Compositional shift in lipid fractions during lipid accumulation and turnover in Schizochytrium sp.

•Formation and mobilization of lipid fractions were investigated thoroughly.•Fatty acid combined on PLs could be changed more easily than NLs.•The shift of NL to PL and the increase of UMs happed in lipid turnover stage.•DHA enrichment in lipid turnover stage mainly happened in PLs.•A positive correlation exited between the synthesis of PUFA and UMs.

Single cell oils (SCOs), a complex lipid system, contains neutral lipids (NLs), polar lipids (PLs) and unsaponifiable matters (UMs). To investigate the dynamic changes and the metabolic competition mechanism of different components of SCOs, changes in lipid composition of Schizochytrium sp. were monitored in lipid accumulation and turnover stages. Lipid content could reach 69.98% in biomass during the lipid accumulation stage, while, after the exhaustion of glucose, the content decreased to 45.51% and 20.6 g/L non-oil biomass was synthesis. Polyunsaturated fatty acids (PUFAs) were easier to bind with PLs. NLs were preferentially converted to PLs during lipid turnover stage, accompanied by the degradation of saturated fatty acids and the increase of UMs. Meanwhile, a positive correlation between the synthesis of PUFAs and unsaponifiable matters exited in Schizochytrium sp., and increasing the content of UMs from 45 to 100 mg/L could increase the PUFA percentage from 64% to 74% effectively.