A New Modular Polyketide Synthase in the Erythromycin Producer <i>Saccharopolyspora erythraea</i>

Abstract

A previously unidentified set of genes encoding a modular polyketide synthase (PKS) has been sequenced in Saccharopolyspora erythraea, producer of the antibiotic erythromycin. This new PKS gene cluster (pke) contains four adjacent large open reading frames (ORFs) encoding eight extension modules, flanked by a number of other ORFs which can be plausibly assigned roles in polyketide biosynthesis. Disruption of the pke PKS genes gave S. erythraea mutant JC2::pSBKS6, whose growth characteristics and pattern of secondary metabolite production did not apparently differ from the parent strain under any of the growth conditions tested. However, the pke PKS loading module and individual pke acyltransferase domains were shown to be active when used in engineered hybrid PKSs, making it highly likely that under appropriate conditions these biosynthetic genes are indeed expressed and active, and synthesize a novel polyketide product.

Roles of rapH and rapG in Positive Regulation of Rapamycin Biosynthesis in Streptomyces hygroscopicus

“…To evaluate the possible role of rapH and rapG in the expression of the polyketide synthase genes rapA and rapB, which are involved in the biosynthesis of the polyketide backbone of rapamycin (Fig. 1), a reporter system was employed that was based on the chalcone synthase (a type III PKS) gene rppA, which is responsible for production of the dark-red pigment flaviolin (5,11). Plasmid pEK61 was constructed, in which the P rapA promoter from the PKS rapA-rapB operon was cloned in front of the rppA gene of the reporter plasmid pEK60.…”

Complete genome sequence of the erythromycin-producing bacterium Saccharopolyspora erythraea NRRL23338

“…Detoxification is a key function for soil bacteria, and S. erythraea like the previously sequenced streptomycetes has numerous genes for transporters mediating resistance to various heavy metals, as well as a substantial cohort (36) of cytochrome P450 enzymes. Some of these have known roles in specific hydroxylation steps during biosynthesis of erythromycin and other secondary metabolites [21][22][23] , but others are predicted to play a role in selective oxidation and detoxification of organic materials.…”

“…The gene clusters for erythromycin (ery) 121 , and for a second modular polyketide synthase (PKS) of unknown function (pke) 22 , have been previously analyzed, as has the gene (SACE_1243, rppA) for a type III PKS, which generates the reddish pigment typical of S. erythraea 23 .…”

“…Two (SACE_5308, pks7; and SACE_5532, pks8) would encode multifunctional single-module PKS enzymes apparently related to the iterative polyketide synthases involved in enediyne or methylsalicylic acid synthesis. None of the hypothetical products of any of these PKSs, or of the pke PKS, have previously been detected, although extensive searches were made using 50 different solid and liquid media 22 . Strikingly, there are no type II PKS genes encoding the biosynthesis of aromatic polyketides, which are such a characteristic component of natural product biosynthesis in typical streptomycetes such as S. coelicolor and S. avermitilis, where they routinely govern the synthesis of antibiotics and spore pigments.…”

Simultaneous production and partitioning of heterologous polyketide and isoprenoid natural products in an Escherichia coli two-phase bioprocess

“…Furthermore, advances in annotation and bioinformatic approaches have aided the identification of secondary metabolite gene clusters from those organisms characterized by genome sequencing. For example, the native erythromycin producer, S. erythraea, contains sequence information for a predicted 25 polyketide, nonribosomal peptide, and terpene compounds [49], even though no products derived from these clusters (besides erythromycin) were identified on 50 different types of solid and liquid media [8]. Similar phenomena have been observed for S. avermitilis [27] and S. griseus [48].…”