title: Nitrotoga-like bacteria are previously unrecognized key nitrite oxidizers in full-scale wastewater treatment plants.
abstract: Numerous past studies have shown members of the genus Nitrospira to be the predominant nitrite-oxidizing bacteria (NOB) in nitrifying wastewater treatment plants (WWTPs). Only recently, the novel NOB 'Candidatus Nitrotoga arctica' was identified in permafrost soil and a close relative was enriched from activated sludge. Still, little is known about diversity, distribution and functional importance of Nitrotoga in natural and engineered ecosystems. Here we developed Nitrotoga 16S rRNA-specific PCR primers and fluorescence in situ hybridization (FISH) probes, which were applied to screen activated sludge samples from 20 full-scale WWTPs. Nitrotoga-like bacteria were detected by PCR in 11 samples and reached abundances detectable by FISH in seven sludges. They coexisted with Nitrospira in most of these WWTPs, but constituted the only detectable NOB in two systems. Quantitative FISH revealed that Nitrotoga accounted for nearly 2% of the total bacterial community in one of these plants, a number comparable to Nitrospira abundances in other WWTPs. Spatial statistics revealed that Nitrotoga coaggregated with ammonia-oxidizing bacteria, strongly supporting a functional role in nitrite oxidation. This activity was confirmed by FISH in combination with microradiography, which revealed nitrite-dependent autotrophic carbon fixation by Nitrotoga in situ. Correlation of the presence or absence with WWTP operational parameters indicated low temperatures as a main factor supporting high Nitrotoga abundances, although in incubation experiments these NOB remained active over an unexpected range of temperatures, and also at different ambient nitrite concentrations. In conclusion, this study demonstrates that Nitrotoga can be functionally important nitrite oxidizers in WWTPs and can even represent the only known NOB in engineered systems.
authors.affiliation: Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Lücker
authors.affiliation: Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria.
authors.forename: Jasmin
authors.initials: J
authors.lastname: Schwarz
authors.affiliation: Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria.
authors.forename: Christiane
authors.initials: C
authors.lastname: Gruber-Dorninger
authors.affiliation: University of Hamburg, Biocenter Klein Flottbek, Microbiology and Biotechnology, Hamburg, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Spieck
authors.affiliation: Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Wagner
authors.affiliation: Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria.
authors.forename: Holger
authors.initials: H
authors.lastname: Daims
mesh_terms: D000641:Ammonia / Q000378:metabolism; D052837:Chemoautotrophic Growth; D017931:DNA Primers; D043372:Gallionellaceae / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D009573:Nitrites / Q000378:metabolism*; D010084:Oxidation-Reduction; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012722:Sewage / Q000382:microbiology*; D064091:Waste Disposal Facilities
chemical_list: D017931:DNA Primers; D009573:Nitrites; D012336:RNA, Ribosomal, 16S; D012722:Sewage; D000641:Ammonia