Filamentous fungi are important producers of secondary metabolites, low molecular weight molecules that often have bioactive properties. One interesting secondary metabolite is calbistrin, a compound recently found to have bioactivity against leukemia cells. This compound consists of two polyketides linked by an ester bond; a decalin containing polyketide similar to lovastatin, and a linear 12 carbon dioic acid structure. Calbistrin is known to be produced by several uniseriate black Aspergilli, Aspergillus versicolorrelated species, and several Penicillia. Among the Penicillia, the recently genome sequenced P. decumbens is interesting as it produces several putative intermediates of the calbistrin pathway, such as decumbenone A and B and versiol. In this study, the molecular and enzymatic mechanisms underlying the biosynthesis of calbistrin are elucidated using a combinatorial approach of bioinformatics, molecular biology and analytical chemistry. Comparative studies of the polyketide synthase (PKS) sequences from the three genome sequenced species A. versicolor, A. aculeatus and P. decumbens resulted in the identification of a putative gene cluster for production of the decalin part of calbistrin. Implementation of CRISPR/Cas9 technologies in P. decumbens facilitated the deletion of the putative PKS in this species. Subsequent UHPLC-MS analysis of extract metabolites revealed that calbistrin and putative intermediate compounds were absent, proving the involvement of the PKS in calbistrin production. Further characterization of the predicted gene cluster is achieved by targeted deletion of the individual biosynthetic genes in the cluster.
Full conference title:
The Fourteenth International Aspergillus Meeting, Asilomar Conference Center, Pacific Grove, CA, USA
- Asperfest 14 (2017)