DIHYDROAERUGINOIC ACID SYNTHETASE AND PYOCHELIN SYNTHETASE, PRODUCTS OF THE PCHEF GENES, ARE INDUCED BY EXTRACELLULAR PYOCHELIN IN PSEUDOMONAS-AERUGINOSA

The siderophore pyochelin of Pseudomonas aeruginosa is derived from on e molecule of salicylate and two molecules of cysteine. Two cotranscri bed genes, pchEF, encoding peptide synthetases have been identified an d characterized. pchE was required for the conversion of salicylate to dihydroaeruginoate (Dha), the condensation product of salicylate and one cysteine residue and pchF was essential for the synthesis of pyoch elin from Dha. The deduced PchE (156 kDa) and PchF (197 kDa) proteins had adenylation, thiolation and condensation/cyclization motifs arrang ed as modules which are typical of those peptide synthetases forming t hiazoline rings. The pchEF genes were coregulated with the pchDCBA ope ron, which provides enzymes for the synthesis (PchBA) and activation ( PchD) of salicylate as well as a putative thioesterase (PchC). Express ion of a translational pchE'-'lacZ fusion was strictly dependent on th e PchR regulator and was induced by extracellular pyochelin, the end p roduct of the pathway. Iron replete conditions led to Fur (ferric upta ke regulator)-dependent repression of the pchE'-'lacZ fusion. A transl ational pchD'-'lacZ fusion was also positively regulated by PchR and p yochelin and repressed by Fur and iron. Thus, autoinduction by pyochel in (or ferric pyochelin) and repression by iron ensure a sensitive con trol of the pyochelin pathway in P. aeruginosa.