BackgroundMicroalgae are uniquely advantageous organisms cultured and harvested for several value-added biochemicals. A majority of these compounds are lipid-based, such as triacylglycerols (TAGs), which can be used for biofuel production, and their accumulation is most affected under nutrient stress conditions. As such, the balance between cellular homeostasis and lipid metabolism becomes more intricate to achieve efficiency in bioproduct synthesis. Lipidomics studies in microalgae are of great importance as biochemical diversity also plays a major role in lipid regulation among oleaginous species.MethodsThe aim of this study was to analyze time-series changes in lipid families produced by microalga under different nutrient conditions and growth phases to gain comprehensive information at the cellular level. For this purpose, we worked with a highly adaptable, oleaginous, non-model green microalga species, Ettlia oleoabundans (a.k.a. Neochloris oleoabundans). Using a mass spectrometry-based untargeted and targeted metabolomics’ approach, we analyzed the changes in major lipid families under both replete and deplete nitrogen and phosphorus conditions at four different time points covering exponential and stationary growth phases.ResultsComprehensive analysis of the lipid metabolism highlighted the accumulation of TAGs, which can be utilized for the production of biodiesel via transesterification, and depletion of chlorophylls and certain structural lipids required for photosynthesis, under nutrient deprived conditions. We also found a correlation between the depletion of digalactosyldiacylglycerols (DGDGs) and sulfoquinovosyldiacylglycerols (SQDGs) under nutrient deprivation.ConclusionsHigh accumulation of TAGs under nutrient limitation as well as a depletion of other lipids of interest such as phosphatidylglycerols (PGs), DGDGs, SQDGs, and chlorophylls seem to be interconnected and related to the microalgal photosynthetic efficiency. Overall, our results provided key biochemical information on the lipid regulation and physiology of a non-model green microalga, along with optimization potential for biodiesel and other value-added product synthesis.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1026-y) contains supplementary material, which is available to authorized users.

Chlorococcum novae-angliae is a terrestrial green microalgae species with remarkable potential to synthesize omega-3 (ω-3) and omega-6 (ω-6) fatty acids. In this study, Chlorococcum novae-angliae has been subjected to varying growth conditions (light, nitrogen, salinity, and temperature) to investigate the accumulation of ω-3 and ω-6 fatty acids. Among tested growth conditions, eicosapentaenoic acid, α-linoleic acid, γ-linoleic acid, and arachidonic acid were enhanced by nitrogen limitation. Significant increases were observed in concentration of linoleic acid, an essential precursor molecule for the production ω-6 fatty acids under decreased nitrogen concentrations. Despite the lowest biomass growth, monounsaturated fatty acids and docosahexaenoic acid were increased by 14.4% and 8.7% under low light intensities, respectively. Meanwhile, the highest concentrations of palmitic acid (C16:0), stearic acid (C18:0), and oleic acid (18:1cis-9) were also detected under nitrogen limitation. Total lowest fatty acid concentrations were obtained under increased salinity while low temperature conditions heavily inhibited cellular growth.

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