Glycinebetaine Promotes Photosynthesis, Biomass Accumulation, and Lipid Production in Nannochloropsis gaditana under Nitrogen Deprivation

The role of exogenous glycinebetaine (GB) in regulating photosynthesis, biomass accumulation, and lipid production in Nannochloropsis gaditana was investigated. Compared to nitrogen repletion, nitrogen deprivation increased the lipid content by 29.7% but inhibited photosynthetic CO2 assimilation process, causing severe oxidative damage to cellular metabolism and decreasing the biomass by 60.6%. The results showed that GB was an efficient stimulator for photosynthesis, biomass accumulation, and lipid production. A concentration of 100 mM of GB was optimum and promoted photosynthetic CO2 assimilation, thereby increasing the biomass and lipid content by 69.1 and 21.9%, respectively, under nitrogen deprivation. GB increased the antioxidant capacity of the cells and alleviated oxidative damage, improving cell survival and accelerating CO2 assimilation and cellular metabolism under nitrogen deprivation. An increase in the substrate pool due to the acceleration of CO2 assimilation and cellular metabolism induced lipid production and thereby increased the biomass. The current study provided a strategy for increasing photosynthetic CO2 assimilation, biomass accumulation, and lipid production and novel insights into the role of GB in regulating lipid production.