Dataset Information

Transient O₂ pulses direct Fe crystallinity and Fe(III)-reducer gene expression within a soil microbiome.

ABSTRACT:

Background

Many environments contain redox transition zones, where transient oxygenation events can modulate anaerobic reactions that influence the cycling of iron (Fe) and carbon (C) on a global scale. In predominantly anoxic soils, this biogeochemical cycling depends on Fe mineral composition and the activity of mixed Fe(III)-reducer populations that may be altered by periodic pulses of molecular oxygen (O₂).

Methods

We repeatedly exposed anoxic (4% H₂:96% N₂) suspensions of soil from the Luquillo Critical Zone Observatory to 1.05 × 10², 1.05 × 10³, and 1.05 × 10⁴ mmol O₂ kg^-1 soil h^-1 during pulsed oxygenation treatments. Metatranscriptomic analysis and ⁵⁷Fe Mössbauer spectroscopy were used to investigate changes in Fe(III)-reducer gene expression and Fe(III) crystallinity, respectively.

Results

Slow oxygenation resulted in soil Fe-(oxyhydr)oxides of higher crystallinity (38.1 ± 1.1% of total Fe) compared to fast oxygenation (30.6 ± 1.5%, P < 0.001). Transcripts binning to the genomes of Fe(III)-reducers Anaeromyxobacter, Geobacter, and Pelosinus indicated significant differences in extracellular electron transport (e.g., multiheme cytochrome c, multicopper oxidase, and type-IV pilin gene expression), adhesion/contact (e.g., S-layer, adhesin, and flagellin gene expression), and selective microbial competition (e.g., bacteriocin gene expression) between the slow and fast oxygenation treatments during microbial Fe(III) reduction. These data also suggest that diverse Fe(III)-reducer functions, including cytochrome-dependent extracellular electron transport, are associated with type-III fibronectin domains. Additionally, the metatranscriptomic data indicate that Methanobacterium was significantly more active in the reduction of CO₂ to CH₄ and in the expression of class(III) signal peptide/type-IV pilin genes following repeated fast oxygenation compared to slow oxygenation.

Conclusions

This study demonstrates that specific Fe(III)-reduction mechanisms in mixed Fe(III)-reducer populations are uniquely sensitive to the rate of O₂ influx, likely mediated by shifts in soil Fe(III)-(oxyhydr)oxide crystallinity. Overall, we provide evidence that transient oxygenation events play an important role in directing anaerobic pathways within soil microbiomes, which is expected to alter Fe and C cycling in redox-dynamic environments.

SUBMITTER: Wilmoth JL

PROVIDER: S-EPMC6199725 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Transient O<sub>2</sub> pulses direct Fe crystallinity and Fe(III)-reducer gene expression within a soil microbiome.

Wilmoth Jared Lee JL Moran Mary Ann MA Thompson Aaron A

Microbiome 20181023 1

<h4>Background</h4>Many environments contain redox transition zones, where transient oxygenation events can modulate anaerobic reactions that influence the cycling of iron (Fe) and carbon (C) on a global scale. In predominantly anoxic soils, this biogeochemical cycling depends on Fe mineral composition and the activity of mixed Fe(III)-reducer populations that may be altered by periodic pulses of molecular oxygen (O<sub>2</sub>).<h4>Methods</h4>We repeatedly exposed anoxic (4% H<sub>2</sub>:96% ...[more]

PMID: 30352628

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Project description:In anoxic subsurface environments, low Fe(III) bioaccessibility greatly limits in situ biodegradation of petroleum hydrocarbons (PHCs). Ferric ammonium citrate is a soluble compound that has the potential to increase the bioaccessibility of Fe(III). However, in neutral to alkaline environments, Fe(III) hydrolysis can produce Fe(III) (oxyhydr)oxides that may subsequently transform or recrystallize to relatively stable and less bioaccessible phases. Accordingly, the objective of this study was to elucidate the transformation and fate of Fe(III) contributed by ferric ammonium citrate in a gasoline-contaminated subsurface environment that was undergoing in situ bioremediation. Ferric ammonium citrate, together with sodium tripolyphosphate, magnesium sulphate, and nitric acid, was continuously injected into the contaminated groundwater for about 22 weeks. Colloids in the groundwater (solid particles retained on a 0.45 μ m filter) and soil cores were collected from the site. Fe speciation in these samples was characterized using X-ray absorption near edge structure (XANES) and Fourier transform infrared (FTIR) spectroscopy. The groundwater colloids (GWCs) contained mostly octahedrally coordinated Fe(III), but the subsoils contained both octahedrally coordinated Fe(III) and Fe(II). The fraction of Fe(II) in the subsoils generally increased after about 22 weeks of continuous amendment injection. Ferric ammonium citrate did not persist in the PHC-contaminated subsurface: the Fe(III) it contained was transformed to solid phases. Fe(III)-organic-matter (Fe(III)-OM) complex/coprecipitate and sulfate green rust were the major phases present in the GWCs; akaganeite, chloride green rust, vivianite, ferrihydrite, Fe(III)-silicate, and magnetite were present as minor phases. The subsoils contained three major phases: Fe(III)-OM complex/coprecipitate, magnetite, and calcium ferric silicate. The presence of major Fe(II) phases in the subsoils strongly indicate that secondary Fe(III) phases (especially Fe(III)-OM complex/coprecipitate) served as terminal electron acceptors during the microbial degradation of PHCs in the contaminated subsurface.

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Dataset Information

Transient O₂ pulses direct Fe crystallinity and Fe(III)-reducer gene expression within a soil microbiome.

Background

Methods

Results

Conclusions

Publications

Transient O<sub>2</sub> pulses direct Fe crystallinity and Fe(III)-reducer gene expression within a soil microbiome.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

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Dataset Information

Transient O2 pulses direct Fe crystallinity and Fe(III)-reducer gene expression within a soil microbiome.

Background

Methods

Results

Conclusions

Publications

Transient O<sub>2</sub> pulses direct Fe crystallinity and Fe(III)-reducer gene expression within a soil microbiome.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Transient O₂ pulses direct Fe crystallinity and Fe(III)-reducer gene expression within a soil microbiome.