Effect of hydroxamate siderophores on Fe release and Pb(II) adsorption by goethite

Abstract

Abstract-Hydroxamate siderophores are biologically-synthesized, Fe(III)-specific ligands which are common in soil environments. In this paper, we report an investigation of their adsorption by the iron oxyhydroxide, goethite; their influence on goethite dissolution kinetics; and their ability to affect Pb(II) adsorption by the goethite surface. The siderophores used were desferrioxamine B (DFO-B), a fungal siderophore, and desferrioxamine D 1 , an acetyl derivative of DFO-B (DFO-D1). Siderophore adsorption isotherms yielded maximum surface concentrations of 1.5 (DFO-B) or 3.5 (DFO-D1) mol/g at pH 6.6, whereas adsorption envelopes showed either cation-like (DFO-B) or ligand-like (DFO-D1) behavior. Above pH 8, the adsorbed concentrations of both siderophores were similar. The dissolution rate of goethite in the presence of 240 M DFO-B or DFO-D1 was 0.02 or 0.17 mol/g hr, respectively. Comparison of these results with related literature data on the reactions between goethite and acetohydroxamic acid, a monohydroxamate ligand, suggested that the three hydroxamate groups in DFO-D1 coordinate to Fe(III) surface sites relatively independently. The results also demonstrated a significant depleting effect of 240 M DFO-B or DFO-D1 on Pb(II) adsorption by goethite at pH Ͼ 6.5, but there was no effect of adsorbed Pb(II) on the goethite dissolution rate.

Roles of Siderophores, Oxalate, and Ascorbate in Mobilization of Iron from Hematite by the Aerobic Bacterium Pseudomonas mendocina

“…Although siderophores are essential for Fe uptake by many aerobic bacteria, they are inefficient at releasing Fe from the surfaces of the mineral species that are the most common terrestrial sources of Fe (6,9,22,25,27). They also inevitably diffuse away from the source of production and into the greater geologic matrix.…”

“…However, proton-promoted dissolution of hematite, which would release Fe(III) into solution for uptake by the siderophore, is likely far faster at pH 3 than at the circumneutral pH used in the biotic experiments described here. Moreover, direct DFO-B adsorption to Fe oxides has been observed to be weak, at least at pH values less than 8 (27), although the hematite-sorptive abilities of the siderophore produced by P. mendocina are unknown. Finally, siderophores might promote the solubility of the mineral (K SP ) in batch systems by forming thermodynamically strong complexes with the released Fe in solution, which would be further enhanced by synergistic contributions from other ligands that interact directly with the mineral.…”

“…A primary means by which aerobic microorganisms enhance Fe mobility and bioavailability is by secreting siderophores, which are structurally diverse, low-molecular-weight chelating agents with extremely high affinities for Fe(III) (12,27,37,40). Fe(III)-siderophore stability constants can be as high as 10 52 (1,40), which is many orders of magnitude higher than the stability constants for low-molecular-weight organic acids, such as oxalic acid [for Fe(III) ϩ 3 oxalate % Fe(oxalate) 3 , K ϭ 10 18.6 ] (45).…”

Iron oxide dissolution and solubility in the presence of siderophores

“…The effect of surface charge on siderophore sorption is illustrated in Figure 7 (Kraemer et al, 1999). DFO-B is a cationic species at pH < 8 due to protonation of the terminal amine group (pK a1 = 8.38).…”

Adsorption of Pb(II) and Eu(III) by Oxide Minerals in the Presence of Natural and Synthetic Hydroxamate Siderophores

“…Europium is a well-known surrogate for transuranic metals (2,30,31), whereas lead is a hazardous trace metal. In the absence of competing organic ligands, lead and europium should adsorb strongly to oxide mineral surfaces (11,32,33). One of the two siderophores selected, DFO-B, is a common trihydroxamate siderophore (16) whose free amine group remains protonated at pH < 10 (11).…”