Polyketide synthase genes in insect- and nematode-associated fungi

Production of polyketides is accomplished through complex enzymes known as polyketide synthases (PKS); these enzymes have highly conserved domains that might be useful in screens for PKSs in diverse groups of organisms. A degenerate PCR-based approach was used to amplify PKS fragments of the ketosynthase domain from genomic DNA of a group of insect- and nematode-associated fungi. Of 157 isolates (representing 73 genera and 144 species) screened, 92 isolates generated PCR products of predicted size (approximately 300 bp). The ability to detect PKS domains was a function of the number of different primer pairs employed in the screen. Cloning and sequencing revealed that 66 isolates had at least one unique PKS sequence; ten members of this set contained multiple PKS fragments, for a total of 76 unique PKS fragments. Since PKS genes appear to be widespread among fungi, a PCR-based screening system appears to be an efficient, directed means to identify organisms having the potential to produce polyketides.