Genome-Based Cluster Deletion Reveals an Endocrocin Biosynthetic Pathway in Aspergillus fumigatus

Abstract

ABSTRACTEndocrocin is a simple anthraquinone frequently identified in extracts of numerous fungi. Several biosynthetic schemes for endocrocin synthesis have been hypothesized, but to date, no dedicated secondary metabolite gene cluster that produces this polyketide as its major metabolite has been identified. Here we describe our biosynthetic and regulatory characterization of the endocrocin gene cluster inAspergillus fumigatus. This is the first report of this anthraquinone in this species. The biosynthetic genes required for endocrocin production are regulated by the global regulator of secondary metabolism, LaeA, and encode an iterative nonreducing polyketide synthase (encA), a physically discrete metallo-β-lactamase type thioesterase (encB), and a monooxygenase (encC). Interestingly, the deletion of a gene immediately adjacent toencC, termedencDand encoding a putative 2-oxoglutarate-Fe(II) type oxidoreductase, resulted in higher levels of endocrocin production than in the wild-type strain, whereas overexpression ofencDeliminated endocrocin accumulation. We found that overexpression of theencAtranscript resulted in higher transcript levels ofencA-Dand higher production of endocrocin. We discuss a model of theenccluster as one evolutionary origin of fungal anthraquinones derived from a nonreducing polyketide synthase and a discrete metallo-β-lactamase-type thioesterase.