Time-course variation of lipid and carotenoid production under high light (300 μE/m2s) and nitrogen starvation conditions was determined in a Dunaliella tertiolecta strain. Nanoelectrospray (nanoESI) chip based direct infusion was used for lipid analysis and ultra-performance liquid chromatography (UPLC) coupled with a photodiode array (PDA) or atmospheric chemical ionization mass spectrometry (APCI-MS) was used for carotenoid analysis. A total of 29 lipids and 7 carotenoids were detected. Alterations to diacylglyceryltrimethylhomoserine (DGTS) and digalactosyldiacylglycerol (DGDG) species were significant observations under stress conditions. Their role in relation to the regulation of photosynthesis under stress condition is discussed in this study. The total carotenoid content was decreased under stress conditions, while ã-carotene was increased under nitrate-deficient cultivation. The highest productivity of carotenoid was attained under high light and nitrate sufficiency (HLNS) condition, which result from the highest level of biomass under HLNS. When stress was induced at stationary phase, the substantial changes to the lipid composition occurred, and the higher carotenoid content and productivity were exhibited. This is the first report to investigate the variation of lipids, including glycerolipid, glycerophospholipid, and carotenoid in D. tertiolecta in response to stress conditions using lipidomics tools.
Microalgae are promising candidates for biofuel production due to their high lipid content. To facilitate utilization of the microalgae for biofuel, rapid quantification of the lipid contents in microalgae is necessary. However, conventional methods based on the chemical extraction of lipids require a time-consuming destructive extraction process. Here, we demonstrate label-free, non-invasive, rapid quantification of the lipid contents in individual micro-algal cells measuring the three-dimensional refractive index tomograms. We measure three-dimensional refractive index distributions within Nannochloropsis oculata cells and find that lipid droplets are identifiable in tomograms by their high refractive index. In addition, we alter N. oculata under nitrogen deficiency by measuring the volume, lipid weight, and dry cell weight of individual cells. Characterization of individual cells allows correlative analysis between the lipid content and size of individual cells.
In this study, Chlorella vulgaris (C. vulgaris) was treated with ethephon at low (50 μM) and high (200 μM) concentrations in medium and harvested at 0, 7, and 14 days, respectively. The presence of ethephon led to significant metabolic changes in C. vulgaris, with significantly higher levels of α-tocopherol, γ-aminobutyric acid (GABA), asparagine, and proline, but lower levels of glycine, citrate, and galactose relative to control. Ethephon induced increases in saturated fatty acids but decreases in unsaturated fatty acids. The levels of highly saturated sulfoquinovosyldiacylglycerol species and palmitic acid bound phospholipids were increased on day 7 of ethephon treatment. Among the metabolites, the productivities of α-tocopherol (0.70 μg/L/day) and GABA (1.90 μg/L/day) were highest for 50 and 200 μM ethephon on day 7, respectively. We propose that ethephon treatment involves various metabolic processes in C. vulgaris and can be an efficient way to enrich the contents of α-tocopherol and GABA.
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