Variations of polyphenols and carbohydrates of Emiliania huxleyi grown under simulated ocean acidification conditions

Abstract. Global environmental changes strongly affect the growth and biochemical composition of microalgae. Cultures of the coccolithophore Emiliania huxleyi were grown under four different CO₂-controlled pH conditions (7.75, 7.90, 8.10, and 8.25) to improve understanding of the adaptive mechanisms of these organisms through changes in phenolic compounds and carbohydrate content and composition under ocean acidification (OA) scenarios. The highest algal biomass peaks, 1.07 (± 0.10) and 1.04 (± 0.06) × 10⁸ cells L⁻¹, were observed in the microcosms with intermediate CO₂ levels (pH 8.10 and 7.90 respectively). Intra- and extracellular phenolic compounds were identified and quantified by Reverse Phase-High Performance Liquid Chromatography (RP-HPLC). The highest concentrations of total exuded phenolics were found in cultures with lower cell densities, at pH 8.25 (43±3 nM) and 7.75 (18.0±0.9 nM). Accumulation of intracellular phenolic compounds was observed in cells with decreasing pH, reaching the maximum level (9.24±0.19 attomole cell^-1) at the lowest pH (7.75). The total carbohydrate content inside the cells increased with decreasing pH from 8.25 to 8.10, remaining constant at pH 7.90, and decreasing at lower pH. The presence of antioxidants was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition and ferric-reducing antioxidant power (FRAP) assays. The highest activity in both tests was exhibited by cells grown at pH 7.75.