title: Coexistence of Microaerophilic, Nitrate-Reducing, and Phototrophic Fe(II) Oxidizers and Fe(III) Reducers in Coastal Marine Sediment.
abstract: Iron is abundant in sediments, where it can be biogeochemically cycled between its divalent and trivalent redox states. The neutrophilic microbiological Fe cycle involves Fe(III)-reducing and three different physiological groups of Fe(II)-oxidizing microorganisms, i.e., microaerophilic, anoxygenic phototrophic, and nitrate-reducing Fe(II) oxidizers. However, it is unknown whether all three groups coexist in one habitat and how they are spatially distributed in relation to gradients of O2, light, nitrate, and Fe(II). We examined two coastal marine sediments in Aarhus Bay, Denmark, by cultivation and most probable number (MPN) studies for Fe(II) oxidizers and Fe(III) reducers and by quantitative-PCR (qPCR) assays for microaerophilic Fe(II) oxidizers. Our results demonstrate the coexistence of all three metabolic types of Fe(II) oxidizers and Fe(III) reducers. In qPCR, microaerophilic Fe(II) oxidizers (Zetaproteobacteria) were present with up to 3.2 × 10(6) cells g dry sediment(-1). In MPNs, nitrate-reducing Fe(II) oxidizers, anoxygenic phototrophic Fe(II) oxidizers, and Fe(III) reducers reached cell numbers of up to 3.5 × 10(4), 3.1 × 10(2), and 4.4 × 10(4) g dry sediment(-1), respectively. O2 and light penetrated only a few millimeters, but the depth distribution of the different iron metabolizers did not correlate with the profile of O2, Fe(II), or light. Instead, abundances were homogeneous within the upper 3 cm of the sediment, probably due to wave-induced sediment reworking and bioturbation. In microaerophilic Fe(II)-oxidizing enrichment cultures, strains belonging to the Zetaproteobacteria were identified. Photoferrotrophic enrichments contained strains related to Chlorobium and Rhodobacter; the nitrate-reducing Fe(II) enrichments contained strains related to Hoeflea and Denitromonas. This study shows the coexistence of all three types of Fe(II) oxidizers in two near-shore marine environments and the potential for competition and interrelationships between them.
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Laufer
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Nordhoff
authors.affiliation: Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Røy
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
authors.forename: Caroline
authors.initials: C
authors.lastname: Schmidt
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.|Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Behrens
authors.affiliation: Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Bo Barker
authors.initials: BB
authors.lastname: Jørgensen
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany andreas.kappler@uni-tuebingen.de.|Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kappler
mesh_terms: D000332:Aerobiosis; D001419:Bacteria / Q000145:classification / Q000302:isolation & purification*; D058448:Biota; D003718:Denmark; D005290:Ferric Compounds / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism*; D019015:Geologic Sediments / Q000382:microbiology*; D009566:Nitrates / Q000378:metabolism*; D010084:Oxidation-Reduction; D052817:Phototrophic Processes; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D009566:Nitrates