FIG. 3.

Extracted ion chromatograms of P. stutzeri cultivated under aerobic conditions with amendment of ferric iron (a) or gallium (b), showing peaks of four siderophores. In the ferric extract (a), the ferric complex of unknown 2 (unk. 2) was detected at 8.6 min and m/z 626 amu, ferrioxamine G (FOG) at 10.7 min and m/z 672 amu, unknown 1 (unk. 1) at 11.8 min and m/z 640 amu, and ferrioxamine E (FOE) at 16.3 min and m/z 654 amu. After replacement of iron with gallium, the same siderophores bound to both ⁶⁹Ga and ⁷¹Ga were detected, i.e., unknown 2 at 7.6 min and m/z 639 and 641 amu, gallium desferrioxamine G at 9.5 min and m/z 685 and 687 amu, unknown 1 at 10.7 min and m/z 653 and 655 amu, and gallium desferrioxamine E at 15.7 min and m/z 667 and 669 amu. For all peaks in panel b, the lowest signal corresponds to the ⁷¹Ga isotope while the most intense signal is produced by the ⁶⁹Ga isotope. Separation conditions: HyPurity C₁₈ column, 100 by 0.5 mm, eluted with 10 μl/min of a mobile phase containing 5% acetonitrile in formiate buffer (pH 4.0), 11 mM.