A Revised Iron Extraction Protocol for Environmental Samples Rich in Nitrite and Carbonate

Schaedler, Franziska; Kappler, Andreas; Schmidt, Caroline

doi:10.1080/01490451.2017.1303554

Cited by 37 publications

(25 citation statements)

References 53 publications

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“…and 100 µL of the supernatant was diluted in 1 M HCl. Fe(II) was quantified in triplicate using the Ferrozine Assay 33 . Statistical differences in As and Fe concentration in the different microcosm setups were analyzed with single factor ANOVA while those at selected time points between pairs of treatments were determined using the Student's t-test.…”

Section: Methodsmentioning

confidence: 99%

Arsenic mobilization by anaerobic iron-dependent methane oxidation

Straub

Jetten

Głodowska

et al. 2020

Commun Earth Environ

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Arsenic groundwater contamination threatens the health of millions of people worldwide, particularly in South and Southeast Asia. In most cases, the release of arsenic from sediment was caused by microbial reductive dissolution of arsenic-bearing iron(III) minerals with organic carbon being used as microbial electron donor. Although in many arsenic-contaminated aquifers high concentrations of methane were observed, its role in arsenic mobilization is unknown. Here, using microcosms experiments and hydrogeochemical and microbial community analyses, we demonstrate that methane functions as electron donor for methanotrophs, triggering the reductive dissolution of arsenic-bearing iron(III) minerals, increasing the abundance of genes related to methane oxidation, and ultimately mobilizing arsenic into the water. Our findings provide evidence for a methane-mediated mechanism for arsenic mobilization that is distinct from previously described pathways. Taking this together with the common presence of methane in arsenic-contaminated aquifers, we suggest that this methane-driven arsenic mobilization may contribute to arsenic contamination of groundwater on a global scale.

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Section: Methodsmentioning

confidence: 99%

Arsenic mobilization by anaerobic iron-dependent methane oxidation

Straub

Jetten

Głodowska

et al. 2020

Commun Earth Environ

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“…Analytical methods. For quantification of Fe(II) and Fe(III) concentrations, we used the revised ferrozine protocol for nitrite-containing samples described by Klueglein and Kappler (9) and Schaedler et al (56). Briefly, 100 l of culture suspension was withdrawn anoxically with a syringe and mixed with 900 l of 40 mM sulfamic acid.…”

Section: Methodsmentioning

confidence: 99%

Growth and Population Dynamics of the Anaerobic Fe(II)-Oxidizing and Nitrate-Reducing Enrichment Culture KS

Tominski

Heyer

Lösekann-Behrens

et al. 2018

Appl Environ Microbiol

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Most isolated nitrate-reducing Fe(II)-oxidizing microorganisms are mixotrophic, meaning that Fe(II) is chemically oxidized by nitrite that forms during heterotrophic denitrification, and it is debated to which extent Fe(II) is enzymatically oxidized. One exception is the chemolithoautotrophic enrichment culture KS, a consortium consisting of a dominant Fe(II) oxidizer, sp., and less abundant heterotrophic strains (e.g., sp., sp.). Currently, this is the only nitrate-reducing Fe(II)-oxidizing culture for which autotrophic growth has been demonstrated convincingly for many transfers over more than 2 decades. We used 16S rRNA gene amplicon sequencing and physiological growth experiments to analyze the community composition and dynamics of culture KS with various electron donors and acceptors. Under autotrophic conditions, an operational taxonomic unit (OTU) related to known microaerophilic Fe(II) oxidizers within the family dominated culture KS. With acetate as an electron donor, most 16S rRNA gene sequences were affiliated with sp. sp. not only was able to oxidize Fe(II) under autotrophic and mixotrophic conditions but also survived over several transfers of the culture on only acetate, although it then lost the ability to oxidize Fe(II). spp. became and remained dominant when culture KS was cultivated for only one transfer under heterotrophic conditions, even when conditions were reverted back to autotrophic in the next transfer. This study showed a dynamic microbial community in culture KS that responded to changing substrate conditions, opening up questions regarding carbon cross-feeding, metabolic flexibility of the individual strains in KS, and the mechanism of Fe(II) oxidation by a microaerophile in the absence of O Nitrate-reducing Fe(II)-oxidizing microorganisms are present in aquifers, soils, and marine and freshwater sediments. Most nitrate-reducing Fe(II) oxidizers known are mixotrophic, meaning that they need organic carbon to continuously oxidize Fe(II) and grow. In these microbes, Fe(II) was suggested to be chemically oxidized by nitrite that forms during heterotrophic denitrification, and it remains unclear whether or to what extent Fe(II) is enzymatically oxidized. In contrast, the enrichment culture KS was shown to oxidize Fe(II) autotrophically coupled to nitrate reduction. This culture contains the designated Fe(II) oxidizer sp. and several heterotrophic strains (e.g., sp.). We showed that culture KS is able to metabolize Fe(II) and a variety of organic substrates and is able to adapt to dynamic environmental conditions. When the community composition changed and became the dominant community member, Fe(II) was still oxidized by sp., even when culture KS was cultivated with acetate/nitrate [Fe(II) free] before being switched back to Fe(II)/nitrate.

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“…One milliliter of sediment slurry was sampled from each microcosm at each sampling point using a sterile anoxic syringe and needle (inner diameter of 1.20 mm) in an anoxic glove box under N 2 atmosphere, without opening the bottles. Of the sampled slurry, 100 l was stabilized in 900 l of 40 mM sulfamic acid/1 M HCl (14,43) and incubated in the dark on a shaker for 1 h at 150 rpm. The samples were then centrifuged for 5 min at 15.4 ϫ g and the supernatant was used for the spectrophotometric ferrozine assay (44) in a spectrophotometric plate reader (MultiScan, Thermo Scientific, USA) to quantify Fe(II) and, after complete reduction of Fe(III) by hydroxylamine hydrochloride, Fe(total).…”

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confidence: 99%

Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments

Schaedler

Lockwood

Lueder

et al. 2018

Appl Environ Microbiol

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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. 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.

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A Revised Iron Extraction Protocol for Environmental Samples Rich in Nitrite and Carbonate

Cited by 37 publications

References 53 publications

Arsenic mobilization by anaerobic iron-dependent methane oxidation

Arsenic mobilization by anaerobic iron-dependent methane oxidation

Growth and Population Dynamics of the Anaerobic Fe(II)-Oxidizing and Nitrate-Reducing Enrichment Culture KS

Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments

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