The interrelation between photorespiration and astaxanthin accumulation in Haematococcus pluvialis using metabolomic analysis

Abstract

To further investigate the interrelation between photorespiration and astaxanthin accumulation, metabolomic analysis of Haematococcus pluvialis during the astaxanthin accumulation period was performed, using gas chromatography–mass spectrometry (GC–MS), in the absence or presence of carboxymethoxylamine (CM), an inhibitor of the photorespiratory pathway. Algal samples were collected on days 0, 6 and 12, which were named as the green phase with green, non-motile cells, the brown phase with astaxanthin-synthesizing, non-motile cells, and the red phase with astaxanthin-enriched, red, non-motile cells, respectively. The inhibition of photorespiration by CM did not affect the biomass, had a slight effect on chlorophyll at the end of the incubation, but significantly suppressed astaxanthin accumulation. A total of 78 metabolites were identified by GC–MS, including 27 amino acids, 16 organic acids, 12 fatty acids, 7 polyols, 3 phosphoric acids, 3 sugars, 2 amines, and 8 other compounds. Multivariate statistical analyses (principal component analysis, partial least squares-discriminant analysis), and hierarchical cluster analysis revealed the clustering of the metabolites. Glycine and glycolic acid had accumulated substantially at both the brown and red phases, indicating that photorespiration was inhibited by CM. In presence of CM, the TCA cycle was restricted at the brown phase due to decreased intermediates, specifically, decreased levels of fructose and glucose. However, inhibiting photorespiration enhanced the levels of many intracellular cytoprotective metabolites, such as amino acids, polyamines, polyols and sucrose. A hypothetical metabolic regulation model of the photorespiratory pathway affecting astaxanthin accumulation of H. pluvialis is proposed. This study provides the first metabolomic evidence that photorespiration enhances astaxanthin accumulation.