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Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments.
Appl Environ Microbiol. 2018 01 15; 84(2)AE

Abstract

Nitrate-reducing iron(II)-oxidizing bacteria have been known for approximately 20 years. There has been much debate as to what extent the reduction of nitrate and the oxidation of ferrous iron are coupled via enzymatic pathways or via abiotic processes induced by nitrite formed by heterotrophic denitrification. The aim of the present study was to assess the coupling of nitrate reduction and iron(II) oxidation by monitoring changes in substrate concentrations, as well as in the activity of nitrate-reducing bacteria in natural littoral freshwater sediment, in response to stimulation with nitrate and iron(II). In substrate-amended microcosms, we found that the biotic oxidation of ferrous iron depended on the simultaneous microbial reduction of nitrate. Additionally, the abiotic oxidation of ferrous iron by nitrite in sterilized sediment was not fast enough to explain the iron oxidation rates observed in microbially active sediment. Furthermore, the expression levels of genes coding for enzymes crucial for nitrate reduction were in some setups stimulated by the presence of ferrous iron. These results indicate that there is a direct influence of ferrous iron on bacterial denitrification and support the hypothesis that microbial nitrate reduction is stimulated by biotic iron(II) oxidation.IMPORTANCE The coupling of nitrate reduction and Fe(II) oxidation affects the environment at a local scale, e.g., by changing nutrient or heavy metal mobility in soils due to the formation of Fe(III) minerals, as well as at a global scale, e.g., by the formation of the primary greenhouse gas nitrous oxide. Although the coupling of nitrate reduction and Fe(II) oxidation was reported 20 years ago and has been studied intensively since then, the underlying mechanisms still remain unknown. One of the main knowledge gaps is the extent of enzymatic Fe(II) oxidation coupled to nitrate reduction, which has frequently been questioned in the literature. In the present study, we provide evidence for microbially mediated nitrate-reducing Fe(II) oxidation in freshwater sediments. This evidence is based on the rates of nitrate reduction and Fe(II) oxidation determined in microcosm incubations and on the effect of iron on the expression of genes required for denitrification.

Authors+Show Affiliations

Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Germany.Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Germany.Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Germany.Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark. NASA Ames Research Center, Moffett Field, California, USA.Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Germany. Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Germany caroline.schmidt@uni-tuebingen.de.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

29101195

Citation

Schaedler, Franziska, et al. "Microbially Mediated Coupling of Fe and N Cycles By Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments." Applied and Environmental Microbiology, vol. 84, no. 2, 2018.
Schaedler F, Lockwood C, Lueder U, et al. Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments. Appl Environ Microbiol. 2018;84(2).
Schaedler, F., Lockwood, C., Lueder, U., Glombitza, C., Kappler, A., & Schmidt, C. (2018). Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments. Applied and Environmental Microbiology, 84(2). https://doi.org/10.1128/AEM.02013-17
Schaedler F, et al. Microbially Mediated Coupling of Fe and N Cycles By Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments. Appl Environ Microbiol. 2018 01 15;84(2) PubMed PMID: 29101195.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments. AU - Schaedler,Franziska, AU - Lockwood,Cindy, AU - Lueder,Ulf, AU - Glombitza,Clemens, AU - Kappler,Andreas, AU - Schmidt,Caroline, Y1 - 2018/01/02/ PY - 2017/09/12/received PY - 2017/10/31/accepted PY - 2017/11/5/pubmed PY - 2019/1/31/medline PY - 2017/11/5/entrez KW - denitrification KW - iron cycling KW - iron metabolism KW - iron(II) oxidation KW - nitrate-dependent iron oxidation JF - Applied and environmental microbiology JO - Appl. Environ. Microbiol. VL - 84 IS - 2 N2 - Nitrate-reducing iron(II)-oxidizing bacteria have been known for approximately 20 years. There has been much debate as to what extent the reduction of nitrate and the oxidation of ferrous iron are coupled via enzymatic pathways or via abiotic processes induced by nitrite formed by heterotrophic denitrification. The aim of the present study was to assess the coupling of nitrate reduction and iron(II) oxidation by monitoring changes in substrate concentrations, as well as in the activity of nitrate-reducing bacteria in natural littoral freshwater sediment, in response to stimulation with nitrate and iron(II). In substrate-amended microcosms, we found that the biotic oxidation of ferrous iron depended on the simultaneous microbial reduction of nitrate. Additionally, the abiotic oxidation of ferrous iron by nitrite in sterilized sediment was not fast enough to explain the iron oxidation rates observed in microbially active sediment. Furthermore, the expression levels of genes coding for enzymes crucial for nitrate reduction were in some setups stimulated by the presence of ferrous iron. These results indicate that there is a direct influence of ferrous iron on bacterial denitrification and support the hypothesis that microbial nitrate reduction is stimulated by biotic iron(II) oxidation.IMPORTANCE The coupling of nitrate reduction and Fe(II) oxidation affects the environment at a local scale, e.g., by changing nutrient or heavy metal mobility in soils due to the formation of Fe(III) minerals, as well as at a global scale, e.g., by the formation of the primary greenhouse gas nitrous oxide. Although the coupling of nitrate reduction and Fe(II) oxidation was reported 20 years ago and has been studied intensively since then, the underlying mechanisms still remain unknown. One of the main knowledge gaps is the extent of enzymatic Fe(II) oxidation coupled to nitrate reduction, which has frequently been questioned in the literature. In the present study, we provide evidence for microbially mediated nitrate-reducing Fe(II) oxidation in freshwater sediments. This evidence is based on the rates of nitrate reduction and Fe(II) oxidation determined in microcosm incubations and on the effect of iron on the expression of genes required for denitrification. SN - 1098-5336 UR - https://www.unboundmedicine.com/medline/citation/29101195/Microbially_Mediated_Coupling_of_Fe_and_N_Cycles_by_Nitrate_Reducing_Fe_II__Oxidizing_Bacteria_in_Littoral_Freshwater_Sediments_ L2 - http://aem.asm.org/cgi/pmidlookup?view=long&pmid=29101195 DB - PRIME DP - Unbound Medicine ER -