Microbial oxidation of Fe(II)-natural organic matter complexes

• Applicant: Professor Dr. Andreas Kappler
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 277898458

Iron speciation and in particular the identity and properties of Fe(III) minerals and dissolved Fe(III)-complexes formed during Fe(II) oxidation strongly impact sorption and thus the mobility and bioavailability of toxic elements such as arsenic, cadmium, copper and mercury (Hg) and thereby affect the quality of water, soils and sediments. It is known that the properties of Fe(III) minerals vary i) depending on whether the Fe(II) is oxidized abiotically or biotically (via Fe(II)-oxidizing bacteria) and ii) depending on the presence and absence of natural organic matter (e.g. humic compounds). It is unknown, however, whether Fe(II)-oxidizing bacteria can oxidize Fe(II)-complexes that contain natural organic matter molecules as ligands. Furthermore, the identity and reactivity of the Fe(III) compounds formed during such a microbial oxidation of Fe(II)-complexes are unknown.The objectives of the present proposal therefore are first to synthesize defined Fe(II)-organic-matter complexes with small organic ligands and purified fulvic and humic acids. In a second step we will determine whether microaerophilic, nitrate-reducing and phototrophic Fe(II)-oxidizing bacteria can oxidize such Fe(II) complexes. Thirdly, we will determine the identity, properties and reactivity of the Fe(III) compounds formed. Finally, we will isolate Fe(II) complexes from a soil and also determine whether they can be oxidized by Fe(II)-oxidizing bacteria and what kind of Fe(III) compounds are formed during this process. The results from the present proposal will ultimately increase our knowledge regarding the environmental fate of contaminants. It will in particular improve our understanding of the role of Fe(II)-oxidizing bacteria and Fe(II)-natural-organic matter complexes for the formation of reactive Fe(III) compounds that interact with contaminants in the environment.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Anneli Sundman