[Community structures of ammonia-oxidizing bacteria in activated sludge of wastewater treatment plants]

In order to investigate the community structure of ammonia oxidizing bacteria (AOB) in wastewater treatment plants and the influence of treatment process and system scale on AOB community. We investigated AOB communities in activated sludges collected from 9 wastewater treatment systems, using specific PCR followed by terminal restriction fragment length polymorphism (T-RFLP), cloning, and sequencing of amoA genes. The T-RFLP fingerprints analysis shows that there are some differences among the AOB community structures from different wastewater treatment systems, and the dominant terminal restriction fragments (T-RFs) are 354, 491 and 291 bp. The T-RFLP profiles and cluster analysis may also indicate the AOB structures are slightly affected by the treatment process, while they are influenced by the system scale to some extent. Phylogenetic analysis of cloned amoA gene shows clearly that all the dominant AOB in the systems were Nitrosomonas spp., not Nitrosospira spp.. The reason may be explained as that Nitrosomonas spp. have higher micromax, than Nitrosomonas spp.. This growth advantage may favor the Nitrosomonas spp. rather than Nitrosomonas spp. being prevail in activated sludge.