Enhanced CO₂ sequestration and paramylon production in acid-tolerant Euglena gracilis: Growth optimization and...

Euglena gracilis is a microalgae suited for acidic environments and efficient CO₂ absorption, making it a strong candidate for biological carbon fixation. This study examined its growth, biomass, lipid and paramylon production, and metabolic responses under varying CO₂ levels (0.04 %, 5 %, 15 %, 30 %). Optimal results were observed at 5 % CO₂, with peak biomass (0.407 ± 0.099 g/L), lipid (0.189 ± 0.025 g/L), and paramylon (0.0159 ± 0.0034 g/L) on day 6. SEM showed oval to ellipsoid paramylon granules (0.5-2.5 µm), while GC-MS revealed isophytol acetate (31.44 %) as the major fatty acid. Upregulation of RubisCO and EgGSL1 genes indicated enhanced carbon fixation and paramylon synthesis. A 12 L pilot-scale culture confirmed high CO₂ uptake (0.429 g·L⁻¹·day⁻¹). These findings support E. gracilis as a promising platform for CO₂ sequestration, bioresource production, and paramylon-based bioproducts, with further research needed for industrial scalability.