• Actinobacteria;
  • enhanced biological phosphate removal;
  • fluorescence in situ hybridization;
  • full scale activated sludge plants;
  • glycogen-accumulating organisms;
  • polyphosphate accumulating organisms;
  • Rhodocyclus


Aims:  To see if the compositions of the microbial communities in full scale enhanced biological phosphorus removal activated sludge systems were the same as those from laboratory scale sequencing batch reactors fed a synthetic sewage.

Methods:  Biomass samples taken from nine full scale enhanced biological phosphate removal (EBPR) activated sludge plants in the eastern states of Australia were analysed for their populations of polyphosphate (polyP)-accumulating organisms (PAO) using semi-quantitative fluorescence in situ hybridization (FISH) in combination with DAPI (4′-6-diamidino-2-phenylindole) staining for polyP.

Results:  Very few betaproteobacterial Rhodocyclus related organisms could be detected by FISH in most of the plants examined, and even where present, not all these cells even within a single cluster, stained positively for polyP with DAPI. In some plants in samples from aerobic reactors the Actinobacteria dominated populations containing polyP.

Conclusions:  The PAO populations in full-scale EBPR systems often differ to those seen in laboratory scale reactors fed artificial sewage, and Rhodocyclus related organisms, dominating these latter communities may not be as important in full-scale systems. Instead Actinobacteria may be the major PAO.

Significance and Impact of the Study:  These findings illustrate how little is still known about the microbial ecology of EBPR processes and that more emphasis should now be placed on analysis of full-scale plants if microbiological methods are to be applied to monitoring their performances.