LAUSR

The unicellular green alga Haematococcus pluvialis is considered the optimal natural source of astaxanthin, a strong antioxidant in nature. In the present study, transcriptome and metabolic profiling of H. pluvialis under 0.16% and 0.04% CO2 levels were performed to explore the underlying mechanism by which CO2 affects growth at the vegetative stage of this alga. Approximately 1665 differentially expressed unigenes were screened in response to different CO2 conditions by transcriptome analysis. The genes related to photosynthesis, the tricarboxylic acid (TCA) cycle, glycolysis, pentose phosphate pathway, and nitrogen metabolism, were mostly up-regulated by 0.16% CO2. A total of 36 differential metabolites were identified in metabolic profiling, of them, citric acid and ribose were accumulated; however, 12 common amino acids and stress-resistant related substrates such as ornithine and putrescine were decreased at 0.16% CO2 level. Combing the results of the algal growth, the elevated CO2 promoted photosynthesis, and carbon utilization including TCA cycle and glycolysis, together with the stimulated nitrogen metabolism, protein synthesis, and energy metabolism, which resulted in rapid growth of H. pluvialis.