A CO2-rich environment-mediated amelioration of nutritional stress effect in an indigenous freshwater green microalga Desmodesmus sp.

Microalgae from natural habitats have the potential for biomitigation of atmospheric CO₂. The nutritional stress induces the microalgae to accumulate metabolites like lipids and carotenoids but limits the growth and biomass yield. The present study focused on the growth, productivity, lipid, chlorophyll, and carotenoid contents of an indigenous fresh water microalga Desmodesmus sp. subjected to nutritional (nitrogen and salinity) stress under a CO₂-rich environment (20% CO₂). The 20% CO₂ supplemented stressed cultures showed a final biomass concentration of 0.28-0.38 g L^-1, productivity of 0.01-0.02 g L^-1day^-1, specific growth rate (μ_max day^–1) of 0.09-0.11, and CO₂ biofixation rate (\(R_{\mathrm{CO}_{2}}\)) of 0.024-0.04 g L^-1day^-1 which was 1.5-2.25 fold, 2-3.63 fold, 1.57-2.25 fold and 2.3-4.3 fold higher, respectively than their corresponding cultures supplemented with ambient level of CO₂. The chlorophyll, carotenoid, and lipid content of stressed cultures supplemented with 20% CO₂ was 1.3-2.2 fold, 3-5 fold and 1.4-2.1 fold higher than the corresponding cultures supplemented with ambient level of CO₂. The relative percentage of oleic acid total fatty acid of stressed cultures supplemented with 20% CO₂ was in the range of 48-58%, i.e., 1.11 to 1.45 fold higher than the corresponding cultures supplemented with ambient level of CO₂. Thus, the supplementation with elevated levels of CO₂ ameliorated the effect of nutritional stress in the microalga enabling the accumulation of high content of metabolites with an increase in biomass.