Identifying and Quantifying the Intermediate Processes during Nitrate-Dependent Iron(II) Oxidation

Abstract

Microbially driven nitrate-dependent iron (Fe) oxidation (NDFO) in subsurface environments has been intensively studied. However, the extent to which Fe(II) oxidation is biologically catalyzed remains unclear because no neutrophilic iron-oxidizing and nitrate reducing autotroph has been isolated to confirm the existence of an enzymatic pathway. While mixotrophic NDFO bacteria have been isolated, understanding the process is complicated by simultaneous abiotic oxidation due to nitrite produced during denitrification. In this study, the relative contributions of biotic and abiotic processes during NDFO were quantified through the compilation and model-based interpretation of previously published experimental data. The kinetics of chemical denitrification by Fe(II) (chemodenitrification) were assessed, and compelling evidence was found for the importance of organic ligands, specifically exopolymeric substances secreted by bacteria, in enhancing abiotic oxidation of Fe(II). However, nitrite alone could not explain the observed magnitude of Fe(II) oxidation, with 60-75% of overall Fe(II) oxidation attributed to an enzymatic pathway for investigated strains: Acidovorax ( A.) strain BoFeN1, 2AN, A. ebreus strain TPSY, Paracoccus denitrificans Pd 1222, and Pseudogulbenkiania sp. strain 2002. By rigorously quantifying the intermediate processes, this study eliminated the potential for abiotic Fe(II) oxidation to be exclusively responsible for NDFO and verified the key contribution from an additional, biological Fe(II) oxidation process catalyzed by NDFO bacteria.

Inhibition of photoferrotrophy by nitric oxide in ferruginous environments

“…Added substrates: 10 mM FeCl2, 2 mM nitrate, 0.5 mM sodium acetate acceptor and donor half saturation coefficients fall within the same order of magnitude. The electron acceptor half-saturation coefficients calibrated in this study fall close to the 3.5×10 -3 [mM] electron acceptor half-saturation coefficient and 7.59 [mM] "encrustation inhibition coefficient" (equivalent to , herein) presented in Jamieson et al, (2018). Moreover, our fitted electron acceptor half-saturation constants and maximum specific growth rate constants ( ) fall within the range of previously reported denitrification parameters (e.g., Almeida et al, 1995;Schreiber et al, 2009;Ni et al, 2011), albeit coupled to organic carbon as the electron donor.…”

Microbial anaerobic Fe(II) oxidation – Ecology, mechanisms and environmental implications

“…However, it was later suggested that this effect is probably a response to the nutritional benefit of iron addition, and not due to enzymatic Fe(II) oxidation (Klueglein and Kappler, 2013). Determination of an enzymatic component in potential mixotrophs is technically challenging to decipher and requires intricate analysis of all reactive intermediates (see most recently Jamieson et al, 2018). These authors claimed to have shown a requirement for an enzymatic component of oxidation in Acidovorax sp.…”

Isotopic evidence of nitrate degradation by a zero-valent iron permeable reactive barrier: Batch experiments and a field scale study

“…The k' was obtained using the integrated form of this equation, from the slope of the regression lines of the ln C/C 0 vs. time graph (Fig. 2 (Till et al, 1998;Shin and Cha, 2008;An et al, 2009;Jamieson et al, 2018;Xu et al, 2018;Zhang et al, 2019).…”