Evaluating CO ₂ concentration effects on growth kinetics and fatty acid composition in <i>Euglena gracilis</i>

Industrial development has significantly increased CO2 emissions, from 280 ppm in the pre-industrial era to over 400 ppm today, contributing to the greenhouse effect and climate change. This study investigates the impact of varying CO2 concentrations on the growth, biomass accumulation, and biochemical composition of Euglena gracilis as microalgae-based carbon capture and utilization. E. gracilis was cultivated with CO2 concentrations of 0%, 5%, 10%, and 30%, using white LED lights at 3000 lux. Growth was monitored through cell counts and optical density, while biomass and primary metabolites were analysed using standard methods. Fatty acid content was assessed using GC-MS and GC-FID. The results showed optimal growth at 5% CO2, with biomass reaching 2.3 g l‒1 on the day of harvest. The highest lipid content was obtained in the 15% CO2 treatment with a total lipid of 0.35 g l‒1. As for the decrease in pH, it showed that each treatment experienced a reduction in pH from 3.5 to almost 2.0. Fatty acid content was dominated by polyunsaturated fatty acids (PUFAs), especially in the control group and 15% CO2 treatment, contributing up to 47.66%, and 46.36% to the group, respectively. The study highlights the importance of optimizing CO2 levels for microalgae cultivation to enhance biomass and lipid production. Elevated CO2 levels boost lipid synthesis but can stress cells if too high, suggesting a need for adaptive CO2 addition methods.