The bacterial community structure and its dynamics were analysed using 16S rRNA gene-based PCReDGGE. A cluster analysis of the DGGE fingerprint patterns was carried out using unweighted pair group method with arithmetic mean (UPGMA) (Fig. 6). Based on the cluster analysis, it can be observed that the 10 samples fell into 2 main groups with a similarity of 50%. This implied a major shift in the community structure during the operation of OMBR between Day 21 and Day 42, which is most likely due to the elevated saline environment in the bioreactor. After the addition of
Ag-NPs, a decrease in community diversity was evident from Day 70 to Day 84. Study has shown that there were two species of bacteria linked to Bacteroidetes and Proteobacteria in the activated sludge that were sensitive to the presence of Ag-NPs. These two species of bacteria are commonly found and are usually dominant in activated sludge from municipal wastewater plants (Sun et al., 2013). In another study, microbial community structure analysis
also indicated a decrease in AOB and nitrite oxidizing bacteria (NOB) population