BACTERIAL COMMUNITY STRUCTURES OF PHOSPHATE-REMOVING AND NON-PHOSPHATE-REMOVING ACTIVATED SLUDGES FROM SEQUENCING BATCH REACTORS

The bacterial community structures of phosphate- and non-phosphate-rem oving activated sludges were compared. Sludge samples were obtained fr om two sequencing batch reactors (SBRs), and 16S rDNA clone libraries of the bacterial sludge populations were established. Community struct ures were determined by phylogenetic analyses of 97 and 92 partial clo ne sequences from SBR1 (phosphate-removing sludge) and SBR2 (non-phosp hate-removing sludge), respectively. For both sludges, the predominant bacterial group with which clones were affiliated was the beta subcla ss of the proteobacteria. Other major groups represented were the alph a proteobacterial subclass, planctomycete group, and FLexibacter-Cytop haga-Bacteroides group. In addition, several clone groups unaffiliated with known bacterial assemblages were identified in the clone librari es. Acinetobacter spp., thought to be important in phosphate removal i n activated sludge, were poorly represented by clone sequences in both libraries. Differences in community structure were observed between t he phosphate-and non-phosphate-removing sludges; in particular, the Rh odocyclus group within the beta subclass was represented to a greater extent in the phosphate-removing community. Such differences may accou nt for the differing phosphate-removing capabilities of the two activa ted sludge communities.