Aromatic Polyketides from a Symbiotic Strain Aspergillus fumigatus D and Characterization of Their Biosynthetic Gene D8.t287.

The chemical investigation of one symbiotic strain, Aspergillus fumigatus D, from the coastal plant Edgeworthia chrysantha Lindl led to the isolation of eight compounds (1-8), which were respectively identified as rubrofusarin B (1), alternariol 9-O-methyl ether (2), fonsecinone D (3), asperpyrone A (4), asperpyrone D (5), fonsecinone B (6), fonsecinone A (7), and aurasperone A (8) by a combination of spectroscopic methods (1D NMR and ESI-MS) as well as by comparison with the literature data. An antimicrobial assay showed that these aromatic polyketides exhibited no remarkable inhibitory effect on Escherichia coli, Staphyloccocus aureus and Candida albicans. The genomic feature of strain D was analyzed, as well as its biosynthetic gene clusters, using antibiotics and Secondary Metabolite Analysis Shell 5.1.2 (antiSMASH). Plausible biosynthetic pathways for dimeric naphtho-γ-pyrones 3-8 were first proposed in this work. A non-reducing polyketide synthase (PKS) gene D8.t287 responsible for the biosynthesis of these aromatic polyketides 1-8 was identified and characterized by target gene knockout experiment and UPLC-MS analysis.