amoA DGGE profiles. The community structure of AOB and removal efficiencies of TKN and ammonia were monitored in each reactor throughout the experiment (Fig. 1). This approach was used to (i) visually assess the stability of AOB community structure and (ii) investigate whether ammonia and TKN removal efficiencies could be related to AOB diversity or to specific AOB species. amoA DGGE profiles showed frequent shifts in the composition and diversity of AOB communities,
as indicated by the appearance and disappearance of certain bands with time. Five bands were successfully isolated and sequenced. BLAST analysis of the sequences revealed that the sequence of band 1 (Fig. 1) shared 99% sequence similarity to the amoA gene of Nitrosomonas sp. strain Nm107 (Table 5).The sequences of bands 2 and 3 shared 91 and 95% sequence similarity to the amoA sequence of Nitrosomonas europaea,respectively. The sequence of band 4 was 91% similar to that of Nitrosomonas sp. strain ENI-11, and the sequence of band 5 shared 92% sequence similarity to the amoA gene of Nitrosospira multiformis.