Haematococcus pluvialis is a green microalga of major interest to industry based on its ability to produce large amounts of astaxanthin. Biosynthesis of astaxanthin and its mono- and di-esters was significantly stimulated under 150 μmol m s of white LED (W-150) compared with lower light intensities, but the highest astaxanthin amounts were produced under 70 μmol m s of blue LED (B-70). Transcripts of astaxanthin biosynthesis genes psy, crtO, and bkt2 were upregulated under W-150, while psy, lcy, crtO, and crtR-B were upregulated by B-70. Total fatty acid content and biosynthesis genes fata and all dgat genes were induced under W-150, while C18:3n6 biosynthesis and dgat2a expression were specifically stimulated by B-70 which was correlated to astaxanthin ester biosynthesis. Nitrogen starvation, various LEDs and the identified upregulated genes may provide useful tools for future metabolic engineering to significantly increase free astaxanthin, its esters and fatty acid precursors in H. pluvialis.

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Food‐grade rather than synthetic or chemical flocculants are needed for microalgae harvesting by settling, if used for food products. Chitosan is effective in harvesting freshwater microalgae, but it is expensive and typically not suitable for marine microalgae like Nannochloropsis . To minimize costs for food‐grade flocculation, a number of potentially important parameters are considered, including chitosan solubility and optimized chitosan‐mediated flocculation of Nannochloropsis sp. BR2 by a five‐factor central composite design experiment. Results show that an optical density (440 nm) of 2 (0.23 g dry weight L −1 ), initial pH of 6, final pH of 10, and 22 ppm chitosan with a viscosity of 1808 cP provide optimum flocculation efficiency, which is predicted to be in the range of 97.01% to 99.93%. These predictions are verified on 4.5 and 8 L Nannochloropsis sp. BR2 cultures.

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Nannochloropsis sp. has been a very attractive microalgae species because of its high omega-3 fatty acid content. However, it is also one of the species with the strongest cell wall. Currently, energy-intensive mechanical techniques and harmful and flammable organic solvents are used for extracting lipids from Nannochloropsis sp. biomass. Thus, in this study, cholinium [Ch] amino acid-based ionic liquids (ILs) were investigated for their capability to extract lipids from Nannochloropsis sp. Among all the ILs tested, cholinium arginate ([Ch]­[Arg]) extracted the highest amount leaving only 1.4 ± 0.2% lipid in the remaining biomass. The extraction was still efficient at room temperature leaving only 7.9 ± 0.3% lipid. Thus, [Ch]­[Arg] is an efficient green solvent for Nannochloropsis lipid extraction.