Oxidative stress enhances lipid production and improves fatty acid composition for biodiesel production in microalga Nannochloropsis oceanica

The depletion of fossil fuel reserves, escalating energy prices, rising global energy demand, and heightened awareness of climate change have accelerated efforts to develop sustainable biofuel alternatives. Microalgae are considered a promising candidate for biodiesel production due to their rapid biomass accumulation, high lipid content, and superior photosynthetic efficiency compared to conventional terrestrial crops. This study examined the effect of oxidative stress, induced by hydrogen peroxide (H₂O₂), on the growth and lipid productivity of the marine microalga Nannochloropsis oceanica . Five concentrations of H₂O₂ (0, 100, 200, 300, and 400 µM) were applied during the exponential growth phase. Cultures were maintained under controlled conditions, and at the end of the cultivation period, biomass was harvested and freeze-dried. Lipids were extracted using a modified Bligh and Dyer protocol, and fatty acid profiles were determined through gas chromatography. The results demonstrated a significant enhancement in lipid accumulation under oxidative stress, with the highest lipid content—a 64% increase over the control—recorded at 400 µM H₂O₂. However, biomass productivity decreased at elevated H₂O₂ levels, highlighting a concentration-dependent trade-off. Palmitic acid was the predominant fatty acid under stress conditions. A strong positive correlation was observed between H₂O₂ concentration and total lipid content, indicating that exogenously induced oxidative stress can serve as a viable strategy to enhance lipid production in N. oceanica for biodiesel applications through a single-phase cultivation approach.