Abstract
Serratia plymuthica strain RVH1, initially isolated from an industrial food processing environment, displays potent antimicrobial activity towards a broad spectrum of Gram-positive and Gram-negative bacterial pathogens. Isolation and subsequent structure determination of bioactive molecules led to the identification of two polyamino antibiotics with the same molecular structure as zeamine and zeamine II as well as a third, closely related analogue, designated zeamine I. The gene cluster encoding the biosynthesis of the zeamine antibiotics was cloned and sequenced and shown to encode FAS, PKS as well as NRPS related enzymes in addition to putative tailoring and export enzymes. Interestingly, several genes show strong homology to the pfa cluster of genes involved in the biosynthesis of long chain polyunsaturated fatty acids in marine bacteria. We postulate that a mixed FAS/PKS and a hybrid NRPS/PKS assembly line each synthesize parts of the backbone that are linked together post-assembly in the case of zeamine and zeamine I. This interaction reflects a unique interplay between secondary lipid and secondary metabolite biosynthesis. Most likely, the zeamine antibiotics are produced as prodrugs that undergo activation in which a nonribosomal peptide sequence is cleaved off.
Highlights
Polyketides (PKs) and nonribosomal peptides (NRPs) represent two large families of structurally diverse and complex microbial metabolites that include many therapeutically valuable antibacterial drugs
We report the cloning, sequencing and analysis of the gene cluster responsible for zeamine biosynthesis and propose that an unprecedented interaction between a hybrid polyketide synthases (PKSs)/nonribosomal peptide synthetases (NRPSs) and an iterative fatty acid synthases (FASs)/PKS system is responsible for the biosynthesis of the zeamine antibiotics
Since the production of the antimicrobial compound in RVH1 is quorum sensing-regulated [11], fermentation cultures were supplemented with synthetic N-(3-oxohexanoyl)-C6-homoserine lactones which made it possible to achieve a yield of 20 mg/l of over 90% pure compounds
Summary
Polyketides (PKs) and nonribosomal peptides (NRPs) represent two large families of structurally diverse and complex microbial metabolites that include many therapeutically valuable antibacterial drugs Both are synthesized with similar logic by large multifunctional enzymes known as polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs), which link simple monomeric building blocks (acyl-CoAs and amino acids, respectively) by a cascade of condensation reactions. The modular architecture and the functional versatility of these enzymes, combined with post-PKS tailoring reactions, generate stereochemically complex compounds, characterized by a high level of structural variation. Depending on their biochemical properties and molecular architecture, PKSs are subdivided into two main classes. Type II synthases work iteratively, being composed of a minimal set of individual proteins that work together to create aromatic compounds [3]
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