Markerless Mutations in the Myxothiazol Biosynthetic Gene Cluster: A Delicate Megasynthetase with a Superfluous Nonribosomal Peptide Synthetase Domain Original Research Article

Myxobacteria are efficient producers of natural products with various biological activities. Nevertheless, genetic systems for markerless mutagenesis are only available for Myxococcus xanthus DK1622, a strain that is not known to produce any secondary metabolites. We report here the development of such a technique for Stigmatella aurantiaca DW4/3-1, a multiproducer of natural products. The system is used to further characterize the combined polyketide synthase/peptide synthetase system responsible for myxothiazol biosynthesis. Analysis of a series of point mutations and in-frame deletions shows that the myxothiazol megasynthetase is a rather specialized and delicate system that is hardly capable of processing unnatural intermediates. An in-frame deletion of the MtaC oxidation domain results in the production of unchanged bis-thiazole myxothiazol instead of the expected thiazoline-thiazole derivative of the compound. This shows that this domain within a nonribosomal peptide synthetase is not necessary for product formation.