Fig. 2.

Phylogenetic trees of AOA (a) and AOB (b). The neighbor-joining trees were constructed using ARB based on Jukes–Cantor-corrected DNA distances, showing the phylogenetic affiliation of amoA gene sequences from the Pearl River Estuary sediment S16 (printed in bold) and from other environmental samples or pure strain retrieved from the GeneBank. In (a), except for the singletons, one clone was selected from each OTU for phylogenetic analysis and the total number of clones grouped to that OTU was listed after the clone name. The bootstraps (based on 1,000 replications) larger than 60% were indicated by the black dots