Aspergillus oryzae type III polyketide synthase CsyB uses a fatty acyl starter for the biosynthesis of csypyrone B compounds

Csypyrones B1, B2 and B3 are α-pyrones that can be obtained from Aspergillus oryzae expressing CsyB, which is a type III polyketide synthase. We investigated the biosynthesis of the csypyrone B compounds using [1-13C] and [2-13C] acetate feeding experiments. 13C NMR analyses of the methyl esters of the csypyrone B compounds fed with the 13C-labeled acetates showed that the carboxyl carbons of the csypyrone B side-chains were derived from the C-2 methyl carbon of the acetate. These results indicated that fatty acyl starters are involved in the CsyB reaction and that the csypyrone B compounds are formed by the oxidation of side-chains by the host fungus.