Recombineering enables genome mining of novel siderophores in a non-model Burkholderiales strain

Iron is essential for bacterial survival, and most bacteria capture iron by producing siderophores. Burkholderiales bacteria produce various types of bioactive secondary metabolites, such as ornibactin and malleobactin siderophores. In this study, the genome analysis of Burkholderiales genomes showed a putative novel siderophore gene cluster crb, which is highly similar to the ornibactin and malleobactin gene clusters but does not have pvdF, a gene encoding a formyltransferase for N-δ‑hydroxy-ornithine formylation. Establishing the bacteriophage recombinase Redγ-Redαβ7029 mediated genome editing system in a non-model Burkholderiales strain Paraburkholderia caribensis CICC 10960 allowed the rapid identification of the products of crb gene cluster, caribactins A-F (1–6). Caribactins contain a special amino acid residue N-δ‑hydroxy-N-δ-acetylornithine (haOrn), which differs from the counterpart N-δ‑hydroxy-N-δ-formylornithine (hfOrn) in ornibactin and malleobactin, owing to the absence of pvdF. Gene inactivation showed that the acetylation of hOrn is catalyzed by CrbK, whose homologs probably not be involved in the biosynthesis of ornibactin and malleobactin, showing possible evolutionary clues of these siderophore biosynthetic pathways from different genera. Caribactins promote biofilm production and enhance swarming and swimming abilities, suggesting that they may play crucial roles in biofilm formation. This study also revealed that recombineering has the capability to mine novel secondary metabolites from non-model Burkholderiales species.