title: Cable Bacteria in Freshwater Sediments.
abstract: In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the freshwater stream Giber Å, Denmark, was incubated in the laboratory. After 2 weeks, pH signatures and electric fields indicated electron transfer between vertically separated anodic and cathodic half-reactions. Fluorescence in situ hybridization revealed the presence of Desulfobulbaceae filaments. In addition, in situ measurements of oxygen, pH, and electric potential distributions in the waterlogged banks of Giber Å demonstrated the presence of distant electric redox coupling in naturally occurring freshwater sediment. At the same site, filamentous Desulfobulbaceae with cable bacterium morphology were found to be present. Their 16S rRNA gene sequence placed them as a distinct sister group to the known marine cable bacteria, with the genus Desulfobulbus as the closest cultured lineage. The results of the present study indicate that electric currents mediated by cable bacteria could be important for the biogeochemistry in many more environments than anticipated thus far and suggest a common evolutionary origin of the cable phenotype within Desulfobulbaceae with subsequent diversification into a freshwater and a marine lineage.
authors.affiliation: Center for Geomicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark nils.risgaard-petersen@bios.au.dk.
authors.forename: Nils
authors.initials: N
authors.lastname: Risgaard-Petersen
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Kristiansen
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Rasmus B
authors.initials: RB
authors.lastname: Frederiksen
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Anders Lindequist
authors.initials: AL
authors.lastname: Dittmer
authors.affiliation: Center for Geomicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Jesper Tataru
authors.initials: JT
authors.lastname: Bjerg
authors.affiliation: Center for Geomicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Daniela
authors.initials: D
authors.lastname: Trojan
authors.affiliation: Center for Geomicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Schreiber
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Lars Riis
authors.initials: LR
authors.lastname: Damgaard
authors.affiliation: Center for Geomicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schramm
authors.affiliation: Center for Geomicrobiology, Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Lars Peter
authors.initials: LP
authors.lastname: Nielsen
mesh_terms: D020564:Deltaproteobacteria / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism; D004560:Electricity; D004579:Electron Transport; D005618:Fresh Water / Q000382:microbiology*; D019015:Geologic Sediments / Q000382:microbiology*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010802:Phylogeny; D013440:Sulfides / Q000378:metabolism
chemical_list: D013440:Sulfides; D010100:Oxygen