Thailandenes, Cryptic Polyene Natural Products Isolated from Using Phenotype-Guided Transposon Mutagenesis.
has emerged as a model organism for investigating the production and regulation of diverse secondary metabolites. Most of the biosynthetic gene clusters encoded in are silent, motivating the development of new methods for accessing their products. In the current work, we add to the canon of available approaches using phenotype-guided transposon mutagenesis to characterize a silent biosynthetic gene cluster. Because secondary metabolite biosynthesis is often associated with phenotypic changes, we carried out random transposon mutagenesis followed by phenotypic inspection of the resulting colonies. Several mutants exhibited intense pigmentation and enhanced expression of an iterative type I polyketide synthase cluster that we term . Disruptions of , , and abolished the biosynthesis of the diffusible pigment, thus linking it to the operon. Isolation and structural elucidation by HR-MS and 1D/2D NMR spectroscopy revealed three novel, cryptic metabolites, thailandene A-C. Thailandenes are linear formylated or acidic polyenes containing a combination of and double bonds. Variants A and B exhibited potent antibiotic activity against and but not against . One of the transposon mutants that exhibited an enhanced expression of contained an insertion upstream of a σ54-dependent transcription factor. Closer inspection of the operon uncovered a σ54 promoter consensus sequence upstream of , providing clues regarding its regulation. Our results showcase the utility of phenotype-guided transposon mutagenesis in uncovering cryptic metabolites encoded in bacterial genomes.