Multiple hybrid polyketide synthase/non-ribosomal peptide synthetase gene clusters in the myxobacterium Stigmatella aurantiaca

Many bacterial and fungal secondary metabolites are produced by polyketide. synthases (PKS) and non-ribosomal peptide synthetases (NRPS). Recently, it has been discovered that these modular enzymatic systems can also closely cooperate to form natural products. The analysis of the corresponding biosy nthetic machineries, in the form of hybrid systems, is of special interest for combinatorial biosynthesis, because the combination of PKS and NRPS can lead to an immense variety of structures that might be produced. During ou r screening for hybrid PKS/NRPS systems from myxobacteria, we scanned the g enome of Stigmatella aurantiaca DW4/3-1 for the presence of gene loci that encode both the PKS and NRPS genes. In addition to the previously character ized myxothiazol system, we identified three further hybrid loci, three add itional PKS and one further NRPS gene locus. These were analyzed by hybridi zation, physical mapping, PCR with degenerate oligonucleotides and sequenci ng of fragments of the gene clusters. The function of these genes was not k nown but it had already been speculated that one compound produced by the s train and detected via HPLC was a secondary metabolite. This was based on t he observation that its production is dependent on an active copy of the ph osphopantetheinyl transferase gene mtaA. We show here that one of the ident ified hybrid gene loci is responsible for the formation of this secondary m etabolite. In agreement with the genetic data, the chemical structure resem bles a cyclic polypeptide with a PKS sidechain. Our data show that S. auran tiaca has a broader genetic capacity to produce natural products than the n umber of compounds isolated from the strain so far suggests. (C) 2001 Elsev ier Science B.V. All rights reserved.