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

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are important polyunsaturated fatty acids (PUFAs) used as nutritional supplements. The natural EPA content in <i>Schizochytrium</i> 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 <i>Schizochytrium</i> 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 <i>Schizochytrium</i> sp. as an efficient cell factory for sustainable EPA and DHA coproduction on an industrial scale.