Sequential anaerobic-aerobic batch reactors were maintained on acetate/peptone and two different P/total organic carbon ratios that select for microbial communities enriched for either glycogen-accumulating organisms (GAO) or polyphosphate-accumulating organism (PAO). The community profiles of the eubacterial population and gram-positive high G-C bacteria (HGC) were characterized and compared by determining the terminal restriction fragment length polymorphisms (T-RFLP) of 16S rDNA. The HhaI+RsaI digested 5′ T-RFLP patterns of the eubacterial 16S rDNA amplified from the GAO- and PAO-enriched communities were made up with 12 and 14 rank-abundant fragments (i.e., ribotypes), respectively. Among those ribotypes detected in the GAO-enriched community, only seven were found in the PAO-enriched community. The HGC group could only account for no more than 6% and 17% of the eubacterial 16S rDNA amplified from the GAO- and PAO-enriched communities, respectively. Within the HGC community, at least 16 and 10 rank-abundant ribotypes were observed in the MspI digested T-RFLP patterns of GAO- and PAO-enriched communities, respectively. Among those HGC ribotypes observed in both communities, only five were in common. These indicate that the enrichment processes leading to the establishment of GAO- and PAO-specific communities caused the dramatic difference and complexity in the microbial population.

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