Sodium acetate can promote the growth and astaxanthin accumulation in the unicellular green alga Haematococcus pluvialis as revealed by a proteomics approach

Haematococcus pluvialis is an ideal natural source of strong antioxidant astaxanthin. Sodium acetate (NaAc) was proven an effective organic carbon source for improving algal growth and astaxanthin production; however, the underlying mechanism remains obscure. To reveal the mechanism of NaAc at the green vegetative stage of H. pluvialis, the physiochemical characteristics and the global protein expression profiles obtained using a tandem mass tag labeling approach were compared between the control (CK) and two NaAc-addition groups. Results show that after NaAc addition, the biomass, nitrate consumption rate, and activities of three carbohydrate metabolism enzymes of H. pluvialis were significantly increased, and the net photosynthetic rate and chlorophyll content decreased. In addition, astaxanthin, total carbohydrates, and total lipids were accumulated, and some red cells appeared in the NaAc5 group. Moreover, 317 differentially expressed proteins (DEPs) with the most altered expression patterns were screened out in the CK vs. NaAc5 comparison in our proteomics study. All the DEPs involved in carbohydrate metabolism and lipid metabolism were significantly increased, while most of the photosynthesis-related proteins were depressed in the two NaAc-treated groups. The proteomics results were verified and supported by parallel reaction monitoring approach and physiochemical data. Our findings demonstrate that NaAc promoted the tricarboxylic acid cycle, glyoxylate cycle, and amino acid and lipid synthesis, and inhibited the photosynthesis-related activities, which consequently speeded up the growth and astaxanthin accumulation in this alga.