Enhancing lipid accumulation in Phaeodactylum tricornutum using cost-effective antioxidant sodium ascorbate: mechanistic insights

Microalgal biofuel production is limited by high costs. This study shows that timed antioxidant supplementation 1 mM sodium ascorbate (SE) on day 3 significantly boosts lipid productivity in Phaeodactylum tricornutum. SE treatment increased biomass by 10 % and total lipids by 40 %, especially C16:0 and C16:1 fatty acids. Mechanistically, SE triggered chloroplast ROS accumulation and enhanced antioxidant defenses (higher VC levels and APX/CAT/SOD activities). This response reduced PUFAs but increased overall lipid yield. Transcriptomics revealed two key mechanisms: (1) upregulation of glycolysis genes supplying lipid precursors, and (2) transient nitrogen metabolism activation (6 h), followed by downregulation (24 h), redirecting carbon toward lipid biosynthesis. Notably, the nitrate transporter NRT showed dynamic regulation. These results highlight SE's dual role in oxidative stress modulation and metabolic reprogramming, providing a cost-effective strategy to enhance algal biofuel production.