Phytohormone combined with nitrogen stress promoted carbon conversion in CO2 chemical absorption and microalgae conversion system

The CO₂ chemical absorption and microalgae conversion (CAMC) system can achieve low-energy consumption CO₂ capture and resource utilization, but the study on enhancing the synthesis of high-value products has been overlooked. In this study, the coupling strategy of nitrogen stress and exogenous phytohormones was applied to induce high-value products accumulation of <i>Dunaliella salina</i> in CAMC system, and the potential mechanism was also discussed. The results showed that phytohormones could promote <i>D. salina</i> growth by alleviating the oxidative damage under nitrogen limited treatment, especially in gibberellin (GA) group, and the biomass increased by 10.24%. In addition, phytohormones combined nitrogen limited changed carbon flow, directing more carbon to polysaccharose synthesis, supplementation with GA under nitrogen-limited conditions resulted in a 1.65-fold increase in polysaccharide content in D. salina compared to the control. Furthermore, supplementation with GA under nitrogen-limited conditions enhanced the accumulation of β-carotene, and the β-carotene yield and content were 18.52% and 14.46% higher than control. This study suggested that GA could further affect carbon metabolism and products synthesis of <i>D. salina</i> under nitrogen stress, and provided a possible insight in improving the production of economical metabolites in CAMC system.