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Microbial iron oxidation under oxygen-limited conditions: Rates, competition and spatial patterns in the rhizosphere of wetland plants
Project leader: Dr. T. Behrends, Prof. dr. P. Van Cappellen
Researcher(s): Dr. S. Vollrath
Starting date: 1-jan-07

Abstract
Oxic-to-suboxic transition zones in sediments and wetland soils provide suitable habitats for active populations of iron-oxidizing bacteria (FeOB). This project will focus on the interplay between the iron and oxygen gradients in these environments and the rates of microbial iron oxidation. Gradient gel and root analogue experimental systems will be used to determine the response of FeOB to variations in water composition and oxygen fluxes, measure the rates of microbial plus abiotic iron oxidation and characterize the oxidation products. We hypothesize that competition with abiotic oxygenation of ferrous iron confines microbial iron reduction to low oxygen pressures. Additionally, the competition of FeOB with ammonium-oxidizing bacteria will be investigated in the same experimental systems, complementing gnotobiotic microcosm experiments performed in project 1. The experimental results will be used to parameterize a reaction transport model linking the rates of microbial iron oxidation with the fluxes of the reactants under dynamic and steady state conditions, and relating the rates or microbial iron oxidation with the rates of other coupled abiotic and biotic processes. The proposed research will yield new conceptual insight into the role of oxygen exudation by plant roots in the biogeochemical cycling of wetland soils and sediments.

Publications
Wang, J., Vollrath, S., Behrends, T., Bodelier, P.L.E., Muyzer, G., Meima-Franke, M., Oudsten, F.D., Van Cappellen, P., Laanbroek, H.J. (2011). Distribution and diversity of Gallionella-like neutrophilic iron oxidizers in a tidal freshwater marsh . Applied and Environmental MicrobiologyVolume 77, Issue 7: 2337-2344.
Darwin Center authors: Behrends T., Bodelier P. L. E., Laanbroek H. J., Van Cappellen P., Vollrath S., Wang J.

Suzann Vollrath (2012). Microbial Fe(II) oxidation at circumneutral pH: Reaction kinetics, mineral products, and distribution of neutrophilic iron oxidizers in wetland soils.. January 2012.
Darwin Center authors: Vollrath S.

Susann Vollrath, Thilo Behrends & Philippe Van Cappellen (2012). Oxygen Dependency of Neutrophilic Fe(II) Oxidation by Leptothrix Differs from Abiotic Reaction . Geomicrobiology Journal26-6: 550-560.
Darwin Center authors: Behrends T., Vollrath S.