Elucidation of crude siderophore extracts from supernatants of Pseudomonas sp. ZnCd2003 cultivated in nutrient broth supplemented with Zn, Cd, and Zn plus Cd.

This research aimed to study siderophores secreted from Pseudomonas sp. PDMZnCd2003, a Zn/Cd tolerant bacterium. The effects of Zn and/or Cd stress were examined in nutrient broth to achieve the actual environmental conditions. Acid and alkali supernatants and liquid-liquid extraction with ethyl acetate and butanol were carried out to obtain crude extracts containing different amounts of the metals. The bacterial growth, UV-visible spectra of the supernatants and siderophore production indicated that the production of siderophores tended to be linked to primary metabolites. Pyocyanin was produced in all treatments, while pyoverdine was induced by stress from the metals, especially Cd. FT-IR spectra showed C=O groups and sulfur functional groups that were involved in binding with the metals. LC-MS revealed that pyocyanin, 1-hydroxy phenazine, pyoverdine, and pyochelin were present in the crude extracts. S K-edge XANES spectra showed that the main sulfur species in the extracts were the reduced forms of sulfide, thiol, and disulfide, and their oxidation states were affected by coordination with Zn and/or Cd. In addition, Zn K-edge EXAFS spectra and Cd K-edge EXAFS spectra presented Zn-O and Cd-O as coordination in the first shell, in case the extracts contained less metal. Although the mix O/S ligands had chelation bonding with Zn and Cd in the other extracts. For the role of S groups in pyochelin binding with the metals, this was the first report. The results of these experiments could be extended to Pseudomonas that respond to metal contaminated environments.