FIG. 6.

Neighbor-joining tree showing phylogenetic relationship of Arctic Ocean sequences to closely related β-Proteobacteria ammonia oxidizer sequences. The tree was generated by using a 1,040-bp region of the 16S rDNA. Clones from this study are indicated in boldface type, and the direct sequence is underlined. Clusters are numbered according to the method of Stephens et al. (36). Bootstrap values higher than 50% are shown. The tree is unrooted, and E. coli is used as an out group. The bar indicate a Jukes-Cantor distance of 0.03. The accession numbers of the sequences used to make the phylogenetic tree are given in Table 2.