Comprehensive metabolic reprograming in freshwater Nitzschia palea strains undergoing nitrogen starvation is likely associated with its ecological origin

Nitrogen deficiency can increase the lipid content in certain microalgae species, including diatoms. However, the molecular and metabolic basis of such changes remains rather unclear. We analyzed strains of freshwater Nitzschia palea collected from a eutrophic pond and from an artificial rock. The habitats, differing in light and nutrient availability, lead to two metabolically distinct strains, BR006 and BR022. Differential accumulation of primary compounds, membrane lipid composition and fatty acid saturation were observed. Metabolic and biophysical analysis demonstrated differential sensitivity to N regimes: depleted, replete and saturated. Whereas N depletion leads to typical stress-related responses in both strains, including reduction of protein and photosynthesis, the response observed in BR006 is far more severe. Our results demonstrated that these strains developed distinct metabolic responses to N conditions. BR022 is able to maintain cellular homeostasis and slows down growth according to N availability. In contrast, BR006 maximizes growth rate even under N limitation, by triggering stress response, relocating carbon pool to lipid compounds and quickly reaching growth arrest after N exhaustion. We identified a relationship between habitat characteristics and metabolic responses, providing a metabolic perspective on ecological plasticity of N. palea, which helps it to survive a wide range of habitats.