Exopolysaccharide from Haematococcus pluvialis enhances photosynthesis, biomass and astaxanthin accumulation

Abstract

Haematococcus pluvialis is recognized as the prime biological source of natural astaxanthin. However, the physiological and metabolic effects of H. pluvialis exopolysaccharide (HPEPS), which is derived from both secretion and cell wall dissolution during cell growth and transformation, remain unclear. This study systematically elucidated the regulatory effects of HPEPS on astaxanthin biosynthesis in H. pluvialis through physiological and metabolomics analyses, and preliminary characterization of its structure was also performed. Under high light stress, exogenous supplementation of 220 mg/L HPEPS induced cell division arrest and increased cell diameter to 1.25-fold of the original size, thereby providing space for biomass and astaxanthin accumulation. Concurrently, it enhanced photosynthetic efficiency and maintained energy metabolic homeostasis, leading to 1.36-fold, 1.82-fold, and 2.6-fold increases in biomass, astaxanthin yield, and astaxanthin content, respectively. Integrated metabolomics analysis revealed that HPEPS activation enhances carbon assimilation, photorespiration, and glyoxylate cycle pathways to enhance precursor supply for astaxanthin biosynthesis. Structural elucidation further identified HPEPS as a heteropolysaccharide primarily containing guluronic acid (GulA, 37.4 %), galactose (18.9 %), and arabinose (12.0 %). Notably, this work reports the first detection of GulA in microalgal exopolysaccharides. Overall, this study not only provides a theoretical basis for elucidating the structural composition and physiological role of HPEPS, but also develops a new approach to optimize the production of natural astaxanthin.