Regulation of glucose and glycerol for production of docosahexaenoic acid in Schizochytrium limacinum SR21 with metabolomics analysis

Abstract

Docosahexaenoic acid (DHA), a member of ω−3 polyunsaturated fatty acids (PUFAs), plays an essential effect in the amelioration of human health. Schizochytrium limacinum SR21 is considered as a potential microalgae for DHA production. The carbon source regulates cell metabolism and PUFAs synthesis in S. limacinum. Flask and fed-batch cultivations were conducted to explore the influence of glycerol and glucose on the biomass, growth rate, and DHA content of S. limacinum SR21. In flask cultivation, the highest cell growth rate (12.2 g/L/day) was obtained when glucose was employed as the sole carbon source, whereas the DHA content reached the maximum value (46.88%) in the medium with glycerol as the sole carbon source. Fed-batch fermentation showed that glycerol had comparable biomass 171 g/L, higher DHA yield (40.7 g/L), and higher DHA production rate (223.8 mg/L/h) compared with glucose as the sole carbon source. We combined the advantages of the two carbon sources and developed a new two-stage fed-batch fermentation strategy using mixed carbon sources (glucose and glycerol). This strategy showed an increase in DHA production rate (229.8 mg/L/h) in comparison with the sole carbon sources. Comparative metabolomics analysis indicated that glycerol added in the medium up-regulated the pentose phosphate and glycolysis pathways. Moreover, tricarboxylic acid cycle and mevalonate pathway were dampened. These outcomes provide metabolic basis for enhancing DHA production rate by S. limacinum SR21.