Exogenous arginine induced metabolic modulation and biomass enhancement in Nannochloropsis oceanica under high CO2 stress.

Given that excessive CO2 induces reactive oxygen species (ROS) which inhibit photosynthesis and microalgal survival, this study explores how exogenous arginine enhances stress resilience and biomass yield of Nannochloropsis oceanica under high CO2 stress. Arginine promoted NO synthesis, enhancing antioxidant enzyme activities to combat ROS damage. Transcriptomic analysis revealed that key enzymes in the Calvin cycle (PRK, GAPDH, FBPase and SBPase) and TCA cycle (CS, IDH, SCS and MDH) were significantly up-regulated, supporting carbon fixation and energy metabolism. Arginine also alleviated cell necrosis by extending the G1 phase, promoting DNA replication and protein synthesis, which increased the proportion of viable cells from 47 % to 84 %. Furthermore, the synthesis of chlorophyll a and carotenoid were enhanced, leading to 46 % increase in biomass yield. The results highlighted arginine as a promising metabolic regulator for enhancing stress tolerance and carbon fixation efficiency of N. oceanica under high CO2 conditions.