Metabolomic and lipidomic profiling in Nannochloropsis salina under sinusoidal temperature control.

The growing demand for large-scale sustainable, low-cost production of polyunsaturated fatty acids (PUFAs), carotenoids, and other high-value bioproducts has led to increased research in prospective microalgal species within the past several decades. The oleaginous marine microalga Nannochloropsis salina has received attention for its high oil yield (37-60% wt.) and production of the dietary PUFA ω-3 eicosapentaenoic acid (EPA). Marine microalgae found in temperate waters are subject to dynamic temperature fluctuations, which require mechanisms for temperature modulation. The incorporation of unsaturated fatty acids into membrane lipid pools is particularly important for maintaining membrane fluidity and cellular structure; therefore, the composition and content of membrane lipid pools is thought to be heavily regulated by temperature. Previous research has shown that N. salina grown under "cold stress" (=10°C below optimal temperature) results in both increased lipid production and desaturation of fatty acids. Reduced biomass productivity is a consequence of cold stress; however, regulation of cold stress through sinusoidal temperature control has been shown to reduce the effect on growth. Here, we demonstrate the effects of cold stress under 12:12 hr sinusoidal control on N. salina using four temperature regimes: 5°C, 10°C, 15°C and 20°C that all increase to 25°C during peak light intensity, while the control is maintained at a constant temperature of 25°C. Physiological stress is determined through growth rate, chlorophyll fluorescence and dissolved oxygen measurements. Metabolomes were sequenced and quantified using GC TOF MS, and the results were analyzed for statistical significance using MetaboAnalyst V3.0. In addition, a pathway enrichment analysis was performed using VANTED V2.6.3 that reveals depletions in TCA cycle intermediates, particularly acetyl-CoA pools, under cold stress. Total fatty acid (TFA) content is quantified using fatty acid methyl ester analysis, and increases in both the amount and desaturation of fatty acid pools are observed at lower temperatures. Whole lipidome profiling is performed using FT ICR MS, and at reduced temperatures there is an increased proportion of EPA in both triacylglycerol and membrane lipid pools. [ABSTRACT FROM AUTHOR]