The pobA gene of Burkholderia cenocepacia encodes a group I Sfp-type phosphopantetheinyltransferase required for biosynthesis of the siderophores ornibactin and pyochelin

Abstract

The opportunistic pathogen Burkholderia cenocepacia produces the siderophores ornibactin and pyochelin under iron-restricted conditions. Biosynthesis of both siderophores requires the involvement of non-ribosomal peptide synthetases (NRPSs). Using a transposon containing the lacZ reporter gene, two B. cenocepacia mutants were isolated which were deficient in siderophore production. Mutant IW10 was shown to produce normal amounts of ornibactin but only trace amounts of pyochelin, whereas synthesis of both siderophores was abolished in AHA27. Growth of AHA27, but not IW10, was inhibited under iron-restricted conditions. In both mutants, the transposon had integrated into the pobA gene, which encodes a polypeptide exhibiting similarity to the Sfp-type phosphopantetheinyltransferases (PPTases). These enzymes are responsible for activation of NRPSs by the covalent attachment of the 4'-phosphopantetheine (P-pant) moiety of coenzyme A. Previously characterized PPTase genes from other bacteria were shown to efficiently complement both mutants for siderophore production when provided in trans. The B. cenocepacia pobA gene was also able to efficiently complement an Escherichia coli entD mutant for production of the siderophore enterobactin. Using mutant IW10, in which the lacZ gene carried by the transposon is inserted in the same orientation as pobA, it was shown that pobA is not appreciably iron-regulated. Finally, we confirmed that Sfp-type bacterial PPTases can be subdivided into two distinct groups, and we present the amino acid signature sequences which characterize each of these groups.