Comparative metabolomic analysis of Haematococcus pluvialis during hyperaccumulation of astaxanthin under the high salinity and nitrogen deficiency conditions.

Revealing the differences of metabolite profiles of H. pluvialis during hyperaccumulation of astaxanthin under the high salinity and nitrogen deficiency conditions was the key issues of the present study. To investigate the optimum NaCl and NaNO₃ concentration and the corresponding metabolic characteristic related to the astaxanthin accumulation in H. pluvialis, a batch culture experiment was conducted. The results indicated that 7.5 g·L^- 1 and 0 g·L^- 1 (nitrogen deficiency) were the optimum NaCl and NaNO₃ levels for the astaxanthin accumulation respectively, under which the highest astaxanthin contents reached up to 7.51mg·L^- 1 and 5.60mg·L^- 1. A total of 132 metabolites were identified using LC-MS/MS technique, among which 30 differential metabolites with statistical significance were highlighted. Subsequently, 18 and 10 differential metabolic pathways in the high salinity (HS) and nitrogen-deficient (ND) treatments were extracted and annotated respectively. The values of Fv/Fm, Yield and NPQ were all at the highest level in the ND group during the experiment. The levels of the metabolites in the ND group were almost lower than those both in the control (CK) and HS group, while which in the HS group were substantially at the higher or close levels compared to the CK group. Finally, 7 metabolic markers related to the astaxanthin accumulation were highlighted in the HS and ND group respectively. L-Proline, L-Aspartate, Uridine 5'-monophosphate (UMP), Succinate, L-2-Hydroxygluterate, L-Valine and Inosine 5'-monophosphate (IMP) were identified as the metabolic markers in the HS group, whose fold change were 0.85, 4.14, 0.31, 0.66, 3.10, 1.32 and 0.30. Otherwise, the metabolic markers were Glyceric acid, Thymine, sn-Glycerol 3-phosphate, Glycine, Allantoic acid, L-Valine and IMP in the ND group, with the fold change 0.23, 2.11, 0.38, 0.41, 0.50 and 2.96 respectively. The results provided the comparative metabolomic view of astaxanthin accumulation in H. pluvialis under the different cultivation conditions, moreover showed a novel insights into the astaxanthin production.