7-Hydroxytropolone produced and utilized as an iron-scavenger by Pseudomonas donghuensis

Pseudomonas donghuensis can excrete large quantities of iron chelating substances in iron-restricted environments. At least two kinds of iron-chelator can be found in the culture supernatant: fluorescent siderophores pyoverdins, and an ethyl acetate-extractable non-fluorescent substance. The non-fluorescent substance was the dominant contributor to the iron chelating activity of the culture supernatant of P. donghuensis. Electron ionization mass spectrometry, NMR spectroscopy, and IR spectroscopy identified the non-fluorescent iron-chelator as 7-hydroxytropolone. The stoichiometry of 7-hydroxytropolone ferric complex was determined to be 2:1 by the continuous variation method. The production of 7-hydroxytropolone was repressible by iron in the medium. Moreover, the inhibited growth of doubly siderophore-deficient strain of P. donghuensis under iron-limiting conditions could be partly restored by 7-hydroxytropolone. Thus, 7-hydroxytropolone was considered to play a previously undiscovered role as an iron-scavenger for P. donghuensis.