It was of interest to perform a phylogenetic analysis of
the AOB based on the ISR sequences, as the 16s
rRNA gene- based phylogeny has previously been
shown to have a very low resolution, owing to highsequence similarity. Phylogenetic trees constructed on
the basis of the ISR sequences (Fig. la) were topologically
quite similar to the trees constructed on the
basis of 16s rDNA sequences (Fig. 1 b). The branching
of the ISR trees was the same regardless of the method
used for tree construction. The resolution, however,