Intimate bacterial–fungal interaction triggers biosynthesis of archetypal polyketides in Aspergillus nidulans

Abstract

Fungi produce numerous low molecular weight molecules endowed with a multitude of biological activities. However, mining the fullgenome sequences of fungi indicates that their potential to produce secondary metabolites is greatly underestimated. Because most of the biosynthesis gene clusters are silent under laboratory conditions, one of the major challenges is to understand the physiological conditions under which these genes are activated. Thus, we cocultivated the important model fungus Aspergillus nidulans with a collection of 58 soil-dwelling actinomycetes. By microarray analyses of both Aspergillus secondary metabolism and full-genome arrays and Northern blot and quantitative RT-PCR analyses, we demonstrate at the molecular level that a distinct fungal-bacterial interaction leads to the specific activation of fungal secondary metabolism genes. Most surprisingly, dialysis experiments and electron microscopy indicated that an intimate physical interaction of the bacterial and fungal mycelia is required to elicit the specific response. Gene knockout experiments provided evidence that one induced gene cluster codes for the long-sought after polyketide synthase (PKS) required for the biosynthesis of the archetypal polyketide orsellinic acid, the typical lichen metabolite lecanoric acid, and the cathepsin K inhibitors F-9775A and F-9775B. A phylogenetic analysis demonstrates that orthologs of this PKS are widespread in nature in all major fungal groups, including mycobionts of lichens. These results provide evidence of specific interaction among microorganisms belonging to different domains and support the hypothesis that not only diffusible signals but intimate physical interactions contribute to the communication among microorganisms and induction of otherwise silent biosynthesis genes.genome mining ͉ lecanoric acid ͉ orsellinic acid ͉ Streptomyces

Bacteria-induced natural product formation in the fungus Aspergillus nidulans requires Saga/Ada-mediated histone acetylation

“…For sterigmatocystin and terrequinone production experiments, experimental cultures were grown at 37°C for 72 h. Samples for RNA isolation were taken after 3 h and 48 h. Cross-linking for ChIP experiments was carried out at the same time points. For coincubation experiments, freshly prepared S. rapamycinicus was added to an A. nidulans culture, as described in Schroeckh et al (13). If required, SAHA (4 mM) and anacardic acid (100 μM) were added at the same time point.…”

“…Isolation of chromosomal DNA and of total RNA of A. nidulans, Northern and Southern blot analysis, and quantitative RT-PCR (qRT-PCR) were performed as described in Schroeckh et al (13). Oligonucleotides are listed in Table S3.…”

“…In this context, we recently discovered that the intimate physical interaction of A. nidulans with a distinct soil-dwelling bacterium identified from a collection of 58 species of actinomycetes, i.e., Streptomyces hygroscopicus (renamed S. rapamycinicus) (12) led to activation of a silent polyketide synthase (PKS) gene cluster. This finding indicated that communication between microorganisms can indeed play a key role in activating silent gene clusters (13). The identified gene cluster encodes the production of the archetypal polyketide orsellinic acid, its derivative lecanoric acid, and the cathepsin K inhibitors F-9775A and F-9775B.…”

Fungal biosynthesis of the bibenzoquinone oosporein to evade insect immunity

“…Biologically, however, an early experiment demonstrated that 14 C-labeled orsellinic acid (OA) (2) could be converted to bibenzoquinone oosporein in B. bassiana cultures (8). It is now clear that OA can be biosynthesized by PKSs in bacteria (21) and fungi (22)(23)(24). These findings suggest that oosporein may be biosynthesized through OA by a PKS gene cluster in Beauveria.…”

Aspernidine A and B, prenylated isoindolinone alkaloids from the model fungus Aspergillus nidulans

“…[10][11][12][13] Furthermore, it was shown that the intimate contact between A. nidulans and a soil-dwelling actinomycete may lead to the specific induction of a cryptic polyketide gene cluster. 14 These strategies resulted in the discovery of a set of novel secondary metabolites, which could not be located by classical screening methods. Another option often preceding genomic approaches is the systematic investigation of the microbial secondary metabolome under various growth conditions.…”