Hormaomycin produced by Streptomyces griseoflavus is a structurally highly modified depsipeptide that contains several unique building blocks with cyclopropyl, nitro, and chlorine moieties. Within the genus Streptomyces, it acts as a bacterial hormone that induces morphological differentiation and the production of bioactive secondary metabolites. In addition, hormaomycin is an extremely potent narrow-spectrum antibiotic. In this study, we shed light on hormaomycin biosynthesis by a combination of feeding studies, isolation of the biosynthetic nonribosomal peptide synthetase (NRPS) gene cluster, and in vivo and in vitro functional analysis of enzymes. In addition, several nonnatural hormaomycin congeners were generated by feeding-induced metabolic rerouting. The NRPS contains numerous highly repetitive regions that suggest an evolutionary scenario for this unusual bacterial hormone, providing new opportunities for evolution-inspired metabolic engineering of novel nonribosomal peptides.

Pederin belongs to a group of antitumor compounds found in terrestrial beetles and marine sponges. It is used by apparently all members of the rove beetle genera Paederus and Paederidus as a chemical defense against predators. However, a recent analysis of the putative pederin biosynthesis (ped) gene cluster strongly suggests that pederin is produced by bacterial symbionts. We have sequenced an extended region of the symbiont genome to gain further insight into the biology of this as-yet-unculturable bacterium and the evolution of pederin symbiosis. Our data indicate that the symbiont is a very close relative of Pseudomonas aeruginosa that has acquired several foreign genetic elements by horizontal gene transfer. Besides one functional tellurite resistance operon, the region contains a genomic island spanning 71.6 kb that harbors the putative pederin biosynthetic genes. Several decayed insertion sequence elements and the mosaic-like appearance of the island suggest that the acquisition of the ped symbiosis genes was followed by further insertions and rearrangements. A horizontal transfer of genes for the biosynthesis of protective substances could explain the widespread occurrence of pederin-type compounds in unrelated animals from diverse habitats.The pederin group of natural products consists of numerous members with potent antitumor and antiviral activities ( Fig. 1) (15). Remarkably, these structurally highly similar substances have been isolated from two entirely unrelated animal groups. Pederin itself occurs in species of the beetle genera Paederus and Paederidus, while almost all other members are known only from marine sponges. In the beetles, pederin serves as a chemical defense against predators such as spiders (11). It is also the cause of Paederus dermatitis, a blistering inflammation that is contracted when the beetles are accidentally crushed on the human skin (20). In regions with a warm climate the beetles can appear in enormous numbers, resulting in notorious epidemics that have forced the evacuation of entire settlements (18,25). Interestingly, they have also been proposed as a cause for 3 of the 10 biblical plagues (16).Several lines of evidence clearly indicate that pederin is not produced by the beetles themselves but by as-yet-uncultured bacterial symbionts. Kellner and Dettner have demonstrated that within each examined beetle species pederin is synthesized in only about 90% of the females, who alone can transfer this trait to their offspring (10). According to 16S ribosomal DNA data, only these pederin-synthesizing females harbor a bacterium with the closest relationship to Pseudomonas aeruginosa (8). If eggs of such beetles are fed to nonproducing females, pederin is again synthesized in their offspring (7). Our search for the pederin biosynthesis genes, motivated by the prospect of generating an alternative biotechnological source of these rare antitumor compounds, has resulted in the isolation of a polyketide synthase cluster spanning 54 kb (19). This operon, designated the ped cluster...