAE), to extract total lipids and eicosapentaenoic acid (EPA) from the microalga Nannochloropsis sp. microalgae. The optimization process involved evaluating critical operating parameters, including the type of extraction solvent, solid-loading (i.e., water: microalgae ratio), extraction time, extraction temperature, and the IL/biomass ratio on the extraction of total lipids and as well as its EPA content. Under optimal conditions, IL-MAE significantly enhanced total lipid yield and EPA content by approximately 2.72 times and 8.1 times, respectively, compared to the traditional Soxhlet extraction. The standard Soxhlet procedure resulted in approximately 6.20% total lipids and 4.61 mg g-1 of EPA. Notably, with IL-MAE, the highest lipid and EPA yields were achieved. These reached 16.87% and 37.28 mg g-1, respectively, under optimal conditions: 90 °C for 25 min, using 2 w/w IL/biomass ratio, with 0.5 g of algae and a 3.3% w/v solid-loading. The obtained FAMEs through transesterification of total lipids exhibited high quality, comprising 37.94% wt polyunsaturated fatty acids (PUFAs). SEM and FTIR confirmed IL-MAE's superior lipid extraction by disrupting glycosidic linkages in the microalgal cell wall, resulting in a significantly higher yield than Soxhlet extraction. Repeated use of recycled [EMIM][Cl], tested up to four times, did not impact lipid and fatty acids recovery. Cost evaluation revealed that the IL-MAE approach for lipid production from Nannochloropsis sp. is more cost-efficient than the Soxhlet method, considering biomass, chemical and energy consumption. The enhanced extraction performance and accelerated rates of the IL-MAE system demonstrate its efficacy in extracting lipids, EPAs, and PUFAs from microalgae. Furthermore, it emphasizes sustainable, green, and efficient approach for extracting bioactive compounds, offering potential applications in the pharmaceutical and nutraceutical industries. [ABSTRACT FROM AUTHOR]

Thalassiosira pseudonana, a fast-growing and nutritionally rich planktonic diatom, has been cultivated on a large scale as high-quality plankton feed. Despite this, studies exploring the impact of light quality on the growth and compositional attributes of this algal species are scarce. This study investigated the effects of five different light qualities—white, red, yellow, green, and blue—on the growth, biomass, fucoxanthin accumulation, and fatty acid composition and content of T. pseudonana. The results indicated that T. pseudonana achieved the highest growth rate and greatest biomass under white and blue light, with the poorest performance observed under red light. Moreover, fucoxanthin accumulation was most pronounced under blue light, reaching 4.729 ± 0.182 mg g-1, followed in descending order by yellow, red, white, and green light. The total lipid content was highest under yellow light at 34%, significantly surpassing the levels observed under other conditions, with the order of effectiveness being blue light > green light ≥ red light ≥ white light. Analysis of fatty acid composition revealed a greater diversity under blue light, with a total of 15 types, whereas green light yielded only 10 types. The proportion of unsaturated fatty acids was highest under blue light at 69.71%, followed by yellow, white, green, and red light. Specifically, the performance of polyunsaturated fatty acids (PUFAs) varied as follows: yellow light (36.7%) > blue light (34.09%) > white light (33.29%) > green light (23.67%) > red light (17%). The concentration of eicosapentaenoic acid (EPA) was significantly greater under blue (17.03%) and yellow (16.31%) light compared to other treatments, with the lowest concentration (8.84%) observed under red light. In conclusion, blue light significantly enhances the growth rate of T. pseudonana and fosters fucoxanthin accumulation. Both yellow and blue light are favorable for the accumulation of PUFAs and EPA. [ABSTRACT FROM AUTHOR]

Green seaweed species of the genus Ulva are promising protein sources for food production. Various factors affect the biochemical composition of Ulva spp. (hereafter Ulva), which can complicate the utilization in a commercial scale food production. This study investigated the composition of Ulva harvested in 2021 in May (dark green/black biomass), June (light green biomass) and August (mixed colored biomass). The August harvest was divided into three different color codes: light green, green, and dark green/black, to explore a relation between color and composition as an indicator for biomass quality. The crude protein (CP) and ash contents were highest in the dark August biomass (16.4±0.4% and 35.9±3.0% of dry matter (DM), respectively) and in the dark biomass harvested in May (20.6±0.5% and 41.2±3.9% of DM, respectively). The light green Ulva harvested in June had a lower CP content (6.5±1.5% of DM) similarly to what was observed for light green biomass in August (7.7±0.1% of DM). The light green biomasses were found to have a higher nitrogen to amino acid (N-to-AA) conversion factor and proportion of essential amino acids (EAA). The lipid content ranged between 1.0-2.2±0.1-0.2% of DM for the different biomasses and a higher lipid content was related with a lighter biomass color. Phosphorus and potassium concentrations were highest in the green fraction, whereas the darker green/black biomass had higher contents of all other elements, including the toxic elements, arsenic and cadmium. [ABSTRACT FROM AUTHOR]

Lipid extraction from microalgae was studied more specifically considering the effects of the extraction method and solvent mixture on cell walls. Chlorella vulgaris and Nannochloropsis oculata were maintained in Bold Basal Medium (BBM) and, Dunaliella salina and Dunaliella tertiolecta in Guillard "F/2" medium, sterile with continuous aeration at 18 ºC at 80 µmol photons m−2 s−1. The objective of the study was to evaluate and compare the lipid content and fatty acid profiles of 4 microalgae species (freshwater and marine species) using two lipid extraction methods, Soxhlet and ultrasonication. Biomass production was greatest in the stationary phase for all microalgae, with D. salina exhibiting the highest production with 0.40–0.42 g L−1. Biomass productivity for freshwater microalgae was higher in the stationary phase (0.0360–0.0407 g L−1 day−1) and in the exponential phase for marine microalgae (0.057–0.064 g L−1 day−1). The highest percentage of lipids in marine microalgae was between 38–54% by weight in the stationary phase, with D. tertiolecta; in comparison, the freshwater microalgae reached between 22–23% by weight in the exponential phase, for the species N. oculata. The highest number of fatty acids observed in marine microalgae was by Soxhlet extraction in D. tertiolecta in both growth phases. The highest percentage of any fatty acid with this method was palmitic acid (61%) in the stationary phase of C vulgaris. The ultrasonication extraction method presented the highest percentages in the stationary phase of N. oculata and D. tertiolecta, palmitic acid (C16:0) showing the highest percentages (87 and 51%) in the exponential phase in both marine microalgae. In short, it was observed that the extraction method and solvent mixture could influence fatty acid profile. [ABSTRACT FROM AUTHOR]

The sulfo-phospho-vanillin assay is a well-known method to measure the lipid content of microalgae. Following hydrolysis with sulfuric acid, a pink color develops after the addition of sulfo-phospho-vanillin and the absorbance at 530 nm is measured. As any colorimetric method, several factors might affect results consistency such as reaction time, matrix effects and sample background color. In this study, the measurement was carried out on freeze-dried samples of Chlorella and Spirulina to assess these impacts. The results showed the increase of absorbance with time even after the usual 30 min resting period. The main observation is a sample background color following acid hydrolysis and phosphoric acid addition, which questions the generally accepted SPV method reaction mechanism. [ABSTRACT FROM AUTHOR]

The oleaginous genera Nannochloropsis and Microchloropsis are recognized for their lipid accumulation capacity. Microalgal lipid accumulation is triggered by nitrogen starvation, negatively affecting photosynthesis and growth. Moreover, light and temperature play pivotal roles in microalgal physiology, lipid accumulation and composition. This study focuses on comparing the responses of eight microalgal strains from Nannochloropsis (N. oceanica Necton, N. oceanica IMET1, Nannochloropsis. sp. CCAP211/78, N. oculata, and N. limnetica) and Microchloropsis (M. gaditana CCFM01, M.gaditana CCMP526, and M.salina) to light, temperature, and nitrogen availability. Biomass, lipid content and productivities were monitored under different light intensities (150 (LL) and 600 μmol photons m−2 s−1 (HL)) and temperatures (15, 25, 30℃) under nitrogen (N-) starvation and replete conditions. Under N-starvation and HL, N. sp. exhibited the highest lipid content (59%) and productivity (0.069 g L-1 day-1), while N. oculata had the lowest lipid content (37.5%) and productivity (0.037 g L-1 day-1) among the eight strains. Notably, M. gaditana CCFM01 achieved the highest EPA content (4.7%), contrasting with N.oceanica IMET1 lowest EPA content (2.9%) under 150 μmol photons m−2 s−1 and N-repletion. The response to temperature fluctuations under LL was strain-dependent. Microchloropsis salina and M. gaditana CCFM01 demonstrated the highest and lowest lipid productivities (0.069 g L-1 day-1 and 0.022 g L-1 day-1, respectively) at 15℃ under N-starvation. Moreover, significant EPA accumulation across various strains was observed in N. oculata (5.7%) under N-repletion at 15°C, surpassing M. gaditana CCFM01 by 40%. Ultimately, the physiological responses to cultivation conditions vary markedly among microalgal strains, even within the same genus or species. This knowledge is essential for selecting suitable strains for the efficient microalgal lipid production industry.Optimi zing cultivation conditions for the maximal lipid production in Nannochloropsis andMicrochloropsisGraphical Abstract: The oleaginous genera Nannochloropsis and Microchloropsis are recognized for their lipid accumulation capacity. Microalgal lipid accumulation is triggered by nitrogen starvation, negatively affecting photosynthesis and growth. Moreover, light and temperature play pivotal roles in microalgal physiology, lipid accumulation and composition. This study focuses on comparing the responses of eight microalgal strains from Nannochloropsis (N. oceanica Necton, N. oceanica IMET1, Nannochloropsis. sp. CCAP211/78, N. oculata, and N. limnetica) and Microchloropsis (M. gaditana CCFM01, M.gaditana CCMP526, and M.salina) to light, temperature, and nitrogen availability. Biomass, lipid content and productivities were monitored under different light intensities (150 (LL) and 600 μmol photons m−2 s−1 (HL)) and temperatures (15, 25, 30℃) under nitrogen (N-) starvation and replete conditions. Under N-starvation and HL, N. sp. exhibited the highest lipid content (59%) and productivity (0.069 g L-1 day-1), while N. oculata had the lowest lipid content (37.5%) and productivity (0.037 g L-1 day-1) among the eight strains. Notably, M. gaditana CCFM01 achieved the highest EPA content (4.7%), contrasting with N.oceanica IMET1 lowest EPA content (2.9%) under 150 μmol photons m−2 s−1 and N-repletion. The response to temperature fluctuations under LL was strain-dependent. Microchloropsis salina and M. gaditana CCFM01 demonstrated the highest and lowest lipid productivities (0.069 g L-1 day-1 and 0.022 g L-1 day-1, respectively) at 15℃ under N-starvation. Moreover, significant EPA accumulation across various strains was observed in N. oculata (5.7%) under N-repletion at 15°C, surpassing M. gaditana CCFM01 by 40%. Ultimately, the physiological responses to cultivation conditions vary markedly among microalgal strains, even within the same genus or species. This knowledge is essential for selecting suitable strains for the efficient microalgal lipid production industry.Optimi zing cultivation conditions for the maximal lipid production in Nannochloropsis andMicrochloropsis [ABSTRACT FROM AUTHOR]

This study examines how salinity reduction triggers the response of three marine microalgae at the molecular and unicellular levels in terms of chemical, mechanical, and behavioral changes. At the lowest salinity, all microalgal species exhibited an increase in membrane sterols and behaved stiffer. The glycocalyx-coated species Dunaliella tertiolecta was surrounded by a thick actin layer and showed the highest physiological activity, negatively affecting cell motility and indicating the formation of the palmella stage. The lipid content of membrane and the hydrophobicity of cell were largely preserved over a wide range of salinity, confirming the euryhaline nature of Dunaliella. The species with calcite-encrusted theca Tetraselmis suecica exhibited the highest hydrophobicity at the lowest salinity of all cells examined. At salinity of 19, the cells of T. suecica showed the lowest growth, flagellar detachment and the lowest cell speed, the highest physiological activity associated with a dense network of extracellular polymeric substances, and a decrease in membrane lipids, which could indicate develepment of cyst stage. The organosilicate encrusted species Cylindrotheca closterium appeared to be salinity tolerant. It behaved hydrophobically at lower salinity, whereas becoming hydrophilic at higher salinity, which might be related to a molecular change in the released biopolymers. This study highlighted the interplay between chemistry and mechanics that determines functional cell behavior and shows that cell surface properties and behavior could serve as stress markers for marine biota under climate change. [ABSTRACT FROM AUTHOR]

Photoautotrophic algal cultivation is challenging due to the shadowing effect produced by an increase in the number of cells; under such circumstances, mixotrophic growth might be an efficient alternative. We grew cultures of the autochthonous acidotolerant microalga Elliptochloris sp. on crude technical glycerin or glucose bubbled with either only air or air containing 2.5 % (v/v) CO2. We found that CO2 strongly influenced the production of Elliptochloris sp., as higher growth occurred in mixotrophy with CO2-enriched air compared to that with only air. Mixotrophy with CO2-enriched air allowed to reach higher biomass productivities and facilitated an increase in the relative abundance of saturated fatty acids. Nevertheless, mixotrophy with only air resulted in an increase of both saturated and unsaturated fatty acids, but biomass productivities were lower. These results, along with the limited biological contamination facilitated by low pH, suggest that this microalga might be attractive for large-scale production within the circular economy model. [ABSTRACT FROM AUTHOR]

Marine microalgae are a promising sustainable source of lipids, omega-3 fatty acids, and carbohydrates. Selected microalgae species belonging to the Bacillariophyceae, Haptophyceae, Eustigmatophyceae, and Prasinophyceae were characterised for cellular content of carbon and nitrogen, and for production yields of lipids, fatty acids, total carbohydrates, and β-glucans. Carbon and nitrogen content showed a hyperbolic decrease with increasing cell numbers for Chaetoceros calcitrans, C. muelleri, Skeletonema costatum, Tetraselmis sp., and Nannochloropsis oculata. Cultures of Pavlova lutheri and Tisochrysis lutea showed an increase in carbon content per cell, but a decrease in nitrogen content. The total lipid content of C. muelleri, C. calcitrans, N. oculata, and T. lutea increased with decreasing relative growth rate; however, the highest productivity of lipids was found in T. lutea grown at 40% of the maximum specific growth rate. The highest content of eicosapentaenoic acid was found in C. muelleri, C. calcitrans, and N. oculata, and the highest content of docosahexaenoic acid was found in T. lutea. The β-glucan fraction of the carbohydrates was highest in C. muelleri and C. calcitrans and was very low in N. oculata. Out of the species investigated, C. muelleri had the highest production yield of β-glucans, obtained when cultivated at a 40% relative growth rate. [ABSTRACT FROM AUTHOR]

Opportunities associated with biomass production and bioproduct isolation from algae-derived feedstocks are plentiful and promising; however, there are challenges associated with realizing these applications. One of the most important, and often overlooked, challenges is the lack of availability of a strong foundation of compositional analysis methods validated on microalgal biomass. Currently, compositional analysis in algae is dominated by the use of interference-prone methods, a lack of full mass balance accounting, and the use of top-down approaches that bin all unaccounted-for mass into a single category, such as carbohydrates. We present here an approach based on a bottom-up algal biomass characterization aimed at moving towards, and highlighting the importance of, full and accurate mass closure to achieve the maximum economic potential from a sustainable and renewable feedstock. Algal biomass representing three genera, Nannochloropsis, Scenedesmus, and Monoraphidium, was subjected to a cell rupture and fractionation process, followed by detailed characterization of each fraction to determine the partitioning of measured and unknown components. The goal of this work is to identify where the missing components partition, and develop a strategy to close the mass balance or identify the unknowns, while utilizing a rigorous characterization approach for characterizing algal biomass. Although only 75–80% of the biomass was accounted for, the fractionation approach utilized here provides key insight into possible chemical components for future investigations. [ABSTRACT FROM AUTHOR]

Under an adequate supply of nitrogen (N) and phosphorus (P), the cyanobacterium Synechocystis sp. PCC 6803 produced a high biomass yield but with a low storage level of glycogen and poly(3-hydroxybutyrate) (PHB). In contrast, deprivation of N or P stimulated accumulation of glycogen and PHB, but reduced biomass yield. In addition, deprivation of N or P had no apparent effect on total lipid accumulation. Here, we examined how partial supply of N or P has effects on the biomass yield and production of glycogen, PHB, and lipids. The N or P supply in the culture media was orderly decreased from 100% (set according to the standard BG11 medium) to 50, 35, 20, 10, and 0%. A 100% supply of both N and P produced biomass of up to 1.4 g L−1, while a 35–50% N supply slightly reduced the biomass to 1.2–1.3 g L−1, and no apparent change in the biomass was detected under a 20–50% P supply. A maximum glycogen accumulation of 51.8% (w/w dry weight; DW) was obtained under 20% P supply, while the maximum PHB storage of 6.3% (w/w DW) was obtained with 10% P supply. Lipid accumulation peaked at 12.7% (w/w DW) under 0% P supply. The maximal co-production of these three bioproducts was obtained under 20% P supply at 765 mg L−1 which is the sum of 72 mg L−1 PHB (corresponding to 5.1% w/w DW PHB), 618 mg L−1 glycogen (43.8% w/w DW glycogen), and 75 mg L−1 lipid (5.3% w/w DW lipid) from the total biomass production of 1.4 g L−1. The glycogen production (618 mg L−1) was higher than those previously reported for Synechocystis. The results indicated that a proper adjustment of initial N and P supplies in the culture is crucial for maximal production of these three bioproducts by Synechocystis. [ABSTRACT FROM AUTHOR]

In recent years biodiesel production has attracted worldwide attention due to the awareness of fossil fuel depletion and microalgae biomass is considered a promising raw material for its formulation. The present study evaluated the effects of different levels of nitrogen limitation (37.5, 18.75, 9.375 mg L−1 NaNO3) on the growth, cell ultrastructure, and biochemical composition of a halophilic native strain of the green alga Picocystis salinarum as a potential raw material source for biodiesel. During a culture period of 20 days, growth measurements and photosynthetic pigments were estimated. Cell density, dry weight, and chlorophylls a, b content decreased with time as nitrogen limitation increase; however, carotenoid content increased. In addition, nitrogen limitation caused an progressive increase in the lipid and carbohydrate yield and a decrease in protein. The high N limitation (9.375 mg L−1) had a significant effect on the accumulation of total lipid content (33.87% dry weight). Carbohydrate content (30.98% dry weight) and protein content (1.89% dry weight) decrease. The lipid content showed a differential FAME profile with high saturated fatty acid values (996.08 μg g−1 dry weight) mainly palmitic acid, compare with the unsaturated ones that showed low values under high N limitation. The gradual increase of lipid content was also corroborated by transmission electron microscopy images with a single large lipid droplet cell formation. Therefore, evaluation of the algal culture conditions such as N limitation, as a strategy to maximize lipid content and improve the fatty acid profile in unexplored strain of P. salinarum, showed a potential biomass yield as a suitable candidate for biodiesel production. [ABSTRACT FROM AUTHOR]

There is a growing demand for marine omega-3 fatty acids (FAs) that is produced in high amounts by some microalgae. Here we determined the FA profiles of two cold water adapted diatoms, Chaetoceros wighamii and Thalassiosira baltica. The cultures were acclimated to different temperatures (3, 7, 11, 15, and 19 °C) and irradiance (20, 40, 130, and 450 μmol photons m−2 s−1) and the FA profiles were determined in exponential and stationary growth phases, the latter induced by different nutrient limitation (N, P, and Si). The maximum growth rate was obtained by both species at 11 °C, ≥ 130 μmol photons m−2 s−1 and was 0.8 day−1 and 0.6 day−1 for C. wighamii and T. baltica, respectively. Both species contained relatively high amounts of eicosapentaenoic acid (EPA). Thalassiosira baltica accumulated maximally ~ 30 mg EPA g−1 ash-free dry weight (AFDW) under Si-limitation. The content of docosahexaenoic acid (DHA) was lower, reaching up to 4 mg DHA g−1 AFDW in T. baltica. The concentration of EPA correlated positively with the chlorophyll a:carbon ratio, suggesting that it is bound to membranes in the photosynthetic apparatus and the EPA content in T. baltica was high enough to consider it as a potent candidate for cultivation under cold (< 15 °C) conditions. Covering a wide range of environmental conditions, the strongest differentiation in FA profiles was observed between the species with the growth phase/nutrient limitation pattern as the second most important driver of the FA composition. [ABSTRACT FROM AUTHOR]

Crypthecodinium cohnii growth was studied on pure carbon sources (glucose, acetate, glycerol) and low-cost complex carbon sources (sugarcane molasses, crude glycerol and vinegar effluent) for lipid and DHA production. Among the pure substrates, glucose induced the highest lipid content (14.75% w/w DCW) and DHA content (7.14 mg g−1 DCW). Among the low-cost substrates, the highest lipid and DHA content were observed for the crude glycerol assay (14.7% w/w DCW and 6.56 mg g−1, respectively). Molasses induced the highest proportion of DHA of total fatty acids (49.58% w/w TFA) among all the substrates studied. Flow cytometric analysis revealed that the vinegar effluent induced the highest proportion of C. cohnii cells with injured membrane (92.8%). These results foresee the possibility of using these low-cost substrates at a larger scale for C. cohnii DHA and biodiesel production, aiming at zero wastes and process costs reduction. [ABSTRACT FROM AUTHOR]

Cyanobacteria are able to absorb light over a wide spectral range due to the presence of photoreceptors, making it possible to modulate the production of high-value compounds by inducing specific pathways. In order to evaluate the influence of light quality in cyanobacteria metabolism, Cyanobium sp. was grown in five different light conditions, by using low-pressure sodium vapor lamp (SOX) supplemented with low irradiances of green, red, and blue light and UV radiation compared to a control with only SOX. The effects of light supplementation on biomass productivity, photosynthetic activity, biochemical composition, and total antioxidant capacity were evaluated. No changes in biomass productivity were induced by any light supplements. The supplementation of red light triggered the production of lipids, phycocyanin, carotenoids, and total antioxidant compounds, while supplementation of green light increased the content of carbohydrates and chlorophyll a. Thus, supplementation of blue light and UV radiation showed little or no improvements to the culture, whereas under UV radiation the photosynthetic activity was reduced. Overall, Cyanobium sp. is a promising strain, mainly due to its accessibility to metabolism photoregulation as to produce various bioactive compounds. [ABSTRACT FROM AUTHOR]

Growing algae in darkness for biodiesel production eliminates the challenges of evaporation and light penetration reported for open ponds and the costs and fouling that plague photobioreactors. The current study demonstrated that Chlorella kessleri str. UTEX 263 could grow heterotrophically in the dark on pure sugars or lignocellulosic hydrolysates of plant biomass. Hydrolysates of a prairie grass native to Kansas, Big Bluestem (Andropogon gerardii), supported the growth of C. kessleri in the dark. Nitrogen limitation stimulated the accumulation of biodiesel lipids by 10-fold in heterotrophic cultures grown on pure sugars or Big Bluestem hydrolysate. Limiting P in the growth medium also was shown to increase cellular lipid accumulation in C. kessleri. Iron limitation was not sufficient to increase cellular lipid content. Crude biomass extracts may have levels of N that cannot be easily removed, which are high enough to relieve N limitations in growth media. This initial study suggests that P might be more easily removed from biomass extracts than N for increasing cellular lipid production by nutrient limitation and further that native prairie grasses are potentially suitable as sources of lignocellulosic sugars. [ABSTRACT FROM AUTHOR]

Chromochloris (Chlorella) zofingiensis (Dönz) Fucíková & Lewis is a carotenogenic chlorophyte producing valuable carotenoids such as astaxanthin and canthaxanthin. Due to a high culture robustness, it has a potential to become a major biotechnological source of natural carotenoid pigments in the nearest future. To the best of our knowledge, this is the first report on the comparative assessment of the biomass, carotenoid, and lipid productivity of C. zofingiensis monoculture under the condition of the two-stage batch cultivation with acetate supplementation. The results proved the feasibility of complete replacement of sodium nitrate by urea in the nutrient medium for C. zofingiensis. Carotenoids (0.3% of dry cell weight) and their composition, as well as the cell lipids and their fatty acid profile, were not affected significantly during the cultivation on urea-containing media as compared to the cultivation on standard media containing nitrate. The carotenoid profile of C. zofingiensis was dominated by the valuable ketocarotenoids astaxanthin, canthaxanthin, and adonixanthin. Furthermore, the use of urea as the sole N source increased the gross yield of lipids by 30.6% as compared to that achieved on the nitrate-based medium. The fatty acid composition of the resulting lipids was compatible with the current European biodiesel standard. The cost efficiency of C. zofingiensis cultivation can be increased by replacing nitrate with urea. [ABSTRACT FROM AUTHOR]

Three macroalgae collected at Madeira Island were included in this study to determine their potential for drug, nutraceutical, food, or supplement application. Fatty acid content was higher in Zonaria tournefortii (12.32 mg g−1 dw) with 16.58% of PUFAs, eicosapentaenoic acid (C20:5ω3), and arachidonic acid (20:4ω6) having concentrations of 2.59 and 1.17%, respectively. The anti-thrombogenic and anti-atherogenicity potential was higher for Z. tournefortii due to relevant fatty acids in the biochemical composition this macroalgae. Lipid classes were assessed in the lipid extract and neutral lipids (NL) were in higher yield in Asparagopsis taxiformis (51.16%) and lower in Z. tournefortii (26.96%). The glycolipids (GL) were between 36.03 and 16.11% in Z. tournefortii and Ulva lactuca. Phospholipids (PL) fraction varied from 35.91 and 31.60% in A. taxiformis and Z. tournefortii. TLC screening identified that U. lactuca contains phytol and cholesterol in its NL, digalactosyldiacylglycerol in its GL, and cardiolipin and L-α-phosphatidylcholine in its PL. Zonaria tournefortii contains phytol and cholesterol in its NL classes, and the PL classes contain L-α-phosphatidylethanolamine and 1-(3-sn-phosphatidyl)-rac-glycerol. The macroalgae A. taxiformis revealed cholesterol in its NL fraction and the same phospholipids as Z. tournefortii in its PL fraction. ATR-FTIR analysis enabled a "fingerprint" spectra and important sulfation absorption bands were identified, revealing the functional polysaccharides within these macroalgae. Anti-cholinesterasic activity was assessed in A. taxiformis, with a low IC50 for AChE (8.92 ± 0.43 μg mL−1) and BuChE (13.96 ± 0.32 μg mL−1), demonstrating dual inhibitory activity, justifying the interest to identify the active principle which may be the scaffold of a novel drug. [ABSTRACT FROM AUTHOR]

Studies on microalgae species and strain selection have demonstrated the potential of a broad range of algal species suitable for large-scale mass production, but provided little data on the reliability and productivity of the cultures under outdoor conditions over a long period. Long-term studies as part of the development of large-scale microalgae mass production are essential at small scale to minimise expenditure in scaling-up and large-scale operations. The current study describes the long-term semi-continuous culture of 4 wild-type isolates of euryhaline Tetraselmis sp. grown in 1 m2 raceway ponds outdoors in 7% (w/w NaCl) saline water enriched with N and P without any additional carbon source under the environmental conditions in Perth, Western Australia. The long-term investigation indicated that Tetraselmis MUR-231 was not able to grow outdoors, while Tetraselmis strains MUR-167, MUR-230 and MUR-233 grew outdoors over long periods. Tetraselmis MUR-167 was cultured for over 16 months outdoors before terminated due to cell clump formation and heavy biofilm development on the pond walls, whereas Tetraselmis strains MUR-230 and MUR-233 were cultured in semi-continuous culture over 20 months. The latter two strains grew at high solar irradiance with daily maximum values of 58890 W m−2 and temperatures ranging from about 40 to 0 °C. Both strains had a similar average specific growth rate of 0.19 day−1 over the experimental period. Maximum biomass productivities were 9.11 g m−2 day−1 and 9.99 g m−2 day−1 for Tetraselmis MUR-230 and MUR-233, respectively. The maximum total lipid productivity of 4.30 g m−2 day−1 of Tetraselmis MUR-230 was slightly higher than Tetraselmis MUR-233 (4.05 g m−2 day−1). These results clearly indicate the potential of these two Tetraselmis strains for commercial application, such as a high lipid yielding feedstock under minimal culture management conditions in arid and semi-arid coastal regions such as northern Western Australia. [ABSTRACT FROM AUTHOR]

Dunaliella tertiolecta was grown in an oilfield-produced water-based medium (PW) over a wide range of salinities (30–210 g total dissolved solids (TDS) L−1). Similar biomass productivity was observed from 30 to 120 g TDS L−1 with decreased growth at the higher salinities of 180 and 210 g TDS L−1. Biomass productivity in all PW conditions was higher than in the commercial f/2 algae growth medium (35 g TDS L−1), which may have been the result of higher bicarbonate concentration of the PW (20 vs. 2 mM). In the lower salinity conditions (30 and 60 g TDS L−1), the total lipid component of biomass was highest at about 35–40% coinciding with nutrient depletion (nitrogen and phosphorus). The lipid fraction then decreased in the nutrient-depleted media as the culture added biomass. Early lipid enrichment in the 30 and 60 g TDS L−1 conditions coincided with peak pH which likely represented maximum bicarbonate uptake. The higher salinities tested (120, 180, and 210 g TDS L−1) displayed a different pattern of an increasing lipid fraction of biomass in a nutrient-depleted media until stationary phase (peak total lipid fraction approximately 31–34%). Fatty acid methyl ester profiles (FAME) at all salinities tested were dominated by C16:0 with a lesser amount of unsaturated C18 carbon chains and should produce a quality biodiesel. The characteristic of the FAME did not vary considerably by salinity. Increased biomass and lipid productivity might result from utilizing hypersaline PW with high bicarbonate concentrations (often already present) for algae cultivation. [ABSTRACT FROM AUTHOR]

Microalgal biomass with a high content of lipids and fatty acids is generally obtained by culture under stress conditions, limiting its growth and increasing production costs. However, it is possible to obtain strains with higher content of some of the desired biochemical component through genetic improvement strategies. Our objective was to increase the lipid content through a mutation-selection procedure in the microalga Nannochloropsis oculata. This procedure involved the ultraviolet radiation exposure of microalgae at different times at different densities and selecting surviving colonies. Subsequently, they were exposed to the herbicide quizalofop-p-ethyl, selecting the colonies with lower survival. An 85% mortality in the UV-exposed microalgae was recorded at 120 min for 1 × 105 cells mL−1. Two strains surviving quizalofop-p-ethyl were obtained, with only one strain surviving in standard culture conditions. The comparison of the new and original strains shows that the growth rate of the new strain of N. oculata (S3) is greater than that of the original strain, and it also had a higher content of total lipids and some fatty acids such as (a) arachidonic acid (up to five times higher than original); (b) oleic and heptadecaenoic acids (more than double than the original strain); (c) elaidic, tridecanoic, and palmitic acids (slightly higher than the original strain). There were significant differences in composition profile (carbohydrates, proteins) in comparison with the original strain. In conclusion, the mutation-selection procedure for obtaining new strains with higher lipid content is suitable for the freshwater microalga N. oculata. It could be considered as a strategy of genetic improvement with potential for aquaculture, food, pharmaceuticals, and biodiesel. [ABSTRACT FROM AUTHOR]

A number of business opportunities may arise from microalgae and wastewater treatment becoming an integrated system, as biofuels and high-added value products could be obtained simultaneously. This study, performed under controlled and non-controlled conditions, aimed at cultivating Chlorococcum sp. using a digestate from pig manure as culture medium and assessing its growth and biochemical composition for further applications. Under controlled conditions, cultures of Chlorococcum sp. were established testing various digestate dilutions (v/v). It was found that all tested dilutions (up to 8% v/v) promoted a higher biomass density, compared to the control culture in modified Bold’s Basal Medium (modified BBM). Under non-controlled conditions, it was found that the biomass productivity using the digestate diluted 5.6% v/v (23.4 mg L−1 day−1) was statistically similar to the one obtained using modified BBM (26.4 mg L−1 day−1). The volatile fatty acids contained in the digestate might have allowed mixotrophic growth for Chlorococcum sp. The intracellular lipid content in Chlorococcum sp. remained constant throughout the experiments in both, treatment and control cultures, while carbohydrates increased from 20 to 45% of the cell dry weight in the treatment and from 20 to 42% in the control one. It was concluded that conditions of nitrogen starvation and fluctuating irradiance and temperature benefit carbohydrate accumulation in this strain, since intracellular carbohydrate content increased nearly two-fold during this period. Additionally, the obtained biomass has the potential to be used as feedstock for bioethanol production. This system can meet the concept of a microalgae-based biorefinery, in which biofuels and high-added value products are produced from microalgae and wastewater. [ABSTRACT FROM AUTHOR]

Manipulation of the nutrient concentration is an inexpensive and efficient method for increasing lipid and TAG accumulation in algal cells. However, high volumetric production requires finding a proper balance between the decrease of biomass production and the increase in the total lipid content. We isolated a strain of green microalga Bracteacoccus bullatus and increased its lipid content from 17 to 59% of biomass dry weight by manipulating of nitrogen and phosphorus content in the medium. The 10-fold reduction of the nitrogen and phosphorus concentration in the medium was the most efficient method of the lipid induction compared to nutrient deplete and high nutrient conditions. The oleic (48-64% mass of total fatty acids) and linoleic (14-24% mass of total fatty acids) acids dominated in the fatty acid profile, thus making this strain a suitable candidate for biodiesel production. [ABSTRACT FROM AUTHOR]

Algae are able to adjust their metabolism according to their environment, maximizing growth rate and production of biomolecules under adverse conditions such as pulses of excess of a contaminant or limitation of a nutrient. In order to evaluate the effects of phosphorus (P) availability on the biochemical composition of the freshwater microalga Selenastrum gracile, we acclimated the microalgae to different phosphorus concentrations. After acclimation, exponentially growing cells were inoculated and after 120 h, samples were processed for the determination of carbohydrate, lipid, fatty acid, chlorophyll, cell density, growth rate, and dry weight. Cell density, growth rate, and dry weight decreased with less P, while chlorophyll a, carbohydrates, lipids, and fatty acids per cell increased under P limitation. According to our lipid class and fatty acid results, algae alter their metabolism and membrane configuration to avoid more structural or metabolic damage under limitation, especially at 23 μmol P L−1. The most sensitive parameters under P limitation were chlorophyll a, lipids, and poly- and monounsaturated fatty acids. The changes in fatty acids contributed to the fluorescence and photosynthesis changes under P limitation, and they occurred before changes were detected in other parameters, such as growth rate. Furthermore, we suggest that prior acclimation to different P affected microalgal physiology and metabolism. [ABSTRACT FROM AUTHOR]

The continuous threat of increasing CO2 concentration in the atmosphere has altered the carbon balance of our planet causing global climate change. Biological fixation of atmospheric CO2 by unicellular microorganisms such as microalgae is a promising technology pursued extensively by researchers as a means for carbon capture. The study aimed to provide an atomic level of study that will demonstrate the effect of the salinity on the mechanism of CO2 absorption across microalgae lipid bilayer. Molecular dynamics simulations were utilized to calculate the free energies of CO2 molecule as it permeates inside the microalgae cell. In thermodynamics, the transport process of a molecule can be demonstrated through its free energy gradient. Thus, calculating the free energies of CO2 molecule across microalgae lipid bilayer can elucidate the mechanisms of permeation processes. Four microalgae lipid bilayer structures were constructed that contains 128-DPPC (dipalmitoylphosphatidylcholine) lipid bilayer with 3640 water molecules with different NaCl concentrations: 0, 3, 13, and 19 NaCl molecules which correspond to a salinity level of 0, 50, 200, and 300 mM, respectively. The cavity insertion Widom method was used to calculate the free energy of CO2 molecule along the lipid bilayer. The results demonstrated that the salinity does not affect the free energies significantly, thus, it does not hamper CO2 transport across microalgae lipid membrane. [ABSTRACT FROM AUTHOR]

Βeta-glucans, widespread glucose polymers in mushrooms, yeasts, and bacteria, but rarely found in microalgae, have wide applications and high medicinal and economical potential. Some β-glucans like paramylon from algae-like Euglena gracilis are well investigated, but there is little information about the β-glucan content of microalgae. Therefore, more than 40 species of cultured microalgae have been investigated for composition of their biomass regarding to lipids, carbohydrates including β-glucans and proteins. Most of algae species showed a rather similar biomass composition of about 10 % lipids, 25 % carbohydrates, and 40 % proteins if they have been cultivated in a full medium, rather low light conditions of 50 μmol photons m s, 12/12 h light/dark cycle under aeration and a temperature of 25 ± 2 °C. The content of β-glucans varied between 1.7 and 24.2 % of dry weight, respectively. Two microalgae, Scenedesmus ovalternus SAG 52.80 and Porphyridium purpureum SAG 1380-1d with a yield of more than 20 % of dry weight were identified as the best β-glucan producers under standard cultivation conditions. Culture optimization experiments revealed that enhanced irradiance increased the β-glucan content of Scenedesmus obtusiusculus A 189, a novel green algae isolate, from 6.4 to 19.5 %, but the β-glucan content of the green alga S. ovalternus SAG 52.80 remained unaffected (24.2 vs. 23.3 %). Nitrate starvation enhanced the β-glucan content of S. obtusiusculus A 189 from 16 to 23 % and of S. ovalternus SAG 52.80 from 23.3 to 36.7 %. [ABSTRACT FROM AUTHOR]

Bacteria are increasingly resistant to common antibiotics. Certain fatty acids are effective antibacterial agents and, when compared to conventional antibiotics, have fewer incidences of bacterial resistance. Algae naturally synthesize these fatty acids and can provide a sustainable source of these antibiotics. To evaluate the antibacterial properties of fatty acids, 29 acids present in algae were tested for topical antibacterial properties on Escherichia coli and Staphylococcus aureus using surface zone inhibition assay. From the set of fatty acids showing good antibacterial activity, five representative fatty acids-capric acid (10:0), palmitoleic acid (16:1), gamma-linolenic acid [18:3 (n-6)], arachidonic acid [20:4 (n-6)], and docosadienoic acid [22:2 (n-6)]-were selected for further analysis. Algal growth conditions (light, temperature, and nutrients) were manipulated to increase the content of the selected target fatty acids in five algal species ( Rhodella maculata, Phaeodactylum tricornutum, Boekelovia hooglandii, Goniochloris sculpta, and Chloridella simplex). P. tricornutum contained the highest content of the target antibacterial fatty acids, with a maximum of 206 mg g dry weight (dw). However, biomass productivity was low; thus, for commercial viability, initial growth should be under optimum conditions and then shifted to enhance antibacterial fatty acid content. B . hooglandii had the highest biomass productivity and a total antibacterial fatty acid content of 32.6 mg g dw in Erddekokt + Salze + Peptone (ESP) medium, 18 °C, 80 μmol photons m s, and 17:7-h light/dark cycle. This study identifies fatty acids that have effective antibacterial properties and potential use as topical antibacterial products and determined growth conditions that result in algae rich in these acids. [ABSTRACT FROM AUTHOR]

The appropriate microalgal species and the optimal nitrogen supply in culture medium are vital factors in maximizing biomass and metabolite productivities in microalgae. Vischeria stellata is an edaphic unicellular eustigmatophycean microalga. Cytological and ultrastructural characteristics and the effects of different initial nitrate-nitrogen concentrations on growth, lipid accumulation, fatty acid profile, and pigment composition were investigated in the present study. The cell structures of V. stellata changed with the degree of nutrient utilization and growth phase. The initial nitrate concentration for the optimal growth of V. stellata ranged from 6.0 to 9.0 mM. The maximum total lipid (TLs), neutral lipid (NLs), and total fatty acid (TFAs) contents were 55.9, 51.9, and 44.7 % of dry biomass, respectively. The highest volumetric productivity of TLs, NLs, and TFAs reached 0.28, 0.25, and 0.21 g L day, respectively. V. stellata had a suitable fatty acid profile for biodiesel production, as well as containing eicosapentaenoic acid (EPA) for nutraceutical applications. In addition, the content β-carotene, increased gradually as culture time was prolonged, resulting in its exclusive production at the end of cultivation. V. stellata is a promising microalgal strain for the production of biofuels and bioproducts. [ABSTRACT FROM AUTHOR]

Diatoms (Bacillariophyta) characteristically accumulate valuable storage lipids throughout their entire life cycle and therefore are an appealing choice to be used as a feedstock for commercial products, like biodiesel. However, the incredible diversity of diatoms poses a substantial challenge when attempting to select the best species for commercial development. The present study compiled previously published data regarding diatom lipid content under nutrient-replete and nutrient(s)-deplete conditions as well as generating novel lipid and growth data from ten species of diatoms within lineages that have been historically under-examined. In this study, lipids were extracted via chloroform-methanol and quantified as percent dry weight and then analyzed for a phylogenetic signal by comparing the variability between lineages to the variability within lineages in an attempt to identify the lineages with the greatest lipid content. A nested ANOVA revealed that there was greater variability between lineages than within lineages when cultures were grown in a silica-deplete medium; the Biddulphiophycidae lineage accumulated a significantly lower amount of lipids than other lineages. The taxa examined in the present study were then paired with the data gathered from the literature and examined for a phylogenetic signal using previously described methods. In this analysis, a statistically significant phylogenetic signal was detected for nutrient(s)-deplete growth experiments ( P = 0.013). These results suggest that under nutrient(s)-deplete conditions, lipid content is, in part, a heritable, evolutionary trait, and therefore, an evolutionary-based approach may be used to facilitate species selection by identifying the differences in lipid content between lineages. [ABSTRACT FROM AUTHOR]

The fatty acid composition of macrophytes is usually quite stable among different taxonomic groups, and thus, several fatty acids can been used as biomarkers. However, variations between species can be affected by seawater temperature and other ambient factors. With higher annual temperatures, we expect less polyunsaturated fatty acids, and changes in the fatty acid signature of algae. Here we analyzed seasonal and interannual variations, in two species of red ( Gelidium robustum and Gracilaria sp.), two brown ( Eisenia arborea and Macrocystis pyrifera), and two green macroalgae ( Ulva lactuca and Ulva sp.), and one species of seagrass ( Phyllospadix torreyi) sampled in a subtropical climate (Bahía Tortugas and Bahía Asunción, BCS, Mexico) from 2002 to 2004. We found that the fatty acid signatures of the red and brown algae were quite stable among seasons and years, in contrast to those of the green algae, which showed a strong annual variation in their fatty acid signature that affected their annual segregation in the factor analysis and are probably a result of net primary production (NPP), which was strongly correlated to individual fatty acids. The fatty acid signature in brown algae is affected by photosynthetically active radiation (PAR), but their variation in the factor analysis is fairly stable despite seasonal or interannual differences. The polyunsaturated fatty acids (PUFAs) were correlated to sea surface temperature (SST) in seagrass. The differences in fatty acid variations between macrophyte groups can provide useful biomarker information for use in trophic analyses. [ABSTRACT FROM AUTHOR]

The combined effect of temperature, light intensity, and NaNO concentration on lipid biosynthesis and fatty acid composition was investigated for the thermophilic cyanobacterium Gloeocapsa gelatinosa (Kützing ) isolated from a thermal spring in Tunisia. Under optimal growth conditions, the lipid content was 7.3 % DW. Fatty acid analysis revealed the predominance of 16:0 and 18:0 (23.7 and 18.2 %, respectively) as main straight carbon chains of saturated fatty acids. Unsaturated fatty acids were also identified with 18:1n9c (18.8 %) and 16:1n7 (5 %) being the predominant components. The effect of environmental factors on fatty acid composition was monitored by using principal component analysis and central composite design. Variation of light intensity (20 to 150 μmol photons m s), temperature (20 to 60 °C), and nitrogen concentration (0 to 3 g L) induced a significant variation in the amount of fatty acid proportions, whereas lipid content was only slightly modified. Results showed that light intensity had the strongest effect on the composition of fatty acids. Temperature had a synergic effect with light intensity while nitrogen concentration had a trivial effect. The combined effect of high light intensity (150 μmol photons m s) and high temperature (60 °C) increased the proportion of saturated 16:0 and 18:0 fatty acids along with long-chain fatty acids to 82 % which was twofold higher than that in optimal growth conditions. This induced fatty acid profile makes G. gelatinosa-based biofuels adaptable for higher energetic efficiency and higher oxidative stability. [ABSTRACT FROM AUTHOR]

Microalgae provide one of the more promising strategies for the production of renewable biodiesel and liquid fuels. Coupling biodiesel production and wastewater treatment based on the use of microalgae can be an effective approach for achieving sustainable production. Several pilot programs aimed at lipid production are currently working with Acutodesmus obliquus, and companies offering algal inocula are increasing in number. A. obliquus strain RL01 was isolated from a pretreated leachate, and preliminary analyses indicated a high growth rate, a final biomass concentration of 1.9 g∙L and a lipid content of 47% DW. With the aim of strictly differentiating and unequivocally identifying the new strain in comparison with other A. obliquus lipid producers available in culture collections, we employed a DNA barcoding approach, targeting conventional and non-conventional genome regions. Genomic analyses were performed using two internal transcribed spacers (nuclear ITS1 and ITS2 sequences) and three selected chloroplast regions (the trnL genic intron and the rpl20- psbA and psbM- psbZ intergenic spacers). Our findings raise some concerns about the discriminant power of the ITS2 nuclear target and place particular emphasis on the psbM- psbZ plastid DNA barcode, which is characterized by high polymorphism, for use in studies addressing intraspecific genetic diversity. [ABSTRACT FROM AUTHOR]

The diatom Odontella aurita has now been industrially cultured and commercialized as a dietary supplement rich in omega-3 fatty acids for several years. In this study, we investigated the effect of three temperatures (8, 16, and 24 °C) on the growth and fatty acid composition of cells harvested during the exponential and stationary growth phases. These temperatures were selected on the basis of photosynthesis responses previously obtained at different temperatures using a modulated fluorometer. Our results confirm that both growth and lipid composition were sensitive to culture temperature. Growth was reduced when O. aurita was cultured at low temperature (8 °C) compared to when it was cultured at high temperatures (16 and 24 °C), but the proportion of polyunsaturated fatty acids (PUFAs, 20:5 n-3 and 22:6 n-3) increased while the level of saturated fatty acids (SFAs, 14:0 and 16:0) decreased in the cells harvested during both the exponential and stationary growth phases. On the other hand, the cells grown at 24 °C displayed a marked decrease in PUFA and an increase in SFA levels. Harvesting time is also a critical parameter in achieving optimum n-3 PUFA productivity during batch cultivation. Indeed, changes in fatty acid composition with growth phase seem to be dependent on the culture temperature, with the most marked effects being observed at 24 °C. PUFA levels (i.e., levels of 20:5 n-3 and 22:6 n-3) increased during the stationary growth phase, while the proportion of SFAs and monounsaturated fatty acids (MUFAs) fell with time. As this species is currently grown in outdoor ponds with seasonal temperature variations (minimal and maximal average temperatures in winter and summer, from 3 to 9 °C and from 13 to 26 °C, respectively), this factor can be expected to have a strong influence on the fatty acid content and composition of the algal biomass harvested and commercialized. [ABSTRACT FROM AUTHOR]