To understand in which way the structural differences of three marine microalgae (Nannochloropsis gaditana, Rhodomonas marina and Isochrysis sp.) affect their carbon partitioning, growth and applicability; a stoichiometric imbalance was imposed by steady carbon and other nutrients variation. Towards high nutrients concentrations/low carbon availability a decrease of 12-51% in C/N microalgae ratio was observed and maximum cell densities were achieved. Moreover, linear correlation between the nutrient input and microalgae protein content were observed. The macromolecular ratios pointed that carbohydrate was the main contributor for the C/N decrement. Although lipid content in R. marina remained constant throughout the experiment, a rise of 37-107% in N. gaditana and Isochrysis sp. was verified. Lipid fractions revealed high percentages of glycolipids in all microalgae (57-73% of total lipids). The present study shows an easy way to understand and modulate microalgae carbon partitioning relying on the field of application.

To maximize and enhance the fatty acid (FA) profiles of microalgae, it is crucial to understand the metabolic pathways that lead to high levels of the desired product. Nannochloropsis gaditana, Rhodomonas marina, and Isochrysis sp. were cultivated in media with various nutrient concentrations, and the biomass was analyzed for protein and fatty acid contents. The long chain polyunsaturated fatty acid (LC-PUFA) and protein contents were maximized in media with high nutrient concentrations. Under these conditions, the reduction in the (SFA + MUFA)/PUFA ratio (by as much as 83%) indicated that R. marina and N. gaditana shifted preference towards PUFA synthesis. The ∑ω3/∑ω6 ratio indicated that R. marina preferentially synthesized ω3 FA towards high nutrient concentrations (depicted by an eightfold increase) in contrast to Isochrysis sp. (which yielded a 35% reduction). In addition, the limitations of LC-PUFA biosynthesis at the level of its precursors (e.g. C18:2ω6, C18:3ω3, C18:4ω3) and further conversion to LC-PUFA as nutrients were increased, suggesting that external variations induced changes in the sets of enzymes that maintain the desaturation and elongation pathways of FA. The present study provides novel insights into the regulation of LC-PUFA biosynthesis and facilitates the modeling of microalgal FA patterns depending on the field of application.

In the Haptophyta Pavlova pinguis J. C. Green 16 only specific classes of compounds have been analyzed to assess its potential as food for larval hatcheries in aquaculture and as ecological biomarkers 13,17,18. For instance, Milke, et al. 11 and Parrish, et al. 12 assessed the ability of P. pinguis and other Pavlova species to sustain postlarval sea scallop growth focusing on its proximate, fatty acid and sterol composition. In this microalga the complete characterization of lipid components (simple and complex lipids) is still largely unexplored 6,9. Thus, in the present study the analysis of the lipophilic fraction of P. pinguis was performed in order to identify its lipophilic features before and after alkaline hydrolysis through gas chromatography-mass spectrometry (GC-MS) and evaluate its prospects for further improvement in bioactive compounds. Materials and Methods Growth and culture conditions. The haptophyta Pavlova pinguis (RCC 1539) was obtained from the Roscoff Culture Collection (RCC). The microalgal cultures were made by inoculating starter cultures into 1L of sterile f/2-Si medium with pH adjusted to 7.0 under 70 μmol m −2 s −1 light intensity with 16:8 h (light: dark cycles) at 25 °C. At the end of the logarithmic phase, the medium was centrifuged for 7 min. at 3720 g and the pellets washed. Microalgae growth was monitored daily with a Neubauer-improved counting chamber (Marienfield-Superior) and a light microscope (Olympus BX41) with a 40x magnification. The specific growth rate was determined as described in Fernandes, et al. 19 .

The fat content and fatty acid profile of commercially important Seriola fasciata (Lesser amberjack) was determined in samples of muscle, liver and gonads of both genders at pre-spawning and spawning stage. Results indicated that edible muscle of pre-spawning fish had high fat content (>8%), lowering to medium fat (4-8%) content during spawning stage. Livers and gonads presented more constant and relatively high lipid contents. Saturated fatty acids constituted the majority of the fatty acids, followed by monounsaturated fatty acids, with palmitic acid and oleic acid as the major fatty acid in all tissues. EPA and DHA content increased in spawning females and highest amounts were observed in the ovaries (222 and 1440 mg/100 g respectively). Livers presented lowest PUFAs content regardless of maturity stage and SnÀ6/SnÀ3 ratio was influenced by gender in this organ. SnÀ3/SnÀ6 was gender related during pre-spawning stage, increasing in spawning maturation stage. Results highlight variations in the nutritional value of the different tissues according to maturity stage and gender, emphasizing the need for consumer awareness of these changes.

Microalgae are often called “sustainable biofactories” due to their dual potential to mitigate atmospheric carbon dioxide and produce a great diversity of high-value compounds. Nevertheless, the successful exploitation of microalgae as biofactories for industrial scale is dependent on choosing the right microalga and optimum growth conditions. Due to the rich biodiversity of microalgae, a screening pipeline should be developed to perform microalgal strain selection exploring their growth, robustness, and metabolite production. Current prospects in microalgal biotechnology are turning their focus to high-value lipids for pharmaceutic, nutraceutic, and cosmetic products. Within microalgal lipid fraction, polyunsaturated fatty acids and carotenoids are broadly recognized for their vital functions in human organisms. Microalgal-derived phytosterols are still an underexploited lipid resource despite presenting promising biological activities, including neuroprotective, anti-inflammatory, anti-cancer, neuromodulatory, immunomodulatory, and apoptosis inductive effects. To modulate microalgal biochemical composition, according to the intended field of application, it is important to know the contribution of each cultivation factor, or their combined effects, for the wanted product accumulation. Microalgae have a vital role to play in future low-carbon economy. Since microalgal biodiesel is still costly, it is desirable to explore the potential of oleaginous species for its high-value lipids which present great global market prospects.