A new pilot-scale fermentation mode enhances Euglena gracilis biomass and paramylon (β-1,3-glucan) production

Paramylon (β-1,3-glucan) extracted from the microalga Euglena gracilis has a range of applications. However, the industrial production of E. gracilis biomass and paramylon is limited by bench-scale conditions. This study utilized a new pilot-scale fermentation mode by combining mixotrophic (MT) and heterotrophic (HT) conditions to evaluate the changes in E. gracilis biomass and paramylon production. This new mode revealed that cell viability was enhanced under MT conditions and paramylon had accumulated under HT conditions. Maximal biomass and paramylon contents were 86.2 g/L and 78.2%, respectively. Metabolomics analysis revealed that the citrate cycle, related amino acids, and the glycerophospholipid biosynthetic pathway were upregulated under MT conditions, while the carbon skeleton entered the paramylon synthesis pathway under HT conditions. These findings present a valuable theoretical basis for the industrial production of E. gracilis and other microalgae. • Euglena gracilis cell viability was enhanced under mixotrophic (MT) conditions. • Paramylon from E. gracilis accumulated under heterotrophic (HT) conditions. • The MT-HT mode efficiently enhanced E. gracilis biomass and paramylon production. • The key metabolic pathways were determined by comparative metabolomics analysis. • The carbon skeleton of fatty acids and amino acids was converted to paramylon.