title: Enrichment of DNRA bacteria in a continuous culture.
abstract: Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are competing microbial nitrate-reduction processes. The occurrence of DNRA has been shown to be effected qualitatively by various parameters in the environment. A more quantitative understanding can be obtained using enrichment cultures in a laboratory reactor, yet no successful DNRA enrichment culture has been described. We showed that a stable DNRA-dominated enrichment culture can be obtained in a chemostat system. The enrichment was based on the hypothesis that nitrate limitation is the dominant factor in selecting for DNRA. First, a conventional denitrifying culture was enriched from activated sludge, with acetate and nitrate as substrates. Next, the acetate concentration in the medium was increased to obtain nitrate-limiting conditions. As a result, conversions shifted from denitrification to DNRA. In this selection of a DNRA culture, two important factors were the nitrate limitation and a relatively low dilution rate (0.026 h(-1)). The culture was a highly enriched population of Deltaproteobacteria most closely related to Geobacter lovleyi, based on 16S rRNA gene sequencing (97% similarity). We established a stable and reproducible cultivation method for the enrichment of DNRA bacteria in a continuously operated reactor system. This enrichment method allows to further investigate the DNRA process and address the factors for competition between DNRA and denitrification, or other N-conversion pathways.
authors.affiliation: Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.
authors.forename: Eveline M
authors.initials: EM
authors.lastname: van den Berg
authors.affiliation: Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.
authors.forename: Udo
authors.initials: U
authors.lastname: van Dongen
authors.affiliation: Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.
authors.forename: Ben
authors.initials: B
authors.lastname: Abbas
authors.affiliation: Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.
authors.forename: Mark Cm
authors.initials: MC
authors.lastname: van Loosdrecht
mesh_terms: D000085:Acetates / Q000378:metabolism; D064751:Ammonium Compounds; D001419:Bacteria / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D061249:Batch Cell Culture Techniques / Q000379:methods*; D019149:Bioreactors; D058440:Denitrification / Q000502:physiology*; D009566:Nitrates / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012722:Sewage / Q000382:microbiology
chemical_list: D000085:Acetates; D064751:Ammonium Compounds; D009566:Nitrates; D012336:RNA, Ribosomal, 16S; D012722:Sewage