Metabolomics of astaxanthin hyperaccumulation in Haematococcus pluvialis under high light stress

Variation in metabolite profiles of Haematococcus pluvialis (a type of unicellular green algal) under light stress is a key issue of study at the present. To investigate the effect of light intensity on accumulation of astaxanthin in H. pluvialis, a 26-day batch culture experiment of H. pluvialis under the light intensity levels at 73, 127, 182, 236, and 291 µmol/(m2·s) was conducted. Therefore, the optimal light intensity and the corresponding metabolic pathways of accumulation in H. pluvialis were determined. Results show that 236 µmol/(m2·s) was the optimum light intensity to induce astaxanthin accumulation, at which a maximum content of 9.01 mg/L was achieved on Day 24. A total of 132 metabolites were identified and quantified, of which 38 differential metabolites were highlighted and classified, including 3 fatty acids or intermediates, 5 amino acids or derivatives, 5 carbohydrates or intermediates, 16 nucleoside derivatives, and 9 other metabolites using LC-MS/MS technique. Subsequently, 16 statistically significant differential metabolic pathways were enriched and annotated based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis between the control and the 236 µmol/(m2·s) treatment group (P<0.05). In addition, the bioprocesses included cellular basal metabolism and signaling systems, such as carbohydrate metabolism, amino acid metabolism, glycerol and derivatives metabolism, nucleotide and derivative metabolism, and inositol phosphate metabolism were activated and regulated under strong light stress conditions. Moreover, 4 hub metabolites containing D-glucose-6-phosphate, L-tyrosine, glycerol-3-phosphate, and L-glutamine were identified, based on which the associated metabolic network was constructed. The study provided a metabolomic view of astaxanthin accumulation in H. pluvialis under strong light stress.