FIG. 2.

ESI-MS spectra of extracts of aerobic cultures of P. stutzeri with iron(III) amendment (a) where the peak at 654 amu was ferrioxamine E and the peak at 640 amu was the ferrioxamine E analogue called unknown 1 (D₂). After replacement of iron(III) by gallium(III) (b), gallium desferrioxamine produced peaks at m/z 667 and 669 (proton adduct), 684 and 686 (ammonium adduct), 689 and 691 (sodium adduct), and 705 and 707 amu (potassium adduct). The gallium complex of the unknown siderophore called unknown 1 produced peaks at m/z 653 and 655 amu (proton adduct) and 675 and 677 (sodium adduct), while the potential ammonium adduct (expected at 670 and 672 amu) and potassium adduct (expected at 691 and 692 amu) were overlapped with adducts of gallium desferrioxamine E. The peaks at 611 and 625 amu were not affected by replacement of iron with gallium.