Characterisation of the microbial 16S rDNA diversity of an aerobic phosphorus-removal ecosystem and monitoring of its transition to nitrate respiration

The microbial community of a conventional anaerobic-aerobic sequencing batc h reactor was investigated by cloning and sequencing bacterial 16S rDNA. Th e 92 16S rDNA sequences analysed ranged across 50 different operational tax onomic units (OTU). The majority of these sequences were not closely relate d to known species. They belonged to 12 different groups, but essentially t o the Cytophagales and the Proteobacteria beta, which represented 38% and 1 7% of the retrieved sequences respectively. No OTU numerically outnumbered the others. However. similarities were observed with previous reports on mo lecular characterisation of phosphorus-accumulating ecosystems, suggesting an enrichment in microorganisms belonging to the Rhodocyclus group. Thereaf ter, the ability of this anaerobic-aerobic microbial community to accumulat e phosphorus with nitrate as its energy source was investigated. The reacto r was shifted from anaerobic-aerobic running conditions to anaerobic-anoxic conditions by injection of nitrate; and its microbial community was monito red by PCR-single strand conformation polymorphism (SSCP). The reactor main tained a good phosphorus accumulation and similar SSCP microbial community patterns for a period of 17 days, suggesting that the same microbial commun ity was able to respire both oxygen and nitrate. However, this situation wa s unstable, since a breakdown in phosphorus accumulation occurred thereafte r.