Biosynthesis of acurin A and B, two novel isomeric fusarin C-like compounds from Aspergillus aculeatus

Peter Wolff
DTU Bioengineering, Technical University of Denmark, Lyngby, Denmark

This study presents the identification and proposed biosynthetic pathway for two stereoisomeric compounds of mixed polyketide-nonribosomal peptide origin that we named acurin A and acurin B. The compounds were discovered in extracts from Aspergillus aculeatus, a filamentous fungus known for the commercial utilization in the production of several enzymes. The structures of acurin A and B highly resemble the mycotoxin fusarin C produced by several Fusarium species. In our work, we used CRISPR-Cas9 to construct a non-homologous end-joining deficient strain of A. aculeatus, which enabled efficient gene deletions in the acurin gene cluster. Using gene-expression analysis in combination with metabolite profiling of gene-deletion strains, the gene cluster responsible for acurin production was delineated, which allowed us to propose a biosynthetic pathway for formation of acurin. Our results show that acurin is biosynthesized by an individual polyketide synthase and non-ribosomal synthetase. Moreover, at least six other enzymatic activities are required to complete the biosynthesis of acurin. This study shows how we exploit the CRISPR-Cas9 system in filamentous fungi for the rapid construction of fungal host strains that can be readily engineered to elucidate biosynthetic pathways.