title: Diversity of freshwater Epsilonproteobacteria and dark inorganic carbon fixation in the sulphidic redoxcline of a meromictic karstic lake.
abstract: Sulfidic redoxclines are a suitable niche for the growth and activity of different chemo- and photolithotrophic sulphide-oxidizing microbial groups such as the Epsilonproteobacteria and the green sulfur bacteria (GSB). We have investigated the diversity, abundance and contribution to inorganic carbon uptake of Epsilonproteobacteria in a meromictic basin of Lake Banyoles. CARD-FISH counts revealed that Epsilonproteobacteria were prevalent at the redoxcline in winter (maximum abundance of 2 × 10(6) cells mL(-1), ≈60% of total cells) but they were nearly absent in summer, when GSB bloomed. This seasonal trend was supported by 16S rRNA gene pyrotag datasets, which revealed that the epsilonproteobacterial community was mainly composed of a member of the genus Arcobacter. In situ incubations using NaH(14)CO3 and MAR-CARD-FISH observations showed that this population assimilated CO2 in the dark, likely being mainly responsible for the autotrophic activity at the redoxcline in winter. Clone libraries targeting the aclB gene provided additional evidence of the potential capacity of these epsilonproteobacteria to fix carbon via rTCA cycle. Our data reinforce the key role of Epsilonproteobacteria in linking carbon and sulphur cycles, extend their influence to freshwater karstic lakes and raise questions about the actual contribution of chemolithotrophy at their redoxcline and euxinic water compartments.
authors.affiliation: Group of Molecular Microbial Ecology, Institute of Aquatic Ecology, Universitat de Girona, Campus de Montilivi, E-17071 Girona, Spain.
authors.forename: Imma
authors.initials: I
authors.lastname: Noguerola
authors.affiliation: Cavanilles Institute for Biodiversity and Evolutionary Biology and Department of Microbiology and Ecology, Edificio de Investigación 'Jeroni Muñoz', Campus de Burjassot, Universitat de Valencia, E-46100, Burjassot, Valencia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Picazo
authors.affiliation: Université Catholique de Louvain, Institut des Sciences de la Vie, Place Croix du Sud, 4/5 L07.07.06, B-1348 Louvain-La-Neuve, Belgium.
authors.forename: Marc
authors.initials: M
authors.lastname: Llirós
authors.affiliation: Cavanilles Institute for Biodiversity and Evolutionary Biology and Department of Microbiology and Ecology, Edificio de Investigación 'Jeroni Muñoz', Campus de Burjassot, Universitat de Valencia, E-46100, Burjassot, Valencia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Camacho
authors.affiliation: Group of Molecular Microbial Ecology, Institute of Aquatic Ecology, Universitat de Girona, Campus de Montilivi, E-17071 Girona, Spain Water Quality and Microbial Diversity, Catalan Institute for Water Research (ICRA), H2O Building, Scientific and Technological Park of the University of Girona, Emili Grahit 101, E-17003 Girona, Spain cborrego@icra.cat.
authors.forename: Carles M
authors.initials: CM
authors.lastname: Borrego
mesh_terms: D020640:Arcobacter / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D052818:Autotrophic Processes / Q000502:physiology; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism*; D019414:Chlorobi / Q000235:genetics / Q000378:metabolism*; D005618:Fresh Water / Q000382:microbiology; D017404:In Situ Hybridization, Fluorescence; D060106:Lakes / Q000382:microbiology; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D012336:RNA, Ribosomal, 16S; D002245:Carbon Dioxide; D002244:Carbon
keywords: Arcobacter; Epsilonproteobacteria; Green Sulfur Bacteria; dark inorganic carbon fixation; euxinic waters; karstic lakes; sulphidic redoxclines