Candidatus Accumulibacter phosphatis (CAP) is an unclassified type of Betaproteobacteria that is a common bacterial community member of sewage treatment and wastewater treatment plants performing enhanced biological phosphorus removal (EBPR)[1] and is a polyphosphate-accumulating organism.

[2] Further work using clone banks and fluorescence in situ hybridization identified a group of bacteria, closely related to Rhodocyclus as the dominant member of lab-scale communities.

To date, the polyphosphate kinase (ppk1)[5] and the PHA synthase (phaC) [6] genes have been used to characterise CAP populations at a higher resolution that 16S rRNA.

During the anaerobic phase, CAP can take up volatile fatty acids and store these simple carbon sources intracellularly as polyhydroxyalkanoates (PHAs).

During the subsequent aerobic phase, PHAs are used for energy production and phosphate is taken up from the medium to form polyphosphate.