Microbial Communities are actively present in the Activated Sludge System. We have applied PCR-based Pyrosequencing to investigate the bacterial communities of Activated Sludge samples from different common effluent treatment plants. A total of 259K effective sequences of 16S rRNA gene V4 region were obtained from these Activated Sludge samples. These sequences revealed huge amount of operational taxonomic units (OTUs) in Activated Sludge, that is, 1183–3567 OTUs in a sludge sample, at 3% cutoff level and sequencing depth of 16 489 sequences. Clear geographical differences among the Activated Sludge samples from effluent treatment Plant No.1 and No.2 were revealed by (1) cluster analyses based on abundances of OTUs or the genus/family/order assigned by Ribosomal Database Project (RDP) and (2) the principal coordinate analyses based on OTUs abundances, RDP taxa abundances and UniFrac of OTUs and their distances. In addition to certain unique bacterial populations in each Activated Sludge sample, some genera were dominant, and core populations shared by multiple samples, including two commonly reported genera of Zoogloea and Dechloromonas, three genera not frequently reported and three genera not well described so far. Pyrosequencing analyses of multiple Activated Sludge samples in this study also revealed the minority populations that are hard to be explored by traditional molecular methods and showed that a large proportion of sequences could not be assigned to taxonomic affiliations even at the phylum/class levels.

pyrosequencing, activated sludge, bacteria, cluster analysis, PCoA