Monascus Azaphilone Pigment Biosynthesis Employs a Dedicated Fatty Acid Synthase for Short Chain Fatty Acyl Moieties

The biosynthetic gene cluster of Monascus azaphilone pigments (MAzPs) encodes a canonical fatty acid synthase, MpFAS2. It is thus proposed that MpFAS2 plays a role in MAzP biosynthesis by supplying short chain (C8 and C10) fatty acyl moieties. Targeted gene inactivation of MpfasB2 in Monascus purpureus generated an F9 mutant, which developed white hyphae that discharged a yellow color on potato dextrose agar. High-performance liquid chromatography analysis demonstrated that F9 was incapable of producing MAzP and accumulated a wide array of chromophoric compounds instead. The main compound found in F9 was monascusone A, a hydrogenated azaphilone lacking a fatty acyl moiety. Gas chromatography analysis of the fatty acid methyl esters indicated that there was no significant difference in the cellular fatty acyl (C16 and C18) contents between WT and F9. The present study demonstrates that the dedicated fatty acid synthase is required to decorate the azaphilone polyketides in MAzP biosynthesis.