title: Unexpected Diversity and High Abundance of Putative Nitric Oxide Dismutase (Nod) Genes in Contaminated Aquifers and Wastewater Treatment Systems.
abstract: It has recently been suggested that oxygenic dismutation of NO into N2and O2may occur in the anaerobic methanotrophic "Candidatus Methylomirabilis oxyfera" and the alkane-oxidizing gammaproteobacterium HdN1. It may represent a new pathway in microbial nitrogen cycling catalyzed by a putative NO dismutase (Nod). The formed O2enables microbes to employ aerobic catabolic pathways in anoxic habitats, suggesting an ecophysiological niche space of substantial appeal for bioremediation and water treatment. However, it is still unknown whether this physiology is limited to "Ca Methylomirabilis oxyfera" and HdN1 and whether it can be coupled to the oxidation of electron donors other than alkanes. Here, we report insights into an unexpected diversity and remarkable abundance of nod genes in natural and engineered water systems. Phylogenetically diverse nod genes were recovered from a range of contaminated aquifers and N-removing wastewater treatment systems. Together with nod genes from "Ca Methylomirabilis oxyfera" and HdN1, the novel environmental nod sequences formed no fewer than 6 well-supported phylogenetic clusters, clearly distinct from canonical NO reductase (quinol-dependent NO reductase [qNor] and cytochrome c-dependent NO reductase [cNor]) genes. The abundance of nod genes in the investigated samples ranged from 1.6 × 107to 5.2 × 1010copies · g-1(wet weight) of sediment or sludge biomass, accounting for up to 10% of total bacterial 16S rRNA gene counts. In essence, NO dismutation could be a much more widespread physiology than currently perceived. Understanding the controls of this emergent microbial capacity could offer new routes for nitrogen elimination or pollutant remediation in natural and engineered water systems.
  
  
  
  NO dismutation into N2and O2is a novel process catalyzed by putative NO dismutase (Nod). To date, only two bacteria, the anaerobic methane-oxidizing bacterium "Ca Methylomirabilis oxyfera" and the alkane-oxidizing gammaproteobacterium HdN1, are known to harbor nod genes. In this study, we report efficient molecular tools that can detect and quantify a wide diversity of nod genes in environmental samples. A surprisingly high diversity and abundance of nod genes were found in contaminated aquifers as well as wastewater treatment systems. This evidence indicates that NO dismutation may be a much more widespread physiology in natural and man-made environments than currently perceived. The molecular tools presented here will facilitate further studies on these enigmatic microbes in the future.
authors.affiliation: Institute of Groundwater Ecology, Helmholtz-Zentrum München, Neuherberg, Germany baoli.zhu@helmholtz-muenchen.de tillmann.lueders@helmholtz-muenchen.de.
authors.forename: Baoli
authors.initials: B
authors.lastname: Zhu
authors.affiliation: Institute of Groundwater Ecology, Helmholtz-Zentrum München, Neuherberg, Germany.
authors.forename: Lauren
authors.initials: L
authors.lastname: Bradford
authors.affiliation: Institute of Groundwater Ecology, Helmholtz-Zentrum München, Neuherberg, Germany.
authors.forename: Sichao
authors.initials: S
authors.lastname: Huang
authors.affiliation: Institute of Groundwater Ecology, Helmholtz-Zentrum München, Neuherberg, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Szalay
authors.affiliation: Chair of Urban Water Systems Engineering, Technical University of Munich, Munich, Germany.
authors.forename: Carmen
authors.initials: C
authors.lastname: Leix
authors.affiliation: Chair of Urban Water Systems Engineering, Technical University of Munich, Munich, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Weissbach
authors.affiliation: Szent István University, Gödöllő, Hungary.
authors.forename: András
authors.initials: A
authors.lastname: Táncsics
authors.affiliation: Chair of Urban Water Systems Engineering, Technical University of Munich, Munich, Germany.
authors.forename: Jörg E
authors.initials: JE
authors.lastname: Drewes
authors.affiliation: Institute of Groundwater Ecology, Helmholtz-Zentrum München, Neuherberg, Germany baoli.zhu@helmholtz-muenchen.de tillmann.lueders@helmholtz-muenchen.de.
authors.forename: Tillmann
authors.identifier: http://orcid.org/0000-0002-9361-5009
authors.initials: T
authors.lastname: Lueders
mesh_terms: D001421:Bacteria, Anaerobic / Q000235:genetics* / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction; D013482:Superoxide Dismutase / Q000235:genetics*; D062065:Wastewater / Q000737:chemistry*; D018508:Water Purification
chemical_list: D009569:Nitric Oxide; D013482:Superoxide Dismutase; D062065:Wastewater
keywords: HdN1; NO dismutase; contaminated aquifers; nitric oxide (NO) dismutation; oxygenic denitrification; wastewater treatment; “Candidatus Methylomirabilis oxyfera”