title: Accessibility of humic-associated Fe to a microbial siderophore: implications for bioavailability.
abstract: Microorganisms in aerobic, circum-neutral environments are challenged to acquire sufficient nutrient Fe due to low solubilities of Fe oxides. To overcome this challenge, many aerobic microbes produce low molecular weight (MW) organic ligands, or siderophores, with extremely high Fe-binding affinities. This research expands the existing understanding of siderophore-mediated Fe acquisition from minerals by examining the effects of the siderophore desferrioxamine B (DFOB) on Fe removal from aquatic humic substances (XAD-8-isolated) and other organic matter (OM) isolates (reverse osmosis, RO; and "transphilic", XAD-4) from several rivers including the Suwannee River (GA, USA). Analysis of samples by asymmetrical flow field-flow fractionation (AsFlFFF) with in-line ICP-MS and UV-vis detectors showed that Fe was naturally abundant and primarily associated with intermediate to high MW OM. An excess of DFOB (relative to naturally present Fe) removed ∼ 75% of Fe and shifted the OM MW distribution to lower MWs, perhaps due to removal of "bridging" Fe, although additional mechanistic study of MW shifts is needed. Removal of other OM-associated metals (e.g., Al, Cu, Zn) by DFOB was minimal for all but a few samples. Fe bound to humic substances and other more "transphilic" organic components therefore should be considered readily bioavailable to aerobic, siderophore-producing microorganisms.
authors.affiliation: Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame , 156 Fitzpatrick Hall, Notre Dame, Indiana, United States.
authors.forename: Keshia M
authors.initials: KM
authors.lastname: Kuhn
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Maurice
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Neubauer
authors.forename: Thilo
authors.initials: T
authors.lastname: Hofmann
authors.forename: Frank
authors.initials: F
authors.lastname: von der Kammer
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D001682:Biological Availability; D003676:Deferoxamine / Q000378:metabolism; D031521:Fractionation, Field Flow; D006812:Humic Substances / Q000032:analysis*; D007501:Iron / Q000378:metabolism*; D008670:Metals / Q000302:isolation & purification; D008970:Molecular Weight; D009995:Osmosis; D011108:Polymers / Q000737:chemistry; D011137:Polystyrenes / Q000737:chemistry; D011145:Polyvinyls / Q000737:chemistry; D017262:Siderophores / Q000378:metabolism*; D013054:Spectrophotometry, Atomic; D013056:Spectrophotometry, Ultraviolet
chemical_list: D006812:Humic Substances; D008670:Metals; D011108:Polymers; D011137:Polystyrenes; D011145:Polyvinyls; D017262:Siderophores; C033942:Amberlite XAD-8; C012101:XAD-4 resin; D007501:Iron; D003676:Deferoxamine