Different carbon and nitrogen sources regulated docosahexaenoic acid (DHA) production of Thraustochytriidae sp. PKU#SW8 through a fully functional polyunsaturated fatty acid (PUFA) synthase gene (pfaB)

Docosahexaenoic acid (DHA, C22:6) production in thraustochytrids is known to be mediated independently through polyunsaturated fatty acid (PUFA) synthase and fatty acid synthase systems. This study elucidates the unresolved effects of different carbon and nitrogen sources on the functionality of PUFA synthase subunit B (pfaB) and corresponding DHA production in Thraustochytriidae sp. PKU#SW8. Carbon and nitrogen sources showed significant effect on the pfaB gene expression and DHA production patterns, but these patterns did not correspond with each other, suggesting the strong role of substrates in differential induction of the two synthase systems. Nitrogen starvation increased DHA yield in parallel with upregulated gene expression, showing strong indication of PUFA synthase activity in N-deficient culture. The fully functional catalytic activity of PfaB subunit from strain PKU#SW8 in a heterologous host was also demonstrated. This study provides the direct evidence of pfaB gene actively for DHA biosynthesis in Thraustochytriidae sp. PKU#SW8.