Modulation of biomass composition by CO2 in two highly productive green microalgae as a sustainable system for byproduct generation

Microalgae have the potential to mitigate atmospheric CO 2 and generate sustainable byproducts. However, how CO 2 impacts C-flux in different species is not clear. This study evaluated the effect of CO 2 concentration from industry exhaust gas on growth and biochemical composition of Desmodesmus abundans and Chlorella vulgaris . Gas supply (25 % v/v CO 2 /air) stimulated growth of both species (1.38 ± 0.02 and 1.56 ± 0.02 g L −1 for D. abundans and C. vulgaris , respectively). Proteins were the major metabolite at high CO 2 , especially for C. vulgaris , while D. abundans showed no variation (51 ± 0 and 49 ± 3 % d.w., respectively). Both species exhibited 1.2–2.2-fold higher carbohydrate and starch content under air. Also, under air, C. vulgaris showed an increase of 2 to 3-fold in lipids, contrary to D. abundans that increased under high CO 2 during exponential growth. However, as biomass production was optimal at high CO 2 , all metabolite concentrations were highest at 25 % CO 2 . Interestingly, D. abundans exhibited 2 to 3-fold higher pigment content under high CO 2 , suggesting a differential adaptation to high CO 2 . Lastly, a rapid and cost-effective protein extraction protocol was optimized (95 °C, 15 min, NaOH 1N) with comparable yields to the standard Micro-Kjeldahl method during exponential growth and some variation at stationary phase (80–89 % yield). The effect of high CO 2 was species-specific, where D. abundans appears as a robust species. Further studies should evaluate the nature of the protein extract for potential applications and consider technical, economic, and environmental feasibility for system scale-up.