Marine microalgae synthetize great amounts of essential metabolites such as fatty acids and amino acids. In addition, their exposure to stress factors can induce the overproduction of these desirable metabolites. Thus, in this work, we assessed the effect of low-temperature stress on lipid production and composition of the diatom Cylindrotheca closterium, in order to evaluate its potential as an alternative feedstock of essential polyunsaturated fatty acids (PUFAs). The alga was first cultured in a photobioreactor at 20°C (control), and stressed by suddenly lowering the culture temperature, from 20°C to 11°C, at the exponential (LTEP) or stationary (LTSP) growth phases. Neutral lipids (NLs) were the main lipid fraction of all conditions assayed, and their production was maximal at LTSP. Fatty acid analysis also showed that the greatest production of PUFAs was observed in the NL fraction at LTSP condition. In terms of essential fatty acids, the production of the omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid was similar in both treatments. The production of omega-6 fatty acids was significantly higher in the LTSP condition due to an increase in arachidonic acid content. Sterols increased under both stress conditions, with a predominance of cholesterol. Considering that the LTSP condition elicited the best PUFA production, the amino acid composition was determined. The 46.81% of total amino acids were essential components for aquatic animals. These findings provide evidence of the potential of C. closterium as an alternative, sustainable source of sterols, essential fatty acids, and amino acids.

The vast majority of the world's fishery by-products are utilized in the fish farming industry. However, due to the high cost and unsustainability of these by-products, alternative sources must be found. Marine diatoms produce important amounts of fatty acids, sterols, proteins and carbohydrates. In this work, we assessed the nutritional value of Halamphora coffeaeformis at the exponential growth phase, to determine its suitability for aquafeed. The strain was grown in a photobioreactor at 20 • C for 6 days. The production of proteins, lipids and carbohydrates was determined, and essential fatty acid, sterol and amino acid composition was assessed. The highest values of triacylglycerides (TAG), free and esterified sterols, proteins and carbohydrates were found after 6 days of growth in the photobioreactor. Fatty acid analysis by gas chromatography showed the presence of eicosapentaenoic (EPA) and arachidonic (ARA) in amounts similar to those for fish oils. In terms of sterols, a predominance of stigmasterol was observed, followed by cholesterol. The amino acid composition revealed 50% of them to be among those essential for fish and other aquatic animals. Finally, a suitable amount of carbohydrates was found in H. coffeaeformis cultures. Together, these findings support the use of H. coffeaeformis as an alternative and sustainable source for aquafeed to partially replace the use of fishery by-products.

Haptophytes are emerging as sustainable sources of high-value metabolites such as polyunsaturated fatty acids (PUFAs). The goal of this work was to isolate a native haptophyte from the southwestern Atlantic coast and to evaluate the effect of low-temperature stress on the production of PUFAs, sterols, and pigments during its cultivation. The strain was identi ed as Pavlova gyrans. Cultures were carried out in a photobioreactor for 10 days at 20°C (Control), lowering the culture temperature to 10°C at the beginning of the stationary growth phase (LTS). The lipid content of the biomass represented 13% of the dry weight, neutral lipids being the main lipid fraction. Under LTS, lipid production increased signi cantly, reaching a value of 305 mg L − 1 . The same effect was observed with PUFA content, which represented 41.3% of total fatty acids. The most abundant omega-3 (ω3) and omega-6 (ω6) fatty acids were eicosapentaenoic (EPA) and docosapentaenoic (DPA), respectively. PUFA production under LTS reached 13.5 mg L − 1 of which 7.41 mg L − 1 corresponded to ω3 and 6.09 mg L − 1 to ω6. EPA production was 5.93 mg L − 1 while DPA production was 3.03 mg L − 1 . The maximum production of phytosterols was obtained during the exponential growth phase. The most abundant phytosterol was 24-Ethylcholesta-5,22-dien-3βol, which represented ≈ 41-49% of the free sterol fraction, with a volumetric concentration of ≈ 320 µg L 1 . Finally, pigment production under LTS was ≈ 700 µg L − 1 . These results open the way for further progress towards the commercial and pro table production of P. gyrans for food and aquaculture applications. Key PointsP. gyrans is a robust strain suitable for biomass production in a photobioreactor.Low-temperature stress increased the production of EPA ω3 and DPA ω6 fatty acids.Phytosterols and pigments added value to the biomass.