Polyketide Synthase Acyltransferase Domain Swapping for Enhanced EPA Recognition and Efficient Coproduction of EPA and DHA in Schizochytrium sp

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are important polyunsaturated fatty acids (PUFAs) used as nutritional supplements. The natural EPA content in Schizochytrium sp. is low, and traditional strategies to increase EPA levels often compromise DHA content or lipid accumulation, hindering industrial coproduction. This study aims to modify the PUFA synthase pathway in Schizochytrium sp. to enable high levels of EPA accumulation while maintaining high levels of DHA production. The native acyltransferase (AT) domain in the PKS_B subunit was replaced with an EPA-specific AT, increasing the EPA content nearly five-fold (3.94%). Additionally, adding food-grade phenolic compounds to boost EPA accumulation and overexpressing C16 elongase to alleviate lipid synthesis inhibition increased the EPA content from 0.80 to 7.86% in a 5L bioreactor. Ultimately, EPA and DHA titers reached 3.79 and 22.06 g/L, respectively. These findings highlight the potential of Schizochytrium sp. as an efficient cell factory for sustainable EPA and DHA coproduction on an industrial scale.