Fig. S3.

Phylogenetic affiliation of the urease alpha subunits (UreC) from Nitrospira, Nitrospina, and other nitrifiers. A Bayesian 80% consensus amino acid tree is shown. The degree of posterior support of a branch is indicated by a single asterisk for >90% posterior probability (PP), a double asterisk for >99% PP or a triple asterisk for >99.9% PP. For metagenomic UreC sequences, the gene ID is followed by the IMG metagenome ID (for UreC received from IMG) and the description of the source habitat. The scale bar shows 7% estimated sequence divergence.