Phylogenetic analysis of nitric oxide reductase gene homologues from aerobic ammonia-oxidizing bacteria

Karen L. Casciotti, Bettie Ward

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82 Scopus citations


Nitric oxide (NO) and nitrous oxide (N2O) are climatically important trace gases that are produced by both nitrifying and denitrifying bacteria. In the denitrification pathway, N2O is produced from nitric oxide (NO) by the enzyme nitric oxide reductase (NOR). The ammonia-oxidizing bacterium Nitrosomonas europaea also possesses a functional nitric oxide reductase, which was shown recently to serve a unique function. In this study, sequences homologous to the large subunit of nitric oxide reductase (norB) were obtained from eight additional strains of ammonia-oxidizing bacteria, including Nitrosomonas and Nitrosococcus species (i.e., both β- and γ-Proteobacterial ammonia oxidizers), showing widespread occurrence of a norB homologue in ammonia-oxidizing bacteria. However, despite efforts to detect norB homologues from Nitrosospira strains, sequences have not yet been obtained. Phylogenetic analysis placed nitrifier norB homologues in a subcluster, distinct from denitrifier sequences. The similarities and differences of these sequences highlight the need to understand the variety of metabolisms represented within a "functional group" defined by the presence of a single homologous gene. These results expand the database of norB homologue sequences in nitrifying bacteria.

Original languageEnglish (US)
Pages (from-to)197-205
Number of pages9
JournalFEMS microbiology ecology
Issue number2
StatePublished - Apr 1 2005

All Science Journal Classification (ASJC) codes

  • Applied Microbiology and Biotechnology
  • Microbiology
  • Ecology


  • Ammonia-oxidizing bacteria
  • Nitric oxide reductase
  • Nitrifier-denitrification
  • Nitrite reductase
  • Nitrous oxide


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