Iron-oxidizer hotspots formed by intermittent oxic–anoxic fluid mixing in fractured rocks

Bochet, Olivier; Béthencourt, Lorine; Dufresne, Alexis; Farasin, Julien; Pédrot, Mathieu; Labasque, Thierry; Chatton, Eliot; Lavenant, Nicolas; Petton, Christophe; Abbott, Benjamin W.; Aquilina, Luc; Borgne, Tanguy Le

doi:10.1038/s41561-019-0509-1

Cited by 64 publications

(71 citation statements)

References 53 publications

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“…At the time of this study, a rust-coloured microbial mat profusely covered the internal wall of the borehole from the surface down to 60m depth (Bochet et al, 2020). Below this depth, the internal wall was bare with only traces of the mat in front of the fractures.…”

Section: Site Descriptionmentioning

confidence: 92%

“…The weathered zone, which is actively recharged, presentsrecent (apparent age ranging from 10 to 20 years), oxygenated groundwater, whereas the deeper fractured area is characterized by ancient (apparent age of about 100 years), anoxic, iron-rich groundwater. The presence of highly-dipping fractures enables mixing of oxygenated and reduced fluids, at fracture intersections, and the connections between the two zones (Touchard, 1998;Bochet et al 2020). The productivity of the fractures triggering oxygenated groundwater, and therefore the mixing conditions, vary over time.…”

Section: Site Descriptionmentioning

confidence: 99%

“…2). Samples collected in F54/59 were also characterized by higher ChloroFluoroCarbone concentrations (Bochet et al 2020) indicating groundwater with a short residence time (Ayraud et al 2008;Roques et al 2014). This trend is in accordance with an upward flux of reduced groundwater that becomes more oxidizing with the contribution of more oxygenated fluids produced by the fractures crossing the borehole.…”

Section: Hydrological and Chemical Characterizationmentioning

confidence: 99%

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Genome reconstruction reveals distinct assemblages of Gallionellaceae in surface and subsurface redox transition zones

Béthencourt

Bochet

Farasin

et al. 2020

FEMS Microbiology Ecology

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Fe-oxidizing bacteria of the family Gallionellaceae are major players in the Fe biogeochemical cycle in freshwater. These bacteria thrive in redox transition zones where they benefit from both high Fe concentrations and microaerobic conditions. We analysed the Gallionellaceae genomic diversity in an artesian hard-rock aquifer where redox transition zones develop (i) in the subsurface, where ancient, reduced groundwater mixes with recent oxygenated groundwater, and (ii) at the surface, where groundwater reaches the open air. A total of 15 new draft genomes of Gallionellaceae representing to 11 candidate genera were recovered from the two redox transition zones. Sulfur oxidation genes were encoded in most genomes while denitrification genes were much less represented. One genus dominated microbial communities belowground and we propose to name it ‘Candidatus Houarnoksidobacter’. The two transition zones were populated by completely different assemblages of Gallionellaceae despite the almost constant upward circulation of groundwater between the two zones. The processes leading to redox transition zones, oxygen diffusion at the surface or groundwater mixing in subsurface, appear to be a major driver of the Gallionellaceae diversity.

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Section: Site Descriptionmentioning

confidence: 92%

Section: Site Descriptionmentioning

confidence: 99%

Section: Hydrological and Chemical Characterizationmentioning

confidence: 99%

See 1 more Smart Citation

Genome reconstruction reveals distinct assemblages of Gallionellaceae in surface and subsurface redox transition zones

Béthencourt

Bochet

Farasin

et al. 2020

FEMS Microbiology Ecology

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“…porous media | reactive transport | chaotic mixing | chemical gradients F luid mixing in porous media plays a key role in a range of natural and industrial systems (1)(2)(3). In these confined environments, mixing enables or limits reactions controlling the degradation of contaminants in the subsurface; the cycles of biogeochemical elements such as nitrogen, iron, and carbon; and the sequestration of CO2 in deep reservoirs (4)(5)(6)(7)(8)(9)(10). Mixing also shapes the nutrient landscapes and chemical gradients seen by bacteria evolving in soils or medical systems (11,12) and facilitates chemical processes in drug delivery, packed bed reactors, flow batteries, or catalysts (13)(14)(15).…”

mentioning

confidence: 99%

Stretching and folding sustain microscale chemical gradients in porous media

Heyman

Lester

Turuban

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Fluid flow in porous media drives the transport, mixing, and reaction of molecules, particles, and microorganisms across a wide spectrum of natural and industrial processes. Current macroscopic models that average pore-scale fluctuations into an effective dispersion coefficient have shown significant limitations in the prediction of many important chemical and biological processes. Yet, it is unclear how three-dimensional flow in porous structures govern the microscale chemical gradients controlling these processes. Here, we obtain high-resolution experimental images of microscale mixing patterns in three-dimensional porous media and uncover an unexpected and general mixing mechanism that strongly enhances concentration gradients at pore-scale. Our experiments reveal that systematic stretching and folding of fluid elements are produced in the pore space by grain contacts, through a mechanism that leads to efficient microscale chaotic mixing. These insights form the basis for a general kinematic model linking chaotic-mixing rates in the fluid phase to the generic structural properties of granular matter. The model successfully predicts the resulting enhancement of pore-scale chemical gradients, which appear to be orders of magnitude larger than predicted by dispersive approaches. These findings offer perspectives for predicting and controlling the vast diversity of reactive transport processes in natural and synthetic porous materials, beyond the current dispersion paradigm.

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“…In fact, a number of bacterial taxa known to be aerophilic or microaerophilic, like Gallionellaceae were identified. This aspect suggests that Po Plain deep aquifers are not confined systems and element exchange might occur to a certain extent, as observed in other European aquifers (Bochet et al, 2020;Voisin et al, 2020).…”

Section: Discussionmentioning

confidence: 59%

Adaptation of Microbial Communities to Environmental Arsenic and Selection of Arsenite-Oxidizing Bacteria From Contaminated Groundwaters

et al. 2021

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Arsenic mobilization in groundwater systems is driven by a variety of functionally diverse microorganisms and complex interconnections between different physicochemical factors. In order to unravel this great ecosystem complexity, groundwaters with varying background concentrations and speciation of arsenic were considered in the Po Plain (Northern Italy), one of the most populated areas in Europe affected by metalloid contamination. High-throughput Illumina 16S rRNA gene sequencing, CARD-FISH and enrichment of arsenic-transforming consortia showed that among the analyzed groundwaters, diverse microbial communities were present, both in terms of diversity and functionality. Oxidized inorganic arsenic [arsenite, As(III)] was the main driver that shaped each community. Several uncharacterized members of the genus Pseudomonas, putatively involved in metalloid transformation, were revealed in situ in the most contaminated samples. With a cultivation approach, arsenic metabolisms potentially active at the site were evidenced. In chemolithoautotrophic conditions, As(III) oxidation rate linearly correlated to As(III) concentration measured at the parental sites, suggesting that local As(III) concentration was a relevant factor that selected for As(III)-oxidizing bacterial populations. In view of the exploitation of these As(III)-oxidizing consortia in biotechnology-based arsenic bioremediation actions, these results suggest that contaminated aquifers in Northern Italy host unexplored microbial populations that provide essential ecosystem services.

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Iron-oxidizer hotspots formed by intermittent oxic–anoxic fluid mixing in fractured rocks

Cited by 64 publications

References 53 publications

Genome reconstruction reveals distinct assemblages of Gallionellaceae in surface and subsurface redox transition zones

Genome reconstruction reveals distinct assemblages of Gallionellaceae in surface and subsurface redox transition zones

Stretching and folding sustain microscale chemical gradients in porous media

Adaptation of Microbial Communities to Environmental Arsenic and Selection of Arsenite-Oxidizing Bacteria From Contaminated Groundwaters

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