Deciphering the distinct roles of polyketide synthase subunits in polyunsaturated fatty acid and lipid accumulation in Schizochytrium sp.

Schizochytrium sp. is a well-known producer of docosahexaenoic acid (DHA). However, optimizing lipid accumulation and polyunsaturated fatty acid (PUFA) synthesis through targeted genetic modifications remains challenging. In this study, we explored the distinct roles of three polyketide synthase (PKS) subunits (ORFA, ORFB, and ORFC) in enhancing PUFA and lipid accumulation. Overexpression of the ORFA subunit significantly improved DHA content and total lipid accumulation, both increasing by 1.13-fold, while substantially reducing the content of saturated fatty acids (SFA). Overexpression of the ORFB subunit also promoted DHA synthesis, but did not improve total lipid yield. In contrast, overexpression of the ORFC subunit increased SFA content, particularly C16:0. However, it also improved the ratio of DHA and Docosapentaenoic Acid (DPA), which is advantageous for industrial production. Under fed-batch fermentation, the ORFA-engineered strain achieved the total lipid titer of 75.8 g/L and DHA titer of 40.6 g/L, with a lipid yield of 0.23 g/g-reaching the highest reported levels. These findings provide new insights and potential targets for optimizing PKS pathways in Schizochytrium sp. for sustainable industrial production of high-value PUFAs, offering a feasible approach for enhancing DHA production while maintaining lipid yields.