Genome sequencing has shown that Aspergillus terreus has the potential to produce a great variety of different natural products. Although several metabolites have been identified, it can be assumed that the potential to produce secondary metabolites is much larger than currently known. Several strategies have been developed to discover new metabolites produced by filamentous fungi. Besides the use of epigenetic modifiers or co-cultivation experiments, targeted overexpression of putative transcription factors provides a promising tool to activate silent gene clusters. Here, we investigated the expression of the only complete PKS-NRPS hybrid gene present in the genome of A. terreus. Since overexpression of a putative transcriptional activator adjacent to the PKS-NRPS gene did not activate gene transcription, we constructed a lacZ reporter to screen for naturally inducing conditions. Results revealed that expression was activated in the presence of several amino acids at alkaline pH. However, glucose mediated carbon catabolite repression remained as the dominating inhibiting factor. When the adjacent transcription factor, which failed to induce PKS-NRPS expression in initial experiments, was expressed under naturally non-inducing, but also non-repressing conditions, activation of the PKS-NRPS gene was observed. Thus, factors involved in regulation of primary metabolism can override activating effects from cluster specific transcription factors. Finally, product identification revealed that the gene cluster is responsible for producing metabolites of the fruit rot toxin family.
Full conference title:
26th Fungal Genetics Conference
- Fungal Genetics Conference 26th (2005)