Imaging redox activity and Fe(II) at the microbe-mineral interface during Fe(III) reduction

Downie, Helen; Standerwick, Joel P.; Burgess, Letitia; Natrajan, Louise S.; Lloyd, Jonathan R.

doi:10.1016/j.resmic.2018.05.012

Cited by 11 publications

(6 citation statements)

References 54 publications

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“…Similarly, we did not observe surface‐bound organisms using fluorescent in situ hybridization. Downie, Standerwick, Burgess, Natrajan, and Lloyd (2018) had previously used fluorescent spectroscopy to observe bacteria grown on similarly prepared metal‐oxide coated slides; however, their study did not use in situ soil conditions but instead used cultured Geobacter sulfurreducens . Material removed from our slide surfaces contained trace amounts of DNA, but it was present in insufficient quantities to amplify and sequence.…”

Section: Resultsmentioning

confidence: 99%

Macro and microscopic visual imaging tools to investigate metal reducing bacteria in soils

Scott

Baldwin

Yarwood

et al. 2021

Soil Science Soc of Amer J

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Indicator of Reduction In Soils (IRIS) technology is an important tool for identifying hydric soils, but it does not allow the user to monitor in real time. IRIS uses metal‐oxide coatings on a polyvinyl chloride surface that, under anaerobic conditions, are removed to varying degrees over a 4‐wk incubation period, during which time the user is not cognizant of the outcome. We document the viability of an alternative IRIS approach using clear‐IRIS tubes, made from cellulose acetate butyrate, that can be continuously monitored in situ with a Wi‐Fi–enabled video camera. This work shows that IRIS and clear‐IRIS tubes are statistically equivalent. Manganese‐oxide coated clear‐IRIS tubes correlated well with IRIS tubes (r = .79) and ferrous‐oxide had a high correlation (r = .97). A time‐series analysis showed that rain‐driven soil saturation induced IRIS metal‐oxide reduction and controlled the rate. Clear‐IRIS tubes enable remote sensing of metal‐oxide removal over time.

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Section: Resultsmentioning

confidence: 99%

Macro and microscopic visual imaging tools to investigate metal reducing bacteria in soils

Scott

Baldwin

Yarwood

et al. 2021

Soil Science Soc of Amer J

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“…The use of G. sulfurreducens enables relatively good control of Hg speciation and its availability for cellular uptake, because it is incapable of sulfate reduction, thus, minimizing the formation of sulfides during the assay (Schaefer and Morel, 2009). Notably, G. sulfurreducens forms biofilms in a variety of settings including iron minerals (Reguera et al, 2007;Wilkins et al, 2007;Downie et al, 2018;Newsome et al, 2018), poised electrodes (Steidl et al, 2016;Li et al, 2017;Chadwick et al, 2019), and glass (Reguera et al, 2007;Klimes et al, 2010;Cologgi et al, 2014;Richter et al, 2017), making it a promising model organism for studying Hg methylation in bacterial biofilms.…”

Section: Introductionmentioning

confidence: 99%

Methylmercury formation in biofilms of Geobacter sulfurreducens

et al. 2023

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IntroductionMercury (Hg) is a major environmental pollutant that accumulates in biota predominantly in the form of methylmercury (MeHg). Surface-associated microbial communities (biofilms) represent an important source of MeHg in natural aquatic systems. In this work, we report MeHg formation in biofilms of the iron-reducing bacterium Geobacter sulfurreducens.MethodsBiofilms were prepared in media with varied nutrient load for 3, 5, or 7 days, and their structural properties were characterized using confocal laser scanning microscopy, cryo-scanning electron microscopy and Fourier-transform infrared spectroscopy.ResultsBiofilms cultivated for 3 days with vitamins in the medium had the highest surface coverage, and they also contained abundant extracellular matrix. Using 3 and 7-days-old biofilms, we demonstrate that G. sulfurreducens biofilms prepared in media with various nutrient load produce MeHg, of which a significant portion is released to the surrounding medium. The Hg methylation rate constant determined in 6-h assays in a low-nutrient assay medium with 3-days-old biofilms was 3.9 ± 2.0 ∙ 10−14 L ∙ cell−1 ∙ h−1, which is three to five times lower than the rates found in assays with planktonic cultures of G. sulfurreducens in this and previous studies. The fraction of MeHg of total Hg within the biofilms was, however, remarkably high (close to 50%), and medium/biofilm partitioning of inorganic Hg (Hg(II)) indicated low accumulation of Hg(II) in biofilms.DiscussionThese findings suggest a high Hg(II) methylation capacity of G. sulfurreducens biofilms and that Hg(II) transfer to the biofilm is the rate-limiting step for MeHg formation in this systems.

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“…Crystalline Fe(III) (oxyhydr)oxides have low solubility at circumneutral pH values, which limits the bioavailability and therefore the extent of microbial Fe(III) reduction. Fe(III)-metabolizing bacteria, however, have evolved strategies to access the poorly soluble electron acceptors, such as direct cell-mineral contact, conductive pili (nanowires), release of chelating compounds to solubilize iron, or via extracellular electron shuttles that facilitate the transfer of electrons to the solid. − Electron shuttles such as natural organic matter and humic substances are present in natural environments and can accelerate Fe(III) (oxyhydr)oxide reduction . However, the electron transfer from electron shuttle substances to Fe(III) minerals represents the rate-limiting step in microbial Fe(III) mineral reduction via electron shuttles .…”

Section: Introductionmentioning

confidence: 99%

Mineral Defects Enhance Bioavailability of Goethite toward Microbial Fe(III) Reduction

Notini

Byrne

Tomaszewski

et al. 2019

Environ. Sci. Technol.

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Surface defects have been shown to facilitate electron transfer between Fe(II) and goethite (α-FeOOH) in abiotic systems. It is unclear, however, whether defects also facilitate microbial goethite reduction in anoxic environments where electron transfer between cells and Fe(III) minerals is the limiting factor. Here, we used stable Fe isotopes to differentiate microbial reduction of goethite synthesized by hydrolysis from reduction of goethite that was further hydrothermally treated to remove surface defects. The goethites were reduced by Geobacter sulfurreducens in the presence of an external electron shuttle, and we used ICP-MS to distinguish Fe(II) produced from the reduction of the two types of goethite. When reduced separately, goethite with more defects has an initial rate of Fe(III) reduction about 2-fold higher than goethite containing fewer defects. However, when reduced together, the initial rate of reduction is 6-fold higher for goethite with more defects. Our results suggest that there is a suppression of the reduction of goethite with fewer defects in favor of the reduction of minerals with more defects. In the environment, minerals are likely to contain defects and our data demonstrates that even small changes at the surface of iron minerals may change their bioavailability and determine which minerals will be reduced.

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Imaging redox activity and Fe(II) at the microbe-mineral interface during Fe(III) reduction

Cited by 11 publications

References 54 publications

Macro and microscopic visual imaging tools to investigate metal reducing bacteria in soils

Macro and microscopic visual imaging tools to investigate metal reducing bacteria in soils

Methylmercury formation in biofilms of Geobacter sulfurreducens

Mineral Defects Enhance Bioavailability of Goethite toward Microbial Fe(III) Reduction

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