Atypical polyphosphate accumulation by the denitrifying bacterium Paracoccus denitrificans

Polyphosphate accumulation by Paracoccus denitrificans was examined under a erobic, anoxic, and anaerobic conditions. Polyphosphate synthesis by this d enitrifier took place with either oxygen or nitrate as the electron accepto r and in the presence of an external carbon source. Cells were capable of p oly-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 phospha te removal in activated sludge systems, it is concluded that P. denitrifica ns is capable of combined phosphate and nitrate removal without the need fo r alternating anaerobic/aerobic or anaerobic/anoxic switches. Studies on ad ditional denitrifying isolates from a denitrifying fluidized bed reactor su ggested that polyphosphate accumulation is widespread among denitrifiers.