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ORIGINAL RESEARCH article

Front. Microbiol.
Sec. Terrestrial Microbiology
Volume 16 - 2025 | doi: 10.3389/fmicb.2025.1504111

Decoupling microbial iron reduction from anoxic microsite formation in oxic sediments: a microscale investigation through microfluidic models

Provisionally accepted
Giulia Ceriotti Giulia Ceriotti 1*Alice Bosco Santos Alice Bosco Santos 1Sergey Borisov Sergey Borisov 2Jasmine Sofia Berg Jasmine Sofia Berg 1
  • 1 Université de Lausanne, Lausanne, Switzerland
  • 2 Graz University of Technology, Graz, Styria, Austria

The final, formatted version of the article will be published soon.

    Iron (Fe) reduction is one of the oldest microbial processes on Earth. After the atmosphere and ocean became oxygenated, this anaerobic process was relegated to niche anoxic environments. However, evidence of Fe reduction in oxic, partially saturated subsurface systems, such as soils and vadose zones, has been reported, with the common explanation being the formation of anoxic microsites that remain undetected by bulk measurements. To explore how microscale oxygen concentrations regulate microbial Fe reduction, we cultivated a facultative Fe-reducing bacterium using a microfluidic setup integrated with transparent planar oxygen sensors. Contrary to expectations, Fe reduction occurred under fully oxic conditions, without the formation of anoxic microsites. Our results suggest that microbially-mediated Fe-reduction could be more widespread in oxic subsurface environments than previously assumed. Moreover, our mathematical modeling of oxygen dynamics around biomass-rich layers revealed that the onset of anoxia is mainly controlled by biomass spatial organization rather than the conventionally used water saturation index. This opens a new perspective on the proxies needed to predict anoxic microsite formation and Fe(III) reduction occurrence.

    Keywords: Iron reduction, Oxygen, Microfluidics, Planar sensors, Diffusion, Shewanella oneidensis, anoxic microsites

    Received: 30 Sep 2024; Accepted: 06 Jan 2025.

    Copyright: © 2025 Ceriotti, Bosco Santos, Borisov and Berg. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Giulia Ceriotti, Université de Lausanne, Lausanne, Switzerland

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