Metabolome of Cadmium Stressed Gracilaria caudata (Rhodophyta)

We report here the effects of cadmium on the metabolome of the macroalga Gracilaria caudata. The IC50 of 3 mg/L (12 µM) was obtained after 48 hrs exposure and induced lower photosynthesis efficiency. Threshold concentrations determined by the Brazilian Environmental Council (CONAMA) in marine waters (0.04 mg/L) and effluent discharge (0.2 mg/L) were also tested, and the latter changed photosynthetic efficiency similarly to IC50. A total of 43 metabolites were identified, including monosaccharides, carboxylic acids, and amino acids. By an unsupervised PCA, we identified significative alterations in the metabolome by the IC50. An OPLS-DA analysis showed that Cd2+ exposure caused the variation of 20 metabolites, mainly glyoxylate-related, ascorbate, floridoside and proline. Five metabolic pathways altered by Cd2+ showed an accumulation of amino acids, carbon metabolism intermediates and antioxidant responses to Cd2+. We recommend a review of the toxicity parameters and methods that guide environmental policies on cadmium levels in Brazilian marine waters.