Comparative Metabolomic and Network Analysis of the Hyperaccumulation of Astaxanthin in <em>Haematococcus pluvialis</em> under the Different Stress Conditions

Abstract

Variation in metabolite profiles of under high salinity and nitrogen constraint conditions are the key issues of study at the present. To investigate the optimum NaCl and NaNO3 concentration and the corresponding metabolic pathways of astaxanthin accumulation in H. pluvialis, a 26-day batch culture experiment of H. pluvialis treated under the variable concentration gradients of NaCl and NaNO3 were conducted. The results indicated that 7.5g&amp;bull;L-1 and nitrogen-deficient were the optimum NaCl and NaNO3 concentration for the astaxanthin accumulation according to single factor experiments respectively, under which the highest contents of astaxanthin accumulated in H. pluvialis reached up to 7.51mg&amp;bull;L-1 and 5.60mg&amp;bull;L-1. A total of 132 metabolites were analysed 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 and nitrogen-deficient treatments with statistic significance were enriched and annotated respectively. Furthermore, the metabolic networks related to the astaxanthin accumulation were constucted based on the crucial pathways and metabolites. Moreover, the major carbon metabolism in H. pluvialis under the high salinity and nitrogen deficient stress were presented, which exhibited the characteristics in the identified metabolites changes under the different stress conditions. The results did not only demonstrate the differential metabolic networks and the distinct changes in the metabolites involved in the major carbon metabolism, related to the astaxanthin accumulation in H. pluvialis under the different stress factors, but provided the regulation targets for astaxanthin production in practice.