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

Subject Area Mineralogy, Petrology and Geochemistry
Term from 2015 to 2018
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 277898458
 
Final Report Year 2019

Final Report Abstract

Fe(II)-organic-matter (Fe(II)-OM) complexes are abundant in the environment and, due to their mobility, reactivity and bioavailability, may play a key role for the behavior of Fe and pollutants. Complexation of Fe has been shown to influence the rates and extent of many chemical and microbial redox reactions. However, it was unknown whether, how fast, and to which extent Fe(II)-OM complexes can be oxidized by anaerobic Fe(II)-oxidizing bacteria which are widespread in many habitats. We used thermodynamic modeling and cell-suspension experiments, and revealed the influence of Fe(II)-OM complexation on the anaerobic microbial Fe(II) oxidation by model anaerobic Fe(II)-oxidizers: Acidovorax sp. BoFeNl, Rhodopseudomonas palustris TIE-1 and Rhodobacter ferrooxidans SW2, representing two types of microbial Fe(II) oxidation. We found that Fe(II)-OM complexation has different effects on different types of microbial Fe(II)-oxidizers. Fe(II)-OM complexation inhibited microbial nitrate-reducing Fe(II) oxidation, i.e. the colloidal and negatively charged Fe(II)-OM complexes showed lower oxidation rates than free Fe(II) by nitrate-reducing Fe(II)-oxidizing bacteria. In contrast, the Fe(II)-OM complexation did not inhibit but significantly accelerate the rates of Fe(II) oxidation by microbial phototrophic Fe(II) oxidizers, with different extent depending on the identity of the Fe(II)-OM complexes. In addition, we have revealed a closer-link between microbial Fe(II) oxidation and microbial denitrification, and demonstrated a cryptic Fe-cycle in which photochemical reduction of Fe(NI)-OM complexes is coupled to microbial phototrophic oxidation of Fe(II)-OM complexes. These results suggest that Fe(II)-OM complexation has a significant influence on the rate, extent and products of microbial Fe(II) oxidation in anoxic environments, and potentially could play an important role in influencing the cycles of carbon and nitrogen in the environment.

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