Photoprotective carbon redistribution in mixotrophic Haematococcus pluvialis under high light stress

Mixotrophy of Haematococcus pluvialis is a potential strategy for producing astaxanthin. However, this strategy has not been extensively commercialized because the mixotrophic mechanisms by which H. pluvialis overcomes high light stress are unclear. This study analyzed the biochemical compositions and differential proteomics of mixotrophic H. pluvialis under different light conditions. High light exposure substantially increased astaxanthin, carbohydrate, and fatty acid contents. A total of 119 and 81 proteins were significantly up- and down-regulated after two days of high light exposure. These proteins mainly enriched pathways for photosynthetic metabolism, glyoxylate cycle, and biosynthesis of secondary metabolites. This study proposed a regulatory model through which mixotrophic H. pluvialis copes with high light stress. The model includes pathways for modulating photosynthetic apparatus, increasing astaxanthin accumulation by enhancing photorespiration, pentose phosphate and Embden-Meyerhof-Parna pathways, while thickening the cell wall by malate-oxaloacetate shuttle.