The redox reaction between iron and nitrogen drives the global biogeochemical cycles of iron and nitrogen and concomitantly, changes the mineralogy and the fate of nutrients. Despite the microbially involved Fe(II)-NO3- process was reported to play a key role of the Fe/N interactions under neutral-anoxic conditions, the understanding of the coupling mechanisms are still unclear. While it was previously known as a microbial nitrate-dependent process, it has been recently documented that this process is mediated by both chemical and biological mechanisms. Specifically, the intermediate products (NO2-, N2O and NO) of biological nitrate reduction, are able to chemically react with Fe(II) in this system. However, the relative contributions of biological processes and chemical processes to Fe(II) oxidation is still not hardly quantified due to the co-occurrence of the reactions. Here, the kinetics and secondary minerals of microbially mediated nitrate-reducing Fe(II) oxidation by Pseudogulbenkiania sp. strain 2002 was investigated. In the treatment of strain 2002+Fe(II)+NO3-, the Fe(II) oxidation and nitrate reduction occurred simultaneously, suggesting their co-occurrence of these two processes. The kinetics of nitrate reduction to nitrite by strain 2002 and the chemical reaction between NO2- and Fe(II) confirmed the occurrence of chemodenitrification in the treatment of strain 2002+Fe(II)+NO3-. The extracellular polymeric substances (EPS) of strain 2002 were extracted, and the c-type cytochromes were observed from the UV-Vis spectra. The spectra of EPS+Fe(II) showed that the oxidized c-type cytochromes could oxidize Fe(II), revealing that the enzymatic Fe(II) oxidation via c-type cytochromes could be directly evidenced. A brief model was established via combining the three reactions (1) nitrate reduction to nitrite by strain 2002, (2) Fe(II) oxidation by nitrite and (3) enzymatic Fe(II) oxidation. Based on the model, for the first time, the unknown kinetics of enzymatic Fe(II) oxidation was derived and compared with that of chemodenitrification.

Microbially mediated nitrate-reducing Fe(II) oxidation: Quantification of chemodenitrification and enzymatic reactions

255th National Meeting (2018)

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