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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-292
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-292
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  31 Jul 2020

31 Jul 2020

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This preprint is currently under review for the journal BG.

Biogeochemical Impact of Cable Bacteria on Coastal Black Sea Sediment

Martijn Hermans1, Nils Risgaard-Petersen2,3, Filip J. R. Meysman4,5, and Caroline P. Slomp1 Martijn Hermans et al.
  • 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O Box 80021, 3508 TA Utrecht, the Netherlands
  • 2Center for Geomicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
  • 3Center for Electromicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
  • 4Center of Excellence for Microbial Systems Technology, Department of Biology, University of Antwerp, Wilrijk, Belgium
  • 5Department of Biotechnology, Delft University of Technology, Delft, the Netherlands

Abstract. Cable bacteria can strongly alter sediment biogeochemistry. Here, we used laboratory incubations to assess whether cable bacteria can establish in iron (Fe) monosulphide-poor coastal Black Sea sediment and to determine the impact of their activity on the cycling of Fe, phosphorus (P) and sulphur (S). Microsensor depth profiles of oxygen, sulphide and pH in combination with electric potential profiling and FISH analyses showed a rapid development (< 5 days) of cable bacteria, followed by a long period of activity (> 200 days). During most of the experiment, the current density correlated linearly with the oxygen demand. Sediment oxygen uptake was attributed to activity of cable bacteria and the oxidation of reduced products from anaerobic degradation of organic matter, such as ammonium. Pore water sulphide was low (< 5 μM) throughout the experiment. Sulphate reduction acted as the main source of sulphide for cable bacteria. Pore water Fe2+ reached levels of up to 1.7 mM during the incubations, due to the dissolution of FeS (30 %) and siderite, an Fe carbonate mineral (70 %). Following upward diffusion of Fe2+, a surface enrichment of Fe oxides formed. Hence, besides FeS, siderite may act as a major source of Fe for Fe oxides in coastal surface sediments where cable bacteria are active. Using µXRF, we show that the enrichments in Fe oxides induced by cable bacteria are located in a thin subsurface layer of 0.3 mm. We show that similar subsurface layers enriched in Fe and P are also observed at field sites where cable bacteria were recently active and little bioturbation occurs. This suggests that such subsurface Fe oxide layers, which are not always visible to the eye, could potentially be a marker for recent activity of cable bacteria.

Martijn Hermans et al.

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Martijn Hermans et al.

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Short summary
This manuscript demonstrates that the recently discovered cable bacteria are capable of using a mineral, known as siderite, as a source for the formation of iron oxides. This work also demonstrates that the activity of cable bacteria can lead to a distinct subsurface layer in the sediment that can be used as a marker for their activity.
This manuscript demonstrates that the recently discovered cable bacteria are capable of using a...
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