Time-dependent metabolic reprogramming in Scenedesmus sp. induced by intermittently sparged CO2 concentrations.

The increasing atmospheric CO2 concentration resulting from anthropogenic emissions has been a major contributor to today's climate change. Microalgae have emerged as an integrated biological route for CO2 capture and utilization; however, the altered metabolic fingerprints of indigenous microalgae to varying CO2 concentrations remain underexplored. This study examines the physiological, biochemical, and metabolic fingerprint of the indigenous microalga Scenedesmus sp. under intermittently sparged varying CO2 concentrations (5%, 10%, and 15%) with the aim of integrating microalgae into the circular economy. The results showed that varying CO2 concentrations altered the physiological and metabolic responses of microalgae, thereby affecting carbon fixation, energy storage, and metabolite abundance related to growth and stress. Untargeted metabolomics identified 81 metabolites and revealed distinct metabolic signatures under varying CO2 levels. Compared to 0.04% CO2, 13 metabolites, including α-tocopherol and β-hydroxybutyric acid, were significantly upregulated (p < 0.05) under 5% CO2 at late-log and stationary phase. At 10% CO2, growth-associated metabolites (8), whereas at 15% CO2, stress-responsive metabolites (8) were significantly upregulated. Overall, the dynamic metabolome signature laid the foundation for carbon partitioning in native Scenedesmus sp., highlighting CO2 concentration-dependent metabolomics that can be utilized for integrated CO2 fixation and metabolite production in circular biorefinery setup.