From CO2 to Bicarbonate: Shifting Inorganic Carbon Sources Rewires Metabolism and Oxidative Stress Resilience in Chlorella vulgaris

Chlorella vulgaris CAMU G–145 demonstrated maximum growth and productivity (1.543 g L−1 and 100.87 mg L−1 day−1), and the highest content of chlorophylls a and b (13.02 mg g−1) when aerated with ambient air. The addition of NaHCO3 yielded comparable values: 1.412–1.522 g L−1 and 92.13–99.47 mg L−1 day−1. The absence of aeration limited the growth of the strain: biomass 0.751 g L−1, productivity—48.07 mg L−1 day−1. The final pH was shifted towards the alkaline side in all experimental variants: from 7.7 in the absence of aeration to 10.5-11 at 1 g L−1 NaHCO3. The levels of TBARS and TBARSin varied within the range of 0.098–0.530 µmol g−1 and 0.142–0.661 µmol g−1, respectively, indicating varying oxidative stress intensities in the strain under different carbon nutrient conditions. Different accumulation dynamics of water-soluble (ascorbic acid and phenolic compounds) and lipophilic (α-tocopherol) antioxidants were also observed. The results demonstrated that carbon nutrient conditions exert different effects on the redistribution of metabolic fluxes and antioxidant defence in Chlorella vulgaris.