Metabolic Adaptation of Chlorella vulgaris InaCCM49 to Cadmium-Salinity Stress: UPLC-MS/MS-Based Identification of Antioxidant Metabolites

Chlorella vulgaris is a microalga species studied for its characteristics and potential applications since 1960. This study investigates the effect of combined salinity and cadmium stress on compound diversity, antioxidant activity, and pigment concentrations in C. vulgaris InaCCM49. Microalgae were cultivated in control and Cd-saline treatments (0.4 M NaCl and 95 μM CdCl₂), followed by biomass harvesting, pigment determination, IC₅₀ measurement, and metabolomic analysis. Cd-salinity stress enhanced antioxidant activity, showing 51.8% lower IC₅₀ values (79.47 ppm) compared to controls (164.99 ppm), and increased carotenoid content to 1.919 mg g^-1. Meanwhile, chlorophyll a and b concentrations were notably higher in control treatment during the half-logarithmic phase. Partial Least Squares Discriminant Analysis revealed clear metabolomic differences between treatments. Stigmatellin Y, maltose, glycolipid 1-hexadecanoyl-3-(6'-sulfo-α-D-quinovosyl)-sn-glycerol, and phenolic derivative (2-phenoxy-3-pyridinyl)[3-(2-thienyl)-1H-pyrazol-1-yl] methanone exhibited VIP scores >15. Stigmatellin Y and glycolipids were highly synthesized in controls, whereas maltose and phenolic derivatives were elevated in Cd-saline treatment. Pheophorbide a and 3-oxo-nonadecanoic acid showed the strongest negative correlations with IC₅₀ (regression coefficients of -14.6047 and - 13.9555), indicating key roles in antioxidant activity. This study represents the first comprehensive metabolomic analysis of C. vulgaris InaCCM49 under combined cadmium-salinity stress, revealing metabolic adaptation through enhanced synthesis of phenolic derivatives and pheophorbide a-mediated antioxidant responses.