| Summary: | The polyketide synthase (PKS) cluster genes are supposed to synthesize polyunsaturated fatty acids (PUFAs) in <i>S. limacinum.</i> In this study, two enyolreductase (<i>ER</i>) genes located on PKS cluster were knocked out through homologous recombination to explore their functions. The knock-out of <i>OrfB-ER</i> (located on <i>OrfB</i> subunit) decreased lipid content and had obvious decrease on PUFAs content, indicating <i>OrfB-ER</i> domain played a vital role on PUFAs synthesis; the knock-out of <i>OrfC-ER</i> (located on <i>OrfC</i> subunit) decreased SFAs content and increased total lipid content, indicating <i>OrfC-ER</i> domain was likely to be related with SFAs synthesis, and lipid production could be improved by down-regulating <i>OrfC-ER</i> domain expression. Therefore, the addition of triclosan as a reported regulator of <i>ER</i> domain induced the increase of PUFAs production by 51.74% and lipids yield by 47.63%. Metabolic analysis indicated triclosan played its role through inhibiting the expression of <i>OrfC-ER</i> to reduce the feedback inhibition of SFAs and further to enhance NADPH synthesis for lipid production, and by weakening mevalonate pathway and tricarboxylic acid (TCA) cycle to shift precursors for lipid and PUFAs synthesis. This research illuminates functions of two <i>ER</i> domains in <i>S. limacinum</i> and provides a potential targets for improving lipid production.
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