Atypical Polyphosphate Accumulation by the Denitrifying Bacterium Paracoccus denitrificans

Polyphosphate accumulation by Paracoccus denitrificans was examined under aerobic, anoxic, and anaerobic conditions. Polyphosphate synthesis by this denitrifier took place with either oxygen or nitrate as the electron acceptor and in the presence of an external carbon source. Cells were capable of poly-beta-hydroxybutyrate (PHB) synthesis, but no polyphosphate was produced when PHB-rich cells were incubated under anoxic conditions in the absence of an external carbon source. By comparison of these findings to those with polyphosphate-accumulating organisms thought to be responsible for phosphate removal in activated sludge systems, it is concluded that P. denitrificans is capable of combined phosphate and nitrate removal without the need for alternating anaerobic/aerobic or anaerobic/anoxic switches. Studies on additional denitrifying isolates from a denitrifying fluidized bed reactor suggested that polyphosphate accumulation is widespread among denitrifiers.