HR: 11:35h
AN: B11E-06    [PDF]
TI: Light Induced Dissolution of Iron Oxides in the Presence of Siderophores
AU: * Kraemer, S M
EM: stephan.kraemer@ito.umnw.ethz.ch
AF: Institute of Terrestrial Ecology, ETH Z\"{u}rich, Grabenstrasse 3, Schlieren, 8952 Switzerland
AU: Borer, P
EM: borerp@student.ethz.ch
AF: Institute of Terrestrial Ecology, ETH Z\"{u}rich, Grabenstrasse 3, Schlieren, 8952 Switzerland
AU: Sulzberger, B A
EM: sulzberger@eawag.ch
AF: Department of Limnology, Swiss Federal Institute for Environmental Science and Technology (EAWAG), Ueberlandstrasse 133, Duebendorf, 8600 Switzerland
AB: Iron is a micronutrient that is essential for a range of important enzymatic processes in most organisms. Iron deficiency is thought to be limiting the primary productivity in marine `High Nutrient Low Chlorophyll' (HNLC) regions which has a significant effect on global carbon cycling. Important iron sources in HNLC regions are upwelling and atmospheric dust inputs. However, the iron bioavailability from atmospheric dust is limited by the low solubility and slow dissolution kinetics of iron bearing minerals. Marine bacteria are known to facilitate weathering reactions by exudation of substances such as low molecular weight organic ligands including siderophores. We investigated if siderophore promoted photoreductive dissolution constitutes an important pathway for increasing the bioavailability of iron oxides. We used the microbial siderophores aerobactin and desferrioxamine-B (DFO-B). Aerobactin and desferrixoamines are excreted by marine and terrestrial bacteria. Aerobactin is a dihydroxamate siderophore containing the potentially photoreactive group alpha-hydroxy carboxylate. DFO-B is a trihydroxamate siderophore which forms soluble iron complexes that are not photoreactive (BARBEAU et al., 2003). Despite the structural differences, both siderophores accelerate iron oxide dissolution in irradiated suspensions compared to dissolution rates in the dark. This suggests that both siderophores are not involved in a light induced ligand to metal charge transfer reaction, but rather accelerate other photreductive dissolution mechanisms. Similarly it was observed that both ligands accelerate light induced dissolution of iron oxides in the presence of oxalate as a chromophore. The observations suggest that light induced dissolution of iron oxides in the presence of siderophores is an important pathway for bacterial iron acquisition. However, the formation of Fe(II) by this mechanism may also lead to an increase of the availability of iron to phytoplankton that generally does not produce siderophores or take up iron(III)siderophore complexes (BARBEAU et al., 2001). References Barbeau K., Rue E. L., Bruland K. W., and Butler A. (2001) Photochemical cycling of iron in the surface ocean mediated by microbial iron(III)-binding ligands. Nature 413(6854), 409-413. Barbeau K., Rue E. L., Trick C. G., Bruland K. T., and Butler A. (2003) Photochemical reactivity of siderophores produced by marine heterotrophic bacteria and cyanobacteria based on characteristic Fe(III) binding groups. Limnology and Oceanography 48(3), 1069-1078.
DE: 4807 Chemical speciation and complexation
DE: 4809 Colloids
DE: 4845 Nutrients and nutrient cycling
DE: 4852 Photochemistry
DE: 4885 Weathering
SC: Biogeosciences [B]
MN: 2003 Fall Meeting