Polyphosphate-accumulating organisms

Polyphosphate-accumulating organisms (PAOs) are a group of microorganisms that, under certain conditions, facilitate the removal of large amounts of phosphorus from their environments.

Many bacteria cannot consume carbon without an energetically favorable electron acceptor and therefore PAOs gain a selective advantage within the mixed microbial community present in the activated sludge.

The classical or "canonical" behavior of PAOs is considered to be the release of phosphate (as orthophosphate) to the environment and transformation of intracellular polyphosphate reserves into polyhydroxyalkanoates (PHA) from volatile fatty acids (VFAs) and glycogen during anoxic conditions.

[4][5] This is generally believed to be seen more often in extracellular environments high in organic compounds, thus containing fermentable substrates like amino acids and sugars.

[8][9] Additionally, it is suggested that the amino acids lysine, arginine, histidine, leucine, isoleucine, valine and phenylalanine may replace the canonical purpose of PHA as an energy substrate during oxic conditions, based on genomic potential and similarity to behavior of other microbial metabolisms.

phosphoribacter, these two actinobacterial organisms exhibit similar metabolisms, however M. phosphovorus has been suggested to hyperaccumulate over ten times the amount of polyphosphate per cell mass dry weight compared to Ca.

[23][24] Quatrionicoccus australiensis is a bacteria isolated from activated sludge which has been found to accumulate polyphosphate and PHA, thus likely having a classical PAO phenotype.

[25][1] Malikia granosa is a bacteria isolated from activated sludge which has been found to accumulate polyphosphate and PHA, thus likely having a classical PAO phenotype.