Adaptive laboratory evolutionary strategies and mechanisms of Synechococcus elongatu PCC 7942 under high concentration of CO₂

To promote the utilization of industrial flue gases by microalgae, this study performed adaptive laboratory evolution (ALE) with CO₂ as the selective pressure, aiming to improve the carbon fixation efficiency of microalgae under high CO₂ conditions. Synechococcus elongatus PCC7942 was sequentially cultured with CO₂ concentrations ranging from 5 % to 20 %, resulting in a domesticated strain S20 with growth advantage and capable of acclimatizing to 20 % CO₂. At a CO₂ concentration of 20 %, the biomass of S20 reached 1.37 g L^–1, and the lipid contents of S20 were significantly elevated, reaching 54.35 % and 32.76 %, respectively. Mechanism analysis showed that the enhanced photosynthesis caused by the increase in chlorophyll a content was the main factor for S20 to tolerate high CO₂ concentration and improve carbon sequestration efficiency. Overall, this study demonstrated that CO₂ ALE is an optimal method to screen efficient carbon sequestering microalgae under high concentrations of CO₂.