title: Cable bacteria generate a firewall against euxinia in seasonally hypoxic basins.
abstract: Seasonal oxygen depletion (hypoxia) in coastal bottom waters can lead to the release and persistence of free sulfide (euxinia), which is highly detrimental to marine life. Although coastal hypoxia is relatively common, reports of euxinia are less frequent, which suggests that certain environmental controls can delay the onset of euxinia. However, these controls and their prevalence are poorly understood. Here we present field observations from a seasonally hypoxic marine basin (Grevelingen, The Netherlands), which suggest that the activity of cable bacteria, a recently discovered group of sulfur-oxidizing microorganisms inducing long-distance electron transport, can delay the onset of euxinia in coastal waters. Our results reveal a remarkable seasonal succession of sulfur cycling pathways, which was observed over multiple years. Cable bacteria dominate the sediment geochemistry in winter, whereas, after the summer hypoxia, Beggiatoaceae mats colonize the sediment. The specific electrogenic metabolism of cable bacteria generates a large buffer of sedimentary iron oxides before the onset of summer hypoxia, which captures free sulfide in the surface sediment, thus likely preventing the development of bottom water euxinia. As cable bacteria are present in many seasonally hypoxic systems, this euxinia-preventing firewall mechanism could be widely active, and may explain why euxinia is relatively infrequently observed in the coastal ocean.
authors.affiliation: Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research, 4401 NT Yerseke, The Netherlands; dorina.seitaj@nioz.nl filip.meysman@nioz.nl.
authors.forename: Dorina
authors.initials: D
authors.lastname: Seitaj
authors.affiliation: Center for Microbiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark;
authors.forename: Regina
authors.initials: R
authors.lastname: Schauer
authors.affiliation: Department of Earth Sciences-Geochemistry, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands;
authors.forename: Fatimah
authors.initials: F
authors.lastname: Sulu-Gambari
authors.affiliation: Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research, 4401 NT Yerseke, The Netherlands;
authors.forename: Silvia
authors.initials: S
authors.lastname: Hidalgo-Martinez
authors.affiliation: Department of Analytical, Environmental, and Geochemistry, Vrije Universiteit Brussel, 1050 Brussels, Belgium.
authors.forename: Sairah Y
authors.initials: SY
authors.lastname: Malkin
authors.affiliation: Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research, 4401 NT Yerseke, The Netherlands;
authors.forename: Laurine D W
authors.initials: LD
authors.lastname: Burdorf
authors.affiliation: Department of Earth Sciences-Geochemistry, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands;
authors.forename: Caroline P
authors.initials: CP
authors.lastname: Slomp
authors.affiliation: Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research, 4401 NT Yerseke, The Netherlands; Department of Analytical, Environmental, and Geochemistry, Vrije Universiteit Brussel, 1050 Brussels, Belgium dorina.seitaj@nioz.nl filip.meysman@nioz.nl.
authors.forename: Filip J R
authors.initials: FJ
authors.lastname: Meysman
mesh_terms: D000693:Anaerobiosis; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology*; D007501:Iron / Q000032:analysis*; D008839:Microelectrodes; D009426:Netherlands; D010084:Oxidation-Reduction; D054712:Salinity; D012621:Seasons; D012623:Seawater / Q000737:chemistry*; D013440:Sulfides / Q000032:analysis*; D013696:Temperature; D041962:Thiotrichaceae / Q000378:metabolism*
chemical_list: D013440:Sulfides; D007501:Iron
keywords: cable bacteria; coastal hypoxia; microbial competition; sediment biogeochemistry; sulfur cycling