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. Author manuscript; available in PMC: 2019 Nov 29.
Published in final edited form as: Trends Microbiol. 2016 Jun 6;24(9):699–712. doi: 10.1016/j.tim.2016.05.004

Figure 2. Phylogenetic Affiliation, Species-Level Diversity, and Habitats of NOB.

Figure 2

The known nitrite oxidizers belong to the genera Nitrobacter [1, 103], Nitrotoga [40], Nitrococcus [104, 105], Nitrospira [68, 72], Nitrospina [58, 104, 106], Nitrolancea [18], and ‘Candidatus Nitromaritima’ [17]. Nitrospinae ‘Clade 2’ is a monophyletic group without a defined taxonomic status [17]. The inner ring indicates which bacterial phyla contain these genera. To assess the species-level diversity within each genus, the 16S rRNA sequences of known NOB and closely related bacteria were retrieved from the SILVA Ref NR 99 database (release 123, July 2015) [107] and clustered in operational taxonomic units (OTUs) using a sequence identity threshold of 98.7% [108]. The obtained OTU numbers are indicated in parentheses for each NOB group or bacterial phylum as an estimate of the NOB species numbers represented in the sequence database. Wedges in the outer ring are drawn proportionally to the OTU numbers. The six Nitrospira lineages are shown separately, whereas ‘other Nitrospira’ does not refer to one coherent lineage but instead comprises all Nitrospira sequences outside the already established lineages of this genus. Colored small circles indicate the known major habitats of each NOB group. Most of the collected 16S rRNA sequences stem from uncultured organisms.