Polyketide Synthase\nAcyltransferase Domain Swapping\nfor Enhanced EPA Recognition and Efficient Coproduction of EPA and\nDHA in <i>Schizochytrium</i> sp

Docosahexaenoic acid (DHA) and eicosapentaenoic\nacid\n(EPA) are\nimportant polyunsaturated fatty acids (PUFAs) used as nutritional\nsupplements. The natural EPA content in <i>Schizochytrium</i> sp. is low, and traditional strategies to increase EPA levels often\ncompromise DHA content or lipid accumulation, hindering industrial\ncoproduction. This study aims to modify the PUFA synthase pathway\nin <i>Schizochytrium</i> sp. to enable high levels of EPA\naccumulation while maintaining high levels of DHA production. The\nnative acyltransferase (AT) domain in the PKS<sub>B</sub> subunit\nwas replaced with an EPA-specific AT, increasing the EPA content nearly\nfive-fold (3.94%). Additionally, adding food-grade phenolic compounds\nto boost EPA accumulation and overexpressing C16 elongase to alleviate\nlipid synthesis inhibition increased the EPA content from 0.80 to\n7.86% in a 5L bioreactor. Ultimately, EPA and DHA titers reached 3.79\nand 22.06 g/L, respectively. These findings highlight the potential\nof <i>Schizochytrium</i> sp. as an efficient cell factory\nfor sustainable EPA and DHA coproduction on an industrial scale.