As one group of the most important functional phosphorus removal organisms, “
Candidatus
Accumulibacter,” affiliated with the
Rhodocyclus
group of the
Betaproteobacteria
, is a widely recognized and studied PAO in the field of biological wastewater treatment. The morphotypes and population structure of clade-level “
Candidatus
Accumulibacter” were studied through novel FISH-staining-flow cytometry, which involved denitrifying phosphorus removal (DPR) achieving carbon and energy savings and simultaneous removal of N and P, thus inferring the different denitrifying phosphorus removal abilities of these clades. Additionally, based on this method,
in situ
quantification for specific polyphosphate-accumulating organisms (PAOs) enables a more efficient process and more accurate result. The establishment of FISH-staining-flow cytometry makes cell sorting of clade-level noncultivated organisms available.