Establishing a new methodology for genome mining and biosynthesis of natural products through fungal molecular genomics

Polyketides (PKs) and nonribosomal peptides (NRPs) have been isolated from Streptomyces and many other source organisms. In recent years, gene clusters encoding PK synthases (PKSs) and NRP synthetases (NRPSs) have been discovered through fungal genome sequencing. While on average 50 gene clusters are identified in a single fungal genome, fewer fungal PK and NRP products can be isolated from a fungal culture grown under a typical growth condition. Thus, simple artificial reactivation of the cryptic gene cluster may be insufficient for an efficient natural product biosynthesis.

To circumvent these obstacles, we examined upregulation of 60 gene clusters encoded in chromosomal DNA of four fungal species, Aspergillus fumigatus, A. flavus, A. oryzae and Chaetomium globosum, using the aforementioned fungal molecular genetics. Thus far, we have isolated seven new PK and NRP compounds successfully. Subsequently, we used our recombination cloning-based yeast expression system to reconstitute these biosynthetic gene clusters quickly and efficiently. Our preliminary results clearly demonstrate successful expression of seven C. globosum PKS gene clusters in Saccharomyces cerevisiae, three of which led to the production of new natural products whose identities have been characterized spectroscopically. Our methodology will facilitate the efforts in isolating novel natural products and rationally engineering in the biosynthetic pathways for production of analogs possessing comparable if not more potent bioactivity.