B. Silakowski et al., Multiple hybrid polyketide synthase/non-ribosomal peptide synthetase gene clusters in the myxobacterium Stigmatella aurantiaca, GENE, 275(2), 2001, pp. 233-240
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.