title: Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment.
abstract: Filamentous bacteria of the Desulfobulbaceae family can conduct electrons over centimeter-long distances thereby coupling oxygen reduction at the surface of marine sediment to sulfide oxidation in deeper anoxic layers. The ability of these cable bacteria to use alternative electron acceptors is currently unknown. Here we show that these organisms can use also nitrate or nitrite as an electron acceptor thereby coupling the reduction of nitrate to distant oxidation of sulfide. Sulfidic marine sediment was incubated with overlying nitrate-amended anoxic seawater. Within 2 months, electric coupling of spatially segregated nitrate reduction and sulfide oxidation was evident from: (1) the formation of a 4-6-mm-deep zone separating sulfide oxidation from the associated nitrate reduction, and (2) the presence of pH signatures consistent with proton consumption by cathodic nitrate reduction, and proton production by anodic sulfide oxidation. Filamentous Desulfobulbaceae with the longitudinal structures characteristic of cable bacteria were detected in anoxic, nitrate-amended incubations but not in anoxic, nitrate-free controls. Nitrate reduction by cable bacteria using long-distance electron transport to get privileged access to distant electron donors is a hitherto unknown mechanism in nitrogen and sulfur transformations, and the quantitative importance for elements cycling remains to be addressed.
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Ugo
authors.initials: U
authors.lastname: Marzocchi
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Daniela
authors.initials: D
authors.lastname: Trojan
authors.affiliation: 1] Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark [2] Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Steffen
authors.initials: S
authors.lastname: Larsen
authors.affiliation: 1] Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark [2] Interdisciplinary Nanoscience Center, Aarhus University, Aarhus, Denmark.
authors.forename: Rikke Louise
authors.initials: RL
authors.lastname: Meyer
authors.affiliation: 1] Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark [2] Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark.
authors.forename: Niels Peter
authors.initials: NP
authors.lastname: Revsbech
authors.affiliation: 1] Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark [2] Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schramm
authors.affiliation: 1] Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark [2] Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Lars Peter
authors.initials: LP
authors.lastname: Nielsen
authors.affiliation: 1] Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark [2] Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Nils
authors.initials: N
authors.lastname: Risgaard-Petersen
mesh_terms: D020564:Deltaproteobacteria / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*; D004583:Electrons; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology*; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D012623:Seawater / Q000737:chemistry; D013440:Sulfides / Q000378:metabolism*; D013455:Sulfur / Q000378:metabolism
chemical_list: D009566:Nitrates; D009573:Nitrites; D013440:Sulfides; D013455:Sulfur; D010100:Oxygen