title: Denitrifying bacterial communities affect current production and nitrous oxide accumulation in a microbial fuel cell.
abstract: The biocathodic reduction of nitrate in Microbial Fuel Cells (MFCs) is an alternative to remove nitrogen in low carbon to nitrogen wastewater and relies entirely on microbial activity. In this paper the community composition of denitrifiers in the cathode of a MFC is analysed in relation to added electron acceptors (nitrate and nitrite) and organic matter in the cathode. Nitrate reducers and nitrite reducers were highly affected by the operational conditions and displayed high diversity. The number of retrieved species-level Operational Taxonomic Units (OTUs) for narG, napA, nirS and nirK genes was 11, 10, 31 and 22, respectively. In contrast, nitrous oxide reducers remained virtually unchanged at all conditions. About 90% of the retrieved nosZ sequences grouped in a single OTU with a high similarity with Oligotropha carboxidovorans nosZ gene. nirS-containing denitrifiers were dominant at all conditions and accounted for a significant amount of the total bacterial density. Current production decreased from 15.0 A · m(-3) NCC (Net Cathodic Compartment), when nitrate was used as an electron acceptor, to 14.1 A · m(-3) NCC in the case of nitrite. Contrarily, nitrous oxide (N2O) accumulation in the MFC was higher when nitrite was used as the main electron acceptor and accounted for 70% of gaseous nitrogen. Relative abundance of nitrite to nitrous oxide reducers, calculated as (qnirS+qnirK)/qnosZ, correlated positively with N2O emissions. Collectively, data indicate that bacteria catalysing the initial denitrification steps in a MFC are highly influenced by main electron acceptors and have a major influence on current production and N2O accumulation.
authors.affiliation: Molecular Microbial Ecology Group, Institute of Aquatic Ecology, Universitat de Girona, Girona, Spain.
authors.forename: Ariadna
authors.initials: A
authors.lastname: Vilar-Sanz
authors.forename: Sebastià
authors.initials: S
authors.lastname: Puig
authors.forename: Arantzazu
authors.initials: A
authors.lastname: García-Lledó
authors.forename: Rosalia
authors.initials: R
authors.lastname: Trias
authors.forename: M Dolors
authors.initials: MD
authors.lastname: Balaguer
authors.forename: Jesús
authors.initials: J
authors.lastname: Colprim
authors.forename: Lluís
authors.initials: L
authors.lastname: Bañeras
mesh_terms: D001674:Bioelectric Energy Sources / Q000382:microbiology*; D018441:Biofilms; D058440:Denitrification; D004566:Electrodes; D018628:Gene Dosage; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D009609:Nitrous Oxide / Q000378:metabolism*; D020560:Proteobacteria / Q000145:classification / Q000235:genetics / Q000502:physiology*; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D012336:RNA, Ribosomal, 16S; D009609:Nitrous Oxide